high performance conductors an international...

High Performance Conductors

An International viewpoint

Brian Wareing

Brian Wareing.Tech Ltd

Chester, UK Overhead Lines & Lightning Protection Consultancy

Phone +44 1244 550578

Mobile +44 7976 123 738

[email protected]

[email protected]

mailto:[email protected]

Brian Wareing.tech

High Performance Conductors - An International viewpoint 2

Introducing myself

Worked in the electricity industry for 48 years

Vibration measurements on OHL since 1995

Author of book on „Wood pole Overhead Lines‟

Deliver OHL courses in UK, Middle East, SE Asia and Australia

Member of Cigré International committees on OHL design, weather loads on OHLs and electrical and mechanical aspects of OHLs – WG29 anti-icing for OHLs

– WG16 weather loads for OHLs

– AG06 Mechanical aspects of OHL design

– WG25 Fittings for OHLs

– WG11/WG46 Vibration of OHLs

– Convenor Cigre AG06 WG48 „Field experience with new conductor types‟

– Secretary Cigre SCB2 WG28 „Meteorological data for assessing climatic loads‟

– SCB2 WG44 „Coatings for protecting power network equipment in winter conditions‟

IEEMA Seminar

Brian Wareing.tech

High Performance Conductors - An International viewpoint 3

Topics

General overview of high performance conductors (HPC)

– Standard conductor materials and choice

– The HPC range of conductors available today

– HPC and the „knee point‟

– Handling of HPC with composite cores

International perspective on the various technologies

available on HPC

International experience and economics

Line Losses - How HPC could help bring down

Transmission losses

Vibration management on HPC

IEEMA Seminar

Brian Wareing.tech

Basic Aluminium Conductors

ACSR Combination of high strength galvanised steel and aluminium Can suffer from internal corrosion due to dissimilar metals Suffers from salt pollution in coastal areas AAC

Good conductivity but Low strength conductor so uses are limited

Not good in coastal areas due to salt pollution

AAAC

High strength/weight ratio conductors with Good conductivity

Doesn‟t suffer from galvanic corrosion

Differing grades of alloy available (e.g. Al59)

ACAR

High strength/weight ratio conductors

Aluminium core heat treated to give higher strength but lower conductivity than external aluminium strands

Doesn‟t suffer from galvanic corrosion but still suffers from salt corrosion in coastal areas.

4

Brian Wareing.tech

5

AAAC Al59 Introduced over 40 years ago in Sweden as an

improvement to the conductivity of standard AAAC.

Previous AAAC conductivity was ~54%IACS whereas AL-59 is 59%IACS (hence it‟s name).

Higher conductivity (~20% more ampacity) is associated with lower strength (15% lower UTS) and hence greater sags (~11% lower sag at 80°C on 350m span at same tension as standard AAAC)

So can have same current carrying capacity

with smaller OD than standard AAAC and

ACSR.

Leads to lower power loss and higher power

transfer capacity.

Note: Al6201 has far better corrosion

resistance than Al59 IEEMA Seminar High Performance Conductors - An International viewpoint

Brian Wareing.tech

6

New Conductor Types

Gap

ACCR

CCC

Invar type

ACSS

IEEMA Seminar High Performance Conductors - An International viewpoint

Multi-strand

Polymer matrix (C7)

Brian Wareing.tech Issues with Gap conductor

IEEMA Seminar High Performance Conductors - An International viewpoint 7

Difficult to use mid-span connectors

– If Gap breaks then the internal steel core immediately

contracts down the conductor core and so a mid-span joint

cannot be made.

– The only alternative is re-conductoring the section

Gap relies on the grease staying put – Oman, Ireland, UK have all experienced Gap losing its grease

– Sometimes dripping onto people‟s roofs and cars

– Commonly burning off on the surface and causing black marks

– The steel is then not protected.

Brian Wareing.tech Issues with Gap conductor

Gap „knee point‟ is at erection temperature, so if

sections are erected at different temperatures (on

different days) then their sag/temperature behaviour will

be different in the different sections and this can put

stresses on tension towers.

