uhvnet 2011 uhvnet · steering group which includes industrial representation from the areva...

UHVnet 2011

uhvnet

Fourth UHVnet Colloquium

January 18th

– 19th

2011

Winchester, UK

This colloquium is supported by:

UHVnet 2011

uhvnet

Welcome to the fourth UHVnet colloquium hosted by the University of Southampton on the 18th and 19

th

January 2011. Previous UHVnet events have been held at Cardiff University, Glasgow Caledonian

University and the University of Manchester. This meeting will take place at Winchester Guildhall and

consist of a registration and poster session on the Tuesday evening to encourage a relaxed discussion of

current work between early career researchers. The second day of the event will consist of oral presentations

covering the following four topic areas; High Voltage Plant, Condition Monitoring, Materials and Theories,

Methods and Models. Each topic will have an opening presentation by a leading researcher in the field

followed by 5 oral presentations by early career researchers and postgraduates.

UHVnet is an informal grouping of universities and was set up in 2005 to further interests of high voltage

research within the United Kingdom. The university members are Cardiff University, Glasgow Caledonian

University, University of Liverpool, University of Leicester, University of Manchester, University of

Southampton, University of Strathclyde and the University of Surrey. These universities are supported by a

steering group which includes industrial representation from the Areva T&D Technology Centre, PPA

Energy, National Grid and Narec.

Specific objectives of the group include raising awareness of the researcher capabilities of group members to

UK high-voltage related industry, particularly manufacturers and electricity supply companies and lobbying

research funding organisations for ear-marked high-voltage related programs.

We would be delighted to receive any feedback about this event as we are keen to further improve our

communication with both UK and overseas stakeholders. Future events will be listed on our website and we

hope to see you again.

UHVnet 2011

i

Table of Contents

Timetable .............................................................................................................................................................. iii

UHVnet Members ................................................................................................................................................ iv

2011 Organising Committee ................................................................................................................................ v

Transport .............................................................................................................................................................. vi

Technical Programme

Oral Session 1: High Voltage Plant .................................................................................................................... 1

A1.1 Characterisation of Earth Electrodes including Experimental Tests on Large-Scale

Systems ............................................................................................................................................................... 2

A1.2 The Variation in Tangential Electric Fields for Different Bushing Shed Profiles in a

Polluted Environment .......................................................................................................................................... 3

A1.3 Environmental Friendly Compact High Voltage Substations ............................................................................. 4

A1.4 A Cascaded Flying Capacitor Multilevel Converter for HVDC and FACTS ..................................................... 5

A1.5 Thermal Performance of High Voltage Power Cables ........................................................................................ 6

A1.6 Detection and Location of Underground Power Cable using Magnetic Field

Technologies ....................................................................................................................................................... 7

Oral Session 2: Condition Monitoring ................................................................................................................ 8

B1.1 Condition Monitoring for High Voltage Equipment ........................................................................................... 9

B1.2 Automated Phase-agnostic Time Domain Analysis of RF Partial Discharge Pulse Data

for Low-power Wireless Sensing Applications ................................................................................................... 10

B1.3 Partial Discharge Analysis of Defective Three-phase Cable .............................................................................. 11

B1.4 Optimum Coil Design for Inductive Energy Harvesting in Substations ............................................................ 12

B1.5 Study of Signal Processing Techniques used for Denoising Partial Discharge Signals in

Cables ................................................................................................................................................................. 13

B1.6 Instrumentation and Condition Monitoring of Composite Cross Arms .............................................................. 14

Oral Session 3: Materials .................................................................................................................................... 15

C1.1 Towards Recyclable Insulation Materials for High Voltage Cables ................................................................... 16

C1.2 Five-Electrode Inclined-plane Tests of Textured Silicone Rubber Samples ....................................................... 17

C1.3 A Raman Microprobe Study of Corona Ageing in a Controlled Atmosphere .................................................... 18

C1.4 FTIR Spectrum of Layered PET Insulation with Artificial Voids Subjected to Electrical

Stressing .............................................................................................................................................................. 19

C1.5 Dielectric Behaviour of Alkyl Esters of Seed-based Oil ..................................................................................... 20

C1.6 The Influence of Spherical Cavity Surface Charge Distribution on PD Events .................................................. 21

Oral Session 4: Theories, Methods and Models ................................................................................................. 22

D1.1 Stochastic and Deterministic models for Electrical Tree Growth ....................................................................... 23

D1.2 Model of Structural Damage to Carbon Fibre Composites Due to Thermo-electric Effects

of Lightning Strikes ............................................................................................................................................. 24

D1.3 Switching Ferroresonant Transient Study using Finite Element Transformer Model ......................................... 25

D1.4 Transient Modelling of Offshore Wind Farm Connections ............................................................................... 26

D1.5 Surface Gradient Calculation for Overhead Lines .............................................................................................. 27

D1.6 Modelling of Electroluminescence in Polymers Using a Bipolar Charge Transport Model ............................... 28

Posters: High Voltage Plant ................................................................................................................................ 29

A2.1 Power Transformer End-of-life Modelling: Incorporating Thermal Lifetime Analysis

with Ordinary Statistical Analysis ....................................................................................................................... 30

A2.2 Location of Partial Discharges within a Transformer Winding Using Principal

Component Analysis ........................................................................................................................................... 31

A2.3 Frequency Response Analysis of Transformer Winding Deformation Based on Multi-

conductor Transmission Line Model ................................................................................................................... 32

A2.4 Effect of Climatic Condition on Polymeric Insulators ........................................................................................ 33

A2.5 Acoustic Noise Evaluation for Overhead Lines .................................................................................................. 34

A2.6 Transient Fault Location in Low Voltage Distribution Networks ....................................................................... 35

A2.7 A Survey on the Potential of CF3I Gas as an Alternative for SF6 ...................................................................... 36

A2.8 A New Technique to Enhance the Earthing System by Increasing the Horizontal Earth

Electrode Effective Length ................................................................................................................................. 37

UHVnet 2011

ii

A2.9 A Novel Portable Testing Device for Surge Protective Systems ....................................................................... 38

A2.10 A Solar Powered Wireless Data Acquisition System for High Voltage Substations ......................................... 39

A2.11 The Performance of Nanocoating on High Voltage insulators ........................................................................... 40

A2.12 Performance of Tower Footings Resistance under High Impulse Current ......................................................... 41

A2.13 High Frequency Performance of a Vertical Rod Electrode ................................................................................ 42

Posters: Condition Monitoring ............................................................................................................................ 43

B2.1 FDTD Modelling of Partial Discharge Detection in Power Distribution Cables using

HFCTs ................................................................................................................................................................ 44

B2.2 Use of Hidden Markov Model for Partial Discharge-led Failure Development Modelling ............................... 45

B2.3 Dynamically Weighted Ensemble of Neural Networks for Classifying Partial Discharge

Patterns ............................................................................................................................................................... 46

B2.4 A Successful On-site PD Testing Experience of 11kV EPR Cable Insulation Systems .................................... 47

B2.5 Radiometric Arc Fault Detection ........................................................................................................................ 48

B2.6 Voltage Transducer for Transient Measurements on High Voltage Overhead Lines ........................................ 49

B2.7 Fault Location using FPGAs and Power Line Communication ......................................................................... 50

B2.8 A New Method to Improve the Sensitivity of Leak Detection in Self-Contained Fluid-

filled Cables ....................................................................................................................................................... 51

B2.9 Energy Harvesting from Electric Fields in Substations for Powering Autonomous

Sensors ................................................................................................................................................................ 52

B2.10 Ageing and Temperature Influence on Polarization/Depolarization Current Behaviour of

Paper Immersed in Natural Ester ........................................................................................................................ 53

B2.11 An On-line Lightning Monitoring System for Transmission Lines ................................................................... 54

B2.12 Energy Harvesting in Substations for Wireless Sensors and a New Arc Capacitor

Structure 55

Posters: Materials ................................................................................................................................................ 56

C2.1 On the use of Raman and FTIR Spectroscopy for the Analysis of Silica-based

Nanofillers .......................................................................................................................................................... 57

C2.2 Dielectric Breakdown Strength of Polyethylene Nanocomposites ..................................................................... 58

C2.3 Influence of Temperature and Moisture Absorbed on Electrical Degradation and

Breakdown in Epoxy Resins ............................................................................................................................. 59

C2.4 Space Charge Behaviour in Oil-Paper Insulation with Different Aging Condition .......................................... 60

C2.5 Modelling the Non-equilibrium Electric Double Layer at Oil-pressboard Interface of

High Voltage Transformers ................................................................................................................................ 61

C2.6 Investigation of Impulsive Corona Discharges for Energisation of Electrostatic

Precipitation Systems ......................................................................................................................................... 62

C2.7 A Comparison of Polymeric Cable Insulation Properties Following Lightning Impulse

Ageing ................................................................................................................................................................ 63

C2.8 Properties and Analysis of Thermally Aged Poly(ethylene oxide) .................................................................... 64

C2.9 Smart Materials as Intelligent Insulation ........................................................................................................... 65

C2.10 AC Breakdown Characteristics of LDPE in the Presence of Crosslinking By-products .................................... 66

C2.11 DC Impulse Discharge Degradation of Mica 67

Posters: Theories, Methods and Models ............................................................................................................. 68

D2.1 Modelling of Partial Discharge Activity in Cavity within a Dielectric Insulation Material ............................... 69

D2.2 Full Wave Modelling of Partial Discharge Phenomena in Power Transformers using

FDTD Methods ................................................................................................................................................... 70

D2.3 Evaluation of an Iterative Method used for Partial Discharge RF Location Techniques ................................... 71

D2.4 Numerical Modelling of Needle-Grid Electrodes Negative Surface Corona Charge

System ................................................................................................................................................................ 72

D2.5 Mathematical Modelling of End-of-Life of Power Transformers in Perspective of System

Reliability ........................................................................................................................................................... 73

D2.6 A Comparison between Electroluminescence Models and Experimental Results ............................................. 74

D2.7 An Improved Pulsed Electroacoustic System for Space Charge Measurement under AC

Conditions ........................................................................................................................................................... 75

Authors Index ...................................................................................................................................................... 76

UHVnet 2011

iii

Timetable

Tuesday 18th

January 2011

1700 – 2000 Registration, Reception and Poster Session

Wednesday 19th

January 2011

0800 – 0830 Registration

0830 – 0845 Welcome by Meeting Chair

0845 – 1015 Session 1: High Voltage Plant

1015 – 1045 Coffee break

1045 – 1215 Session 2: Condition Monitoring

1215 – 1330 Lunch and Poster Session

1330 – 1500 Session 3: Materials

1500 – 1515 Coffee break

1515 – 1645 Session 4: Theory, Methods and Models

1645 – 1700 Closing Remarks

UHVnet 2011

iv

UHVnet Members

Glasgow Caledonian University

Prof. Brian Stewart (Chairman)

School of Engineering, Science and Design

70 Cowcaddens Road

Glasgow, G4 0BA

Email: [email protected]

Cardiff University

Prof. Manu Haddad

High Voltage Research Group

School of Engineering

Cardiff University

PO Box 925

Cardiff, CF24 0YF


University of Strathclyde

Dr. Martin Judd

Dept. Electronic & Electrical Eng.

University of Strathclyde

Royal College

204 George Street

Glasgow, G1 1XW


University of Leicester

Prof. J. Forthergill

Department of Engineering

University of Leicester

University Road

Leicester, LE1 7RH


University of Liverpool

Dr. Joe W. Spencer

Centre for Intelligent Monitoring Systems

University of Liverpool

Liverpool, L69 3BX


University of Manchester

Dr. Ian Cotton

School of Electronic & Electrical Eng.

Room C3, Ferranti Building

University of Manchester

Manchester, M60 1QD


University of Southampton

Prof. Paul Lewin

The Tony Davies High Voltage Laboratory

University of Southampton

Highfield

Southampton, SO17 1BJ


University of Surrey

Prof. Gary Stevens

University of Surrey

Guildford

Surrey, GU2 7XH


Areva T&D Technology Centre

Dr. Fabrice Perrot

HV & Electrical Materials Consultancy

AREVA T&D Technology Centre

St. Leanards Avenue

Stafford, ST17 4LX


PPA Energy

Mr. Cliff Walton

1 Frederick Sanger Road

Surrey Research Park

Guildford

Surrey, GU2 7YD


Narec

Mr. Alex Neumann

National Renewable Energy Centre

Eddie Ferguson House

Ridley Street

Blyth

Northumberland, NE24 3AG


National Grid

Dr. Jenny Cooper

National Grid

Warwick Technology Park

Gallows Hill

Warwick

CV34 6DA

E-mail: [email protected]

UHVnet 2011

v

2011 Organising Committee

Colloqium Chair: Prof. Paul Lewin Email: [email protected]

Treasurer: Prof. Alun Vaughan Email: [email protected]

Technical Chair: James Pilgrim Email: [email protected]

Local Arrangements Chair: Jack Hunter Email: [email protected]

IOP Dielectrics Group Liaison: Dr. David Swaffield Email: [email protected]

Publicity / Media Chair: David Mills Email: [email protected]

Registration Chair: Nicky Freebody Email: [email protected]

Session Chairs

High Voltage Plant Qi Li University of Manchester

Peter Baker University of Strathclyde

Condition Monitoring David Smith Glasgow Caledonian University

Minan Zhu University of Strathclyde

Materials Martin Reading University of Southampton

Abdelghaffar A Abdelmalik University of Leicester

Theory, Methods and Models Liwei Hao University of Southampton

Fabian Moore University of Cardiff

mailto:[email protected]







UHVnet 2011

vi

Transport

Winchester Taxis

Wessex Cars +44 (0)1962 877749

Wintax Winchester Taxi Co +44 (0)1962 878727

City Taxis Ltd +44 (0)1962 841212

South West Trains service to Weymouth / Poole

Departs Winchester Arrives Southampton Airport

1705 1714

1725 1733

1733 1749

1800 1816

1825 1844

1830 1846

1900 1918

South West Trains service to London Waterloo

Departs Winchester Arrives London Waterloo

1717 1823

1724 1834

1747 1847

1817 1920

1824 1934

1847 1951

1917 2020

UHVnet 2011 A1

1

Oral Session 1: High Voltage Plant

0845 – 1015

A1.1

Invited

Lecture

Characterisation of Earth Electrodes including Experimental Tests on Large-Scale

Systems ............................................................................................................................................................... 2

A1.2 The Variation in Tangential Electric Fields for Different Bushing Shed Profiles in a

Polluted Environment ......................................................................................................................................... 3

A1.3 Environmental Friendly Compact High Voltage Substations ............................................................................. 4

A1.4 A Cascaded Flying Capacitor Multilevel Converter for HVDC and FACTS ..................................................... 5

A1.5 Thermal Performance of High Voltage Power Cables ........................................................................................ 6

A1.6 Detection and Location of Underground Power Cable using Magnetic Field

Technologies ....................................................................................................................................................... 7

UHVnet 2011 A1.1

2

Characterisation of Earth Electrodes including Experimental Tests on

Large-Scale Systems

H. Griffiths

Cardiff University, UK


Understanding the behaviour of earthing systems under impulse currents is fundamental for the design of

new systems and for improving the performance of existing systems under transient conditions. Several

analytical approaches and powerful computation tools for the analysis and design of earthing systems have

been developed; Analytical calculation methods deal with uniform or layered soil structures only, and there

is little experimental evidence to validate the accuracy of these methods. As can be found in the literature,

there is a significant set of test results on laboratory scaled-models of earth electrodes as well as some

limited data on earthing systems of operational electrical substations and transmission lines. The difficulty

with laboratory scaled-models is related to the boundary conditions, which makes them less suitable for the

validation of calculation/computation methods. On the other hand, operational electrical installations are

located in areas characterised by non-uniform soil structures with both lateral and vertical variations and

there is limited scope for high current testing due to system operation and safety constraints.

This paper describes experimental investigations carried out on earth electrodes (i) in test cells under

laboratory conditions, (ii) at operational electricity substations and , (iii) at two outdoor earthing test

facilities; the first at Llanrumney Fields where several different types of earth electrode have been installed,

and, the second at a pumped-storage power station in Dinorwig, North Wales, where a test rig has been built

on a large water reservoir in order to achieve close to uniform resistivity conditions. The experimental results

(DC, AC and impulse) are compared with computed values obtained from different numerical models.

UHVnet 2011 A1.2

3

The Variation in Tangential Electric Fields for Different Bushing

Shed Profiles in a Polluted Environment

D. J. Smith*1

, S. G. McMeekin1, B. G. Stewart

1 and P. A. Wallace

1

1Glasgow Caledonian University, UK

*E-mail: [email protected]

Today, the majority of power transformer high voltage bushings are of the oil impregnated paper (OIP)

condenser type. Typically, these bushings have low partial discharge activity, low dielectric losses, and are

cost effective [1]. However, over one quarter of transformer failures are as a result of a bushing fault, often

an electrical discharge. External surface flashover can occur from excessive surface pollutant on the bushing

sheds, and can deteriorate the component, reducing asset reliability. The distribution of the electric field is

dependent on the shed profile, and OIP bushings have different profiles specific to the operational

environment and manufacturer. During operation, the accumulation of pollutant on the shed surfaces results

in uneven distribution of the electric field, and increases the possibility of surface flashover.

Using numerical methods, it is possible to model and compare complex bushing geometries under different

pollutant conditions. In the literature, numerical models of the potential and electric field distributions for a

bushing with varying surface conditions are under investigation [2]} . However, current studies do not

consider different shed profiles for similar bushing voltage rating, or the variation in maximum tangential

electric field due to the geometry.

A finite element method (FEM) numerical model is built for an OIP condenser high voltage power

transformer bushing. COMSOL Multiphysics software is utilised using the electric currents application

mode, at 50Hz power frequency. The dielectric properties of the material within the model are based on

values published in the literature. Using the model, the tangential electric field is evaluated over the bushing

creepage path for four shed profiles. For porcelain bushings, surface flashover may occur for a tangential

electric field of 5kV/cm [ 3], and this is used as a comparison value. The maximum tangential electric field

and its location are determined for each different shed profile for a medium industrial polluted environment.

It is expected this work will help develop an improved understanding of the sensitivity and criticality of shed

profile selection in polluted environments.

Figure 1: Equipotential and tangential electric field distribution

over the bushing creepage path.

[1] J. S. Graham, "High voltage bushings," in 15th IET International School on High Voltage Engineering and

Testing, Newcastle Upon Tyne, UK, 2008, pp. 375–398.

[2] P. Cardano et al., "Application of Composite Housing to High Voltage Bushings," CIGRE, Paris, A3-307, 2008.

[3] M. Vitelli, "Numerical Performance Analysis of Semiconductor Coatings for Corona Suppression," IEEE

Transactions on Dielectrics and Electrical Insulation, vol. 6, no. 6, pp. 774-780, December 1999.

UHVnet 2011 A1.3

4

Environmental Friendly Compact High Voltage Substations

M. Albano*1

, A. Haddad1, H. Griffiths

1, and P. Coventry

2

1 Cardiff University, UK

2 National Grid, U.K


In electric power systems, the preferred gaseous insulating medium is air, and for specific applications such

as circuit breaker and very compact substations, sulphur hexafluoride (SF6) is successfully adopted.

However, many studies show that the high environmental impact of SF6 due to its green-house effect [1]. In

addition, the increase in electricity demand and difficulties for obtaining land for new developments

introduce the challenge of building new compact substations with higher voltage ratings on existing sites.

Research at Cardiff investigates the possible reduction in size of transmission substations using new air-

insulated designs, avoiding to use of large quantity of insulating gas and proposing the substitution of small

quantities of SF6 as insulating media in HV apparatus, e.g. in circuit breakers, with the more environmental

friendly CF3I gas.

The investigations of the adoption of CO2 - CF3I mixture for circuit breaker applications show promising

properties. The mixture exhibits high specific heat and high thermal conductivity, and these two properties

are the preliminary characteristics for a gas to be adopted in circuit breakers. As a high voltage insulating

medium replacement for SF6, the gas mixture 70%-30% (CO2 – CF3I) gives the best performance with

optimal gas phase stability to replace SF6 [2].

The application of proposed design and combinations of compact solutions to a standard 400kV switch bay

indicates that significant reduction in ground area can be achieved [3]. The introduction of new technologies

offer significant additional benefits in the measurement performance and avoidance of risk of explosion

compared with equipment filled with oil. The adoption of small quantities of CF3I as insulating medium in

HV equipment permits to reduce significantly the potential green-house effects associated with current

insulating media. Therefore, the overall footprint of future high voltage substations can be significantly

reduced.

Figure 1: 400kV substation switch bay footprint for a conventional

(on the left) and a compact substation (on the right).

[1] Working Group I Contribution to the Fourth Assessment Report of the IPCC - Intergovernmental Panel on

Climate Change, Addendum-Errata of Climate Change 2007 - The Physical Science Basis IPCC WG1 AR4

Report, 31 July 2008, web source: http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Errata_2008-08-05.pdf,

accessed on 23.11.2009.

[2] M. S. Kamarudin, M. Albano, N. Harid, A. Haddad, P. Coventry, "Study on the potential of CF3I gas as

alternative for SF6 in high voltage applications", Proceedings of International International Universities‘ Power

Engineering Conference –UPEC2010, Cardiff, Wales, UK, 2010.

