multi-agent based fault localization and isolation …820607/fulltext01.pdfdegree project in...

Degree project in

Multi-Agent Based Fault Localization and Isolation in Active Distribution

Networks

CHAITANYA DESHPANDE

Stockholm, Sweden 2015

XR-EE-ICS 2015:004

ICSMasterthesis,

Abstract

Liberalized electricity markets, increased awareness of clean energy resources and theirdecreasing costs have resulted in large numbers of distributed power generators beinginstalled on distribution network. Installation of distributed generation has altered thepassive nature of distribution grid. A concept of Active Distribution Network is proposedwhich will enable present day infrastructure to host renewable energy resources reliably.Fault management that includes fault localization, isolation and service restoration ispart of active management of distribution networks.

This thesis aims to introduce a distributed protection methodology for fault localizationand isolation. The objective is to enhance reliability of the network. Faults are identi-fied based on root mean square values of current measurements and by comparing thesevalues with preset thresholds. The method based on multi-agent concept can be usedto locate the faulty section of a distribution network and for selection of faulty phases.The nodal Bus Agent controls breakers that are associated with it. Based on indicationof fault, adjacent bus Agents communicate with each other to identify location of fault.A trip signal is then issued to corresponding Breakers in adjacent Bus Agents, isolatingthe faulty section of line. A case study was carried out to verify suitability of the pro-posed method. A meshed network model and multi-agent based protection scheme wassimulated in Simulink SimPowerSystems. Considering nature of Distribution Network,separate breakers for each phase are considered. The distribution network protectionsystem identified fault introduced in the network correctly along with interrupting thefault current.

Keywords

Distributed Energy Resources, Active Distribution Network, Fault Localization and Iso-lation, Multi-Agent, MATLAB-SimPowerSystems, Distribution Network Protection.

2

Acknowledgements

I would like express my deep and sincere gratitude to my supervisors PhD studentsYiming Wu and Mikel Armendariz Perez, their vast knowledge and guidance helped meget through toughest of situations. I would also like to thank teachers at ICS; Arshad,Nicholas and Davood, for their guidance during courses and in completion of this thesis.

I would like express gratitude towards Prof Lars Nordstrom for agreeing to be examinerto this thesis.

I would also like to thank fellow students Farhad, Buland, Clipton for their support.Last but not least, I thank Annica for helping around with bureaucratic routine.

Chaitanya Deshpande

Contents

Abstract 1

Acknowledgements 2

Contents 3

List of Figures 6

List of Tables 10

1 Introduction 11

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.2 Thesis Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.3 Contribution of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.4 Organization of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2 Related Work 13

2.1 Distributed Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1.1 Wind Farms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.1.2 Solar Photovoltaic . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1.3 Micro Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1.4 Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 Impact of DG on Distribution Network . . . . . . . . . . . . . . . . . . . . 15

3

Contents 4

2.3 Impact on Distribution Network Protection . . . . . . . . . . . . . . . . . 17

2.4 Active Distribution Networks . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.4.1 ICT Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.4.2 Active Resources and Aggregators . . . . . . . . . . . . . . . . . . 18

2.4.3 Active Network Management . . . . . . . . . . . . . . . . . . . . . 19

2.5 Faults in Distribution Network . . . . . . . . . . . . . . . . . . . . . . . . 19

2.5.1 Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.5.2 Single Line to Ground Fault . . . . . . . . . . . . . . . . . . . . . . 21

2.5.3 Line to Line Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.5.4 Three Phase to Ground Fault . . . . . . . . . . . . . . . . . . . . . 24

2.5.5 Consequences of Faults . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.5.6 Fault Clearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.5.7 Current Limiters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.5.8 Fault Clearing System . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.5.8.1 Relay Protection System . . . . . . . . . . . . . . . . . . 27

2.5.8.2 Circuit Breaker . . . . . . . . . . . . . . . . . . . . . . . . 28

2.5.9 Protection Principles . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.5.10 Fault Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.6 Multi-Agent Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3 Methodology Employed 32

3.1 Distribution Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.2 Simulink Modelling of Distribution Network . . . . . . . . . . . . . . . . . 35

3.2.1 Three Phase Programmable Voltage Source . . . . . . . . . . . . . 35

3.2.2 Three Phase Two Winding Transformer . . . . . . . . . . . . . . . 36

3.2.3 Three Phase Stub-Lines . . . . . . . . . . . . . . . . . . . . . . . . 37

3.2.4 Three Phase Dynamic Load . . . . . . . . . . . . . . . . . . . . . . 39

Contents 5

3.2.5 Three Phase VI Measurement Block . . . . . . . . . . . . . . . . . 40

3.2.6 Three Phase Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.2.7 Three Phase Breakers . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.3 Fault Identification and Localization . . . . . . . . . . . . . . . . . . . . . 43

3.4 Implementation of Fault Identification and Localization in Simulink . . . . 44

3.4.1 Fault Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

3.4.2 Fault Localization and Phase Selection . . . . . . . . . . . . . . . . 46

3.4.2.1 Single Phase Fault . . . . . . . . . . . . . . . . . . . . . . 47

3.4.2.2 Line to Line Fault and Three Phase to Ground Fault . . . 48

4 Results 50

4.1 Scenario 1- Fault at Bus 10 . . . . . . . . . . . . . . . . . . . . . . . . . . 50

4.1.1 Three Phase fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

4.1.2 Line to Line Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

4.1.3 Single Phase Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

4.2 Fault on Line 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4.2.1 Three Phase fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