Because the aluminium is not connected with the steel

core, the whole conductor can be twisted easily by hand

This means that wet snow can also twist the conductor

and hence Gap accretes higher snow loads than, for

example, CCC.

It is filthy and very slow to erect as the steel core has to

be stripped bare and pre-tensioned for 12 hours


Brian Wareing.tech

High Temperature Conductors

With the ever growing need for more power to be

transmitted along existing lines new types of

conductors have been developed to run at higher

temperatures than traditional materials

According to Cigré, these conductors can be put into 4

basic clarifications

Type 1. Conductors composed of a steel core and

an envelope for which the high temperature

effects are controlled by means of thermal-

resistant aluminium alloys (e.g. GAP, Thermal)

Type 2. Conductors composed of a steel core and

an envelope for which the high temperature

effects are controlled by means of annealed

aluminium or aluminium alloy (e.g. ACSS)

9

Brian Wareing.tech

High Temperature Conductors

New conductor types

Type 3. Conductors composed of a non-metallic

core, and an envelope for which the high

temperature effects are controlled by means of

thermal resistant aluminium alloys (e.g. ACCR)

Type 4. Conductors composed of a non-metallic

core, and an envelope for which the high

temperature effects are controlled by means of

annealed aluminium or aluminium alloys (e.g.

CCC)

10

Brian Wareing.tech Aluminium – how hot?

Standard Aluminium and Aluminium Alloys can only operate continuously at temperatures up to 93ºC without causing metallurgical decay resulting in lifetime reduction

TAL and ZTAL aluminium have a lower conductivity but essentially the same tensile strength as ordinary electrical conductor grade aluminium but can operate continuously at temperatures up to 150ºC and 210ºC, respectively, without any loss of tensile strength over time.

Fully annealed aluminium is chemically identical to ordinary hard drawn aluminium and can operate indefinitely at temperatures at 250ºC (and higher) without any change in mechanical or electrical properties but has a much reduced tensile strength.

11 IEEMA Seminar High Performance Conductors - An International viewpoint

Brian Wareing.tech

12 High Performance Conductors - An International viewpoint IEEMA Seminar

Brian Wareing.tech Core Material

Galvanised steel is the normal core material for standard

ACSR conductors.

This is subject to corrosion and potential failure when the

galvanising has disappeared due to corrosion – a big

problem in corrosive or coastal areas.

High Tensile steel is used when stronger conductors with

less sag are required but this is still subject to corrosion.

Invar steel is used for low sag because of its very low

thermal expansion coefficient but it is very expensive.

High strength, low conductivity aluminium alloy can be

used as a core material to give improved strength to AAAC

conductors.


Brian Wareing.tech

14

Core Materials Description ASTM

Spec

MOE (Gpa) TS (Mpa) Cf(x10-6

/°C Unit wght

(mg/mm³)

HS Steel B498 200 1379-1448 11.5 7.778

EHS Steel B606 200 1517 11.5 7.778

EXHS Steel

galvanised

200 1965 11.5 7.778

Aluminium clad

20.3% IACS

B502 162 1103-1345 13 6.588

Galvanised Invar

alloy

B388

B753

162 1034-1069 1.5-3.0 7.778

Mischmetal Std

HS

A856

A857

200(I)-

186(F)

1379-1448

1517-1620

11.5 7.778

Aluminium Oxide

matrix

B976 210 1380 6.3 3.337

Carbon fibre B987 112.3 2158 1.61 1.88


ACS ~4

Brian Wareing.tech

15

Knee Point

To take advantage of the high temperatures (and so Ampacities) for „redundancy‟, low sag is also required and this uses the technique of the „Knee point‟

The knee point occurs for all ACSR type conductors when the tensile load is transferred from the (high expansion coefficient) aluminium to the (low expansion coefficient) core

This produces a change of angle in a sag/temperature graph

The region over which this occurs is known as the „Knee point‟ although in practice it is not a specific point.