[3] M. Albano, A. Haddad, H. Griffiths, and P. Coventry, "Electric and magnetic fields in 400kV compact

Substations", Proceedings of International Symposium on High Voltage Engineering – ISH 2009, Cape Town,

South Africa, 24-28 August 2009.

UHVnet 2011 A1.4

5

A Cascaded Flying Capacitor Multilevel Converter for HVDC and

FACTS

I. B. Efika*1

and L. Zhang2

1University of Leeds, UK


Over the last three decades, semiconductor devices like IGBT‘s (insulated gate bipolar transistors) and SIT‘s

(static induction transistors) have been developed to reach high switching frequencies at considerable power

levels. This opens up completely new research and development areas and fields of applications especially

for power transmission and distribution systems such as high voltage direct current (HVDC) and Flexible AC

Transmission systems (FACTS).

The limits concerning voltage and power can be pushed even further by placing these converter circuits in

series. This paper presents a Cascade Flying Capacitor Multilevel Converter (CFCMC). The basic unit in this

system is a 3-level full bridge flying capacitor converter. Each block switches between 0 to +Vdc and 0 to -

Vdc at any point. One leg of a three phase CFCMC system can be formed as shown in Figure 1 by cascading

these units. This circuit has some advantages when compared to the cascaded H-Bridge converter; the

waveform performance is better due to the additional voltage level control, the stress upon switches is also

lower. The presence of capacitors in each unit may seem to have cost implications, however each unit can

handle higher power ratings therefore fewer units are required. The size of the capacitors required is also

small when compared to those required for a standard flying capacitor multilevel converter. The particular

merit of CFCMC also lies on its ability of supplying reactive power due to additional capacitors in each unit.

This will improve system stability margin especially when many large renewable sourced generators with

low reactive power output are connected to the utility network.

Future research will be to employ the estimation and reduction of switching losses. Phase Shifted Sine-

triangle PWM scheme [1], is used to generate the switching signals for each individual block and the entire

cascaded system. The phase shift angle of the carrier signal, calculated as l

2 can be adjusted to

control the stress impact on the switches in flying capacitor block. This feature is important when the effect

of switching losses is considered.

Find below the simulation results. (fS =540Hz), THD = 3.27%.

Figure 1: Switch mode configuration; (Waveforms Top: 1 –

Line to ground Voltages, 2 – Line to Neutral Voltages, 3 – Line

to Line voltages, 4 – Current Waveforms 4 – FFt Analysis)

[1] L. Yiqiao and C.O. Nwankpa, ―A Power-Line Conditioner Based on Flying-Capacitor Multilevel Voltage-

Source Converter with Phase-Shift SPWM‖, IEEE Transactions on Industry Applications, Vol. 36, No. 4,

July/August 2000.

UHVnet 2011 A1.5

6

Thermal Performance of High Voltage Power Cables

J. A. Pilgrim1, D. J. Swaffield

1, P. L. Lewin

1 and D. Payne

2

1University of Southampton, UK

2National Grid, UK


The UK high voltage electricity transmission network continues to face annual rises in demand, with ever

greater volumes of power supplied to load centres throughout the country. To operate this network

effectively, it is vital to accurately calculate the maximum allowable electric current which can be safely

carried by each component in the power system. In high voltage power cables, this limit is defined by the

maximum operating temperature of the cable insulation. Specify this current rating to be too low and the

cable asset will never be used to its full potential; conversely setting the rating to be too high risks damage to

the asset as the excessive heating can cause premature failure. Thus the rating calculation must be optimised

to maintain security of supply by minimising the risk of cable failure, while also maximising the returns from

capital investment on the power network.

This project has employed a variety of mathematical techniques to improve the methods by which current

ratings are calculated. Modern computational techniques such as finite element analysis (e.g Figure 1) and

computational fluid dynamics are used to create more advanced circuit rating techniques. These have been

compared and refined with input gained from field data. By eliminating simplifications from existing

methods, it has been possible to identify ways of increasing the utilisation of the existing network. In

addition the new techniques allow examination of the potential benefits of future developments in cable

technology.

Benefits are being derived from this work on both a day to day and strategic planning levels. For instance,

by re-evaluating the current rating method for cables installed in tunnels, it has proved possible to consider

the benefits from co-locating more cables in one tunnel to best use these expensive assets. The application of

this method has allowed the quantification of the benefits which might be available from next generation

cable technologies, enabling the prioritisation of future research effort in cable materials. Upon completion,

the knowledge gained from this work is to be used to revise the international standard on calculating current

ratings in cable tunnels. Techniques such as these underpin the concept of smart grids with improved

operational flexibility and capability. Simultaneously the requirement to build expensive new components

into the network is limited, whilst still meeting the need to supply ever increasing volumes of power across

the country.

Figure 1: Contours of air velocity within a cable tunnel

UHVnet 2011 A1.6

7

Detection and Location of Underground Power Cable using Magnetic

Field Technologies

P. Wang1, K. F. Goddard

1, P. L. Lewin

1 and S. G. Swingler

1



The location of buried underground electricity cables is becoming a major engineering and social issue

worldwide. Records of utility locations are relatively scant, and even when records are available, they almost

always refer to positions relative to ground-level physical features that may no longer exist or that may have

been moved or altered. The lack of accurate positioning records of existing services can cause engineering

and construction delays and safety hazards when new construction, repairs, or upgrades are necessary.

Hitting unknown underground obstructions has the potential to cause property damage, injuries and, even

deaths. Thus, before commencing excavation or other work where power or other cables may be buried, it is

important to determine the location of the cables to ensure that they are not damaged during the work.

This paper describes the use of an array of passive magnetic sensors (induction coils) together with signal

processing techniques to detect and locate underground power cables. The array consists of seven identical

coils mounted on a support frame; one of these coils was previously tested under laboratory conditions, and

relevant results have been published in [1]. A measurement system was constructed that uses a battery

powered data acquisition system with two NI 9239 modules connected to the coil array, and controlled by a

laptop. The system is designed to measure the magnetic field of an underground power cable at a number of

points above the ground.

A 3 by 3 m test area was chosen in one of our campus car parks. This area was chosen because the

university‘s utility map shows an isolated power cable there. Measurements were taken with the array in 16

different test positions, and compared with the values predicted for a long straight horizontal cable at various

positions. Finally, error maps were plotted for different Z-coordinate values, showing the minimum fitting

error for each position in this plane. One such map is shown in Figure 1; the low error values of 4-5% give a

high degree of confidence that most of the measured signal is due to a cable near to these positions. This

view is supported by the fact that the university‘s utility map shows the cable at X = 1.4 m, and by amplitude

measurements taken with a hand-held magnetic field meter.

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0.04

0.06

0.08

0.1

0.12

0.14

Figure 1: a typical result for car park tests at Z = 2m.

(possible cable position is X=1.4 m and Depth = 0.6m. 96%

accuracy)

P. Wang, P. Lewin, K. Goddard, and S. Swingler, ―Design and testing of an induction coil for measuring the

magnetic fields of underground power cable‖, IEEE International Symposium on Electrical Insulation, San Diego,

California, USA 2010

Horizontal distance, X (m)

Dep

th (

m)


UHVnet 2011 B1

8

Oral Session 2: Condition Monitoring

1045 - 1215

B1.1

Invited

Lecture

Condition Monitoring for High Voltage Equipment ...................................................................................... 9

B1.2 Automated Phase-agnostic Time Domain Analysis of RF Partial Discharge Pulse Data

for Low-power Wireless Sensing Applications ................................................................................................... 10

B1.3 Partial Discharge Analysis of Defective Three-phase Cable .............................................................................. 11

B1.4 Optimum Coil Design for Inductive Energy Harvesting in Substations ............................................................. 12

B1.5 Study of Signal Processing Techniques used for Denoising Partial Discharge Signals in

Cables .................................................................................................................................................................. 13

B1.6 Instrumentation and Condition Monitoring of Composite Cross Arms .............................................................. 14

UHVnet 2011 B1.1

9

Condition Monitoring for High Voltage Equipment

Martin D Judd

University of Strathclyde , UK


Advances in electronic technology have yielded impressive processing power, increased bandwidth and low

power consumption, opening up a myriad of possibilities for new, specialised condition monitoring systems.

Many businesses have sprung up to exploit these opportunities by bringing new condition monitoring

equipment to market. After initial enthusiasm, some techniques have not proved successful, or their

effectiveness has turned out to be variable, depending on the expertise of the system supplier or the end user.

This has led to the evolution of a more cautious approach to new condition monitoring techniques, which

must be properly scrutinised by those who would adopt them.

This presentation will begin by addressing some of the issues that researchers should take into account when

developing new technologies for deployment on high voltage equipment in the context of power

transmission and distribution. Some accounts of experience with the development of commercial monitoring

technologies will be given to illustrate the key role that sustained fundamental scientific research can play in

ensuring that, where possible, research activities lead on to real industrial and commercial benefits.

Examples will be drawn from the author‘s past experience in the field of partial discharge monitoring and

from current work on autonomous wireless sensor nodes for use in substations.

UHVnet 2011 B1.2

10

Automated Phase-agnostic Time Domain Analysis of RF Partial

Discharge Pulse Data for Low-power Wireless Sensing Applications

P. C. Baker*1

, A. J. Mair1, M. D. Judd

1 and S. D. J. McArthur

1

1University of Strathclyde, UK


The use of partial discharge (PD) diagnostics on substation equipment is limited by operational and financial

constraints involved in deploying sensing systems at the plant level. To circumvent these constraints,

modern wireless sensor network technology can provide a robust and flexible architecture upon which

condition monitoring applications can be built, without the need for extensive wiring and at a much lower

cost than conventional wired systems. A low-power approach to PD diagnostics using this technology has

previously been demonstrated in [1] .

One key constraint on the deployment of wireless PD sensors is the availability of an absolute phase

reference, which is a prerequisite for conventional phase resolved PD pattern analysis. Phase resolution

requires a VT connection to the electrical phase under observation, which for wireless sensing applications is

impractical, as cabling must be kept to a minimum. Therefore, an alternative approach is ideally required

which does not rely on an absolute phase reference.

To address this, a novel PD diagnostic technique is proposed that is capable of ―phase-agnostic‖ time-

domain analysis of RF PD pulse data, specifically suited to operation within the resource constraints of a

wireless sensor node. Derived from an automated diagnostic technique for identification of faults in

shipboard power systems [2] this method analyses relative pulse magnitude, pulse density and inter-pulse

distance for a travelling window of PD pulse measurements.

Using laboratory data representing typical PD patterns for defects in GIS, machine learning algorithms were

trained on random data samples with their accuracy tested on previously unseen data. The split between

training and test data was 50/50 and the time window considered was well below 1 second. The machine

learning algorithms tested were: a C4.5 decision tree, a Naïve Bayesian network, a Support Vector Machine,

a Nearest neighbour classifier, and Radial Basis Function algorithm. It was determined that out of these

algorithms the C4.5 produced the most accurate classifier for this data type.

Testing different window sizes established that training on a window size of 4 electrical cycles generated the

most accurate classifier. An initial study has demonstrated that the diagnostic technique, upon identifying

the presence of PD, gives promising results across seven defect types. Future work will use a wider training

set to train the classifier, ideally leading to a more robust and generalised classifier. The classifier will then

be deployed on a wireless sensor node connected to a low-power PD detector and validated in laboratory

tests.

[1] P. C. Baker, ―Enhancing substation condition monitoring through integrated diagnostics, wireless sensor networks

and multi-agent systems‖, PhD Thesis, University of Strathclyde, September 2010

[2] Mair, A.J.; Davidson, E.M.; McArthur, S.D.J.; Srivastava, S.K.; Schoder, K.; Cartes, D.A.; ―Machine learning

techniques for diagnosing and locating faults through the automated monitoring of power electronic components in

shipboard power systems,‖ Electric Ship Technologies Symposium, 2009. ESTS 2009, pp.469-476, 20-22 April

2009

UHVnet 2011 B1.3

11

Partial Discharge Analysis of Defective Three-phase Cable

J. A. Hunter*1

, L. Hao1, D. J. Swaffield

1, P. L. Lewin

1, N. Cornish

2, C. Walton

2 and M. Michel

3


2PPA Energy, UK

3UK Power Networks


Power distribution cable networks represent a dynamic and complex challenge with regard to the issues of

maintenance and providing a reliable, high quality supply of electrical power. Utilities historically used

regular off-line testing to investigate the health of their assets. This method of testing is reasonably effective

for this purpose but does have certain drawbacks associated with it; customer supply can be interrupted

during the testing process and the cables are generally not tested under normal operating conditions.

Meaning that the test data is not representative of the Partial discharge (PD) activity that is apparent under

on-line conditions and the testing activity itself could trigger previously dormant PD sources.

The modern approach for understanding the health of medium voltage (MV) cable distribution networks is to

continuously monitor the assets whilst on-line. Analysis if the field data is then used to inform decisions

regarding asset replacement and maintenance strategies. PD activity is widely recognised as a symptom

linked to the degradation of the dielectric properties of high voltage plant. UK Power Networks sponsored

research is being undertaken to investigate the evolution of PD activity within three-phase paper insulated

lead covered (PILC) cables containing introduced defects. An experiment has been designed to stress cable

lengths in a manner that is representative of the conditions met by on-line circuits [1]. A cable section

containing a defect that is known to lead to the premature failure of in-service cables has been PD tested over

a range of operating temperatures. The experiment utilizes three-phase energization at rated voltage as well

as thermal cycling of the cable to replicate the daily load pattern experienced by circuits in the field. The

extension to this work involves PD testing cable samples containing a range of defects to produce a data set

consisting of PD pulses produced by varied sources. Analysis of this data should lead to a better

understanding of the signals produced by the premature ageing of these types of cable.

Figure 1: 3PARD plot showing produced by cable sample at

37 ºC.

a: PD activity generated by the defect.

[1] J. A Hunter, L. Hao, D. J. Swaffield, P. L. Lewin, N. Cornish, C. Walton and M. Michel, ―Partial discharge in

medium voltage three-phase cables‖, Conference record of the 2010 IEEE International Symposium on

Electrical Insulation, 2010

UHVnet 2011 B1.4

12

Optimum Coil Design for Inductive Energy Harvesting in Substations

N. M. Roscoe*1

and M. D. Judd1



The reliability and life expectancy of electrical supply equipment can be improved through the use of

condition monitoring. However, expansion of existing condition monitoring through the addition of new

sensors is challenging since power to condition monitoring sensors has traditionally been supplied by mains

power, which is not available in many locations where monitoring would be useful, or by batteries, which

require their own maintenance regime. Energy harvesting in substations has the potential to power a new

class of ―fit-and-forget‖ wireless sensors, thus enabling more affordable expansion of condition monitoring.

There are many potential sources of energy in substations (solar, wind, thermal, etc.), each of which may

have a role in a particular range of sensor applications. This paper is concerned with inductive energy

harvesting from the ambient magnetic fields, focussing on optimal coil design. By this means, the intention is

to develop a class of ―free-standing‖ inductive energy harvesting devices, which can be placed at a safe

distance from high voltage conductors, as defined in Figure 1.

In this paper, all aspects of coil design are considered, including core material, core geometry and number of

turns. A coil is then designed for a representative application, taking practical limitations into account, and

its output power is characterised while harvesting from a uniform 50 Hz magnetic field generated within a

set of Maxwell coils. Experimental results are presented and discussed.

Figure 1: (a) ―Threaded‖ inductive energy harvesting. (b)

―Free-standing‖ inductive energy harvesting.

UHVnet 2011 B1.5

13

Study of Signal Processing Techniques used for Denoising Partial

Discharge Signals in Cables

F.P.Mohamed*1

, W.H.Siew1, J.J. Soraghan

1, S.S.Strachan

1



Ageing of cable insulation is an increasing problem which necessitates the development of on-line condition

monitoring for cables. On-site Partial discharge (PD) measurements have been widely considered to be the

most effective diagnostic tool for insulation assessment. As a result of PD, fast varying current pulses flow in

the cable conductors and these pulses can be detected using high frequency current transformers which are

working in the VHF band. However on-site measurements are often hampered by various noise sources

which makes the process of extracting useful information from the raw data more difficult. Presented here is

a review of the various signal processing techniques used for extracting PD information from the corrupted

data with special focus on the advantages and disadvantages of each.

Signal averaging is the most common method for removing random noise from the raw data. This can be

done by alighning the various data sets and then added together. Moving average filter, ensemble average

filters are widely used to remove random noises in the signal. Over smoothing of the signals, by this

method, results in loss of sharp edges in the PD signal which is not recommended for PD mapping.

Wavelet transform is the most widely accepted tool for denoising on-site data which involves selecting a

wavelet basis function followed by decomposition, threshold selection and reconstruction [1]. Basis function

can be scaled and translated to match the desired signal information to be extracted from the raw data.

Selection of proper basis function makes the denoising more efficient which is often more difficult since the

PD signal undergoes dispersion in the cable. Debauchees‘ family wavelets are most widely used by

researchers to extract PD from the raw data. Both discrete wavelet transform (DWT) and stationary wavelet

transform (SWT) are used. Due to the dyadic decomposition in DWT, shift invariance property is lost which

will introduce uncertainties in PD mapping. SWT is most suitable method for locating partial discharges due

to shift invariance. However processing time required by SWT is high. Recently second generation wavelet

transform (SGWT) which is used for the construction of wavelets has been applied to denoise the on-ste PD

data. SGWT is a fast way of implementing wavelet transform which makes the processing time low. Also

using the prior information about the PD signature, filter banks can be modified which makes denoising

more efficient than classical wavelet based techniques [2]. Wavelets techniques discussed so far require

prerequisites like choice of wavelet basis function and decomposition level to denoise the data. Hence novel

techniques of signal processing which does not require any prerequisites are being investigated to compare

its performance with respect to wavelet based denoising. Various signal processing tools discussed above

were applied to on-site PD data and the results were compared

[1] Hao Zhang, T.R. Blackburn, B.T. Phung and D. SenA Novel Wavelet Transform Technique for On-line Partial

Discharge Measurements Part 1: WT De-noising Algorithm, IEEE Transactions on Dielectrics and Electrical

Insulation Vol. 14, No. 1; February 2007

[2] Xiaodi Song, Chengke Zhou, Donald M. Hepburn, Guobin Zhang ,Second Generation Wavelet Transform for Data

Denoising in PD Measurement. IEEE Transactions on Dielectrics and Electrical Insulation Vol. 14, No. 6; December

2007

UHVnet 2011 B1.6

14

Instrumentation and Condition Monitoring of Composite Cross Arms

C. A. Veerappan*1

, C. Zachariades1, S. M. Rowland

1, I. Cotton

1, P. R. Green

1, F. Allison

1

1University of Manchester, UK


Providing an alternative solution to glass and porcelain insulators, composite insulators exhibit enhanced

performance under polluted conditions. Tangentially, while the idea of composite cross-arms is not new,

they have only seen commercialisation on lower voltage towers, where structural requirements permit

standard engineering solutions.

Over the last few years a team from The National Grid High Voltage Research Centre at The University of

Manchester and an industrial partner, EPL Composite Solutions Ltd have developed a composite cross-arm

platform aiming to increase power transfer capacities of existing transmission infrastructure. This paper

presents an instrumented field-trial of the composite cross-arm. The trial consisted of installing composite

cross-arms on four adjacent towers on a line being decommissioned in the Scottish Highlands. This

unenergised trial will examine mechanical performance, particularly with respect to ice, snow and wind.

The remote location and the area's designation as a Site of Special Scientific Interest limited certain aspects

of the system's design; having a big impact on power sourcing and data retrieval, where simple but reliable

wire-line methods could not be employed.

Power is generated by wind turbines and employs a battery storage system. The use of conventional

communication networks for data recovery was not viable; bespoke systems for data storage and periodic

physical collection were required. The premises of a local a ski centre were used for data collection and

wireless networking equipment was used to bridge the gaps to and between the towers.

Mechanical performance is to be measured through the use of embedded strain gauges and a combination of

a load cell, accelerometer and inclinometer at the cross-arm nose. An industrial data capture and control

platform is used to capture sensor outputs and store them until retrieval. Network cameras with local storage

capabilities are used to capture normal and time-lapse videos of the installed cross-arms.

Ultimately this trial has become more about instrumentation and data transfer in hostile environments, rather

than cross-arm performance. After the first winter a second generation system is expected to be

implemented. Accumulated data will be used to optimise the cross-arm design. Figure 1, shows the

installation site.

Figure 1: Picture of Installation Site, depicting, relay station,

one non-instrumented tower and the first instrumented tower

UHVnet 2011 C1

15

Oral Session 3: Materials

1330 - 1500

C1.1

Invited

Lecture

Towards Recyclable Insulation Materials for High Voltage Cables ............................................................ 16

C1.2 Five-Electrode Inclined-plane Tests of Textured Silicone Rubber Samples ...................................................... 17

C1.3 A Raman Microprobe Study of Corona Ageing in a Controlled Atmosphere .................................................... 18

C1.4 FTIR Spectrum of Layered PET Insulation with Artificial Voids Subjected to Electrical

Stressing .............................................................................................................................................................. 19

C1.5 Dielectric Behaviour of Alkyl Esters of Seed-based Oil ..................................................................................... 20

C1.6 The Influence of Spherical Cavity Surface Charge Distribution on PD Events ................................................. 21

UHVnet 2011 C1.1

16

Towards Recyclable Insulation Materials for High Voltage

Cables

I. L. Hosier*, A. S. Vaughan

and S. G. Swingler

University of Southampton, UK


The preferred material for modern extruded high voltage transmission cables is cross-linked polyethylene

(XLPE). This material has excellent thermo-mechanical and dielectric properties, however it is not easily

recycled at end of use, raising questions as to its long term sustainability [1]. Therefore research work at

Southampton has sought to identify suitable recyclable alternatives to XLPE. Such candidate materials need

to have low temperature flexibility and high temperature mechanical stability combined with a sufficiently

high electrical breakdown strength.