4.2.2 Line to Line fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

4.2.3 Line to Ground Fault . . . . . . . . . . . . . . . . . . . . . . . . . 65

5 Discussion and Conclusion 69

6 Future Work 70

Bibliography 71

A Network, Line and Transformer Parameters 74

List of Figures

2.1 Wind Farm [9] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.2 Solar Photovoltaic [10] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3 Representation of a Faulted Line . . . . . . . . . . . . . . . . . . . . . . . 20

2.4 Thevenin Equivalent Voltage Representation . . . . . . . . . . . . . . . . . 21

2.5 Single Line to Ground Fault . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.6 Single Line to Ground Fault- Fault Current . . . . . . . . . . . . . . . . . 22

2.7 Single Line to Ground Fault- Fault Voltage . . . . . . . . . . . . . . . . . 22

2.8 Line to Line Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.9 Line to Line Fault- Fault Current . . . . . . . . . . . . . . . . . . . . . . . 23

2.10 Line to Line Fault- Fault Voltage . . . . . . . . . . . . . . . . . . . . . . . 24

2.11 Three Phase to Ground Fault . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.12 Three Phase to Ground Fault-Fault Current . . . . . . . . . . . . . . . . . 25

2.13 Three Phase to Ground Fault . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.14 Single Phase Fault Identification . . . . . . . . . . . . . . . . . . . . . . . 29

2.15 Negative sequence quantities during two phase fault . . . . . . . . . . . . 29

2.16 Negative sequence quantities during two phase fault . . . . . . . . . . . . 30

3.1 Distribution Network Diagram . . . . . . . . . . . . . . . . . . . . . . . . 33

3.2 Network Model in Simulink . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.3 Grid Model in Simulink . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.4 Three Phase Programmable Voltage Source . . . . . . . . . . . . . . . . . 35

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List of Figures 7

3.5 Generator Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.6 Three Phase Two Winding Transformer . . . . . . . . . . . . . . . . . . . 36

3.7 Transformer Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.8 Three Phase StubLine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.9 Three Phase Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.10 Sample Load Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.11 Three Phase VI Measurement Block . . . . . . . . . . . . . . . . . . . . . 40

3.12 Three Phase Fault Settings . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.13 Three Phase Fault Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.14 Three Phase Breaker Block . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.15 Three Phase Breaker Block Parameters . . . . . . . . . . . . . . . . . . . . 42

3.16 Fault Identification and Localization Algorithm . . . . . . . . . . . . . . . 43

3.17 Agent Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

3.18 Fault Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.19 Three Phase Fault Identification . . . . . . . . . . . . . . . . . . . . . . . 45

3.20 Two Phase Fault Identification . . . . . . . . . . . . . . . . . . . . . . . . 46

3.21 Single Phase to Ground Fault . . . . . . . . . . . . . . . . . . . . . . . . . 46

3.22 Multi-Agent based controller for Breaker46 . . . . . . . . . . . . . . . . . 47

3.23 Multi-Agent based controller for Breaker42 . . . . . . . . . . . . . . . . . 47

3.24 Localization of Single Phase to Ground Fault . . . . . . . . . . . . . . . . 48

3.25 Single Phase Fault- Phase Selection . . . . . . . . . . . . . . . . . . . . . . 48

3.26 Two Phase Fault Localization . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.27 Fault Localization Algorithm for Phase A . . . . . . . . . . . . . . . . . . 49

4.1 Three Phase Fault Identification on Line 6 . . . . . . . . . . . . . . . . . . 51

4.2 Trip Signal for Fault on Line 6 . . . . . . . . . . . . . . . . . . . . . . . . 51

4.3 Fault current after issuing trip signal . . . . . . . . . . . . . . . . . . . . . 52

List of Figures 8

4.4 Voltage, Current and PQ at Bus 6 . . . . . . . . . . . . . . . . . . . . . . 52


4.6 Fault Identification for Line to Line Fault at Bus 6 . . . . . . . . . . . . . 53

4.7 Trip Signal issued for Line to Line Fault at Bus 6 . . . . . . . . . . . . . . 54

4.8 Fault Current for Line to Line Fault at Bus 6 . . . . . . . . . . . . . . . . 54

4.9 Voltage, Current and PQ at Bus 6 for Line to Line fault . . . . . . . . . . 55

4.10 Voltage, Current and PQ at Bus 10 for Line to Line fault . . . . . . . . . 55

4.11 Voltage, Current and PQ at Bus 4 for Line to Line fault . . . . . . . . . . 56

4.12 Fault Identification for Line to Ground Fault at Bus 6 . . . . . . . . . . . 56

4.13 Trip Signal issued for Line to Ground Fault at Bus 6 . . . . . . . . . . . . 57

4.14 Fault Current for Line to Ground Fault at Bus 6 . . . . . . . . . . . . . . 57

4.15 Voltage, Current and PQ at Bus 6 for Line to Ground fault . . . . . . . . 58



4.18 Network Simulation for fault on Line 4 . . . . . . . . . . . . . . . . . . . . 59

4.19 Three Phase Fault Identification on Line 4 . . . . . . . . . . . . . . . . . . 60

4.20 Trip Signal for Fault on Line 4 . . . . . . . . . . . . . . . . . . . . . . . . 60




4.24 Line to Line Fault Identification on Line 4 . . . . . . . . . . . . . . . . . . 63

4.25 Trip Signal for Line to Line Fault on Line 4 . . . . . . . . . . . . . . . . . 63




4.29 Line to Line Fault Identification on Line 4 . . . . . . . . . . . . . . . . . . 65

4.30 Trip Signal for Line to Ground Fault on Line 4 . . . . . . . . . . . . . . . 66

List of Figures 9





List of Tables

2.1 Distributed Generation Categories . . . . . . . . . . . . . . . . . . . . . . 14

A.1 Network Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

A.2 Line Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

A.3 Line Resistance, Inductance and Capacitance . . . . . . . . . . . . . . . . 75