It has always been there but at too high a temperature for „standard‟ ACSRs

The following graph is schematic but shows how the different expansion coefficients affect sag.


Brian Wareing.tech

16

8

9

10

11

12

13

14

15

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Sa

g o

f 3

66

m S

tan

da

rd L

2 S

pa

n, m

Conductor Temperature, 0C

620 mm2 Matthew GZTACSR38 kN @ 10 0C

Original 400 mm2 Zebra ACSR26.5 kN @10 0C

570 mm2 Sorbus AAAC36.9 kN @ 10 0C

560 mm2 ZTACIR38 kN @ 10 0C

Original design maximum sag,

1950s

620 mm2 Matthew GZTACSR38 kN @ 10 0C

Knee points


ACCC Drake 30 kN @ 10 0C

Brian Wareing.tech

17

Fittings

Most new conductor types require special fittings

An exception is the ZTAL/Thermal ACSR which

can use existing conventional fittings

These fittings may run hotter than normal and so

may incur some overheating unless specifically

designed for high temperature operation

But commonly many HT conductors are run at

<100ºC in normal operation so fittings only have

to withstand high temperatures for short periods

More information in Cigré Technical Brochure (in

course of publication)


Brian Wareing.tech Cigré WG 48 TB


Brian Wareing.tech

Proposed new WG


Brian Wareing.tech

International perspective on

the various technologies

available on HPC


Brian Wareing.tech

Cigré Survey of

experience with HPC

As part of the Cigré WG48 TB, a survey

was made of suppliers and utilities and

their experience with HPC.

The following slides are a brief summary

of the utilities‟ views.


Brian Wareing.tech

High Performance Conductors - An International viewpoint

Dealing with new conductor types

These are the views of 35 utilities world-wide

Why choose new conductor types?

Types of Installations

Installation

Fittings

Are utilities still putting them up?

Are they economic?

Did they perform?

Is training given?

IEEMA Seminar 22

Brian Wareing.tech


Why choose new conductor types?

• Reasons for new conductor use

• 75% said increased ampacity (average 85% increase required)

• 40% said ground clearance problems

• Only 2 utilities mentioned voltage drop

• However 22 utilities (63%) said it was an economic choice

• Two said limited corridor

• Other reasons:

• optimise (n-1) criteria

• Reduce visual impact (replacing bundle)

• Insufficient outage time to rebuild

• Planning permits and outages

• Minimise line losses. Reliable corridor

IEEMA Seminar 23

Brian Wareing.tech


Type of installations of new

conductors

• Reconductor upgrade: 48%

• Replacing aged conductor: 12%

• New line: 15%

• Special application (e.g. long crossings,

heavy ice loads, high ambient

temperatures): 10%

• Trial/pilot: 15%

IEEMA Seminar 24

Brian Wareing.tech


Installation • 77% said special requirements were needed (2

mentioned CCC)

• 70% said special training was required (one mentioned

Gap)

• 40% installed in-house; 67% by contractor (7% did both)

• 100% found following installation instructions easy!

• 35% installed with one circuit live

• 35% said some changes to utilities'

equipment/procedures necessary

• 100% said no problem with different conductor types on

same line

•

IEEMA Seminar 25

Brian Wareing.tech


Installation

86% said special conductor hardware fittings

were necessary

87% said these fittings were easy to install

Conductors with composite cores (CCC, ACCR)

should not be bent round small wheels – normally

a 1 metre diameter bull wheel is fine

Most conductors can be pulled up as a complete

conductor but Gap requires the steel core to be

pulled separately and tensioned for 12 hours

IEEMA Seminar 26

Brian Wareing.tech


Fittings Most new conductor types require special fittings

Extensive testing has shown that an HTLS conductor

dead-end operates at about ½ the temperature of the

conductor (Slightly higher at the nose, cooler at the

jumper pad).

The dead-ends and splices were designed with

reliability as paramount

When CCC conductor is operated at temperatures up

to 215°C the temperature of jumper pads (at dead-

ends) and suspension clamp bolts only reach

temperatures of 60° to 70°C.