Initially ethylene based systems [2] were considered, however, low density polyethylene (LDPE) has poor

mechanical stability at temperatures exceeding 80 oC whereas high density polyethylene (HDPE) is too

brittle at low temperatures. To overcome these difficulties, a series of blends combining either an ethylene

vinyl acetate (EVA) co-polymer or a low density polyethylene (LDPE) with a high density polyethylene

(HDPE) were considered. A blend of 20 % HDPE in LDPE crystallised relatively rapidly (Figure 1a), was

found to offer a good balance between high temperature mechanical stability and flexibility at low

temperatures (Figure 1b) combined with excellent dielectric strength. In the remaining EVA based blends,

increasing the vinyl acetate content resulted in a more rubbery composite but with a reduced high

temperature stability and breakdown strength.

Propylene based systems were then considered, these included traditional syndiotactic (sPP) and isotactic

polypropylene (iPP) and a range of propylene-ethylene co-polymers. Such systems offered enhanced high

temperature stability and with sufficient ethylene content, low temperature flexibility [3], combined with

good dielectric breakdown strength provided that the crystallisation was rapid enough to avoid the formation

of large spherulites. In further efforts to optimise the properties, two blend systems composed of iPP mixed

with either a propylene ethylene co-polymer (with 40 % ethylene content; ―PE40‖) or sPP were considered.

Provided that the crystallisation was relatively rapid, both blends provided excellent dielectric performance

and high temperature stability. A blend of 20 % iPP in PE40 (Figure 1c) offers the best level of mechanical

flexibility at low temperatures and would therefore be suitable for the manufacture of enhanced, recyclable

high voltage cables.

Figure 1: (a) Morphology of the optimised LDPE/HDPE blend

system (b) mechanical properties of selected ethylene based

systems (c) mechanical properties of iPP, PE40 and its blends

[1] C. P. Martin, ―The impact of mechanical stress on the integrity of XLPE cables‖, PhD Thesis, University of

Southampton, 2004.

[2] I. L. Hosier, A. S. Vaughan and S. G. Swingler, ―An investigation of the potential of ethylene vinyl

acetate/polyethylene blends for use in recyclable high voltage cable insulation systems‖, , J. Mat. Sci., vol. 45,

no. 10, pp. 2747-2459, 2010.

[3] I. L. Hosier, L. Cozzarini, A. S. Vaughan and S. G. Swingler, ―Propylene based systems for high voltage cable

insulation applications‖, J. Phys.: Conf. ser., vol. 183, 012015, 2009.

UHVnet 2011 C1.2

17

Five-Electrode Inclined-plane Tests of Textured Silicone Rubber

Samples

P. Charalampidis*1, A. Haddad

1, R. T. Waters

1, H. Griffiths

1, N. Harid

1 and P. Sarkar

2

1Cardiff University, UK

2National Grid, UK


The shank region of polluted polymeric insulators is susceptible to thermal damage where high current

density and high electric field magnitude occurs. The recently proposed [1] textured design consisting of

hemispherical protuberances, aims to reduce the current density and the electric field gradient and increase

the longitudinal creepage length without increasing the overall length of the insulator. Moreover, the

formation of parallel current paths can lead to less harmful discharges. For the purpose of having a more

detailed insight of the formation of these parallel current paths, the IEC-60587 standard [2] that deals with

the inclined plane test was modified by replacing the single ground electrode by five smaller separate

electrodes. The test results of this modified inclined plane test of textured and conventional untextured

rectangular samples are presented along with an analysis of the current distribution and the discharge

activity. The improved performance of textured samples, in terms of resistance and tracking, has been

excellent [3].

Figure 1: Evidence of thermal damage after testing on

untextured and textured samples.

[1] R. T. Waters and A. Haddad, ―Insulating Structures‖, UK Patent GB2406225B, Dec 2006.

[2] IEC 60587: 1984:, ―Methods for evaluating resistance to tracking and erosion of electrical insulating materials

used under severe ambient conditions‖, IEC standard.

[3] P.Sarkar et al., ―Inclined Plane Tests of Textured Silicone Rubber Samples‖, 2010 International Conference on

High Voltage Engineering and Application, New Orleans, U.S.A., 11-14 October 2010

UHVnet 2011 C1.3

18

A Raman Microprobe Study of Corona Ageing in a Controlled

Atmosphere

N. A. Freebody 1, A. S. Vaughan

1



Raman microprobe spectroscopy is widely used in the analysis of polymers due to its high spatial resolution

and its ability to characterise the exact chemical composition of a material and, for this reason, it can be

applied to study electrical ageing in solid dielectrics. For example, it enables us to probe the chemical

processes involved in electrical treeing, whereby solid polymer is converted into decomposition products

through a number of electrical processes [1].

This study takes a novel approach to this problem through ex-situ experiments that seek to reproduce the

chemistry of electrical treeing in bulk. Plaque specimens of a range of polymers, including polyethylene,

polystyrene, PEEK and silicone rubber, were subjected to surface ageing via corona discharge, and the

residual products on both the sample surface and the high voltage electrode (as seen in figure 1) were

characterised by Raman microprobe spectroscopy. These experiments were performed as a function of

applied voltage, electrode geometry etc both in air and within a closed cell that enabled the atmosphere to be

controlled and adjusted. The resulting Raman fingerprints were compared with those previously identified

within electrical trees [2,3].

After corona discharge was applied to the samples, despite a large change in surface texture, no residues

were seen on the sample and few chemical changes were detected via Raman spectroscopy, thus implying

that erosion of the material occurs by fragmentation of the polymer. Analysis of the electrodes aged in air

and nitrogen, revealed varying evidence of sp2 hybridized carbon, and fluorescence, both of which are

products previously associated with the processes involved in electrical treeing. The similarity in these

results and previous published works [2,3] suggest that there are common processes involved between

corona surface ageing and electrical treeing especially when an inert atmosphere is used.

Figure 1: Optical image of deposit found on electrode of aged Si

rubber (scale bar = 10µm).

[1] A.S. Vaughan, S.J. Dodd, and S.J. Sutton, ―A Raman microprobe study of electrical treeing in polyethylene‖. J.

Matter. Sci. 39(1): p. 181-191, 2004.

[2] X.S. Liu, A.S. Vaughan, and G. Chen, ―A Raman spectroscopic study of bulk and surface ageing phenomena in

polyethylene‖. Annual Report Conference on Electrical Insulation and Dielectric Phenomena: p. 145-148, 2003.

[3] A.S. Vaughan, I.L. Hosier, S.J. Dodd, S.J. Sutton, ―On the structure and chemistry of electrical trees in

polyethylene‖. J. Phys. D-App. Phys. vol 39(5): pp. 962-978, 2006.

UHVnet 2011 C1.4

19

FTIR Spectrum of Layered PET Insulation with Artificial Voids

Subjected to Electrical Stressing

D. Adhikari*1, D. M. Hepburn1 and B. G. Stewart

1



Partial Discharge (PD) results from faults, such as voids, in power insulation systems and exacerbates

failure. It is difficult to completely eliminate voids in polymeric materials. These may be formed during the

manufacturing process by air leakage into the mould or by evaporation of volatile decomposition products.

Sometimes insufficient pressure on a liquid epoxy during curing causes a cavity to develop. Voids in

polymer insulation are gas filled cavities which have a much lower permittivity and lower breakdown

strength than the solid insulation material. The lower permittivity gives rise to a higher electric field in the

cavity, as a result of which the gas in the cavity will generally break down as the applied voltage is raised.

The samples used in this work are created from layers of poly-ethylene-terephthalate (PET) which are 50μm

thick. Multiple layers of polymer are set between a plane electrode connected to ground and a second plane

electrode connected to a high voltage AC source. Artificial cylindrical voids are created by removing circular

sections from one layer of polymer. Samples with single void and multiple voids (placed both horizontally

and vertically) were created. These samples are electrically stressed and PD activity is monitored and

recorded [1]. To determine the changes to the surface of the voids as a result of the chemical processes

produced by PD, the FTIR spectrum of the polymer specimens subjected to PD were examined. The FTIR

spectra from samples of unstressed material, and from surfaces of single void and multiple voids were

compared and analysed. The measurement of FTIR spectrum was conducted by Attenuated Total Reflection

(ATR) method, which is commonly used for the chemical analysis of the surface layer of specimens. As

ATR is surface specific, depth of investigation being ~5 microns, this allows investigation of initial

processes in material degradation. The changes in the spectra shown below indicate changes to the carbon-

hydrogen bonds (~3000cm-1

) and production of carbon-oxygen (~1700cm-1

) bonds.

The paper will discuss changes to surface chemistry in stressed samples and correlate change with stress

applied.

Figure 1: Comparison of the FTIR Spectra of Unstressed PET

and Stressed PET with artificial voids

[1] D. Adhikari, D. M. Hepburn and B. G. Stewart, ―Analysis of Partial Discharge Characteristics in Artificially

Created Voids‖, 45th

International Universities’ Power Engineering Conference, Cardiff, Wales, UK 2010

[2] L. A. Dissado and J. C. Fothergill, ―Electrical Degradation and Breakdown in Polymers‖, Peter Peregrinus Ltd.,

pp.292-310, 1992

[3] P. Hyvonen, ―Prediction of Insulation Degradation of Distribution Power Cables Based on Chemical Analysis and

Electrical Measurements‖, Doctoral Dissertation – Helsinki University of Technology, 2008

UHVnet 2011 C1.5

20

Dielectric Behaviour of Alkyl Esters of Seed-based Oil

A. A. Abdelmalik*1, J. C. Fothergill

1, S. Dodd

1

1University of Leicester, UK

* E-mail: [email protected]

The dielectric response of palm kernel oil alkyl esters of straight and branched carbon chain were studied

over the frequency range of 10-3

to 104 Hz and temperature range of 20 ˚C to 80 ˚C. The straight chain alkyl

ester (PKOME) was synthesized through esterification reaction of laboratory purified palm kernel oil with

methanol in the presence of catalyst. It was then followed by epoxidation reaction involving the alkyl ester

product and insitu peracid in the presence of catalyst to synthesize the corresponding epoxy alkyl ester. The

epoxy alkyl ester was then reacted with propionic anhydride in the presence of catalyst under nitrogen. This

reaction opens the epoxy ring of the epoxy alkyl oleate component of the epoxy alkyl ester to attach side

chains for the synthesis of a side-branched alkyl ester (PropPKOAE). The dielectric response of these

materials shows that the relaxation processes corresponds to ionic conduction and electrode polarization

phenomena. The real part is constant and the imaginary part is inversely proportional to frequency up till

about 10-1

Hz. This is symptomatic of a constant capacitance in parallel with conductance. Below 10-1

Hz,

the imaginary part of the relative permittivity maintains a slope of -1, whilst the real part of PKOME and

PropPKOAE acquired an average slope of -1.2 and -1.5 within the temperature range studied. This suggests

that grafting of side chain alters the dynamics of the adsorbed ions at the electrode-liquid interface. The

complex impedance plot which separates the interfacial effect from the bulk has a discontinuity at

frequencies that correspond to tan δ peak. This peak corresponds to the relaxation frequency of electrode

polarization, fEP. The estimated fEP of PKOME and PropPKOAE at 20 ˚C are 7.1 × 10-3

Hz and 3.7 × 10-2

Hz

respectively. This implies that the relaxation time for electrode polarization in PropPKOAE is lower than

that of PKOME, suggesting a faster dynamics of ions involved in electrode polarization in branched alkyl

ester of vegetable oil. The change in the dynamics of electrical double layer formation may be responsible

for increase in conductivity of PropPKOAE. Temperature increase lead to a shift in fEP towards high

frequency with a corresponding increase in AC conductivity, and thinner diffuse electrical double layer.

Figure 1: Relative Permittivity of PKO Alkyl esters at 20 ˚C

[1] A.K. Jonscher, 1996, Universal Relaxation Law, Chelsea Dielectrics Press, London.

[2] A.K. Jonscher, 1983, Dielectric relaxation in solids, Chelsea Dielectric Press, London.

[3] R.J. Sengwa, S. Choudhary, S. Sankhla, 2008, Low frequency dielectric relaxation processes and ionic conductivity

of montmorillonite clay nanoparticles colloidal, suspension in poly(vinyl pyrrolidone)-ethylene glycol blends,

eXPRESS Polymer Letters, Vol. 2, No. 11, Pp. 800–809.

10-3

10-2

10-1

100

101

102

103

104

10-3

10-2

10-1

100

101

102

103

104

105

Frequency (Hz)

Rela

tive P

erm

ittivity

PKOME Real Part

PKOME Imag Part

PropPKOAE Real Part

PropPKOAE Imag Part

UHVnet 2011 C1.6

21

The Influence of Spherical Cavity Surface Charge Distribution on PD

Events

H. A. Illias*1

, G. Chen1 and P. L. Lewin

1



Modelling of partial discharge (PD) events allows a better understanding of the phenomena itself. In this

work, an improved model representing PD behaviour within a spherical cavity in a homogeneous dielectric

material has been developed to study the influence of cavity surface charge distribution on the electric field

distribution in the cavity and the material. Comparison of measurement and simulation results has been

undertaken to validate the model.

The model uses a two-dimensional (2D) axial symmetric Finite Element Analysis (FEA) method, which is

solved for local electric potentials. Figure 1 shows the model geometry, which consists of a homogenous

dielectric material (2.0 mm thickness, 5 mm radius) and a hemispherical cavity (1.4 mm diameter). The upper

and lower cavity surfaces are divided into 10 boundaries each. A sinusoidal voltage is applied to the upper

electrode while the lower electrode is always grounded.

Discharge is assumed to occur along the symmetry axis in the cavity. Once the discharge has passed through

the cavity to the opposite surface, it is assumed that charge then propagates along the cavity wall [1, 2]. The

charge propagation is assumed only on the first 2 boundaries from the symmetry axis of the upper and lower

cavity surfaces. Charge distribution is assumed identical on the upper and lower cavity surface.

During discharge, charge density increases on the cavity surface boundaries where charge propagates, until

the electric field in the cavity centre is less than the extinction field. To model the charge movement along

the cavity surface through conduction at other times, the change in the charge density on each cavity surface

boundary is set as dependent on the cavity surface conductivity and the electric field on each boundary.

Thus, surface charge distribution will become non-uniform, influencing the electric field distribution in the

cavity and the material, affecting the likelihood of the next PD event.

The simulation result from the model agrees with a range of measurement results for a 50 Hz, 16 kV ac

applied sinusoidal voltage (Figure 1b). Therefore, the modelling of PD events by consideration of charge

distribution on the cavity surface is reasonable.

(a) (b)

Figure 1: (a) 2D axial symmetric model geometry and (b) measurement and simulation results for

500 applied voltage cycles

[1] W. Kai, S. Yasuo and L. A. Dissado, ―The contribution of discharge area variation to partial discharge patterns

in disc-voids‖, Journal of Physics D: Applied Physics, vol. 37, pp. 1815-1823, 2004

[2] W. Kai, T. Okamoto and Y. Suzuoki, "Effects of discharge area and surface conductivity on partial discharge

behavior in voids under square voltages," IEEE Transactions on Dielectrics and Electrical Insulation, vol. 14,

pp. 461-470, 2007

UHVnet 2011 C1.6

22

Oral Session 4: Theories, Methods and Models

1515 - 1645

D1.1

Invited

Lecture

Stochastic and Deterministic models for Electrical Tree Growth ................................................................ 23

D1.2 Model of Structural Damage to Carbon Fibre Composites Due to Thermo-electric

Effects of Lightning Strikes ................................................................................................................................ 24

D1.3 Switching Ferroresonant Transient Study using Finite Element Transformer Model ......................................... 25

D1.4 Transient Modelling of Offshore Wind Farm Connections ................................................................................ 26

D1.5 Surface Gradient Calculation for Overhead Lines .............................................................................................. 27

D1.6 Modelling of Electroluminescence in Polymers Using a Bipolar Charge Transport

Model .................................................................................................................................................................. 28

UHVnet 2011 D1.1

23

Stochastic and Deterministic models for Electrical Tree Growth

S. Dodd 1University of Leicester, UK


Electrical treeing is a long term electrical degradation process in polymeric insulating materials which can

lead to early failure of HV electrical equipment. A number of approaches have been taken in the literature for

the computer simulation of electrical tree growth. These are usually based on either stochastic or

deterministic principles, see figure 1, for tree growth extension (or combinations of these two approaches). In

this presentation, the physics on which these two methodologies are based are introduced and discussed in

terms of their appropriateness in representing the electrical tree growth mechanisms driven by partial

discharge activity. The presentation will conclude with a discussion on what can be learnt from the different

approaches which contribute to our understanding the electrical tree growth mechanisms.

Figure 1. (a) Stochastic and (b) deterministic approach for the

computer simulation of electrical tree growth.

UHVnet 2011 D1.2

24

Model of Structural Damage to Carbon Fibre Composites Due to

Thermo-electric Effects of Lightning Strikes

R. D. Chippendale*1

, I. O. Golosnoy1, P. L. Lewin

1, G.S. Murugan

1, J Lambert

1



The impact of a lightning strike causes a short high electrical current burst through Carbon Fibre Composites

(CFC). Due to the electrical properties of CFC the large current leads to a rapid heating of the surrounding

impact area which degrades and damages the CFC. It is therefore necessary to study in detail the thermal

response and possible degradation processes caused to CFC. The degradation takes place in two ways, firstly

via direct mechanical fracture due to the thermal expansion of the CFC and secondly via thermo-chemical

processes (phase change and pyrolysis) at high temperatures.

The main objective of this work is to construct a numerical model of the major physical processes involved,

and to understand the correlation between the damage mechanisms and the damage witnessed in modern

CFC. For this work we are only considering the thermo-chemical degradation of CFC. Bespoke numerical

models have been constructed to predict the extent of the damage caused by the two thermo-chemical

processes separately (e.g. a model for phase change and a model for pyrolysis).

The numerical model predictions have then been verified experimental by decoupling of the damage

mechanisms, e.g. the real Joule heating from a lightning strike is replaced by a high power laser beam acting

on composite surface. This was done to simplify the physical processes which occur when a sample is

damaged. The experimentally damaged samples were then investigated using X-ray tomography to

determine the physical extent of the damage.

The experimental results are then compared with the numerical predictions by considering the physical

extent of the polymer removal. The extent of polymer removal predicted by the numerical model, solving for

pyrolysis, gave a reasonable agreement with the damage seen in the experimental sample. Furthermore the

numerical model predicts that the damage caused by polymer phase change has a minimal contribution to the

overall extent of the damage.

UHVnet 2011 D1.3

25

Switching Ferroresonant Transient Study using Finite Element

Transformer Model

R. Zhang1, H.Y. Li

1 and Z.D. Wang

*1

1University of Manchester , UK


In the UK a typical distribution network (Figure 1) is configured as a grid transformer in the downstream

substation to be operated by the circuit breaker in the upstream substation via a fair length of cable or

overhead line. De-energising a transformer with a long cable/overhead line connected to it can induce the

occurrence of switching ferroresonant transients.

Following the normal de-energising switching sequence which is to open downstream circuit breaker first to

shed the load and after a few more minutes to open the upstream circuit breaker in order to de-energise the

no-loaded transformer, the no-load transformer would give a loud noise. This noise is caused by the core

saturation and vibration when the cable/overhead line discharges via the non-loaded transformer. Core

saturation and strayed flux can have some impacts and the worst scenario could be eddy current heating up

insulation locally leading to excessive gassing and eventually localized core melting and failure.

This paper aims to introduce two methods for switching transient ferroresonance study:

Firstly using EMTP to build a distribution network circuit model in the aim to understand how each

component influences the transient voltage and current results. Examples will be 1) circuit breaker grading

capacitor and opening time which would affect initial condition of ferroresonance, 2) ground capacitor of

cable and transformer core characteristics which would affect the magnitude of overvoltage and overcurrent

or/and over-fluxing; and 3) the total resistance in the system which would affect the resonance damping

time;

Secondly using Finite Element to build a detailed transformer model in the aim to understand the details

inside the transformer such as how flux density and power loss distribute and their influence on insulation

ageing when ferroresonance and inrush transient phenomena occur. Examples will be the comparison of

main and leakage flux distribution under normal operating and core saturation conditions; the influences

made by design factors of transformer such as joint angles, steel materials and structures.

This study intends to present the methodologies on how to merge traditional transient study with the

insulation system studies to predict potential damages of system events on insulation materials.

Figure 1 – Typical UK distribution network diagram

UHVnet 2011 D1.4

26

Transient Modelling of Offshore Wind Farm Connections

F. Moore *1

, A Haddad1 and H Griffiths

1



There is currently over 30GW of offshore wind generation projects at various stages of development,

resulting from government targets and incentives for renewable energy [1]. As a result, several large offshore

wind generation projects are being connected to the GB Transmission system.