A.4 Transformer Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

A.5 External Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

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Chapter 1

Introduction

This chapter presents a brief introduction to the thesis topic, the objective, the method-ology employed in the presented project and organization of thesis report.

1.1 Background

Modern society has become increasingly dependent on electricity to meet its energydemands. The advantage of electricity being easily transported at high efficiency andreasonable cost has made it a popular form of energy. There has been an ever increasingdemand for electricity all across the globe. World Energy Outlook 2012 published byInternational Energy Agency projects over 70Traditional power plants have long beeninstalled near the sources of energy and many a times, are away from centres of consump-tion. They are connected to the transmission network. The high voltage transmissiongrid though reliable suffers from possibility of cascading failures. The centrally concen-trated generation is also not efficient as it converts only about 35

To realise energy efficient solution to rising demand of electricity is having distributedgeneration near the centres of consumption, to maintain system stability, provide thespinning reserve and reduce the transmission and distribution with distributed optimizingcontrol. The role of distribution network has been limited to servicing loads. This madethe design of distribution network simpler as the power flow was unidirectional. Withincreased integration of DG the simplicity of network is set to disappear, which presents achallenge for distribution system in the form of new protection requirements and voltagestability issues.

To maximize use of renewable energy generated and to avoid long and unnecessary out-ages, a distributed approach to design distribution network protection has been consid-ered. Multi-Agent System is made of dynamic and autonomous agents working coopera-tively to achieve the overall aim, while deployed in a distributed fashion and working with

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Chapter 1.Introduction 12

local constraints. Application of multi-agent system in power system has been possiblewith advancement in ICT, making it feasible to communication faster with equipments.Agent based protection systems consist of distributed equipment combined with a com-munication network to cooperate in the realization of protection functions. The agentscan also be provided with the capability of acting autonomously when the communicationchannels fail.

1.2 Thesis Statement

With increased integration of DER the distribution network can no longer be assumedto be radial networks. This requires changing the simplistic protection scheme that hasbeen traditionally employed to protect network from faults. The power flow no longerbeing unidirectional presents new challenges to be addressed before integration of moreDG.

This thesis tries to address the issue of fault localization on distribution network basedon distributed protection through multi-agent system. Protection malfunctions on onehand can raise safety issues while they can also be a reason for underutilization of DG.The aim of the thesis is to minimize outage in case of fault while servicing maximumload and making sure optimum utilization of infrastructure.

1.3 Contribution of Thesis

The thesis tries to address following issues-

1. Survey effects of integration of DG on distribution network 2. Proposes a faultlocalization algorithm based on distributed control applying multi-agent concept. 3.Models a distribution network and multi-agent system in Simulink- SimPowerSystems 4.Undertakes a case study to verify the proposed algorithm.

1.4 Organization of Thesis

The thesis is organized as follows- Chapter 2 summarizes Literature Review and PreviousWork. Chapter 3 discusses the Methodology Employed in accordance with the thesisstatement. Chapter 4 presents the results obtained for the cases considered. Chapter 5includes conclusion and future work. The Simulink model of network and implementationof Multi-Agent concept is included in the Appendices at the end of the report.

Chapter 2

Related Work

This chapter presents the theoretical background related to the thesis topic. The chapterpresents different types of Distributed Generation and their impact on DN, Active Dis-tribution Networks, Fault characterization and Protection Schemes.The chapter further discusses Multi-Agent concept and its application for protection inDistribution Network.

Early power systems were designed to cater local loads through a simple infrastructureconnecting generator to loads. The advent of AC system and efficiency constraints madeit necessary to have centralized generation. These centralized generators, of higher ca-pacity were all connected to transmission network. The role left to distribution networkwas to service loads, by transferring power from transmission networks to loads.

The deregulation of energy market in the early 90s, has led to changing the centralizedapproach of generation, enabling power plants to produce electricity according to itsmarginal cost. This model resulted in a more complex power system with greater uncer-tainties. In addition, the advent of renewable energy further complicated the ability ofutilities to adhere to the traditional system. Renewables have âœgrid priorityâ and thelowest marginal cost, meaning the grid is obligated to purchase their electricity first [5].

In recent developments, model of personal power plants [6] is being discussed where abuilding will have its own self-sufficient grid. Prosumer, a new term has been coined forpower system participants who consume, produce as well as store energy while optimizingits utilization.