IEEMA Seminar 27

Brian Wareing.tech


Fittings

The added mass of the dead-ends, splices, and

suspension clamps serve to reduce operating

temperatures of these components.

During EPRI-ANSI testing degradation of the

conductivity between the dead-ends and conductor

did not occur until an CCC conductor was operated

at temperatures to 330°C

But commonly many HT conductors are run at

<100ºC in normal operation so fittings only have to

withstand high temperatures for short periods

70% used Stockbridge dampers; 30% no dampers at

all: 90% said no vibration problems

IEEMA Seminar 28

Brian Wareing.tech


Are utilities still putting them up?

12 utilities are currently planning new

conductor use

• Planned installations: • 68 route km<100kV (all single)

• 704 route km 100<200kV (all single)

• 2 route km single, 115 route km bundled at 200<300kV

• 100 route km single, 2761 route km bundled at >300kV

No concerns expressed about use in bundled

formation

IEEMA Seminar 29

Brian Wareing.tech Are they economic?

Economic justification

• Commonly 20-50% cheaper than a new line

• Benefits 80% (up to 200%) better than new line

• Time advantage 1 to 5 years compared with new line

• 50% of utilities said lack of need for regulatory approval

was a major economic justification

• Tower modifications including change to foundations

require a building licence which means additional project

time and risk; HTLS conductors offered a quick (and so -

economic) solution

High Performance Conductors - An International viewpoint IEEMA Seminar 30

Brian Wareing.tech Did they perform?

• Performance compared with expectation • Performance as expected with 100% normal operation levels and

x2 for emergency. Highest noted as 240MVA for CCC

• Reliability given as 100% (but not many answered the question)

• Recorded faults were due to poor

installation or excessive weather loads


Brian Wareing.tech Training

Training up to 3 days provided by

suppliers

Fittings available from at least 20

manufacturers.


Brian Wareing.tech Summary of the survey

Reasons for new conductor use

75% said increased ampacity (average 85% increase required)

40% said ground clearance problems

Types of installation:

Reconductor upgrade: 48%

Replacing aged conductor: 12%

New line: 15%

Fittings:

– 86% said special conductor hardware fittings were necessary

– 87% said these fittings were easy to install

No utility expressed any regrets in their use

All users said they were an economic choice

Performed up to expectation

No problems with installation or fittings

Adequate training is given


Brian Wareing.tech

Westnetz

IEEMA Seminar 34 High Performance Conductors - An International viewpoint

HTLS Re-conductoring for upgrade of

an OHL in Hunsrück area near Koblenz

Brian Wareing.tech

Grid problems

From 2011 to 2012 the energy generated by wind energy

converters (WEC) in Hunsrück area multiplied by nearly six.

Particularly in times of poor load for example on Sundays with a

lot of wind and little consumption, more energy has to be

transported into the transmission grid.

Wind farm in Hunsrück near Bl. 0738


Brian Wareing.tech

Increase of the transmission capacity to 200 MVA Model 1:

Reconductoring using high temperature conductors

2x3x 264-AT1/34-A20SA (TAL/Stalum 265/35) (ACS core)

150° design temperature

In order to fulfill the requirements regarding ground clearances a

reconstruction of 16 of the 36 towers is required.

Costs:

Conductors: 220.000 €

Insulator strings: 125.000 €

Steel: 260.000 €

Tower installation + foundation: 840.000 €

Circuit installation: 490.000 €

Permission process: 100.000 €

Total: 2.035.000 €

Reconductoring 110-kV-Overhead line Anschluss Simmern, Bl 0738


Brian Wareing.tech


Reconstruction of the whole OHL using 110 kV-towers capable to carry twin

bundle circuits and a conductor configuration of

2x3x2x 264-AL1/34-ST1A

80° design temperature

Costs: ca. 6.500.000 €

Long lasting permission procedure has to be considered

Costs were determined within following requirements: 12,3 km line length

Conductor: 264-AL1/34-ST1A, 2er-Bundle

Earth wire: 264-AL1/34-ST1A, Einfachseil

26 Suspension towers, 10 WA, 4 WE Tension tower

Insulator strings: 210 double tension strings, 156 double suspension strings

Temporary road construction: overall 150 m per tower

crossings: federal motorway, 13 other streets

Dismounting existing overhead line: 40 towers and foundation without sump pumping