The location of these wind farms out at sea means that long lengths of submarine cable are required to

connect the wind farms to the onshore transmission network. It is thought that these long lengths of cable

will influence the level of electromagnetic transient overvoltages seen on the transmission network which is

principally constructed using overhead lines. Understanding the transient overvoltage levels allows plant to

be correctly specified, and protected from transient overvoltages. Overvoltages can potentially be mitigated

by using particular switching sequences, installing surge arrestors, or installing harmonic filters.

Offshore transmission networks are governed by various industry codes and practices. These include the

National Electricity Transmission System Security and Quality of Supply Standard (NETS SQSS) [2], which

influences network architecture. By interpreting these standards, and the guidance provided by National Grid

in their Offshore Development Information Statement [3], a representative offshore network is used to

investigate the transient response of such networks.

In this paper, a simple offshore network model (figure 1) for transient simulation in EMTP-ATP, is used to

explore switching surges at various locations on the onshore and offshore networks.

Figure 1: Simple Network Model in ATPDraw (EMTP-ATP)

[1] http://www.thecrownestate.co.uk/rounds-one-two and http://www.thecrownestate.co.uk/round3

(Accessed November 2010).

[2] http://www.nationalgrid.com/uk/Electricity/Codes/gbsqsscode/DocLibrary/

NETS SQSS (Accessed November 2010)

[3] http://www.nationalgrid.com/uk/Electricity/ODIS

Offshore Development Information Statement 2010, National Grid (Accessed November 2010)

UHVnet 2011 D1.5

27

Surface Gradient Calculation for Overhead Lines

Q. Li*1

, S. M. Rowland1 and R. Shuttleworth

1



The most important factor that influences the generation of corona is the electric field distribution in the

vicinity of the conductor surface, so calculation of the electric field strength on the surface of HV conductors

becomes critical when studying corona phenomenon.

The calculation of surface gradients on overhead conductor dates back to the 1950s when the Maxwell's

Potential Matrix was first employed as an analytical tool [1] Over the past 60 years, a number of numerical

methods [2, 3] have been applied on this subject due to the increasing power of computers. All these

calculations are based on a simplified model of transmission line conductors—‗a series of cylinders in

parallel to smooth ground‘.

In the first part of this paper, five major methods are reviewed in detail and programmes using these methods

have been written using MATLAB. One of National Grid‘s transmission line configurations—L2 RUBUS—

has been selected as an example to compare the results for different methods.

Following the theoretical study of existing methods, the second part represents the characteristics of different

methods, and analyzes the possibilities for improving the calculation accuracy.

‗Finite Element Analysis‘ has the advantage of being able to analyze geometries with irregular shapes (Fig 1)

coupled with different fields. However it is limited by the scale of geometries it can simulate. The effect of

stranding has been considered in a 2-D model built in commercial software COMSOL. By making best use

of the advantages and bypassing the disadvantages, a comprehensive method which employs both analytical

methods and the ‗Finite Element Method‘ was developed. The transmission line is then converted to

relatively small scale geometry to analyze the surface stress. Not only stranding shapes but also protrusions,

dust or water droplets were analysed.

Figure 1: FEA simulation results for GAP-Type Conductor

[1] M. Temoshok, ―Relative Surface Voltage Gradients of Grouped Conductors‖, Trans. AIEE, Vol. 67, 1948, pp.

1583-1591.

[2] Maruvada P. Sarma and W. Janischewskyj ―Electrostatic Field of a System of Parallel Cylindrical Conductors‖,

IEEE Trans. on Power Apparatus and Systems, vol. PAS-88, pp. 1069 1969.

[3] H. Singer, H. Steinbigler, P. Weiss, ―A Charge Simulation Method for the Calculation of High Voltage Fields‖,

IEEE Trans. PAS, Vol. 93, pp. 1660-1668 Sept. 1974.

UHVnet 2011 D1.6

28

Modelling of Electroluminescence in Polymers Using a Bipolar Charge

Transport Model

J. Zhao*, D. H. Mills, G. Chen and P. L. Lewin



Electroluminescence (EL) in polymeric materials is thought to occur due to the energy dissipation process

from the recombination of opposite polarity charge carriers. It is considered as an indication of storage and

transport of charge carriers in cable insulation subject to electrical stresses and may indicate the change in

charge movement due to aging or degradation processes. Under ac electric fields, the interaction of opposite

polarity charge carriers at the interface of polymer/conductor is enhanced compared with dc conditions, and

seems to contribute a lot to the electroluminescence rather than the charge behaviours in the bulk of

polymers. The dynamics of charge carriers both at the interface of polymer/conductor and in the bulk of

polymers is investigated through a simulation work using a bipolar charge transport model. Figure 1

compares experimental electroluminescence results with simulated data from the recombination of injected

charge carriers. The paper will give more details on EL model and comparison under various waveforms and

frequencies.

0 45 90 135 180 225 270 315 3600

1

2

3

4

5

6

Norm

aliz

ed E

L inte

nsity

angle ()

Simulation 6kV Experiment 6kV

Figure 1: Comparison of electroluminescence simulation and experimental measurement

[1] P. L. Lewin, S. J. Dodd and A. M. Ariffin, ―Simulation of Electroluminescence using a Bipolar Recombination

Model‖, IEEE International Conference on Solid Dielectrics, 2007, pp. 15-18.

[2] J. Zhao, Z. Xu, G. Chen and P. L. Lewin, ― Numerical Modeling of Space Charge in Polyethylene under AC

Fields‖, 2010 IEEE International Conference on Solid Dielectrics, 2010, Potsdam, Germany. pp. 565-568.

UHVnet 2011 A2

29

Posters: High Voltage Plant

A2.1 Power Transformer End-of-life Modelling: Incorporating Thermal Lifetime Analysis

with Ordinary Statistical Analysis ...................................................................................................................... 30

A2.2 Location of Partial Discharges within a Transformer Winding Using Principal

Component Analysis ........................................................................................................................................... 31

A2.3 Frequency Response Analysis of Transformer Winding Deformation Based on Multi-

conductor Transmission Line Model .................................................................................................................. 32

A2.4 Effect of Climatic Condition on Polymeric Insulators ....................................................................................... 33

A2.5 Acoustic Noise Evaluation for Overhead Lines .................................................................................................. 34

A2.6 Transient Fault Location in Low Voltage Distribution Networks ...................................................................... 35

A2.7 A Survey on the Potential of CF3I Gas as an Alternative for SF6 ..................................................................... 36

A2.8 A New Technique to Enhance the Earthing System by Increasing the Horizontal Earth

Electrode Effective Length ................................................................................................................................ 37

A2.9 A Novel Portable Testing Device for Surge Protective Systems ....................................................................... 38

A2.10 A Solar Powered Wireless Data Acquisition System for High Voltage Substations .......................................... 39

A2.11 The Performance of Nanocoating on High Voltage insulators ........................................................................... 40

A2.12 Performance of Tower Footings Resistance under High Impulse Current ......................................................... 41

A2.13 High Frequency Performance of a Vertical Rod Electrode ................................................................................ 42

UHVnet 2011 A2.1

30

Power Transformer End-of-life Modelling: Incorporating Thermal

Lifetime Analysis with Ordinary Statistical Analysis

D.Y. Feng1, Z.D. Wang

1* and P. Jarman

2


2National Grid, UK


In many developed countries such as the UK, majority of power transformers operating in the power system

networks have passed their designed lifetime. It is of great importance to establish a model to accurately

predict transformers‘ lifetime so that this model can help asset managers plan the replacement of wear-out

transformers, because firstly designed lifetime was not based on operation of old transformers but rather on

educated guess; secondly the re-investment in transmission and distribution system infrastructure requires

excessive capitals and must be done in a planned manner.

In this paper, an intensive statistical analysis on UK‘s transmission transformer population during 1952 to

2004 has been carried out and confirms, with high confidence, a low and stable failure rate for transformers

exist till 40 years of age. However, due to the very limited data of older transformers, statistical tools are

unable to predict the failure rate of aged transformers and have therefore lost their values to asset managers.

In order to compensate statistical tools‘ incapacity in dealing with incomplete dataset, the conservative view

of ‗transformer lifetime equals to insulating paper‘s life‘ is taken to assist the statistical approaches. Thermal

lifetimes of 77 retired transformers are derived using the lowest DP measured from the paper insulation

samples. A correlation of thermal failure rate and transformer ages could thereby be derived and combined

with the statistical results to form a complete trend of the transformer failure rate as age progresses (Fig.1).

Since the 77 retired transformers‘ representativeness to the entire transformer population in terms of thermal

lifetime span is uncertain, to enlarge this sample size, the IEC thermal model is used to model a transformer

population‘s thermal lifetimes. The second part of the paper focuses on discussing the suitability and

applications of IEC thermal model: firstly inputs to the model are defined with a statistical range to reflect

the design and operating conditions of a specific transformer population, secondly introducing various

practical thermal aging mechanisms (e.g. oxidation- or hydrolysis-dominated) to improve the IEC thermal

model.

Ultimately these improvements on thermal modelling approach would assist the statistical analysis in

transformers‘ end-of-life modelling.

Figure 1 : Full life cycle of a transformer‘s failure rate (0.24%

derived from historical data using statistical approaches

incorporated with the thermal failure rate derived from the IEC

thermal model)

UHVnet 2011 A2.2

31

Location of Partial Discharges within a Transformer Winding Using

Principal Component Analysis

M. S. Abd Rahman*1

, P. L. Lewin1 and L. Hao

1



Partial discharge (PD) may occur in a transformer winding due to ageing processes or defects introduced

during manufacture. A partial discharge is defined as a localised electric discharge that only partially bridges

the dielectric insulator between conductors when the electric field exceeds a critical value. The presence of

PD does not necessarily indicate imminent failure of the transformer but it is a serious degradation and

ageing mechanism which can be considered as a precursor of transformer failure. PD might occur anywhere

along the transformer winding and the discharge signal can propagate along the winding to the bushing and

neutral to earth connections. As far as maintenance and replacement processes are concerned, it is important

to identify the location of PD activity so any repair or replace decision is assured to be cost effective.

Therefore, identification of a PD source as well as its location along the transformer winding is of great

interest to both manufacturers and system operators. The wavelet transform is a mathematical function that

can be used to decompose a PD signal into detail levels and an approximation. Wavelet filtering is often used

to improve signal to noise ratio (SNR) of measured signals, but in this case it is used to identify the

distribution of signal energies in both the time and frequency domains. This method produces a feature

vector for each captured discharge signal. The use of principle component analysis (PCA) can compress this

data into three dimensions, to aid visualisation. Data captured by sensors over hundreds of cycles of applied

voltage can be analysed using this approach. An experiment (Figure 1) has been developed that can be used

to create PD data in order to investigate the feasibility of using PCA analysis to identify PD source location.

Figure 1: Experimental diagram for measuring partial

discharge within transformer winding

[1] L. Hao, P. L. Lewin and S. G. Swingler, ―Identification of Multiple Partial Discharge Sources‖, IEEE International

Conference on Condition Monitoring and Diagnosis, 2008.

[2] E. M. Lalitha and L. Satish ―Wavelet Analysis for Classification of Multi-source PD Patterns‖, IEEE Transactions

on Dielectrics and Electrical Insulation, vol. 7, no. 1, pp.40-47, February 2000

[3] K. X. Lai, B. T. Phung and T. R. Blackburn, ―Partial Discharge Analysis using PCA and SOM‖, IEEE Power Tech,

2007, pp.2133-2138.

UHVnet 2011 A2.3

32

Frequency Response Analysis of Transformer Winding Deformation

Based on Multi-conductor Transmission Line Model

T. Y. Ji1, W. H. Tang

1*, C. H. Wei

1 and Q. H. Wu

1

1University of Liverpool, UK


This paper presents a multi-conductor transmission line (MTL) model of a transformer winding to perform

frequency response analysis (FRA) for the detection of winding deformation. The MTL model is built based

on the travelling wave theory [1-3]. It views every disc of a transformer winding as a transmission line and

these lines are parallel with each other and with the ground. The winding conductor is composed of infinite

segments of length dx and each unit is described by the parameters of inductance, resistance, capacitance and

conductance. These parameters need to be identified in order to model a transformer for FRA analysis. The

construction of the MTL model is explained in detail in the paper. The geometry parameters of a test

transformer and its measured FRA data in normal condition are provided in this paper. The winding

parameters of the MTL model of the transformer are firstly obtained by theoretical calculation, then refined

by optimisation towards the minimum error between the frequency response of the model and the measured

frequency response. By comparing the measured frequency response of the test transformer and the

frequency response of its MTL model, it has shown that the MTL model is accurate enough for FRA, as long

as the winding parameters are properly given. The winding parameters of the MTL model with deformed

winding are estimated using finite element method (FEM), and the frequency response is calculated

correspondingly. Two deformation scenarios are involved in the simulation study, and the FRA results have

been presented to show that the deformation can be detected and the degree of deformation can be reflected

as shown in Figure 1.

Figure 1: The frequency responses of the normal and the

deformed windings.

[1] E. P. Dick and C. C. Erven. Transformer diagnostic testing by frequency responce analysis. IEEE Transactions

on Power Apparatus and Systems, 1(6):2144–2153, 1978.

[2] E. Rahimpour, J. Christian, and K. Feser. Transfer function method to diagnose axial displacement and radial

deformation of transformer windings. IEEE Transactions on Power Delivery, 18(2):493–505, 2003.

[3] R. Rudenberg. Electrical shock waves in power systems: traveling waves in lumped and distributed circuit

elements. Harvard University Press, Cambridge, Massachusetts, 1968.

UHVnet 2011 A2.4

33

Effect of Climatic Condition on Polymeric Insulators

A.S. Nekeb*1

, N. Harid1, A. Haddad

1



The problem of aging or degradation of outdoor polymeric insulators has been a major concern for electrical

utilities and researchers. Their surface hydrophobicity can be significantly reduced with time as they are

subjected to variable climatic conditions such as temperature, humidity, and ultraviolet radiation. These can

accelerate the aging process depending on their severity and the geographic location of the insulators, and

may lead to loss of their insulating properties and subsequent flashover. Fig. 1 summarises the effect of

various climatic conditions on polymeric insulators.

This paper reviews the effect of climatic conditions on polymeric insulators, with emphasis on the effect of

ultraviolet radiation. Previous research work on this subject is reported and discussed. The standards

covering UV irradiation methods on insulator samples are reviewed. Initial tests consisting of subjecting

insulator samples to various cycles of irradiation are described. The test facility, which also provides

automatic temperature and humidity control for a given test cycle, is described.

Figure 1: Effect of Climatic conditions on polymeric insulators

UHVnet 2011 A2.5

34

Acoustic Noise Evaluation for Overhead Lines

Qi. Li*1

, G. Zhang1, S. M. Rowland

1 and R. Shuttleworth

1



Followed by the rapid increase of voltage level in modern power systems, audible noise is now becoming

one of the critical design and environmental considerations for overhead lines. Power utilities have carried

on plenty of experimental measurements to evaluate the noise level emitted from high voltage conductors.

Not only outdoor measurements which are carried out close to a whole span of overhead line [1] but also

indoor measurements [2, 3] which employ cage configurations to simulate sections of overhead line have

been reviewed in the first section of this paper. Processes for predicting audible noise of overhead lines have

been summarized.

Cage experiments have been well proven to be an effective way to study the environmental impact of

transmission lines. It is employed to control the surface gradient in acoustic noise testings for different

conductors. A cage set-up (National Grid High Voltage Lab in Manchester) for audible noise examination is

proposed in the second section of this paper.

An appropriate cage radius was first selected by considering the various conductor configurations. In order to

mitigate the excessive corona activities in each end of conductor, a corona guard is installed at each end. The

radius of this guard, so as to eliminate corona, is then determined by FEA simulation results. The non-

uniformly distributed electric field within the cage is finally examined. The length of middle section which

provides a uniformly distributed electric field is then determined, enabling effective experimental design.

Besides the electrical design, the tensioning system design and acoustic measurement techniques for the cage

experiment are introduced. An anechoic chamber was introduced to cover the whole cage so as to shield the

whole cage from background noise.

Figure 1: A typical cage set-up [2]

[1] R.A. Popeck and R.F. Knapp "Measurement and Analysis of Audible Noise from Operating 765 kV

Transmission Lines", IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, pp. 2138 1981.

[2] M. J. Lekganyane, N. M. Ijumba, and A. C .Britten, ―Corona Audible Noise Measurements in a Small Indoor

Corona Cage under HVDC Voltages‖, 2006 International Conference on Power System Technology

[3] Minhua Ma, Yuming Zhao, Zhicheng Guan, Liming Wang, ―The influence of contaminations on HVDC conductor

corona characteristics‖, Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2007.

UHVnet 2011 A2.6

35

Transient Fault Location in Low Voltage Distribution Networks

Yuxian Tao*1

, W.H.Siew1 and J.J. Soraghan

1



Underground cables are widely used in the UK for electricity distribution. Additionally, many of the cables

are approaching the end of their design-life. Distribution Network Operators (DNOs) will normally keep

these aged cables in service to extend their service lifetime. However, the aged cables are prone to develop

faults, which result in loss of power supply. This leads to customer minutes lost -- a parameter that is

monitored by the Electricity Regulator (ER). Hence, it becomes desirable to know where in their power

network, a fault might be developing. The early stage of a fault could be classified as transient faults. Time

domain reflectometry (TDR) is mainly used to pre-locate faults in low voltage underground cable network.

However the success of this technique to address transient faults relies both on the simplicity of the cable

circuit being diagnosed and the point of diagnosis. This is because T-joints in a cable network and parallel

circuits at the point of diagnosis could result in a complicated waveform being acquired and therefore

making unreliable pre-location. Hence current technologies for identifying and locating transient faults either

require access to residential homes or use of a heavy blocking inductor to ensure that only a particular circuit

is being investigated. Furthermore, the network operators are not able to pre-locate after the event because

transient faults are not predictable and may not recur during the investigation. Transient faults that occur in

underground cable networks are mostly electric arcing caused by insulation failure. Electric arcing in low

voltage cables is often self-extinguishing [1] and does not present an immediate hazard. This is the reason for

their unpredictability. This presentation will therefore review the existing technologies and to present a

strategy for overcoming the restrictions or limitations posed by the existing strategies for locating transient

faults.

[1] W. Charytoniuk, Wei-Jen Lee, Mo-Shing Chen, & J. Cultrera. ―Arcing fault detection in underground distribution

networks - feasibility study‖, IEEE Transactions on Industry Applications, Volume 36, Issue 6, pp. 1756-1761,

2000

UHVnet 2011 A2.7

36

A Survey on the Potential of CF3I Gas as an Alternative for SF6

M. S. Kamarudin*1

, M. Albano1, P. Coventry

2, N. Harid

1 and A. Haddad

1


2National Grid UK


Sulphur hexafluoride (SF6) has been widely used as an insulator in gas-insulated switchgear (GIS)

applications. But due to the fact that it is a greenhouse gas, many researchers have been trying to find

alternative solutions for it. Furthermore, SF6 produces highly toxic and corrosive substances when it is

subjected to electrical discharges. Trifluoroiodomethane (CF3I) has recently been regarded as a candidate for

replacing SF6. CF3I has been used as a fire suppressor and now many investigations have been carried out

throughout the world to assess its capability in high voltage applications. This paper surveys this previous

work and identifies some of the properties which are relevant to high voltage applications.

With a global warming potential 23,900 times greater than carbon dioxide (CO2), and atmospheric lifetime

3,200 years, SF6 is the most potent greenhouse gas in existence. Its production is now restricted under Kyoto

Protocol. Table 1 shows the general properties comparison between CF3I with SF6.

Table 1: General properties of CF3I and SF6

Material CF3I SF6

Molecular mass 195.91 146.05

Characteristic Colourless

Non-flammable

Colourless

Non-flammable

Global Warming Potential (GWP) Less than 5 23,900

Ozone Depleting Potential (ODP) 0.0001 0

Lifetime in atmosphere (year) 0.005 3,200

Boiling point (0.1 MPa) – 22.5°C – 63.9°C

At 0.5 MPa, the boiling point of CF3I is around 25°C, compared to –30°C for SF6 [1]. For this reason, it can

be difficult to compress CF3I in HV switchgear at temperature common in winter. The adoption of other

gases such as nitrogen (N2) or CO2 helps in reducing the boiling point, and it is required for outdoor

application. Using Dalton‘s law, the partial pressure in a CF3I- N2 gas mixture can be expressed as

Pgas mixture = PCF3I + PN2 (1)

where

Pgas mixture total pressure of the gas mixture

PCF3I partial pressure of CF3I gas

PN2 partial pressure of N2

A study by Toyota et. al in 2006 [2] revealed that for a same gap length of electrodes, CF3I gas has a higher

dielectric strength of SF6, which is about 1.2 times higher. Another study by the same researchers revealed

that a mixture of 60% CF3I with 40% N2 has a dielectric strength as equal to that of SF6.

With a dielectric strength of 1.2 times better than SF6, CF3I has been identified as a very good candidate to

replace SF6 as a gas insulator. More research works should be carried out on the capabilities of CF3I,

particularly with regards of its mixtures, its performance under uniform and non-uniform field and also to

control the by-products produced after a successful discharge. Work is in progress to develop a test facility to

explore the properties of CF3I and its mixtures for insulation and switchgear applications.