2.1 Distributed Generation

Since there are many definitions available, the paper "Distributed generation: a defi-nition" [7] considered different issues that may be used to define DG precisely. These

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Chapter 2.Related Work 14

included, purpose, location, rating, power delivery area, technology, mode of operation,ownership and penetration of DG. Much of these issues were found to be irrelevant indefining the term. An attempt to present an inclusive definition from known internationaland regional definitions was made in "Review of the Distributed Generation Concept:Attempt of Unification" [8]. The general definition arrived at is, distributed generation isan electric power source that is directly connected to distribution network or on the con-sumer side of the network, which is smaller in size compared to a centralized generator.Different DG technologies available are- Wind Turbines, Solar Photovoltaic and SterlingEngine, Micro-Turbines, Combined Heat and Power Plants and Fuel Cells. Electricity isgenerated by employing suitable technology depending on available local resources. Thecategories suggested for types of DG depending on their capacities are as follows-

Table 2.1: Distributed Generation Categories

Category Capacity

Micro 1 Watt<5 kWattSmall 5 kWatt<5 MWattMedium 5 MWatt<50 MWattLarge 50 MWatt<300 MWatt

Some of the available DG technologies are-

2.1.1 Wind Farms

Wind power generation harnesses energy of wind to generate electricity. The turbinesblades rotate as wind blows, generating lift. The hub of the turbine rotates in turn,which is connected to a drive train and coupled with a synchronous generator. Powerelectronic converters are connected to shape output of turbine and also to offer supportto grid reactive power support in case of voltage sag.

Figure 2.1: Wind Farm [9]


2.1.2 Solar Photovoltaic

Series connected arrays of solar cells convert solar irradiance into usable electrical energy.Maximum Power Point Tracking (MPPT) method is used to extract maximum powerfrom solar panels. A battery bank and a charge controller are associated with the solarphotovoltaic plant to store energy.

Figure 2.2: Solar Photovoltaic [10]

2.1.3 Micro Turbine

Micro-gas turbines are a type of internal combustion engine where chemical energy offuels is converted into electricity. Gas turbines accept most commercial fuels, such aspetrol, natural gas, propane, diesel, and kerosene as well as renewable fuels such as E85,biodiesel and biogas [10].

2.1.4 Fuel Cells

Fuel cell generates DC voltage based on interaction of hydrogen and oxygen in presenceof a conducting electrolyte. The DC voltage thus generated is converted to AC by meansof an inverter. Advantage of fuel cells is absence of any moving component. Higher costof operation is the disadvantage.

2.2 Impact of DG on Distribution Network

Addition of DG has positive and negative impacts on various aspects of distribution net-work operation. These include impact on voltage regulation, losses in feeder, harmonicsin the network and on level of short circuit currents. Distribution networks are often builtin mesh structures but operated in open loop configuration. This results in the networkbeing a radial one with unidirectional power flow. This assumption has traditionally


influenced operation of distribution network. In radial distribution systems voltage isregulated with the help of load tap changing transformers (LTC) at substations, by lineregulators on distribution feeders and shunt capacitors on feeders or along the line. Theconnection of DG may result in changes in voltage profile along a feeder by changing thedirection and magnitude of real and reactive power flows. The impact can be either pos-itive or negative depending on nature and location of DG. Medium-sized and especiallysmall DG technologies often use asynchronous generators (also known as induction gen-erators), as they are significantly cheaper than synchronous generators. Grid-connectedasynchronous generator is not capable of providing reactive power. It actually requiresreactive power from the grid during the start-up process and at operation [10] thus af-fecting voltage profile. DG can provide voltage support to raise the low voltage at theend of the feeder. However, the voltage where DG is injected may be raised over theupper limit [? ]. Optimally located DG units can help in minimising feeder losses bysupplying active and reactive power to the network. However, most DGs are customerowned and hence grid operator canâTMt decide location of DGs. Normally it is assumedthat, DGs located away from Distribution Substation would help in reducing losses overdistribution network. DGs may introduce harmonics to the network depending on typeof generator and interconnection configuration. The harmonics could be from generatoritself, for example from synchronous generator or from power electronic converter. Theolder SCR based inverter that are line commutated and produce high levels of harmoniccurrent. Most new inverter designs are based on IGBTs that use pulse width modulationto generate the injected "sine" wave. These newer inverters are capable of generatinga very clean output and they should normally satisfy the IEEE 1547 requirements [12].For radial feeders the symmetrical short circuit current is calculated as the ratio betweenvoltage and the total impedance from the source to the fault location. This implies thatthe short circuit current decreases as the fault location moves away from the source. Inabsence of DG connected down-stream to the fault, there is no contribution to the faultother than the one coming from the source. Under these premises the coordination ofprotective devices is necessary only for upstream protective devices neglecting any otherdown-stream devices. When DG is connected to the system a secondary short circuitcurrent contribution coming from the DG to the fault takes place. This contribution issimilarly calculated as the ratio between the voltage and the total impedance from theDG to the fault. This short circuit current contribution coming from the DG adds to themain source contribution current at the fault location increasing the total short circuitlevel of the fault [13]. Impact of DG on distribution network costs was assessed in [14];it presents quantification of how DG affects distribution network costs in presence ofdistributed generation. The results show that total distribution network costs increasewith DG penetration.


2.3 Impact on Distribution Network Protection

Reliability of power system depends closely on its protection system. The addition ofdistributed generation (DG) to the power distribution system imposes a challengingand unconsidered fault condition to the traditional distribution overcurrent protectionscheme. In the event of fault, DG short circuit contribution may cause erroneous opera-tion of protective devices located downstream to the fault. The fundamental principle ofthe vulnerability assessment is the comparison of maximum and minimum short circuitlevels before and after the distributed generation is added. Those protective devicesinstalled at buses where the DG short-circuit contribution exceed the pre-DG minimumshort circuit level are the most likely to miss-operate under fault conditions.