Permission process

supervision



Brian Wareing.tech


Reconductoring using HTLS-conductors CCC 317/60 (Oslo)

130° design temperature (1050 A)

In order to fulfill the requirements regarding ground clearances a

reconstruction of only one of the 36 towers is required. Verifications of

the distance calculations were done with the programme “FM-Profil“

(EPE-Model)

Costs:

Conductors: 1.032.000 €

Insulator strings : 260.000 €

Steel: 19.850 €

Tower installation +foundation: 50.500 €

Circuit installation : 731.250 €

Total: 2.093.600 €


Costs 264-AT1/34A20SA

Conductors: 220.000 €

Insulator strings : 125.000 €

Steel: 260.000 €

Tower installation + foundation: 840.000 €

Curcuit installation : 490.000 €

Permission process: 100.000 €

Total: 2.035.000 €


Brian Wareing.tech

Line losses - how HPC could help

bring down Transmission losses

Radiative losses

Thermal losses

Corona losses

Reactive power gains and losses

Optimising SIL

BUT – all the time the sag requirements

and power capacity (including n-1) should

be kept in mind


Brian Wareing.tech

Network Requirements

Affordable re-conductoring or new-build

Efficient (low loss) conductor

High capacity

Low Sag

– The carbon fibre composite core has lowest electrical sag of all HT

conductors

– Invar steel has a much lower coefficient of thermal expansion than

other steels

Running cooler – a conductor that delivers high

ampacity at a lower temperature has

– Lower line losses

– Longer fitting life

– Less chance of breaking regulatory clearances


Brian Wareing.tech

Real power losses - radiative and thermal losses

All conductors gain and lose real power

(excluding reactive power) by I²R, solar

gain, radiation and convection.

Heat Balance Equation:

Where – PS = Solar Heat gain

– PC = Convective Heat Loss

– PR = Radiative Heat Loss


Brian Wareing.tech

How does conductor choice help?

- Standard aluminium alloys (54-59%IACS)

Main input/output power

– Wind speed

– Radiation losses (emissivity)

– Solar gain

– Current

Typically the largest power input is due to the

current.

Current limited by keeping the aluminium below

93°C or the electrical sag.

Higher current may therefore require larger

diameter which may result in sag or structure

problems.


Brian Wareing.tech

How does conductor choice help? - Zirconium aluminium alloys (58-60%IACS)

The limitation on temperature is not as severe

with Zirconium alloys as they can reach between

150 and 210°C.

Sag limitations are dictated by the core material if

they can be operated above the knee point.

The generally higher conductivity means that for

increasing currents, the diameter can be kept low

depending on the core size

However, the higher temperature mean increased

thermal radiation losses


Brian Wareing.tech

How does conductor choice help?

- Annealed aluminium alloys (63%IACS)

The limitation on temperature is generally even better

than Zirconium alloys as annealed aluminium can

reach between 250°C.

Sag limitations are dictated by the core material if

they can be operated above the knee point – this is a

limitation for ACSS but generally not for CCC.

The significantly higher conductivity means that for

similar currents, the conductor temperature will be

lower than the equivalent ACSR and so thermal power

losses will be smaller.

The savings can compensate for the more expensive

conductor within a few years.


Brian Wareing.tech Explanation!

Using annealed aluminium generally means that, compared with

AAAC, the conductor will operate at a lower temperature for the

same ampacity and so have lower thermal losses.

It is quite common for high temperature conductors to operate at

similar ampacities to standard conductors and to use their high

temperature capability only for n-1 situations.

In the tables in the next few slides it can be seen that operating an

ACSR Panther (21mm OD) will have a thermal power loss (at 75°C)

of 5231MWh per 10km at the rated current of 473A.