[1] M. Taki, D. Maekawa, H. Odaka, H. Mizoguchi and S. Yanabu, ―Interruption Capability of CF3I Gas as a

Substitution Candidate for SF6 Gas‖, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 14, no. 2,

2007.

[2] H. Toyota, S. Matsuoka and K. Hidaka, ―Measurement of Sparkover Voltage and Time Lag Characteristics in CF3I-

N2 and CF3I-Air Gas Mixtures by using Steep-Front Square Voltage‖, Electrical Engineering in Japan, vol. 157,

no. 2, 2006.

UHVnet 2011 A2.8

37

A New Technique to Enhance the Earthing System by Increasing the

Horizontal Earth Electrode Effective Length

A Elmghairbi*1

, N Harid1, H Griffiths

1, A Haddad

1



Horizontal earth electrodes are commonly used to enhance earthing systems located in areas with high soil

resistivity, in order to reduce overall earth impedance. Such electrodes are commonly used, for example, to

interconnect adjacent earthing grids or the individual earthing systems of turbines on windfarms. The ability

of a horizontal earth electrode in reducing earth potential rise is limited because, no further reduction is

obtained by increasing its length beyond a certain length known as the effective length. It is also well known

that the behaviour of earthing systems subjected to transients is different from that under power frequency

faults. This results in a shorter effective length under transient conditions than at power frequency.

In this paper, field experiments and computer simulations of a sectionalised 88m length horizontal earth

electrode under different energisations (dc, variable frequency ac and transients of different shapes) are

reported. From measurements of the voltage and current at the injection point, and by incrementally

increasing the length of the test electrode, the effective length of the horizontal earth electrode was

determined under the different energisations for the soil conditions pertaining to this particular installation.

Moreover, current and voltage distribution along the length of the electrode was recorded. The experimental

and simulation results of voltage and current show reasonably close agreement and also that quite good

prediction of the effective length using simplified formulae is possible.

Using the same experimental facility and test electrode, a new proposed method to increase the effective

length of the horizontal earth electrode was investigated by installing an additional above ground insulated

parallel conductor which is bonded to the bare underground horizontal electrode at points along its length.

The results show that the current and voltage distributions are changed such that a greater length of buried

conductor is utilised and that this contributes to an additional reduction in the earth impedance, and hence the

developed earth potential rise, at the point of current injection.

20

25

30

35

40

45

50

1 1.5 2 2.5 3 3.5 4 4.5 5

Co

nd

uct

or

len

gth

(m

)

Rise time (ms)

Measured CDEGS formula

Figure 1: Effective length of a horizontal earth electrode

[1] M. Muhr, S. Pack and S. Jaufer, ―Usage and Benefit of an Overhead Line Monitoring System‖, International

Conference on High Voltage Engineering and Application, November 2008

[2] M. M. Werneck, and A. C. S. Abrantes, ―Fiber-Optic-Based Current and Voltage Measuring System for High-

Voltage Distribution Lines‖, IEEE Transactions on Power Delivery, vol. 19, no. 3, July 2004

[3] C. A. Spellman, A. Haddad D.M. German and R. T. Waters, ―Improved Three-Phase Voltage Measurement Using

Capacitive Probe‖, Proceeding of the UniversitiesPower engineering Conference, vol. 1, pp.352-355, 1999

UHVnet 2011 A2.9

38

A Novel Portable Testing Device for Surge Protective Systems

C. Long*1, W. Zhou

2, C. Zhou

1, J. Yu

2


2Wuhan University, China


With significant increase in penetration of the Surge Protective Devices (SPDs) into areas such as

telecommunications, electricity, meteorology, railway, petrochemical industry, field testing of SPDs has

become a great concern. At the present, however, impulse wave generators, generally utilized as laboratory

equipments, are too heavy to be utilised for the purpose. In this paper, a novel, portable testing device

providing with a combination of maximum amplitude of 6kV/3kA and DC voltage supply of maximum

amplitude of 2kV is presented. It is designed to test on site the condition of SPDs which have been utilized

for many years. The device is equipped with a PWM and a high frequency circuit in order to minimize DC

voltage supply. The device uses a DSP as the core component to measure and determine the peak impulse

voltage and impulse current automatically. Meanwhile, simulation of EMTP-ATP has been carried out to

evaluate the design of the combination wave generator circuit which needs to generate IEEE standard

combination waveforms. The calculation, simulation and field testing data demonstrate that the portable test

device with weight of mere 13kg is capable of characterising and diagnosing the condition of SPDs.

[1] C. Long, et. al., ―Study on Portable SPD Site Test System, Shaanxi Electric Power‖, 2010, 20(6):55-58

[2] ―IEC 61643-1: 1998 Low-voltage surge protective devices – Part 1: Surge protective devices connected to low-

voltage power distribution systems – Requirements and tests‖, 1998

[3] L. Liu, G. Zhang, et. al., ―Design of Combined Wave Generator by Using Universal Variable Method‖, High

Voltage Engineering, 2007, 33(1): 123-130

UHVnet 2011 A2.10

39

A Solar Powered Wireless Data Acquisition System for High Voltage

Substations

A.C. Bogias*1

, N. Harid1, and M. Haddad

1



Wireless communication systems can offer significant advantages when applied to power system monitoring

applications and may become attractive to power utilities [1].

In this work a wireless solar battery powered data acquisition system for monitoring high voltage substation

equipment was developed. An example-application to a surge arrester was used to illustrate the capabilities

of the developed system. Various diagnostic methods for monitoring surge arresters exist. However, those

that measure the operating voltage and leakage current and carry out signal processing can provide more

accurate diagnostic information [2, 3].

The proposed WLAN system, shown in Figure 1, consists of a solar panel, four lithium-ion batteries, surge

protection and signal conditioning IC‘s, power electronic IC‘s, a microcontroller and Wireless Local Area

Network (WLAN – IEEE 802.11b/g) module, making up the WLAN Sensor. The WLAN Sensor acquires

and transmits the current and voltage signals from the test surge arrester. The transmitted data is received by

a WLAN access point connected to a remote Personal Computer (PC), data processing using LabVIEW. A

prototype wireless data acquisition system has been built and successfully used to measure the leakage

current and applied voltage of a surge arrester tested in the Cardiff High Voltage laboratory.

The results are in close agreement with those recorded directly through a Data Acquisition (DAQ) card and

transmitted via coaxial cable.

.

Figure 1: The WLAN Sensor with the solar panel.

[1] F. Cleveland, ―Use of Wireless Data Communications in Power System Operations‖, Power Systems Conference

and Exposition, 2006. PSCE '06. 2006 IEEE PES. 2006.

[2] M. Haddad, D. Warne. (2004). ZnO surge arresters . In: Advances in High Voltage Engineering . London:

Institution of Engineering and Technology. 191-244.

[3] J. Lundquist, L Stenstrom, A. Schei, and B. Hansen, ―New method for measurement of the resistive leakage

currents of metal-oxide surge arresters in service‖', IEEE Transactions on Power Delivery,Vol. 5(4), pp. 1811-

1822, 1990.

UHVnet 2011 A2.11

40

The Performance of Nanocoating on High Voltage insulators

S. Braini *1

, A. Haddad* 2



The most important factor for dimensioning outdoor insulation is pollution performance. Depending on the

pollution severity of the site, outdoor insulators need to have sufficient surface leakage length to ensure that

dry band formed and surface arcing is minimised.

Conventional insulators, made of porcelain and glass, have shown good performance over decades of in-

service performance. However, they suffer from a hydrophilic surface property, thus allowing high surface

leakage current to flow on the wetted surface. Such currents cause dry bands at areas of high current density

and lower wetting rates, which eventually causes surface arcing and frequently complete flashover of the

insulator. A number of remedies were used in the past to improve the surface properties, including greasing

and RTV coatings. These mitigation techniques, although effective, are very labour intensive and expensive

solutions.

A recently proposed solution consists of the application of a nano-coating on the surface of the insulator. The

nano-coating used in this work is a Voltshield coating, which is a chemically cross-linked polymeric resin

with extremely good 'non-stick' properties. This coating bonds to the surface of the insulator and forms a

very thin layer which gives highly hydrophobic properties to the surface of the insulator. The coated surface

permits the rapid dispersal of water and does not allow adherence of solid pollutant due to its cross-linked

molecular bonding [1].

In this work, the performance of this nano-coating is investigated under artificial pollution conditions using

the dry layer method of IEC60507. It was found that the nano-coated porcelain insulator performs much

better than the non-coated porcelain insulator both in suppressing the leakage current activities and retaining

its surface hydrophobicity.

Figure 1 shows the test results obtained using a dry pollution layer and clean fog as recommended in IEC

60507.

a) nano-coated insultors b) standard insulator

Figure 1: Pollution test results on standard and nano-coated porcelain insulators

[1] J. Blacket, ―VOLTSHIELD- ANTI-POLLUTANT TREATMENT FOR GLASS AND GLAZED PORCELAIN

INSULATORS― 20th

International Conference on Electricity Distribtion, Praque,8-11 June 2009

UHVnet 2011 A2.12

41

Performance of Tower Footings Resistance under High Impulse

Current

M. Ahmeda, N. Harid, H. Griffiths and A. Haddad



The rise of earth potential associated with the flow of fault current through transmission towers is important

for assessing the lightning performance of lines, and more importantly, the risk of hazardous step and touch

voltages at tower bases. Studies on full-scale tower base grounding systems available in the literature are

limited [1,2]. Measurements on such electrodes offer a valuable means of understanding their lightning

behaviour and for validating theoretical models. In this work, the tests on the tower footings were intended to

determine impulse resistance and demonstrate its non-linear variation with current magnitude.

In this paper, a high-current test set-up consisting of a 20kA impulse generator and a 30m-long overhead line

suspended on wood poles of 1.6m height connecting the current (A) impulse generator to the test tower base.

A ring electrode connected to 8 peripheral rods was used as a return current electrode. The tower base

potential rise with reference to the current return point of the generator was measured.

Figure 1 shows the impulse resistance decreasing as a function of peak current magnitude for all tower

footings. This fall is attributed to soil ionisation around the test electrode.

Figure 1: Variation of impulse resistance of tower footings with current magnitude.

The highest reduction in resistance occurs with the footing which has the highest DC resistance (Leg 1).

When the current increases from 600A to 6kA, the impulse resistances decreased by 47% for Leg 1, 40% for

Leg 3, 22% for Leg 2 and 14% for Leg 4. For the complete tower base, with all four legs connected in

parallel, the percentage reduction in the impulse resistance is relatively small due to the current division

between the legs which leads to limited ionisation progression around the individual legs.

[1] M Takeuchi, Y. Yasuda, H. Fukuzono, K. Kawabata, T. Hara and S. Sekioka, ―Impulse Characteristics of a 500kV

Transmission Tower Footing Base with Various Grounding Electrodes‖, International Conference on Lightning

Protection, ICLP, 1998

[2] E. A. Cherney, K. G. Ringler, N. Kolcio and G. K. Bell P. L. Lewin and S. J. Dodd, ―Step and Touch Potentials at

Faulted Transmission Towers‖, IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, no. 7,

pp.3312-3321, 1981

UHVnet 2011 A2.13

42

High Frequency Performance of a Vertical Rod Electrode

S. Mousa, N. Harid, H. Griffiths and A Haddad



Earth electrodes are known to have variable frequency dependence. This was verified by several published

papers on the subject [1, 2]. Such behaviour is thought to be affected by inductive and capacitive stray

components of the earth electrodes. Computations have shown that for given geometries and soil conditions,

a sharp departure of the earth electrode impedance from the DC/low frequency values can occur.

To date, most experimental and measurement techniques use low magnitude DC, low frequency ac an

impulse currents. No established technique is available to investigate experimentally the performance of

these electrodes under variable high frequency up to hundreds of kilohertz.

In this work, we explore the performance of vertical rods using a high frequency source and a test electrode

of 1.2m length in non-uniform soil. Figure 1 shows the measured impedance over the frequency range of DC

to 120kHz. As can be seen, there is a sharp decrease of impedance at about 60kHz. At this value the

downturn frequency happens and the capacitive behaviour appears also the ground resistance decreases from

100.95 to around 8 .

1

10

100

1000

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

Imp

ed

an

ce

()

Frequency (Hz)

Figure 1: Measured frequency response of 1.2m long vertical

earth electrode.

[1] Davies A M, H.Griffiths and T.E.Charlton, ‗High Frequency Performance of a Vertical Earth Rod‘,

Proceedings of the 24th International Conference on Lightening Protection (ICLP), Birmingham UK, 1998,

pp.536-540.

[2] Griffiths H, Haddad A and Harid N, ‗Characterisation of earthing systems under high frequency and transient

conditions‘, Proc. of the 28th Universities Power Engineering Conference (UPEC 2004), Vol. 1, pp.188-192,

Bristol, England, 6-8 September 2004.

UHVnet 2011 B2

43

Posters: Condition Monitoring

B2.1 FDTD Modelling of Partial Discharge Detection in Power Distribution Cables using

HFCTs ................................................................................................................................................................. 44

B2.2 Use of Hidden Markov Model for Partial Discharge-led Failure Development Modelling ............................... 45

B2.3 Dynamically Weighted Ensemble of Neural Networks for Classifying Partial Discharge

Patterns ............................................................................................................................................................... 46

B2.4 A Successful On-site PD Testing Experience of 11kV EPR Cable Insulation Systems ..................................... 47

B2.5 Radiometric Arc Fault Detection ........................................................................................................................ 48

B2.6 Voltage Transducer for Transient Measurements on High Voltage Overhead Lines ........................................ 49

B2.7 Fault Location using FPGAs and Power Line Communication .......................................................................... 50

B2.8 A New Method to Improve the Sensitivity of Leak Detection in Self-Contained Fluid-

filled Cables ....................................................................................................................................................... 51

B2.9 Energy Harvesting from Electric Fields in Substations for Powering Autonomous

Sensors ................................................................................................................................................................ 52

B2.10 Ageing and Temperature Influence on Polarization/Depolarization Current Behaviour of

Paper Immersed in Natural Ester ........................................................................................................................ 53

B2.11 An On-line Lightning Monitoring System for Transmission Lines .................................................................... 54

B2.12 Energy Harvesting in Substations for Wireless Sensors and a New Arc Capacitor

Structure 55

UHVnet 2011 B2.1

44

FDTD Modelling of Partial Discharge Detection in Power Distribution

Cables using HFCTs

X Hu*1

, A J Reid1, M D Judd

1 and W H Siew

1

1University of Strathclyde, UK *E-mail: [email protected]

Partial discharge (PD) is an electrical discharge that bridges only part of the insulation material in an

insulation system such as those in power cables. If these discharges are left to develop, they will gradually

erode the insulating material and may lead to complete failure of the cable or accessory. PD measurement

has been widely used in power industries as a practical tool to evaluate insulation condition of cables because

the pulses can often be detected at the cable ends using high frequency current transformers (HFCTs). PD

propagation in cables experiences significant attenuation [1-3] and thus PD pulse magnitude and shape may

change a lot by the time it finally reaches a detection point, which might be up to a few kilometres away. If

propagation effects can be properly characterised, diagnostic post-processing tasks like classification and

identification might be enhanced.

In order to bridge the gap between PD measurement and interpretation of the results, finite difference time

domain (FDTD) methods are being evaluated as a means of modelling the entire PD process from current

pulse at source to detection by a remote HFCT. Various dimensions and types of cables have been modelled

using commercial software (XFdtd [4]) and the modelling has been oriented towards a comparison with the

PD measurement using HFCTs. The source current pulse can be derived from experimental PD data while

the PD current pulse at the location where the HFCT would be attached must be calculated numerically from

the simulated magnetic field data by applying Ampere‘s Law.

This paper describes how a PD current pulse is modelled using FDTD and examples of the propagating

electric field will be given. Figure 1 shows a slice of electric fields travelling along the cable after a PD has

been excited on the inner conductor. The principle of simulating the HFCT will be introduced and results

will be presented to demonstrate the accuracy of the Ampere‘s Law current sensor. Output will then be

suitable for combination with the HFCT‘s transfer function to obtain HFCT‘s response. The findings of this

work may helpfully improve the understanding of existing results from PD measurement in cables.

Figure 1. FDTD model of a 1m cable sample

[1] C. Xu, L. Zhou, J. Y. Zhou, and S. Boggs. High frequency properties of shielded power cable part 1: Overview of

mechanisms. IEEE Electrical Insulation Magazine, 21(6):24–28, Nov/Dec 2005.

[2] S. Boggs, A. Pathak, and P. Walker.Partial discharge XXII: High frequency attenuation in shielded solid dielectric

power cable and implications thereof for PD location. IEEE Electrical Insulation Magazine, 12(1):9–16, Jan/Feb

1996.

[3] N. Oussalah, Y. Zebboudj, S. Boggs. Partial Discharge Pulse Propagation in Shielded Power Cable and Implications

for Detection Sensitivity. IEEE Electrical Insulation Magazine, 23(6):5-10, Nov/Dec 2007.

[4] http://www.remcom.com/

UHVnet 2011 B2.2

45

Use of Hidden Markov Model for Partial Discharge-led Failure

Development Modelling

D. Zhou1,2

, C.R.Li2 and Z. D. Wang

1*


2North China Electric Power University, China


Partial discharge (PD) detection and monitoring is of vital importance to confirm the insulation integrity of

the insulation of high voltage equipment, especially for equipment with a complex insulation system, such as

power transformers. In power transformers, PD can lead to surface tracking on solid insulating materials,

which causes irreversible damage and may eventually lead to a breakdown of the concerned operating

component. PD can also decompose the insulating oil and pollute the oil system in such a way that the

insulation properties of the oil can no longer be guaranteed.

Continuous on-line monitoring of partial discharges becomes possible with the development of advanced

sensors and data-acquisition systems. However, there is still a lack of effective data analysis and modelling

methods for the correct interpretation of the obtained PD monitoring data to prevent PD-led failures.

The severity and evolution stage of PD led insulation degradation process must be recognized before the full

utilisation of continuous on-line PD monitoring. In this paper a hidden markov model (HMM) with left-right

topology for PD development modelling is proposed.

HMM, as a double stochastic process, comprises an underlying stochastic process that is not directly

observable but can be visualized through another set of stochastic processes that produce a sequence of

observations. This is in accordance with the nature of partial discharge developing process as we know. In

the proposed HMM model, initiation stage, developing stage I, developing stage II and pre-breakdown stage

are defined as the four underlying PD evolution stages. Pulse repetition rate, maximum pulse amplitude and

average pulse amplitude are chosen as the observations. Two sets of experimental data are utilized for the

training of the model. A third set of data is used for verification. Promising results show that a highly

successful recognition rate of PD evolution stage can be achieved using HMM through the decoding process.

Training Stage Recognition Stage

Data Acquisition

Data Preprocessing

Feature Extraction

HMM training

Data Acquisition

Data Preprocessing

Feature Extraction

HMM State Decoding

Figure 1: the flowchart of partial discharge development

modelling process

UHVnet 2011 B2.3

46

Dynamically Weighted Ensemble of Neural Networks for Classifying

Partial Discharge Patterns

A. Abubakar Mas‘ud*1

, B. G. Stewart1, S. G. McMeekin

1 and A.Nesbitt

1



Partial discharges (PD) measurements are used to monitor the degradation of insulation subjected to High

Voltage (HV) electrical stress. Recently, the pursued goal has been identifying a robust method for

recognition of different categories of PD data using expert systems. This can be achieved through the

ensemble of neural networks (ENN), where by different NN models are trained and their predictions

combined as shown in Fig.1. The training data for the ENN considered here comprises 9 statistical

parameters obtained on different PD measurements of corona from a point-plane arrangement. Dynamically

weighted averaging of neural networks is adopted where the ensemble output gives the weighted average of

the output of each NN. Using this strategy it is shown that the ENN output has the best accuracy of 98.12%,

while single NNs such as the Multi-Layered Perception Network (MLPN), Elman Recurrent Network

(ERNN) and Radial Basis Function Network (RBFN) have independent accuracies of 97.5%, 96.97% and

97.4% respectively. The results demonstrate that the ENN model has potential for further application to

other PD scenarios.

Figure 1: An ensemble of Neural Networks.

[1] Z. Zhao, Y. Zhang and H. Liao, ―Design of ensemble neural network using the Akaike information criterion‖,

Engineering Applications of Artificial Intelligence, 2008.

[2] D. Jimenez, ― Dynamically weighted Ensemble Neural Networks for Classification‖, IEEE World Conference on

Computational Intelligence, 1998

[3] T. Hong, M.T.C Fang, ―Detection and Classification of Partial Discharge Using a Feature Decomposition-Based

Modular Neural Network, vol.50, no.5, October 2001.

UHVnet 2011 B2.4

47

A Successful On-site PD Testing Experience of 11kV EPR Cable

Insulation Systems

Xiaosheng Peng*1

, Chengke Zhou1, Donald M. Hepburn

1, Xiaodi Song

1

Glasgow Caledonian University, UK

* Email: [email protected]

A power generating station in the United Kingdom has reported a number of in service failures in its 11kV

single core Ethylene-Propylene Rubber (EPR) insulated cables. Several industrial companies have carried

out on-site condition assessment to determine whether other insulation defects were present but no

conclusive results have been found due to presence of strong background electrical noise. The present

authors were invited to carry out on-site testing to demonstrate the effectiveness of their denoising

techniques. This paper presents the processes of the on-site cable partial discharge signal detection

experience and the signal processing of the raw data. Following a brief introduction to the tests, equipments

and connections, the paper analyses sources of different types of interference signals. These are found to

originate mainly from UPS Inverter Supplies or 11kV Motor drive circuits. Thereafter, second generation

wavelet transform (SGWT) data denoising algorithm is introduced. SGWT is proved to be an effective

denoising technique for the detected data. Also presented in the paper are PD pattern identification and PD

source localization methods which are used to identify the source of the PD signal. Finally the diagnosis

results, with indication of potential insulation defect and cable joint problems, are provided.