Protection schemes implemented for Distribution Network protection traditionally in-volve over current protection with suitable time delays, circuit breakers, auto-reclosersand fuses. Fault protection is obtained by means of over-current relay, earth fault direc-tional relays and zero sequence voltage and current relays. Overcurrent relays are notdirectional. But load flow may not remain unidirectional in case of DG connected to DNand it can introduce short circuit current in the opposite direction to that of introducedby main grid. This DG contribution may prompt the uncoordinated operation of de-vices located downstream to the fault location unveiling a potential vulnerability of theprotection system [13].

The presence of DG can cause various problems related to incorrect operation of systemprotections. Conflicts between DG and protection schemes are typically due to:

• unforeseen increase in short circuit currents;

• lack of coordination in the protection system;

• ineffectiveness of line reclosing after a fault using the ARD

• difficult lines back-feeding

• Undesired islanding and untimely tripping of generators interface protections [15].

Moreover, assuming the possibility to manage portions of distribution networks in is-landed configuration, it would be necessary to consider the potential difficulties in settingup adequate protection schemes that can operate properly when the Microgrid is bothconnected to and disconnected from the main network to cope with internal faults.

Thus issues associated with introduction of DGs to a distribution network include "blind-ing of protection", "false/sympathetic tripping", "recloser-fuse miscoordination", and"failed auto-reclosing" [16].


2.4 Active Distribution Networks

Active Distribution Network is a migration from earlier "fit and forget" version of dis-tribution grid. It is proposed to make grid more flexible by providing ways to exercisecontrol and management in an optimal way. ADN enables better utilization of infras-tructure by means of control function and ICT.

In its report for the project IDE4L on Specifications of Active Distribution Networks [17],Active distribution network is defined as follows- Active distribution network consistsof infrastructure of power delivery, active resources and active network management.It combines passive infrastructure with active resources, ANM functionalities and ICTinfrastructure.

2.4.1 ICT Infrastructure

Extensive use of ICT makes it possible to collect information from various points in anetwork which can be utilised for

• Network Planning and operation

• Network performance optimization

• Network control and protection

For collecting data, monitoring of entire network needs to be done. Installation of Ad-vanced Metering Infrastructure, Micro-PMUs, increasing the number of IEDs on distri-bution side is a few measures to improve distribution side monitoring. A strong com-munication network is necessary to transmit the measurements collected to a centrallyconnected location where it could be utilized for monitoring and management of networkin real time.

2.4.2 Active Resources and Aggregators

Active resources are the ones that could be monitored and controlled by ANM. ActiveDERs, Micro-grids, flexibility services from Aggregator, STATCOMs, could be classifiedamongst active resources. The Aggregator is a service provider and can supplement theproduction and consumption portfolios of an electricity retailer by flexible DERs [17].

Services offered by the aggregator for commercial purposes are-

• Price elasticity at day-ahead market to manage price risk


• Demand response to manage forecasting risks and to minimize balance costs

• Demand response offer for regulation power market

• Distributed generation offer to day-ahead and intraday markets

Services provided by Technical aggregator to TSOs and DSOs are-

• Reserve market (disturbance and control reserves: virtual inertia, spinning, fastand slow reserves)

• Power flow management (e.g. control offer for regulation power market)

• Reactive power support and Voltage control

• Power quality control

• Back-up power

2.4.3 Active Network Management

Active network management is based on distribution network automation and DERs.It includes distribution control centre information systems, substation automation, sec-ondary substation automation and advanced metering infrastructure.

Active distribution network enables optimal management of the whole network with dif-ferent DG scenarios, EV and heat pump penetration levels and DER scenarios that willaffect the loading of networks and transformers, the voltage profile of LV network and lineoverloading. The new functionalities required for the operation of the distribution net-works like distribution state estimation, automatic FLISR, coordinated voltage control,power flow control, static and dynamic distribution model order reduction to coordinatewith TSOs, and the availability of stability indicators [17].

2.5 Faults in Distribution Network

Faults that occur in Distribution network include Symmetrical 3 phase faults and asym-metrical Line- Ground fault, Line â“ Line and Double Line to Ground faults. This sectionhas taken inspiration from [18].


2.5.1 Fault

For fault current calculation purpose following assumptions are made-

• The power system is balanced before the fault occurs such that of the three sequencenetworks only the positive sequence network is active. Also as the fault occurs, thesequence networks are connected only through the fault location.

• The fault current is negligible such that the pre-fault positive sequence voltagesare same at all nodes and at the fault location.

• All the network resistances and line charging capacitances are negligible.