Switching to AL-59 241 (20.1mm OD) at 473A operates at a lower

temperature and so lower losses of 4488MWh, a saving of

743MWHr/10km of line.

However, using CCC (21.8mm OD) has a loss of just 3222MWh – a

saving of over 2000MWh/pa/10km.


Brian Wareing.tech Conductor comparisons

Consider a 350m span with ACSR Panther

(201mm² aluminium area) and 21mm OD.

At 75°C this has current carrying capacity of 473A

and a sag of 10.06m (tension of 3.8kN at 32°C at

25%UTS).

Assumptions:

– Ambient temp: 40°C, Wind 0.6m/s, Sun Radiation 1045 W/m²,

Elevation 350 m; Solar/Emissivity 0.5.

Compare CCC , AL59, ACCR, ACSS, Invar and

Gap (all Hawk equivalent).

Look at 473A and doubling capacity to 946A


Brian Wareing.tech Power losses (Thermal)


Conductor

Name

Units CCC

Casablanca

CCC Lisbon ACSR

PANTHER

AL59 241 ACCR/TW -

HAWK

ACSS/TW-

HAWK

INVAR

HAWK

GAP 240

HAWK

Max DC

Resistance @

20°C

ohm/km 0.1024 0.0887 0.132 0.123 0.1153 0.1136 0.111 0.119

Overall

Diameter of

Conductor

mm 20.5 21.79 20.98 20.1 21.64 21.79 19.66 20.60

Rated Tensile

Strength of

Conductor

kg 10,312 10,554 9,708 5,659 8,708 7,077 8,515 8,851

Maximum

Working

Current @ 75°C

A 548 598 473 503 518 517 477 515

Line Losses

per 10 km line

length @ 473

Amps

MWh 3756 3,222 5,231 4,488 4,197 4,214 4,979 4,323

Line Losses

per 10 km line

length @ 946

Amps

MWh 18,613 15,390 N/A N/A 21,432 21,641 26,507 21,532

Conductor

Temperatures

@ 946 Amps

°C 139°C 122°C N/A N/A 153°C 154°C 176°C 152°C

Brian Wareing.tech

But what about sags at high

ampacity levels?


The two Invar conductors and ACSS

cannot make the sag if >90°C

ACCR is OK up to 130°C

CCC and Gap are OK throughout their range

Brian Wareing.tech And ampacity?


The two INVAR need 162 and 176°C

to reach 946A but break sag at <90°C

ACSS needs 154°C but breaks sag at <90°C

ACCR needs 153°C but breaks sag at 130°C

GAP needs 152°C and can make the sag

CCC Lisbon needs just 122°C

and can make the sag

CCC Casablanca needs 139°C

And can make the sag

Brian Wareing.tech Conductor capability

It can be seen that the sag limitation reduces the

capability of INVAR, ACSS and ACCR by restricting

their temperature and hence ampacity.

Both CCC and Gap can make the full capability (946A)

and maintain sag but Gap loses 21,532MWh/10km

compared with 15,390MWh for CCC Lisbon and

18,613MWh for CCC Casablanca due to their lower

temperatures and hence lower thermal power losses.

Whilst these conductors are more expensive than, say,

AL59, the savings in power losses can pay back these

higher capital costs in just a few years.


Brian Wareing.tech Corona losses

Corona occurs when the electric field at the conductor surface is

strong enough to break down the air.

It is very noticeable in damp weather and is often associated with

audible crackling or fizzing.

Although sometimes occurring at voltages down to 33kV it is

more of a problem at EHV voltages.

However, it is generally a fairly small component of the losses

overall.

Surface electric fields are related to conductor and sub-conductor

diameter and bundling but not conductor type, as they are a

surface area, surface condition, voltage and weather related

phenomenon.

Corona losses should not normally be a factor in selecting the

type of conductor


Brian Wareing.tech

Re-conductoring and

increasing power transfer For this it is necessary also to look at reactive power losses and

the ability to achieve a high SIL - Is this conductor dependent?