[1] X. Zhou, C. Zhou, I. J. Kemp, ―An improved Methodology for Application of Wavelet Transform to Partial

Discharge Measurement Denoising‖, IEEE Trans. Dielectrics and Electrical Insulation, Vol. 20, No. 2, March,

2005.

[2] C. Zhou, X. Zhou, B. Stewart, A. Nesbitt, D. Hepburn and D. Guo: ―Comparisons of Digital Filter, Matched Filter

and Wavelet Transform in PD Detection‖, Recommended by CIGRE UK panel to CIGRE 2006.

[3] X. Song, C. Zhou, D.M. Hepburn and M. Michel, ―Second Generation Wavelet Transform in PD Measurement

Denoising‖, IEEE Trans. Dielectrics and Electrical Insulation, Vol. 14 (6), 2007

UHVnet 2011 B2.5

48

Radiometric Arc Fault Detection

R. M. Harris*1

, M. D. Judd1 and P. J. Moore

2


2Elimpus Ltd., UK


When arcs are formed they are accompanied by the radiation of electromagnetic transients which can be

captured as a signal which propagates in the radio spectrum. Such captures are commonly utilised in the

study and location of lightning arcs [1], where the emissions are referred to as sferics. Our aim in recent

research has been to capture radiometric emissions emitted by arcs resulting from faults on power

distribution networks. The advantage of being able to do this is that the detection equipment does not require

a direct connection to the power system, and there may be potential for wide-area coverage.

To achieve this, four monitoring stations have been installed, each equipped with a receiving antenna and

sampling equipment, as shown in Figure 1. Monitoring has been carried out in the High Frequency (HF)

range of the radio spectrum, since previous studies have suggested that this is the range most likely to yield

successful capture of this class of signal [2]. This choice of frequency range has a sound theoretical footing

stemming from the fact that the length of the radiating element determines the wavelength of the emissions.

Arcs resulting from faults and the radiating structures connected to the arc current path in the power systems

equipment itself are of a size that is more compatible with emissions in the HF range. This is why most

lightning detection systems operate in the Very Low Frequency (VLF) range. The long-channel, high-current

arcs induce VLF and LF emissions readily detectable over great distances. Despite this fact, the equipment

has proved able to capture and locate the origin of lightning sferics by utilising their smaller, but numerous

components in the HF range [3], as well as successfully capturing emissions emanating from power system

arcs.

This paper presents a selection of results to date and discusses the challenges that this type of measurement

presents.

Figure 1: Radiometric Arc Detection System.

[1] H.D. Betz, U. Schumann and P. Laroche (Eds.), Lightning: Principles, Instruments and Applications, Springer

Science and Business Media, 2009

[2] E. J. Bartlett, M. Vaughan and P. J. Moore, ―Investigations into Electromagnetic Emissions from Power System

Arcs‖, IEE Electromagnetic Compatibility Conference , 1999

[3] R. M. Harris, M. D. Judd and P. J. Moore, ―A Novel Approach to Lightning Location: Potential for Reducing

Electrical Supply Disruption‖, Proc. International Conference on Gas Discharges and Their Applications,

Greifswald, Sept. 2010, pp.534-537

UHVnet 2011 B2.6

49

Voltage Transducer for Transient Measurements on High Voltage

Overhead Lines

M. F. Hussin*1

, A. Haddad1 and N. Harid

1



Overhead lines provide the best economic and practical solution for energy transport but suffer from faults.

Overvoltages resulting from these faults can cause degradation or failure of high voltage plant. The main

origins for the faults are lightning and switching surges in addition to weather related causes such as heavy

wind and ice [1]. Therefore, it is vital that measurement and monitoring of the voltage on HV lines are

assessed accurately to maintain safe and economic operation of HV substation and overhead line equipment.

Voltage transformers are widely used for measurement and monitoring purposes but they are bulky and

costly [2]. Moreover, their frequency response is not adequate for the measurement of fast transient. In this

work, a capacitive-type transducer is developed for voltage measurements on HV lines. The transducer uses

similar principles as the contactless capacitive probe developed in previous work [3]. However, in this new

design, the probe is connected to the HV line instead of the ground. Laboratory experiments are carried out

to calibrate the transducer under AC, fast and slow front impulses. An impulse generator is used for the

impulse tests while a variac was used for the AC tests. The constructed probe was tested using a number of

low-voltage arm capacitance values (2.2nF to 10nF) with the probe installed around a HV conductor above

ground. A number of conductor height levels (0.5m to 2.5m) and low-voltage arm capacitance were used to

investigate the effect on the output voltage. Figure 1 shows a comparison between the probe output voltage

and a standard HV capacitive divider obtained at a height of 2.5m. As can be seen on the figure, good

linearity is obtained for all voltage types. Increasing the value of the low-voltage-arm capacitance cause the

output to decrease significantly in a non-linear way. This can be particularly useful for the measurement of

higher surge voltage. Future tests are planned at the University test overhead line.

Figure 1: Output Voltage produced by the transducer

[1] M. Muhr, S. Pack and S. Jaufer, ―Usage and Benefit of an Overhead Line Monitoring System‖, International

Conference on High Voltage Engineering and Application, November 2008

[2] M. M. Werneck, and A. C. S. Abrantes, ―Fiber-Optic-Based Current and Voltage Measuring System for High-

Voltage Distribution Lines‖, IEEE Transactions on Power Delivery, vol. 19, no. 3, July 2004

[3] C. A. Spellman, A. Haddad D.M. German and R. T. Waters, ―Improved Three-Phase Voltage Measurement Using

Capacitive Probe‖, Proceeding of the UniversitiesPower engineering Conference, vol. 1, pp.352-355, 1999

UHVnet 2011 B2.7

50

Fault Location using FPGAs and Power Line Communication

S. Robson*1

, A. Haddad1 and H. Griffiths

1



This work demonstrates a fault location scheme based on the time domain measurement of the fault-induced

transient. The combination of high speed analog to digital conversion, GPS time-stamping and customisable

triggering control logic is shown to be a possible way of cost effectively resolving transient arrival times to

within 30 ns. The simultaneous gathering of the initial transient induced by a fault event can be carried out

by several devices scattered across a power network, facilitating the possibility of determining the position of

the fault by triangulation, even in branckhed networks. Within the same FPGA chip as the fault detection

control logic, an Orthogonal Frequency Division Multiplexing (OFDM) modulator can also be implemented,

allowing a means of sending the measured time-stamp information back to an entry point to a wired

communication infrastructure, e.g. a SCADA interface at the primary substation. Synchronisation at the

receiver is achieved via FPGA hardware implementation of the Schmidl and Cox algorithm [1].

Demonstration and verification of the system has been carried out in a simulation environment. For the

OFDM modulator, the various parameters (e.g. number of subcarriers, sampling frequency and cyclic prefix

length) have been determined by performance evaluation on a typical rural 11 kV network modelled within

the ATP/EMTP environment and MATLAB. Under assumptions of noise levels and a used bandwidth no

greater than 300 kHz, it is shown that with a simple time-multiplexed multi-node implementation with a

carefully considered choice of OFDM parameters, satisfactory performance can be achieved. The high level

block diagram of the system is shown in fig. 1.

It is recognised that extensive field trials are required to fully test the proposed concept. Potential difficulties

are the non-linear shape of the fault transient (i.e. due to arcing) and ensuring an accurate timestamp. Field

trials using coupling capacitors for the modulator coupling to the line and a rogowski coil current transducer

are planned.

Figure 1: Block diagram of the FPGA based fault locator

[1] T.M. Schmidl and D.C. Cox, ―Robust frequency and timing synchronization for OFDM,‖ IEEE Trans. Commun.,

vol. 45, no.12, pp. 1613-1621, 1997.

UHVnet 2011 B2.8

51

A New Method to Improve the Sensitivity of Leak Detection in Self-

Contained Fluid-filled Cables

L. Hao*1

, P. L. Lewin1, S. G. Swingler

1 and C. Bradley

2


2National Grid, UK


A method of real-time detection of leaks for self-contained fluid-filled cables without taking them out of

service has been assessed and a novel machine learning technique, i.e. support vector regression (SVR)

analysis has been investigated to improve the detection sensitivity of the self-contained fluid-filled (FF)

cable leaks.

The condition of a 400 kV underground FF cable route within the National Grid transmission network has

been monitored by Drallim pressure, temperature and load current measurement system. These three

measured variables are used as parameters to describe the condition of the cable system. In the regression

analysis the temperature and load current of the cable circuit are used as independent variables and the

pressure within cables is the dependent variable to be predicted. As a supervised learning algorithm, the SVR

requires data with known attributes as training samples in the learning process and can be used to identify

unknown data or predict future trends.

The load current is an independent variable to the fluid-filled system itself. The temperature, namely the tank

temperature is determined by both the load current and the weather condition i.e. ambient temperature. The

pressure is directly relevant to the temperature and therefore also correlated to the load current. The

Gaussian-RBF kernel: has been used in this investigation as it has a good

performance in general application. The SVR algorithm was trained using 4 days data, as shown in Figure 1,

and the optimized SVR is used to predict the pressure using the given load current and temperature

information.

Figure 1: Predicted pressure on training data and measured pressure for cable

1_1_R_A_NC.

When compared the predicted pressure and the measured pressure in 6 cables for 3 days, the average error

rate ( , pp-predicted pressure, pm-measured pressure) is between 0.11% and 0.19%

and the maximum error rate ( ) is between 0.24% and 0.43%.

A comparison between the existing system alarm strategy and the alarm sensitivity achieved using the SVR

method has also been assessed using equation , where pfa is the falling alarm pressure.

The adjusted average error rate is between 0.7% and 1.09% and the maximum error rate is between 1.62%

and 2.38%. The results represent that the new machine learning based technique has a 50 times better

sensitivity than the existing alarm system.

[1] L. Hao, P. L. Lewin, S. G. Swingler and C. Bradley, ―Leak Detection for Self-Contained Fluid-Filled Cables using

Regression Analysis‖, IEEE International Symposium on Electrical Insulation, 2010

[2] G. F. Moore, Electrical Cables Handbook, 3rd edition. Blackwell Science, 1997

[3] B. Scholkopf and A. J. Smola, Learning with Kernels: Support Vector Machines, Regularization, Optimization, and

Beyond, The MIT Press, 2002

UHVnet 2011 B2.9

52

Energy Harvesting from Electric Fields in Substations for Powering

Autonomous Sensors

M. Zhu*1

and M. D. Judd1



The benefits of enhanced condition monitoring in the asset management of the electricity transmission

infrastructure can only be fully realised if the sensors used to measure operating parameters are reliable and

economical to operate. While adding more sensors can help to track the plant health more accurately, the

installation and operating costs of any additional sensors might outweigh the benefits they bring due to the

requirement for new cabling or battery maintenance.

Advances in wireless communication technology are reducing the power consumption, especially when the

average data transfer rate is low [1]. In a high voltage substation, condition monitoring sensors are

surrounded by relatively high strength electric and/or magnetic fields. Harvesting energy from the ambient

environment therefore becomes a viable alternative for powering the sensor nodes. This would remove the

barriers preventing the uptake of wireless sensor networks. Previous studies, which focussed on health and

safety issues for utility personnel, recorded typical maximum electric field strengths of about 10 kV/m at 1 m

above ground within 400 kV substations [2]. Subsequently, field measurements targeted for potential

wireless sensor node installations on the surfaces of substation structures have recorded substantially higher

readings.

The technical challenge for using a capacitive energy converter to harvest energy from the electric field is

similar to the difficulty in developing a piezoelectric energy harvester, where a relatively large voltage is

generated with an extremely high source impedance [3]. This study investigates the techniques for improving

the harvesting efficiency from 50 Hz electric fields and effectively processing the energy harnessed. The

harvested energy is intended for use in powering a new generation of low power consumption wireless

sensors. A demonstration device which illustrates the feasibility of harvesting energy from the electric field

to power a useful measurement function will be described and possible improvements and challenges will be

discussed.

[1] E.M. Yeatman ―Advances in Power Sources for Wireless Sensor Nodes‖, Proc. International Workshop on

Wearable and Implantable Body Sensor, 2004. [Online] Available at.

http://www.doc.ic.ac.uk/vip/bsn\textunderscore2004/program/papers/Eric%20Yeatman.pdf

[2] J. Latva-Teikari et al. ―Measuring Occupational Exposure to Electric and Magnetic Fields at 400 kV Substations‖,

Proc. Transmission and Distribution Conference and Exposition, pp. 1-4, April 2008

[3] N. Shenck and J. Paradiso, ―Energy Scavenging with Shoe-Mounted Piezoelectrics‖, IEEE Micro, pp. 30-42, May-

June 2001

http://www.doc.ic.ac.uk/vip/bsn/textunderscore2004/program/papers/Eric%20Yeatman.pdf

UHVnet 2011 B2.10

53

Ageing and Temperature Influence on Polarization/Depolarization

Current Behaviour of Paper Immersed in Natural Ester

Jian Hao*1,2

, Ruijin Liao2, G. Chen

1


2University of Chongqing, China


Transformers play an important role in providing a reliable and efficient electricity supply and are one of the

most critical equipments in electric power transmission and distribution systems. The most commonly used

liquid in power transformers is mineral oil due to its low price and good properties. However the

performance of mineral oil starts to be limited due to environmental consideration [1]. Natural ester

insulating fluid offers fire safety, environment and insulation aging advantages over mineral oil and are

found to be suitable for the use in transformer insulation system [1]. However, transformer owners require to

assess the status of the cellulose insulation in transformer non-destructively. Polarization/depolarization

Current (PDC) measurement [2] is one of the non-destructive techniques which have been used to achieve

this aim.

At the present, there are few publications about the PDC behaviour of natural ester-paper insulation, though

the natural ester becomes more widely used in transformers. In this paper, the influence of ageing and

temperature on the PDC behaviour of the paper immersed in natural ester and mineral oil were compared.

Results show PDC technique can be used to assess the aging condition of the natural-ester paper insulation.

The ageing and temperature have similar influence on the PDC behaviour of the paper immersed in natural

ester and in mineral oil. The depolarization current of paper immersed in natural ester is lower than that

immersed in mineral oil at the same test temperature. The depolarization current of the paper immersed in

natural ester and mineral oil increase with the aging time increased. Therefore, the depolarization current can

be used to indicate the aging status of natural ester-paper insulation.

(a) paper immersed in mineral oil (b) paper immersed in natural ester

Figure 1: The depolarization current of paper immersed in

natural ester and mineral oil with different aging condition

[1] D. Martin, I. Khan, J. Dai, Z. D. Wang, ―An overview of the suitability of vegetable oil dielectrics for use in large

power transformers‖, Proceedings of the TJH2b Euro Tech Con, Chester, pp.1-20, 2006

[2] W. S. Zaengl, ―Application of dielectric spectroscopy in time and frequency domain for HV power equipment,‖

IEEE Electr. Insul. Mag., vol. 19, no. 6, pp. 9-22, 2003

100

101

102

103

104

10-12

10-11

10-10

10-9

10-8

0 day

31 days

60 days

97 days

123 days

I dep

/A

Time/s10

010

110

210

310

410

-12

10-11

10-10

10-9

10-8

10-7

0 day

31 days

60 days

97 days

123days

I dep

/A

Time/s

UHVnet 2011 B2.11

54

An On-line Lightning Monitoring System for Transmission Lines

Bojie Sheng*1

, Wenjun Zhou2 , Chengke Zhou

1 and Jianhui Yui

2


2Wuhan University, China


In order to identify the exact location of lightning strikes on a transmission line, an on-line monitoring

system has been developed by the authors comprising front-end lightning detection systems installed on

transmission towers, and a remote server running in the control room. The on-line monitoring system can not

only obtain the current waveform, the tower number, the exact line and stroke polarity, but also determine

the stroke pattern as a result of either lightning shielding failure or back flashover. In order to overcome the

difficulties associated with multiple lightning strikes which often occur in quick succession along lightning

channel after the main discharge, a novel method is developed to acquire multiple lightning strikes according

to their characteristics. The system is deigned to communicate with the remote server automatically by a

GPRS wireless module. Finally, the examination results of the effectiveness of the on-line monitoring

system, carried out by experiments in a lab.

[1] F. Fuchs, E. Ulrich Landers, R. Schmid,et al. ―Lightning Current and Magnetic Field Parameters Caused by

Lightning Strikes to Tall Structures Relating to Interference of Electronic Systems‖. IEEE Trans. On EMC,1998

[2] Zhang Qi1in, Qie Xiushu, Kong Xiangzhen. ―Comparative Analysis on Return Stroke Current of Triggered and

Natural Lightning Flashes‖. Proceedings of the CSEE, 2007

[3] Wang Hui, Chen Shuiming, He jinliang, Sun weimin, Luo Yi. ―Influence of Lightning Monitoring Device Position

on Measured Lightning Current Parameters‖. High Voltage Apparatus. 2009

UHVnet 2011 B2.12

55

Energy Harvesting in Substations for Wireless Sensors and a New Arc

Capacitor Structure

Jinxin Huang*1,2

, Qingmin Li2, Martin D. Judd

1 and W. H. Siew

1


2Shandong University, China


The past several years have seen an increasing interest in the development of wireless sensor networks.

Wireless sensor nodes are usually ‗smart‘, not taking too much space, and their data can be transmitted

wirelessly. These advantages make them particularly suitable for certain locations, such as dangerous

environments, small spaces or locations where installing cables poses difficulties. However, the problem of

powering a large number of nodes in a dense network becomes critical when one considers the prohibitive

cost of wiring power to them or replacing batteries. One solution method is energy scavenging technology

which can harvest energy from the environment, using sources such as solar, vibration, air flow, temperature

difference, ambient electromagnetic fields, etc. An attractive characteristic of this approach is that the

lifetime of the node would only be limited by failure of its own components.

Equipment in a high voltage substation is surrounded by electric and magnetic fields. Some measurements

recorded in ChongQing suggest that typical maximum AC electric field strength in a 500 kV substation is 18

kV/m, therefore the energy of electric field is very rich. And it would be preferable to use the electric field

also because it is independent of load current and predictable. Additionally, advances in wireless

communication technology have resulted in reduced power consumption of the electronic circuitry required,

especially when the average data transfer rate is low due to the lower switching losses. So, harvesting energy

from the electric field to power sensor nodes becomes viable. In this paper, the principle of electric field

energy harvesting which can change electric field to voltage difference through plane-parallel capacitor is

analyzed and a new arc structure of capacitor which reform the traditional plane capacitor plate to arc is

proposed. Initial simulation results by Maxwell indicate that the new structure can make the charge induced

on the surface of electrode increase by a factor of nearly threefold and can improve the harvesting efficiency.

UHVnet 2011 C2

56

Posters: Materials

C2.1

On the use of Raman and FTIR Spectroscopy for the Analysis of Silica-based

Nanofillers ........................................................................................................................................................... 57

C2.2 Dielectric Breakdown Strength of Polyethylene Nanocomposites ...................................................................... 58

C2.3

Influence of Temperature and Moisture Absorbed on Electrical Degradation and

Breakdown in Epoxy Resins ............................................................................................................................. 59

C2.4 Space Charge Behaviour in Oil-Paper Insulation with Different Aging Condition ........................................... 60

C2.5

Modelling the Non-equilibrium Electric Double Layer at Oil-pressboard Interface of

High Voltage Transformers ................................................................................................................................. 61

C2.6

Investigation of Impulsive Corona Discharges for Energisation of Electrostatic

Precipitation Systems .......................................................................................................................................... 62

C2.7

A Comparison of Polymeric Cable Insulation Properties Following Lightning Impulse

Ageing ................................................................................................................................................................. 63

C2.8 Properties and Analysis of Thermally Aged Poly(ethylene oxide) ..................................................................... 64

C2.9 Smart Materials as Intelligent Insulation ............................................................................................................ 65

C2.10 AC Breakdown Characteristics of LDPE in the Presence of Crosslinking By-products..................................... 66

C2.11 DC Impulse Discharge Degradation of Mica ...................................................................................................... 67

UHVnet 2011 C2.1

57

On the use of Raman and FTIR Spectroscopy for the Analysis of

Silica-based Nanofillers

C. Yeung*1, G. Gherbaz

1 and A. S. Vaughan

1



The potential of polymeric nanocomposites as solid insulation systems has been a topic of great discussion.

Although this approach as a means to engineering materials with improved properties has been well

established, many of the fundamentals aspects of this class of materials remains poorly understood. For

example, the long term dielectric characteristics of so-called nanodielectrics is one of these topics. Whilst

the nature of the interfacial region within such systems is believed to be key in determining performance,

further investigation is required in order better to understand the macroscopic behaviour of nanocomposites.

Such studies are vital for fundamental change, bringing an alternative to conventional polymers and filled

composites and so making a massive impact on industry.