Based on assumptions above the voltage at the faulted point will be denoted by Vf andcurrent in the three faulted phases are Ifa ,Ifb and Ifc. Faults in 3 phase system are

Figure 2.3: Representation of a Faulted Line

divided into two groups of symmetrical and unsymmetrical faults. Symmetrical faultoccurs when all 3 phases are grounded at the same time. In that case it is considered tobe equivalent to 3 line-ground faults. A more detailed discussion of asymmetrical faults isprovided here. For phase currents to be denoted by Ia, Ib, Ic and the sequence componentsfor both currents and voltages are I1, I2, I0 and U1, U2, U0 where I1 represents the positivesequence, I2 represents the negative sequence and I0 represents the zero sequence. Thesame applies for voltages. The phase current can be expressed asIa = I1 + I2 + I0

Ib = a2I1 + aI2 + I0

Ic = aI1 + a2I2 + I0 (a)

It can be derived that,

I0 = 1/3(Ia + Ib + Ic)

I1 = 1/3(Ia + aIb + a2Ic)

I2 = 1/3(Ia + a2Ib + aIc) (b)

U1 = V − I1Z1

U2 = −I2Z2


Figure 2.4: Thevenin Equivalent Voltage Representation

U3 = −I0Z0 (c)

Following section presents all three types of faults along with fault voltage and currentplots.

2.5.2 Single Line to Ground Fault

A single line to ground fault occurred at node is depicted in the figure. Assuming thatphase-a has touched the ground through an impedance Zf.

Figure 2.5: Single Line to Ground Fault

Since the system is unloaded before the occurrence of the faultIf c = If b = 0 (2.1)

Fault current and voltages for a single line to ground fault are shown in the figures below-


Figure 2.6: Single Line to Ground Fault- Fault Current

Figure 2.7: Single Line to Ground Fault- Fault Voltage


2.5.3 Line to Line Fault

Line to Line fault can be represented as shown in the figure below. In this the phases band c got shorted through the impedance Zf .

Figure 2.8: Line to Line Fault

For an unloaded system,Ifa = 0 (2.2)Since fault is between phases b and c,Ifb = −Ifc (2.3)

Two phase fault current and voltage quantities are plotted in the figures below-

Figure 2.9: Line to Line Fault- Fault Current


Figure 2.10: Line to Line Fault- Fault Voltage

2.5.4 Three Phase to Ground Fault

In three-phase to ground fault can be represented by figure below-

Figure 2.11: Three Phase to Ground Fault

An example of fault current and voltage in the event of a three phase fault is given belowrespectively-


Figure 2.12: Three Phase to Ground Fault-Fault Current

2.5.5 Consequences of Faults

The consequences of electrical faults in power systems strongly depend on the magnitudeof the fault current, which in turn depends on the type of fault, the location of the fault,the system earthing, the source impedance, and the impedance of the fault. The durationof the fault is also of considerable importance when estimating the consequences of a fault.Consequences of fault include-

1. Mechanical stresses- Conductor exert stress on each other which depends on squareof current flowing in them. Fault current being higher than rated current themechanical stress exerted is higher than what the line was designed for.

2. Thermal Stress â“ Losses within the conductor are given by I2R. Since current risesduring fault the losses are higher. The higher energy that is to be dissipated in theconductors leads to higher thermal stress.

3. Arcing- If a fault is not cleared immediately, it may cause arcing within cables orwithin the equipment.

4. Cost- Fault current causes eventual wearing of insulation of cables. It also affectstips of circuit breaker contacts and instrument transformers, transformers and gen-erators as well. Replacing the system and the subsequent down time cause losses


Figure 2.13: Three Phase to Ground Fault

not just to the utility as well as to overall commercial activities based in the affectedregion.

2.5.6 Fault Clearing

Devices that are used for fault clearing are-

1. Fuses

2. Circuit Breakers

Fuses- Fuses work to limit the first peak current of the short circuit fault. Fuses tend tomelt down in case of higher energy dissipation within them thus breaking off contactsbetween two terminals. The drawback in its use is, it has to be replaced once used.Circuit Breaker- Circuit breakers break fault current based on natural zero crossing ofshort circuit current. At that moment arcing between the tips of circuit breaker contactscan be extinguished and current could be interrupted.


2.5.7 Current Limiters

Current limiting is used to protect power system from mechanical forces associated withthe first current peak. Series reactors and solid state based current limiters are someexamples of current limiters. Series reactors- The traditional method limiting fault cur-rent is to install series reactor in main circuit. The drawback of this installation being,additional losses that occur when load current passes through the reactor. It also failsto limit the fault current to the requisite extent. Solid State Current Limiter â“ Solidstate devices do not depend on natural zero crossing to interrupt the current. Whena signal is sent to the control circuit of solid state device, it immediately turns off thecurrent through the device. Drawbacks of solid state limiter include 1. Cost of the com-ponents and 2. Probability of damage due to dissipation of energy within componentswhen current is interrupted at peak value. Other current limiters include Switch andFuse combination current limiter.

2.5.8 Fault Clearing System

Fault clearing system consists of relay protection system and circuit breaker.

2.5.8.1 Relay Protection System

Relay protection system consists of sensors/ transducers, trip coil, relays and auxiliarypower supply. To detect fault, quantities that are commonly observed are currents andvoltages. The measuring devices introduce a delay. According to IEC, a delay of 0.17ms is allowed for a network working on frequency of 50 Hz.

Trip coil- Circuit breakers are operated by releasing energy stored in a large spring.The latch which holds the spring is released by energizing a coil that provides a forcethat acts on the latch thus releasing it. The opening coil needs a rather large powerto operate the latch. The power is supplied by a circuit to which the contact of therelay is connected. Relays- Relays are classified into Electromechanical, Solid State andDigital/Numerical Relays. Electromechanical relays were the first relays to be used inpower systems for protection purposes. The operation of electromechanical relay dependson physical characteristics of current and voltage. Solid State Relay- Designed based onworking of Operational Amplifier.