Replacing conductors such as ACSR or AAAC with an HPC such

as CCC or ACSS of the same diameter can be a cost effective way

to increase the transfer capacity of transmission lines.

Maintaining the same conductor diameter/weight/tension makes it

likely that existing structures can be used and with proper

conductor selection and application ground clearances can

normally be maintained.

But increasing power transfer will impact reactive power

consumption, and therefore voltage, as well as real power losses.

Voltage drop and reactive power flow are related and

interdependent and to understand how these are affected by

conductor choice, a brief explanation is required.


Brian Wareing.tech Reactive power

Reactive power is either trapped in the capacitive (electric field) or

inductive (magnetic field) elements of an AC system, or is in transit

between the capacitive and inductive elements of the system.

Reactive power flow does affect system voltage and can be

managed by application of equipment which will offset or

supplement reactive power flow occurring in the electrical system.

Reactive power is normally described as being:

– “consumed” or “lost” in inductive circuit elements, typically the series

inductive impedance in electric transmission lines or shunt connected inductors

(shunt reactors). Inductive elements store energy in magnetic fields.

– “supplied” by capacitive circuit elements, typically the shunt capacitive

impedance in electric transmission lines or shunt connected capacitors.

Capacitive elements store energy in electric fields.


Brian Wareing.tech

Reactive power consumed (energy

loss) and supplied (energy gain)

The reactive power consumed in an inductor every cycle, Q=

V²/XL= I². XL, where XL the inductive reactance (in Ω).

So if the power capacity is increased by doubling the current, I,

the real power, P, will double but the reactive power loss, Q, will

quadruple.

The reactive power supplied by a capacitor and released every

cycle, Q = I². XC = V²/XC where XC the capacitive reactance (in Ω).

1/ XC is known as susceptance (BC).

So the reactive power supplied, Q, varies as the square of the

voltage across the capacitance or the square of the current

through the capacitance.


Brian Wareing.tech Reactive power loss

Reactive power loss is dependent on the inductive

reactance of the circuit which varies with conductor

diameter for single conductor designs

Larger diameter conductors reduce inductive reactance of

the line e.g. for example going from single conductor

170mm² ACSR to 800mm² (large change) will reduce

reactive power loss by ~10% (relatively low).

But going from 800mm² single ACSR to 2x400mm² bundle

will reduce reactive power loss by ~25% - so geometric

conductor spacing is more important than conductor

choice.


Brian Wareing.tech Reactive power gain

Reactive power gain is dependent on the shunt capacitance of the

circuit

Larger diameter conductors increase the susceptance of the line

e.g. for example going from single conductor 170mm² ACSR to

800mm² will increase reactive power gain by ~13%.

But going from 800mm² single ACSR to 2x400mm² bundle will

increase reactive power gain by ~30% - so again geometric

conductor spacing is more important.

Both reactive power gains and losses vary with line length.


Brian Wareing.tech SIL

Surge Impedance Loading (SIL) is the point at which the Q supplied

by the shunt capacitance of the line equals the Q lost in the series

inductance of the line.

Changes in line design that increase susceptance (BC) and

consequently increase the Q supplied (more sub-conductors, larger

bundle spacing, and closer phase spacing) move the red “Q

Supplied” curve up.

These same changes in line design also reduce series inductive

reactance (XL) and the Q losses moving the blue “Q Lost” curve to

the right.

The net effect is to increase the SIL point, located at the intersection

of these two curves, thereby allowing increased power levels whilst

maintaining the line voltage within acceptable levels.


Brian Wareing.tech What effect do conductors have?


It can be seen that conductor diameter makes very little difference.

The biggest effect is the reduced SIL from the INVAR conductor.

This is due to the increase inductive losses due to the smaller diameter and

the magnetic core of this conductor but the effect is still minor.

As loading increases above the SIL reactive power losses quickly increase and

so larger amounts of reactive power compensation (typically shunt capacitors)

will need to be applied to maintain system voltage (at a cost).

Data for 150kV 100km line.