This paper concerns interfaces in nanodielectrics and sets out to explore the effect of quantified changes in

surface functionalisation. Specifically, we have used vibrational spectroscopy to examine and characterise

the relevant effects of modifying the surface chemistry of nanosilica with commercial silane methods.

Confocal Raman spectroscopy is used to provide qualitative data concerning the functionalization level,

whilst Fourier Transform Infrared spectroscopy is used to provide more quantitative data. In this paper, we

present the first step towards the design and quantification of nanoparticle surface chemistry - a step that we

believe will ultimately allow the interphase to be optimized to meet demanding dielectric requirements.

UHVnet 2011 C2.2

58

Dielectric Breakdown Strength of Polyethylene Nanocomposites

K. Y. Lau*1, 2

, A. S. Vaughan1 and G. Chen

1


2Universiti Teknologi Malaysia, Malaysia


The term ―nanometric dielectrics‖ or simply ―nanodielectrics‖ was introduced in 1994 when Lewis [1]

anticipated the potential property changes that would benefit electrical insulation due to nano-sized

inclusion. Such materials, containing homogenous dispersion of small amount (normally less than 10wt%) of

nanoparticles (with at least one dimension in nanometre range) in host matrix, are of specific dielectric

interest. Although much effort has been put forth to investigate the potential dielectric benefit of such newly

emerging materials, many uncertainties remain unanswered, and much remains to be explored [2].

Current experimental work is to investigate the preparation of nanodielectrics via solution blending

approach. Polyethylene blend composed of 20wt% of high density polyethylene (HDPE) in low density

polyethylene (LDPE) is proposed as the base polymer, with varying content of nanosilica (between 0wt%

and 10wt%) as the fillers. Although expensive, solution blending method, when compared with melt

compounding method, is expected to provide better dispersion of nanoparticles in polymers, thus providing

qualitative data in understanding the behaviour of nanodielectrics [3].

Upon successful preparation of polyethylene nanocomposites, breakdown strength based on ASTM Standard

D149-87 is to be conducted to determine the feasibility of such dielectric materials in engineering point of

view. Figure 1 illustrates the schematic diagram of the breakdown test configuration. The samples are placed

between two 6.3mm diameter steel ball bearings immersed in silicone fluid. AC voltage at a preset ramp rate

will be applied until the samples fail and the values of breakdown voltages will be recorded and analysed

using two-parameter Weibull distribution. Based upon top-down research approach, the underlying physics

and chemistry associated with dielectric property changes will then be explored.

Figure 1: Dielectric breakdown test configuration.

[1] T. J. Lewis, ‗‗Nanometric Dielectrics‘‘, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 1, no. 15,

pp. 812-825, 1994.

[2] M. F. Frechette, A. Vijh, L. Utracki, M. L. Trudeau, A. Sami, C. Laurent, P. Morshuis, A. S. Vaughan, E. David, J.

Castellon, D. Fabiani, S. Gubanski, J. Kindersberger, C. Reed, A. Krivda, J. Fothergill, F. Guastavino and H.

Alamdari, ―Nanodielectrics: A Panacea for Solving All Electrical Insulation Problems?‖ IEEE International

Conference on Solid Dielectrics, 2010.

[3] T. Tanaka, G. C. Montanari and R. Mülhaupt, ―Polymer Nanocomposites as Dielectrics and Electrical Insulation –

Perspectives for Processing Technologies, Material Characterization and Future Applications‖, IEEE Transactions

on Dielectrics and Electrical Insulation, vol. 11, no. 5, pp. 763-784, 2004.

UHVnet 2011 C2.3

59

Influence of Temperature and Moisture Absorbed on Electrical

Degradation and Breakdown in Epoxy Resins

S.J. Dodd1, N.M. Chalashkanov

1*, L.A. Dissado

1, J.C. Fothergill

1

1University of Leicester, UK


In the current study, a set of experiments has been carried out to establish the influence of temperature and

moisture on the electrical degradation mechanisms, in particular electrical treeing. A set of pin-plane

samples were prepared from Araldite CY1311 epoxy resin and conditioned in sealed containers with

different levels of relative humidity over the range 15-100%. The treeing experiments were performed over

the temperature range 20-70oC. The glass transition temperature of this resin is 0

oC, therefore all test were

performed above Tg. It has been confirmed that temperature and moisture absorbed in the samples affect the

tree growth in similar way. The growth time and the fractal dimension of the trees have been found to

decrease with both increasing temperature and moisture concentration (see Fig.1). Pairs of values of

temperature and moisture concentration were identified for which the degradation mechanism (electrical

treeing) changes to thermal breakdown. Figure 1: Figure caption here, this is an example figure with the

correct dimensions.

a)

b)

c)

d)

Figure 1: Electrical degradation and breakdown at

different levels of moisture absorbed, temperature 20

oC, applied voltage 13.5kV rms, pin-plane distance

2mm;

a) moisture level less than 0.1%, b) 1.0%, c) 2.4%, d)

6.9%

UHVnet 2011 C2.4

60

Space Charge Behaviour in Oil-Paper Insulation with Different Aging

Condition

Jian Hao*1, 2

, G. Chen2, Ruijin Liao

1, Wei Li

1

1University of Chongqing, China



Oil-paper insulation system is widely used in power transformers and cables. The dielectric properties of oil-

paper insulation play an important role in the reliable operation of power equipment. Oil-paper insulation

degrades under a combined stress of thermal (the most important factor), electrical, mechanical, and

chemical stresses during routine operations, which has great effect on the dielectric properties of oil-paper

insulation [1]. Space charge in oil-paper insulation has a close relation to its electrical performance [1]. In

this paper, space charge behaviour of oil-paper insulation sample with three different ageing conditions (aged

for 0, 35 and 77 days) was investigated using the pulsed electroacoustic (PEA) technique. The influence of

aging on the space charge dynamics behaviour was analysed.

Results show that aging has great effect on the space charge dynamics of oil-paper insulation. The

homocharge injection takes place under all three aging conditions above. Positive charges tend to accumulate

in the sample, and increase with the oil-paper insulation sample deterioration. The time to achieve the

maximum injection charge density is 30s, 2min and 10min for oil-paper insulation sample aged for 0, 35 and

77 days, respectively. The maximum charge density injected in the sample aged for 77 days is more than two

times larger than the initial sample. In addition, the charge decay speed becomes much slower with the aging

time increase. There is an exponential relationship between the total charge amount and the decay time. The

decay time constant increases with the increasing deterioration condition of the oil-paper insulation sample.

The value may be used to reflect the aging status of oil-paper insulation.

0 5 10 15 20 25 30 35

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Aging for 0 day

Aging for 35 days

Aging for 77 days

Decay Time (min)

a

Tot

al C

har

ge A

mou

nt

(10-7

C)

Figure 1: Relationship between total charge amount in the oil-paper insulation sample

with different aging condition and decay time

Table 1: Fitting parameters of total charge amount (y) and decay time (x)

according to

x

y A Be

sample Constant

R2 A B

0 day 0.0367 1.1832 0.0715 0.9968

35 days 0.2054 1.4754 0.1350 0.8945

77 days 0.3386 2.1976 0.2044 0.9212

: decay time constant; R2: fitting coefficient

[1] Chao Tang, G. Chen, M. Fu, Rui-jin Liao, ―Space charge behavior in multi-layer oil-paper insulation under

different DC voltages and temperatures‖, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 17, no.

3, pp. 778-788. 2010

UHVnet 2011 C2.5

61

Modelling the Non-equilibrium Electric Double Layer at Oil-

pressboard Interface of High Voltage Transformers

H. Zainuddin*1

, P. L. Lewin1 and P. M. Mitchinson

1



In large oil-filled power transformers, cellulose-based pressboard and paper are used throughout for

electrical insulation. Microscopic views have shown that pressboard insulation is a fibrous and porous

structure with non-homogeneous surface. It has been recognised that the pressboard structure is more porous

towards the edge [1]. The pores within the pressboard allow oil absorption during impregnation process and

provide paths for oil to penetrate until saturation is reached. The ratio of fibre and oil changes as the material

structure changes from a medium of bulk oil-pressboard composite toward the bulk oil medium. The

porosity of pressboard can also result in impurities within the oil being drawn into the pressboard. It has also

been recognised that physicochemical process of a liquid in contact with solid wall leads to the formation of

electric double layer (EDL) in the liquid region [2, 3]. The material properties and geometry of pressboard

thus lead to a complex oil-pressboard interface. A 2-D model of oil-pressboard interface has been

constructed using Comsol Multiphysics Finite Element Analysis software and this is shown in Figure 1. The

mathematical model considers the dissociation of a generic impurity in the oil into positive and negative ions

and considers the role of the porous and non-homogeneous wall of pressboard in the formation of the EDL.

The pressboard, which is represented by different arrays of fibre, promotes preferential adsorption and

desorption processes between ions in the oil and unoccupied fibre surfaces of oil impregnated pressboard.

The model studies the non-equilibrium charge density profile in the EDL at the oil-pressboard interface when

the oil is in the stationary condition. Results of the simulation will be presented in the Colloquium.

Figure 1: 2-D model of oil-pressboard interface

[1] P.M. Mitchinson, P.L. Lewin, B.D. Strawbridge, P. Jarman, ―Tracking and surface discharge at the oil-pressboard

interface‖, IEEE Electrical Insulation Magazine, vol. 26, pp. 35-41, March/April 2010.

[2] G.G. Touchard, T.W. Patzek and C.J. Kadke, ―A physicochemical explanation for flow electrification in low-

conductivity liquids in contact with a corroding wall‖, IEEE Transactions on Industry Applications, vol. 32, pp.

1015-1057, September/October 1996.

[3] A.P. Washabaugh and M. Zahn, ―A chemical reaction-based boundary condition for flow electrification‖, IEEE

Transactions on Dielectrics and Electrical Insulation, vol. 4, pp. 688-709, December 1997.

UHVnet 2011 C2.6

62

Investigation of Impulsive Corona Discharges for Energisation of

Electrostatic Precipitation Systems

A. C. Mermigkas*1

, I. V. Timoshkin1, S. J. MacGregor

1, M. J. Given

1, M. P. Wilson

1 and T. Wang

1



Various industrial and domestic processes as well as developing nano-technologies generate micron and sub-

micron particles. This phenomenon is more prevalent in large cities where population density and industrial

activities are much higher, meaning that a large percentage of the world population is being exposed to

everyday inhalation of particulate matter (PM). This may result in negative health effects, many of which are

not investigated fully yet [1].

The current research project is focused on the development of a small scale impulsive micro- electrostatic

precipitator (IMP) for the removal of PM at homes or in public environments, being small in contrast with

the industrial ones. This IMP will implement superimposed DC and sub-microsecond electric fields in order

to charge and remove PM efficiently. As the impulse breakdown voltage in a gap is much greater than the

DC one, the IMP will also avoid operating close to DC breakdown voltage levels.

The designed IMP system composes of a plasma-generation and particle-collection electrodes. For the

former, threaded rods of 3 and 6mm have been used as well as a smooth 1.5mm one, while the latter consists

of a stainless-steel tube of 28mm internal diameter. The rods were placed coaxially into the tube, with the

particle laden air flowing homogenously from the top to the bottom of the reactor. The transmission line

based pulse generator developed is able to produce 270ns pulses with frequency of up to 100Hz. The

efficiency of precipitation of micron sized particles was evaluated for different DC and impulse voltage

levels by measurements of mass of collected particles. Breakdown voltage, corona initiation voltage and

parameters of impulse coronas have been obtained under different energisation regimes. Precipitation

experimental results showed that the positive or negative charging regimes play an important role in the

system efficiency.

The ultimate objective of this research project is to investigate precipitation levels of PM2.5, which

constitutes a range of lower precipitation efficiency for available ESPs [2], as well as potential

microbiological decontamination efficiency of impulsive non-thermal plasmas.

[1] J. G. Ayres, ―Long term exposure on air pollution: effect on mortality‖, Committee On the Medical Effects of Air

Pollutants, 2009, COMEAP report, pp. 1-4, [Online]. Available: http://www.dh.gov.uk/ab/COMEAP/DH_108151

[2] K. Parker, ―Electrical operation of electrostatic precipitators‖, The Institution of Electrical Engineers, 2003, pp.

16.

http://www.dh.gov.uk/ab/COMEAP/DH_108151

UHVnet 2011 C2.7

63

A Comparison of Polymeric Cable Insulation Properties Following

Lightning Impulse Ageing

N. L. Dao*, P. L. Lewin, I. L. Hosier and S. G. Swingler



LDPE and HDPE are common materials used within high voltage insulation systems. These materials will be

aged after working under high voltage for a long time. The ageing process of these materials may be affected

by external factors. The application of repetitive lightning impulse over-voltages is one of these factors and

will be considered in this paper. This paper includes the sample preparation process, the ageing of samples

under identical conditions and finally the analysis of electrical properties after the ageing process. The

obtained results are used to compare the effect of repetitive lightning impulses with these two materials.

These results are also used to highlight the possible mechanisms behind the lighting impulse ageing process.

[1] S. Boev ―Electric aging of polyethylene in pulsed electric field‖ 12th IEEE International Pulsed Power

Conference. (Cat. No.99CH36358) 1999 , Monterey, CA, USA, Page(s): 1365-8 vol.2

[2] G.C. Stone, R.G. Van Heeswijk, R. Bartnikas ―Electrical aging and electroluminescence in epoxy under repetitive

voltage surges‖ IEEE transaction on electrical insulation, volume 27, issue 2, April 1992 Page(s):233 – 244

[3] R.A Hartlein, V.S. Harper, Harry Ng ―Effects of voltage surges on extruded dielectric cable life project update‖

IEEE transactions on power delivery, volume 9, issue 2, April 1994 Page(s):611 – 619

UHVnet 2011 C2.8

64

Shear rate (s-1

)

1 10 100 1000 10000

Vis

co

sity (

Pa

.s)

0.01

0.1

5% aged 100k

5% unaged 100k

10% aged 100k

10% unaged 100k

Wavenumber cm-1

1000200030004000

Abso

rba

nce

0.0

0.5

1.0

1.5

2.0

100k unaged

100k aged

Properties and Analysis of Thermally Aged Poly(ethylene oxide)

M. Reading* and A. S. Vaughan



Recent studies have been performed into the use of polyethylene oxide (PEO) as a model system for

observing the fundamental effects of adding micro and nano sized fillers to create polymeric composite

systems. Many factors contribute to the successful creation of such a composite system, including dispersion

of the filler and treatment of the material during creation. For example, while producing thin films of the

materials for testing, high temperatures were used for short periods of time in open air to press the samples

into small discs. It is well known that prolonged high temperature exposure can alter the chemistry and

structure of polymeric materials and that small variations in the original chemistry, such as longer molecular

weights or introduction of fillers, can reduce or possibly accelerate this 'ageing' effect. From these previous

investigations many property changes were observed during addition of filler or variation of molecular

weight, therefore to accurately attribute these changes to a cause the thermal ageing of the material should be

observed.

This investigation looks at the same 3 molecular weight PEO systems as those used in the previous

investigations and analyses them for their vulnerability to thermal ageing. One thermally aged sample is then

taken and tested alongside an unaged sample to observe the effects that the process has on the properties.

This includes rheology in solution, differential scanning calorimetry (DSC), AC electrical breakdown,

dielectric spectroscopy and fourier transform infra-red (FTIR). By observing the property changes of aged

samples it is possible to better understand the thermal ageing process occurring and possibly a way to reduce

the effect, along with considering the effect with regard to the behaviour of the previously tested composite

samples.

Figure 1: Viscosity of plots of aged and unaged samples (left)

and FTIR spectra of aged and unaged samples (right)

UHVnet 2011 C2.9

65

Smart Materials as Intelligent Insulation

A. F. Holt*1

, R. C. D. Brown1, P. L. Lewin

1, A. S. Vaughan

1 and P. Lang

2


2EDF Energy Networks Ltd, Crawley, UK


In order to provide a robust infrastructure for the transmission and distribution of electrical power,

understanding and monitoring equipment ageing and failure is of paramount importance. Commonly, failure

is associated with degradation of the dielectric material; therefore the introduction of a smart moiety into the

material is a potentially attractive means of continual condition monitoring.

It is important that any introduction of smart groups into the dielectric does not have any detrimental effect

on the desirable electrical and mechanical properties of the bulk material. Initial work focussed on the

introduction of fluorophores into a model dielectric system. Fluorescence is known to be a visible effect

even at very low concentrations of active fluorophores and therefore was thought well suited to such an

application. It was necessary both to optimise the active fluorophore itself and to determine the most

appropriate manner in which to introduce the fluorophores into the insulating system.

This presentation will describe the effect of introducing fluorophores into polymeric systems on the

dielectric properties of the material and the findings thus far [1]. Alternative smart material systems will also

be discussed along with the benefits and limitations of smart materials as electric field sensors.

[1] A. F. Holt, A. C. Topley, R. C. D. Brown, P. L. Lewin, A. S. Vaughan and P. Lang, ―Towards Intelligent

Insulation Technologies‖, Conference on Electrical Insulation and Dielectric

UHVnet 2011 C2.10

66

AC Breakdown Characteristics of LDPE in the Presence of

Crosslinking By-products

N. Hussin*1

, and G. Chen1



LDPE films of 50µm thick were soaked into crosslinking byproducts which are acetophenone, α-

methylstyrene and cumyl alcohol. The samples were used to perform the breakdown strength (Eb) of the

LDPE with the byproducts chemical reside in the sample. The AC breakdown measurements were conducted

at a ramp rate of 50V/s at room temperature. Weibull plot is used to analyse the ac breakdown result.

Comparing the soaked and un-soaked (fresh LDPE) samples, it does show a small reduction of the eta values

as the LDPE films were soaked into the sample. It suggests that the breakdown strength is reduced by adding

the byproducts in the LDPE film. However, as the range of breakdown strength of all samples are to be

compared, these values fall in the same region which indicate no significant difference can be seen in all

samples.

Breakdown Stress (kV/mm)

100 150 200 250 300 350

Weib

ull

Bre

akdow

n P

robabili

ty (

%)

0.1

0.5

1.0

5.0

10.0

20.0

50.0

70.0

95.0

99.0

Clean LDPE

confidence Bound

Figure 1: The Eb plot of clean LDPE

[1] T. Andrews, R.N. Hampton , A. Smedberg, D. Waldm, V. Waschk, and W. Weissenberg. ―The Role of Degassing

in XLPE Power Cable Manufacture‖, IEEE Electrical Insulation Magazine December 2006 5-16.

[2] N. Amyot, S.Y Lee, E. David, I. H. Lee. “Effect of residual crosslinking by-products on the local dielectric

strength of HV extruded cables.‖ 2000 Annual Report Conference on Electrical Insulation and Dielectric

Phenomena, Oct. 2000 Volume 2(No 2):743 – 746

[3] N. Hussin and G. Chen, ― Space Charge Accumulation and Conductivity of Crosslinking Byproducts Soaked

LDPE‖. In: 2010 Conference on Electrical Insulation and Dielectric Phenomena, 17 - 20 October 2010, Purdue

University, West Lafayette, Indiana, USA. pp. 125-128

http://eprints.ecs.soton.ac.uk/21639/

http://eprints.ecs.soton.ac.uk/21639/

UHVnet 2011 C2.11

67

DC Impulse Discharge Degradation of Mica

J Paterson, A J Shields, D M Hepburn, C Zhou

Glasgow Caledonian University , UK


Mica is a vital component of the insulation systems of stator bars in High Voltage (HV) machines. Its

inherent resistance to electrical discharge activity has resulted in its use for HV insulation for many years,

however, the degradation of insulation containing mica is not yet fully understood. Difficulties associated

with laboratory aging of mica, principally the lengthy time scales required in AC partial discharge (PD)

stressing before damage occurs, has led to a more aggressive electrical stressing strategy. DC Impulse testing

has the capability to reduce the time required to initiate onset of damage in mica. The transient nature and

high energy delivered to a mica sample during an impulse discharge results in physical damage that is

observable by traditional and advanced microscopy techniques. Material damage, such as localised

dislocation and fracture of the mica surface and melting at the impact site, can be analysed. The energy of

DC impulse stressing can be readily calculated enabling correlation between energy input and type and

severity of damage.

DC impulse testing, carried out in accordance with BS 923 1/50µs, produces damage to mica by a variety of

mechanisms. The very high temperature associated with the plasma discharge causes thermal damage that

manifests itself as localised melting. Electrical stress causes tracks to form on the mica surface [1] and to

cause bond cleavage of mica [2] and in polymer/mica composites [3].

The work presented in this paper addresses the issue that micaceous insulation used in high power rotating

plant operates at elevated temperatures. Use of thermally stressed samples in DC impulse testing allows

assessment of variation in mica degradation resulting from prior thermal exposure. Comparing thermally

stressed with unstressed mica samples will help quantify the contribution thermal stress has on the

degradation of mica. Mica samples exposed to elevated temperature for extended periods were stressed using

DC impulses and optical investigation of the material carried out.

This work aims to better identify the structural and chemical changes occurring in mica under electrical and

thermal stress. Although the degradation of mica has previously been investigated, e.g. [4, 5, 6,], the studies

occurred prior to the micro- and nano-scale physical and chemical techniques of the present age revealing

previously hidden detail. The changes identified and correlation with energy input will be reported.