Digital/ Numerical Relays- These relays investigate fault condition based on computa-tions carried out by microprocessor. These consist of a signal conditioning subsystem, aconversion subsystem, and a digital processing subsystem.


2.5.8.2 Circuit Breaker

Circuit breaker as the name suggest are necessary to break the contacts. On detection offault, contacts within the circuit breaker must open to interrupt the circuit. Separationof contacts is carried out by mechanically-stored energy. Different types of circuit breakerinclude air circuit breaker, air-blast circuit breaker, Oil circuit breaker, vacuum circuitbreaker, SF6 circuit breaker etc. These breakers are used depending on breaking capacityof the breaker.

2.5.9 Protection Principles

Magnitude relay In this case magnitude of current or voltage is compared to a pre-determined threshold level. In this case, instantaneous value of the quantity cannotbe used for comparison. RMS value of quantity is compared to threshold. DirectionalRelay “ Phase angle between current and polarizing quantity is estimated. It is possibleto tell if the fault is forward or in reverse direction, based on the measure of angle asseen from relay. Impedance Relay “ Measuring value of voltage and current, estimationof impedance of protected object can be made. Differential Relay- Differential relayare used for equipment protection. It requires two sets of inputs to determine healthof the system. Generators, Transformers and machines are protected by differentialrelays. Pilot relay- Pilot relay consists of any of the relays mentioned above along withcommunication between two or more adjacent relays.

2.5.10 Fault Identification

Positive sequence quantities are found in all fault types as well as normal system op-eration. Negative sequence quantities are found in line-line (LL) and line-ground (LG)faults. Zero sequence quantities are found only in line to ground faults. In overcurrentprotection, zero sequence quantities are used to detect the ground faults. Zero sequencequantities are absent in balanced systems and other fault events. Hence it makes senseto use zero sequence quantities for identification of single phase to ground fault.

Positive sequence currents are typically used for the three Phase and LL faults. Posi-tive sequence phase pickup current must be set above load current to prevent nuisancetripping. This decreases the sensitivity to LL faults. Because there are no zero sequencecurrents in LL faults, zero sequence ground fault protection will not work. In this sit-uation, negative sequence currents found in LL faults are useful. Because no negativesequence quantities exist in a balanced system, negative sequence pickups can be setbelow load current [19].


Figure 2.14: Single Phase Fault Identification

Figure 2.15: Negative sequence quantities during two phase fault


For three phase fault identification, principle of Magnitude relay is employed. RMS valueof current in each phase is compared to a threshold. Threshold for identification of athree phase fault is set to thrice the rated current, Irated.

2.6 Multi-Agent Concept

Multi-Agent based systems are being increasingly used for monitoring and control ofpower system. Agent based system has inherent benefits of flexibility, extensibility, au-tonomy, reduced maintenance and makes possible to implement network control throughintelligent decision making. For distributed control of a system, it is divided into mul-tiple subgroups and each subgroup is assigned an agent. The agent collects informationfor its assigned subgroup and communicates with other agents. The decision is arrivedat by optimization of the information exchanges amongst cooperating agents. A central-ized system may be plagued by resource limitations, performance bottlenecks, or criticalfailures, an MAS is decentralized and thus does not suffer from the "single point of fail-ure" problem associated with centralized systems. Application of Multi-agent conceptalso covers distribution network automation and self healing grids. The paper titled"Multi-agent application in protection coordination of power system with distributedgenerations" [20] presents use of agent technology applied to substations protection co-ordination of power system. The architecture of MAS could be represented as shownin the figure below. The agent receives information from its surrounding environment,applies the set logic and issues command through actuator as shown in the figure.

Figure 2.16: Negative sequence quantities during two phase fault


In its thesis, Sandia National Laboratories concluded that, "agents are a valuable frame-work for operating microgrids. Intelligent agents offer a secure, distributed means tomanage electric power production, enforce system policy, and respond to unexpectedevents in the power network" [21]. In multi-agent systems, several agents work in tan-dem to achieve the specified goal of the system. The agents perceive and react to theirenvironment and communicate amongst each other. This ensures autonomous behaviourof agents and rules out need of any human intervention. Multi-Agent concept has previ-ously been applied for power system control and management applications. Managementof distribution system with distributed generation with the help of Multi-Agent systemwas shown in [22] for dynamic and efficient power dispatch. In [20], it has been used forprotection coordination and [23] used it for system restoration purpose.

Chapter 3

Methodology Employed

In this chapter the working process is described. The distribution network under studyis presented. It is followed by steps taken for simulating the network in SimPowerSys-tems. The fault localization algorithm is then presented and eventually implementationof multi-agent based protection algorithm in SimPowerSystems is described.

3.1 Distribution Network

The distribution network simulated, consists of a 60:11 kV OLTC Distribution Trans-former which steps down voltage from 60 kV to 11 kV. The network operates at 2 voltagelevels and consists of 11 Buses and 8 distribution lines of lengths ranging from 100 m to2.4 km. There are 8 loads connected to the network as shown in the diagram. Total loadconnected to the network is 18.45 MW with reactive power consumption of 8.93 MVARat a power factor of 0.9. Transformer connected is Yg-D11 type transformer with ratedprimary and secondary voltages of 60 kV and 11 kV respectively and rated power of 50MVA. The distributed generators are connected at Buses 5 and 7 and of capacity 5 MWand 10 MW respectively. The network studied is depicted in the figure below.