Brian Wareing.tech

Power losses overall


Lower resistance means lower electrical

losses whilst higher power flow

increases reactive losses. For a single

conductor line at:

100MW power flow: reactive losses are

12MVAR whilst electrical losses vary

from 8.5MW (CCC) to 12MW (INVAR)

150MW power flow: reactive losses are

37MVAR whilst electrical losses vary

from 12.8MW (CCC) to 18MW (INVAR)

Brian Wareing.tech Conductor type

The previous slides illustrate that real power

losses are dependent upon internal conductor

construction, and that conductors with smaller

cores and trapezoidal stranding, such the

CCC/TW Amsterdam, can provide more

aluminium cross sectional area in the same

diameter significantly reducing resistance and

real power losses.

However, reactive losses show very little change

with conductor diameter or type


Brian Wareing.tech

61

Aeolian vibration

In standard conductors, line design is influenced by

the erection tension and maintaining an Every Day

Stress (EDS) so that Aeolian vibration does not cause

vibration fatigue and shorten the conductor life.

Such failures are caused by dynamic stresses

resulting from reverse bending by wind-induced

conductor motions such as wake-induced oscillations


Brian Wareing.tech New and Old

Vibration damage occurs when the energy input (from

wind) is not matched by self-damping (from the

conductor)

It is accepted that, for conventional ACSR and AAAC,

vibration levels are higher as the conductors age due

to long term geometrical compaction which stop the

strands sliding (and hence self-damping decreases and

damage potential increases).

In contrast, HTLS conductors, when operated above

the knee point, have much slacker strands which can

move and so increase self-damping and reduce

damage potential.


Brian Wareing.tech Self damping

The self damping characteristics of a conductor are basically

related to the freedom of movement or “looseness” between the

individual strands or layers of the overall construction.

In standard conductors the freedom of movement (self damping)

will be reduced as the conductor ages or tension is increased.

It is for this reason that vibration activity is most severe in the

coldest months of the year when the tensions are the highest.

Conductors with trapezoidal shaped outer strands have higher

self damping performance due to the gaps between layers.

Conductors, such as ACSS and CCC, utilise fully annealed

aluminium strands that become inherently looser when the

conductor progresses from initial to final operating tension.

So the best self-damping HTLS conductors are those that use fully

annealed aluminium with trapezoidal strands.


Brian Wareing.tech

Vibration Monitor installations

64

Deadwater Fell tests

UK IEEMA Seminar High Performance Conductors - An International viewpoint

Brian Wareing.tech Load shifting

Conductors such as CCC exhibit load

shifting after a tension is applied.

This tension can occur naturally (e.g. after

a snow/ice incident) or be applied on

erection (pre-tensioning).

The load shift moves (permanently)

tension from the aluminium to the core,

thereby reducing aluminium stress levels.

It also reduces the knee point temperature


Brian Wareing.tech Effect of Load shifting

Lisbon CCC with no pre-tension was tested at the

Deadwater in comparison with a load-shifted version

(load share ~80% core ~20% on the aluminium) to see

how load shifting affected the vibration level.

The data showed that new HT conductor types which

depend on the core above their knee point do not follow

the same vibration pattern as standard conductors where

the load is mainly on the aluminium

With little load on the aluminium, it is only there for the

ride and the data indicates that vibration levels are

reduced significantly above the knee point

So – are there benefits to pre-tensioning?


Brian Wareing.tech

67

Comparison of load-

shifted and new Lisbon

ACCC at the same tension

The vibration level is

reduced substantially as

the conductor goes

through load shift.

Load shifting can be

achieved at erection by

pre-tensioning.

This may require the use

of back stays on the

crossarms

„Load shifted‟ Lisbon

„New‟ Lisbon


Brian Wareing.tech Summary

Brief description of HPC including the

component materials

Showed how power losses can be reduced

by the use of HTLS conductors

International perspective: – Results of world-wide survey

– Specific example of economic choice from Germany

Bit about vibration levels on new

conductor types.


Brian Wareing.tech That‟s it!

Thank you!


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