[1] Shields A.J and Kemp I.J, ―Impulse discharge erosion and breakdown of mica‖, Ph.D. thesis, 1980, p186

[2] Shields A.J and Kemp I.J, Degradation and breakdown of mica under partial discharge stressing, IEE Proc.

Science, Measurement & Technology, May 2000, Vol 147, pp105 – 109, ISSN 1350-2344

[3] Jia Z.D., Hao Y.P. and Xie H.K., ‗The degradation Assessment of epoxy/mica insulation under multi stress aging‘,

IEEE Trans. on Dielectrics and Electrical Insulation Vol. 13 No 1, Feb 2006, pages?.

[4] Jia Z.D and Xie H.K, ‗The change of microstructure of epoxy mica insulation in multi-stress aging.‘

973772searchabstractProceedings of 2001 International Symposium on Electrical Insulating materials, pp 693 –

696

[5] Davidson A.T. and Yoffe A.D., ―Dielectric breakdown in thin mica crystals‖, Nature, 1965, p.1247

[6] Silk E.C.H. and Barnes, R.S., ―The observation of dislocations in mica‖, Acta. Metall., 1961, Vol.9, p558-563

http://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=Authors:.QT.Jia,%20Z.D..QT.&newsearch=partialPref

UHVnet 2011 D2

68

Posters: Theories, Methods and Models

D2.1 Modelling of Partial Discharge Activity in Cavity within a Dielectric Insulation Material ............................... 69

D2.2 Full Wave Modelling of Partial Discharge Phenomena in Power Transformers using

FDTD Methods ................................................................................................................................................... 70

D2.3 Evaluation of an Iterative Method used for Partial Discharge RF Location Techniques .................................... 71

D2.4 Numerical Modelling of Needle-Grid Electrodes Negative Surface Corona Charge

System ................................................................................................................................................................. 72

D2.5 Mathematical Modelling of End-of-Life of Power Transformers in Perspective of System

Reliability ............................................................................................................................................................ 73

D2.6 A Comparison between Electroluminescence Models and Experimental Results .............................................. 74

D2.7 An Improved Pulsed Electroacoustic System for Space Charge Measurement under AC

Conditions ........................................................................................................................................................... 75

UHVnet 2011 D2.1

69

Modelling of Partial Discharge Activity in Cavity within a Dielectric

Insulation Material

Tianyu Bai*1, D. J. Swaffield

1 and P. L. Lewin

1



The pattern of partial discharge（PD）occurrence at a defect site within a solid dielectric material is

influenced by the conditions of the defect site. This is because the defect conditions such as its size and

location determine the electric field distributions at the defect site which influence the patterns of PD

occurrence. A model for a spherical cavity and ellipsoidal cavity within a homogeneous dielectric material

has been developed by using Finite Element Analysis (FEA) software. The model is used to study the

influence of different conditions of the cavity on the electric field distribution in the cavity and the PD

activity. Also, experimental measurements of PD in spherical cavity and ellipsoidal cavity of different size

within a dielectric material will be displayed.

At present, only the model for the PD has been prepared. The cavity in the silicon rubber is now produced.

The pre-cure time , post-cure time and temperature for the product of cavity are being determined by

researchers now. And the bubbles in the small sample with silicon rubber are easier to be made than in the

bigger sample. Once cavity in silicon rubber is successful to be made, PD measurement will proceed. Figure

1 shows the schematic diagram of the object test for the research.

Figure 1: schematic diagram of the object test

UHVnet 2011 D2.2

70

Full Wave Modelling of Partial Discharge Phenomena in Power

Transformers using FDTD Methods

A. M. Ishak*1,2

, M. D. Judd1 and W. H. Siew

1


2National Defence University of Malaysia, Malaysia


The occurrence of defects in the insulation system of power transformers will degrade the insulation

properties and compromise the life of the equipment. The consequences of unexpected failure can be costly

and replacement units may not be readily available. Small electrical sparks which are known as partial

discharge (PD) are usually being produced at the degraded location. PD is a localized electrical discharge

that only partially bridges the insulation between conductors. Although the magnitude of the discharge is

usually small at first, it can cause progressive deterioration with time and then lead to massive failure of the

equipment. Therefore, it is important to detect and monitor the occurrence of PD by using non-destructive

test equipment. PD signals can be detected in the ultra high frequency (UHF) band (300-3000 MHz) because

the short current pulses radiate a wideband electromagnetic transient. The advantages of UHF approach are

wide detection range, high sensitivity and good immunity to interference signals during on-site

measurements.

Once a PD pulse occurs, electromagnetic waves propagate in all directions from the PD source. Different

materials impose different propagation properties on the radiated waves. Finite-difference time-domain

(FDTD) is a method to model electromagnetic wave propagation and interactions with the structure of

materials. Provided the results can be validated, modelling full wave PD phenomena by using the FDTD

method will be much safer than attempting it with high voltage experiments. Furthermore, it will be much

easier to change parameters in the model and study their influence on the PD detection, thereby contributing

to your understanding and ability to interpret measurements. This paper describes the modelling of PD

current sources, the modelling of UHF sensors, and demonstrates by way of example a method to estimate

the location of a PD source by measuring the arrival time of UHF PD signals at several sensors.

UHVnet 2011 D2.3

71

Evaluation of an Iterative Method used for Partial Discharge RF

Location Techniques

O. El Mountassir*1

, B.G. Stewart1, S. G. McMeekin

1 and A. Ahmadinia

1

1Glasgow Caledonian University , UK


To date many experimental studies have succeeded in determining the location of partial discharges (PD) in

3 dimensions using time difference of arrival technique and iterative algorithms (e.g. Moore et al. 2005,

Stewart et al. 2009). In order to locate PDs accurately, many studies have focused on analyzing the

propagation of the PDs electromagnetic waves (e.g. Kawada, 2009).

Despite the fact that Radio Frequency (RF) technique is being heavily investigated, few studies have

attempted to study the performance of a number of iterative methods and their influence in accurately

determining the locations of PDs.

This paper evaluates the performance of the Hyperbola Least Square algorithm (HLS) to locate different

PDs. A software platform was developed for the simulation and localisation of a range of PDs using a Y

shaped arrangement of four antennas. The HLS algorithm was applied and evaluated using (0, 0, 0) as the

initial values, with different error bounds on the iteration method evaluated. The performance of the

algorithm was compared in terms of location accuracy and also computing efficiency (Figure1 shows the

iteration efficiency for 64 PD points). The paper will also look at location accuracy.

The results obtained by this algorithm were different in terms of (i) accuracy and (ii) number of iterations.

Both were also found to be highly dependent on the selected error bounds. The error bounds and the

maximum number of iterations needed in order to provide the best results have been quantified and

compared to each other. This is an important result as it shows that the accuracy of an algorithm can in some

way be evaluated for PD location despite the non-linear nature of the triangulation equations.

Figure 1: Number of iterations for HLS using Y shaped

antennas arrangements.

[1] P. J. Moore, P. I. Portugués and I. Glover, ―Radiometric Location of Partial Discharge Sources on Energized High-

Voltage Plant‖, IEEE Transactions on Power Delivery, vol. 20, no. 3, 2005

[2] B. G. Stewart, A. Nesbitt and L. Hall, ―Triangulation and 3D Location Estimation of RFI and Partial Discharge

Sources Within a 400kV Substation‖, Proceedings of the IEEE 29th

Electrical Insulation Conference, pp.164-168,

2009

[3] Y. Tian, P. M. Kawada and K. Isaka, ―Locating Partial Discharge Source Occurring on Distribution Line by using

FDTD and TDOA Methods‖, IEEJ Transactions on Fundamentals and Materials, 2009

UHVnet 2011 D2.4

72

Numerical Modelling of Needle-Grid Electrodes Negative Surface

Corona Charge System

Y. Zhuang*1

, G. Chen1 and M. Rotaru

1



Surface potential decay measurement is a simple and low cost tool to examine electrical properties of

insulation materials. During corona charging stage, needle-grid electrodes system is often used to achieve

uniform charge distribution on the surface of the sample. However, there is little report on the effects of

geometrical parameters and voltage values of the charging system on the surface potential and its

characteristics.

In the present report simulations based on gas discharging physics similar to [1] have been carried out to

investigate dynamic surface charge formation. The geometry of in the model includes a 174µm radius of

curvature needle setting perpendicular to a 0.5mm thickness grid electrode and a 27.5mm diameter with

50µm thickness polyethylene. The bottom surface of the polyethylene is grounded and it is 3cm and 1.5cm

away from the needle electrode and grid electrode respectively. The simulations were initially performed

under the following conditions: the needle electrode was set as -8000V and the grid electrode -2000V. It has

been found that an impulse current appeared after 0.3µs charging which represented the corona effect. The

effect of adding a grid electrode can be clearly seen from the logarithmic plot of electrons. Finally, surface

charge density on the sample has been obtained.

[1] T. N. Tran, I. O. Golosnoy, P. L. Lewin and G. E. Georghiou, ―Two Dimensional Studies of Trichel Pulses in Air

Using the Finite Element Method‖, 2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 18-

21 October 2009

UHVnet 2011 D2.5

73

Mathematical Modelling of End-of-Life of Power Transformers in

Perspective of System Reliability

B. Patel1, Z.D. Wang

1*, J.V. Milanovic

1 and P. Jarman

2


2National Grid, UK


Never before have the consequences of loss of supply been so great, due to the fact that electricity is now a

vital part of our everyday lives. The importance of security of supply is also reflected by the financial

penalties incurred onto transmission and distribution companies for not maintaining supply and the

immeasurable damage this can cause to their public image.

Transformers form a vital part of any power system and the UK transmission system contains nearly one

thousand power transformers. Transformers are often the most expensive pieces of equipment in any

transmission system. Because of the number of transformers, the capital cost of transformer assets and the

financial consequences of failure it is necessary for transmission companies to have short term and

medium/long term asset replacement plans in order to effectively maintain security of supply. Capital

investment planning is a vital process for any business.

Because of these factors mentioned above there has been a shift to condition based asset replacement

programmes by transmission companies, in which assets are replaced based on condition as opposed to age.

In order for such programmes to be successful a deep coherent understanding of the ageing, deterioration and

failure of transformers is required.

In this project the general methodology on how to create a mathematical model of transformer failure is

discussed in order to determine how the probability of transformer failure is affected due to a series of

operating scenarios and phenomena such as overloads, short circuits, lightning strikes and etc. The current

technical debate focuses on two distinctively different approaches on choosing parameters based on which a

mathematical transformer failure probability model is built: one is based on the design information and

operating history and the other one is based on condition.

After the mathematical transformer failure probability model is built, the subsequent effect on system

reliability can then be calculated which takes account of transformer age, transformer condition and system

operating conditions.

A demonstration case will be given using a test system consisting of three transformers operating in parallel

and by utilising a variety of statistical tools including Monte Carlo simulations and Markov models.

UHVnet 2011 D2.6

74

A Comparison between Electroluminescence Models and

Experimental Results

D. H. Mills*1

, F. Baudoin2, P. L. Lewin

1 and G. Chen

1


2University of Toulouse, France


Electrical insulation ages and degrades until its eventual failure under electrical stress. One cause of this

relates to the movement and accumulation of charge within the insulation. The emission of a low level of

light from polymeric materials while under electrical stressing occurs before the onset of currently detectable

material degradation. This light is known as electroluminescence (EL) and under an ac electric field is

thought to relate to the interaction of charge in close proximity to the electrode-polymer interface.

Understanding the cause of this light emission gives a very high-resolution method of monitoring charge

interaction and its influence on material ageing.

A possible cause of this light emission is the bipolar charge recombination theory. This theory involves the

injection, trapping and recombination of charge carriers during each half cycle of the applied field [1]. This

work compares two models that to simulate the EL emission according to this bipolar charge recombination

theory. Model 1 assumes a fixed space charge region and all injected charge is uniformly distributed in this

region with charges able to either become trapped or to recombine with opposite polarity charge carriers [2].

This recombination relates directly the excitation needed for the emission of a photon of light as measured in

experiments. Model 2 develops on this by accounting for the transport and extraction of charge with an

exponential distribution of trap levels rather than a uniform distribution [3]. Figure 1 shows a good

correlation between the two models and experimental data. The full paper will describe the models in more

detail and present results comparing the simulated and experimental results under various applied

waveforms. Model 1 and model 2 both provide a good correlation with experimental data but model 2 allows

a greater understanding of the space charge profile in the region close to the electrodes as well as the shape

of the conduction current.

Further work involves developing these models to support changes in the charge trapping profiles due to

material ageing and supporting simulated results with measured conduction current.

Figure 1: Phase resolved electroluminescence emission and

simulation results under a 50Hz sinusoidal 6kVpk applied field

[1] A. Mohd Ariffin and P. L. Lewin, ―Phase-Resolved Measurement and Modelling of Electroluminescence

Phenomenon in Polyethylene Subjected to High Electrical Stress‖, International Conference on Condtion

Monitoring and Diagnosis, 2008

[2] A. Mohd Ariffin, N. Mat Tajudin, S. Sulaiman, Y. H. M. Thayoob and P. L. Lewin, ―Comparing Simulation

Results and Experimental Measurements of Electroluminescence Phenomenon in Dielectric Materials‖, IEEE

International Symposium on Electrical Insulation, 2010

[3] F. Baudoin, D. H. Mills, P. L. Lewin, S. Le Roy, G. Teyssedre and C. Laurent, ―Contribution to the Modelling of

Electroluminescence in High Voltage Polymeric Materials‖, Conference on Electrical Insulation and Dielectric

Phenomena, 2010

UHVnet 2011 D2.7

75

An Improved Pulsed Electroacoustic System for Space Charge

Measurement under AC Conditions

Z. Xu*1

, J. Zhao1 and G. Chen

1


*Email: [email protected]

In this paper, an improved space charge measurement system based on the pulsed electro acoustic technique

(PEA) is presented. The new system gives an essential way to examine the role of space charge in electrical

aging process under AC conditions. The system setup for AC measurement is presented and detailed in this

paper with comparison to the old system. There are two features with improved PEA system. A pulse

generator with a 3 kHz repetition rate is utilized to reduce the measurement time. The Eclipse data

acquisition system is used to achieve the high data acquisition rate. The results which were taken from both

old and new PEA system show that hetero-charge can be formed in the region close to the lower electrode

under AC electric field. Apparently the results captured from the new system have better phase resolution

than the old system. The space charge decay profile measured by the new system can reflect vividly on the

charge dynamically changing. The utmost space charge information was saved as the measurement time was

dramatically shortened by the improved system.

Figure 1: Space charge profile udner AC condition, f=1Hz,

every 15° in one cycle.

[1] C. Laurent, G. Teyssedre, G. C. Montanari, ―Time-resolved space charge and electroluminescence measurement in

polyethylene Under ac stress,‖ IEEE Trans. Diel. Electr. Insul., vol. 11, pp554-560, 2004

[2] Wu X, Chen G, Davies A E, Tanaka Y and Sutton S J, ―Space charge measurements in polyethylene under dc and

ac operating conditions using the PEA technique,‖ IEE DMMA conf. pub473, 2000, pp 57–62.

[3] C. Thomas, G. Teyssedre and C. Laurent, ―A new method for signal averaging resorting to space charge

measurement by the pulsed electro-acoustic method under AC stress,‖ IEEE ICSD, Winchester, UK, 2007, pp 490-

493

UHVnet 2011

76

Authors Index

Abd Rahman, M. S. ............................................31

Abdelmalik, A. A................................................20

Abubakar Mas‘ud, A. .........................................46

Adhikari, D. ........................................................19

Ahmadinia, A......................................................71

Ahmeda, M. ........................................................41

Albano, M. ...................................................... 4, 36

Allison, F. ...........................................................14

Bai, T. .................................................................69

Baker, P. C. .........................................................10

Baudoin, F. .........................................................74

Bogias, A. C. ......................................................39

Bradley, C. ..........................................................51

Braini, S. .............................................................40

Brown, R. C. D. ..................................................65

Chalashkanov, N. M. ..........................................59

Charalampidis, P. ................................................17

Chen, G. .............. 21, 28, 53, 58, 60, 66, 72, 74, 75

Chippendale, R. D. .............................................24

Cotton, I. .............................................................14

Coventry, P. .................................................... 4, 36

Dao, N. L. ...........................................................63

Dissado, L. A. .....................................................59

Dodd, S. J. .............................................. 20, 23, 59

Efika, I. B. ............................................................5

El Mountassir, O. ................................................71

Elmghairbi, A. ....................................................37

Feng, D. Y. .........................................................30

Fothergill, J. C. ............................................. 20, 59

Freebody, N. A. ..................................................18

Gherbaz, G. .........................................................57

Given, M. J. ........................................................62

Goddard, K. F. ......................................................7

Golosnoy, I. O. ...................................................24

Green, P. R. ........................................................14

Griffiths, H. .................. 2, 4, 17, 26, 37, 41, 42, 50

Haddad, A. ..... 4, 17, 26, 33, 36, 37, 39, 40, 41, 42,

49, 50

Hao, J. ........................................................... 53, 60

Hao, L. .................................................... 11, 31, 51

Harid, N. ................... 17, 33, 36, 37, 39, 41, 42, 49

Harris, R. M. .......................................................48

Hepburn, D. M. ............................................. 19, 47

Holt, A. F. ...........................................................65

Hosier, I. L. ................................................... 16, 63

Hu, X. ................................................................. 44

Huang, J. ............................................................ 55

Hunter, J. A. ....................................................... 11

Hussin, M. F. ..................................................... 49

Hussin, N. .......................................................... 66

Illias, H. A. ......................................................... 21

Ishak, A. M. ....................................................... 70

Jarman, P. ..................................................... 30, 73

Ji, T. Y. .............................................................. 32

Judd, M. D. ................ 9, 10, 12, 44, 48, 52, 55, 70

Kamarudin, M. S. ............................................... 36

Lambert, J. ......................................................... 24

Lang, P. .............................................................. 65

Lau, K. Y. .......................................................... 58

Lewin, P. L.6, 7, 11, 21, 24, 28, 31, 51, 61, 63, 65,

69, 74

Li, C. R. ............................................................. 45

Li, H. Y. ............................................................. 25

Li, Qi. ........................................................... 27, 34

Li, Qingmin. ....................................................... 55

Li, W. ................................................................. 60

Liao, R. ........................................................ 53, 60

Long, C. ............................................................. 38

MacGregor, S. J. ................................................ 62

Mair, A. J. .......................................................... 10

McArthur, S. D. J. .............................................. 10

McMeekin, S. G. ...................................... 3, 46, 71

Mermigkas, A. C. ............................................... 62

Michel, M. ......................................................... 11

Milanovic, J. V................................................... 73

Mills, D. H. .................................................. 28, 74

Mitchinson, P. M. .............................................. 61

Mohamed, F. P. .................................................. 13

Moore, F. ........................................................... 26

Moore, P. J. ........................................................ 48

Mousa, S. ........................................................... 42

Murugan, G. S. ................................................... 24

Nekeb, A. S. ....................................................... 33

Nesbitt, A. .......................................................... 46

Patel, B. .............................................................. 73

Payne, D. .............................................................. 6

Peng, X. ............................................................. 47

Pilgrim, J. A. ........................................................ 6

Reading, M. ....................................................... 64

Reid, A. J. .......................................................... 44

UHVnet 2011

77

Robson, S. .......................................................... 50

Roscoe, N. M. ..................................................... 12

Rotaru, M. .......................................................... 72

Rowland, S. M. ....................................... 14, 27, 34

Sarkar, P. ............................................................ 17

Sheng, B. ............................................................ 54

Shuttleworth, R. ............................................ 27, 34

Siew, W. H. ................................ 13, 35, 44, 55, 70

Smith, D. J. ........................................................... 3

Song, X. .............................................................. 47

Soraghan, J. J. ............................................... 13, 35

Stewart, B. G. ..................................... 3, 19, 46, 71

Strachan, S. S. .................................................... 13

Swaffield, D. J. ......................................... 6, 11, 69

Swingler, S. G. ................................... 7, 16, 51, 63

Tang, W. H. ........................................................ 32

Tao, Y. ................................................................ 35

Timoshkin, I. V. ................................................. 62

Vaughan, A. S. ..................... 16, 18, 57, 58, 64, 65

Veerappan, C. A. ................................................ 14

Wallace, P. A. ....................................................... 3

Walton, C. .......................................................... 11

Wang, P. ............................................................... 7

Wang, T. ............................................................. 62

Wang, Z. D. ...................................... 25, 30, 45, 73

Waters, R. T. ....................................................... 17

Wei, C. H. ........................................................... 32

Wilson, M. P. ...................................................... 62

Wu, Q. H. ............................................................ 32

Xu, Z. .................................................................. 75

Yeung, C. ............................................................ 57

Yu, J. ................................................................... 38

Yui, J................................................................... 54

Zachariades, C. ................................................... 14

Zainuddin, H. ...................................................... 61

Zhang, G. ............................................................ 34

Zhang, L. .............................................................. 5

Zhang, R. ............................................................ 25

Zhao, J. ......................................................... 28, 75

Zhou, C. .................................................. 38, 47, 54

Zhou, D. .............................................................. 45

Zhou, W. ....................................................... 38, 54

Zhu, M. ............................................................... 52

Zhuang, Y. .......................................................... 72

uhvnet 2011 uhvnet · steering group which includes industrial representation from the areva...

Documents