32

Chapter 3.Methodology Employed 33

Figure 3.1: Distribution Network Diagram


Figure 3.2: Network Model in Simulink

The model simulated in SimPowerSystems is as shown below:

Figure 3.3: Grid Model in Simulink


3.2 Simulink Modelling of Distribution Network

The Simulink SimPowerSystems was used for modelling of network. The componentsused are-

1. Three Phase Programmable Voltage source

2. Three Phase Two Winding Transformer

3. Three Phase Stub Lines

4. Three Phase Dynamic Loads

5. Three Phase VI Measurement Blocks

6. Three Phase Fault

7. Three Phase Breakers

3.2.1 Three Phase Programmable Voltage Source

3 Phase programmable voltage block is used in the network to specify external grid. Asthere is a need of a swing bus in the network, Load flow of the programmable voltagesource is set to swing.

Figure 3.4: Three Phase Programmable Voltage Source


Figure 3.5: Generator Type

3.2.2 Three Phase Two Winding Transformer

The external source is connected to a 3 phase 2 winding transformer which steps down60 kV primary voltage to 11 kV secondary voltage. Rated capacity of Transformer is 50MVA.

Figure 3.6: Three Phase Two Winding Transformer


Figure 3.7: Transformer Parameters

3.2.3 Three Phase Stub-Lines

Artemis Stubline is part of Artemis Toolbox. It has been used keeping in mind real timesimulation of network. Stubline enables a user to connect multiple phase networks. Theinductance and resistance parameters are specified based on length of each line segmentof network. Based on value of sample time Ts, the block estimates value of capacitanceof the line.


Figure 3.8: Three Phase StubLine

The block is suitable for a short line. As a rule of thumb, if length of line is smaller thanTs*30000, Stubline is preferred over other blocks in Artemis Toolbox.


3.2.4 Three Phase Dynamic Load

Three Phase dynamic load implements dynamic load with active power and reactivepower as function of voltage or controlled from external input. In this case the load isassumed to varying with the change of time hence active and reactive power.

Figure 3.9: Three Phase Load

Figure 3.10: Sample Load Profile


3.2.5 Three Phase VI Measurement Block

The Three-Phase V-I Measurement block is used to measure instantaneous three-phasevoltages and currents in a circuit. When connected in series with three-phase elements,it returns the three phase-to-ground or phase-to-phase peak voltages and currents [24].

Figure 3.11: Three Phase VI Measurement Block

3.2.6 Three Phase Fault

The Three Phase Fault block was used to introduce fault in the network.

Fault is introduced when First input to the block is 1. Input 2 specifies type of the fault.Here a 3 phase symmetrical fault is introduced. For Input 2 = 1, the block will introducefault in phase A of the network and for fault type set to 2, the block will be introduced inphases A and B. The connection of phases could be altered to introduce fault in specificphase in the network.


Figure 3.12: Three Phase Fault Settings

Figure 3.13: Three Phase Fault Block


3.2.7 Three Phase Breakers

Three phase breaker implements three-phase circuit breaker opening at zero crossing ofcurrent.

Figure 3.14: Three Phase Breaker Block

The Three-Phase Breaker block implements a three-phase circuit breaker where the open-ing and closing times can be controlled either from an external Simulink signal, or froman internal control timer. External signal equal to 1 closes the breaker and the signalequal to 0 opens it. High value of Snubber resistor is to minimize current in the networkin case of opening of breaker. Few basic IGBT based solid state breakers were introducedto minimize transient in simulation results.

Figure 3.15: Three Phase Breaker Block Parameters


3.3 Fault Identification and Localization

Based on the discussions in previous chapter fault identification and localization algo-rithm was formulated. The diagram below depicts the algorithm employed for identifi-cation and localization purpose.

Figure 3.16: Fault Identification and Localization Algorithm


The algorithm presented above is for an individual node agent as depicted in the diagrambelow. The node agent receives measurements from the bus; it identifies the type of

Figure 3.17: Agent Architecture

fault based on the steps mentioned in algorithm. It then communicates with its adjacentnode agents, as shown in the diagram; to identify the faulty section of network. Afteridentification of faulted phase, trip signal is issued to respective breaker to isolate thefaulted phase.

3.4 Implementation of Fault Identification and Localizationin Simulink

The algorithm shown in figure 3.16 was implemented in Simulink. The task to be per-formed is divided into two parts- Fault Identification and the next Fault Localization.

3.4.1 Fault Identification

Components that were used for Fault Identification purpose are-

1. RMS- Root Mean Square of a signal.

2. Switch

3. Sequence Analyser

Simulink representation of Fault Identifier is as shown in the figure below- Detaileddescription of Fault Identification is as follows- Identification of Three Phase fault is doneby Magnitude Relay principle where RMS value of current is compared to a thresholdset three times the rated value.


Figure 3.18: Fault Identification

Figure 3.19: Three Phase Fault Identification

Since a 3 phase fault is nothing but a combination of 3 single phase faults the networkshowed above works well to identify a 3 phase fault. 2 Phase fault is identified bycomparing negative sequence component of the current with a threshold value. Sincenegative sequence quantities are found in Line- Line faults, the same could be utilizedto identify 2 Phase faults.

Single Phase to ground fault is determined by taking RMS value of sum of all phasequantities. This sum has a very small value of the range 10-6 otherwise. In case ofLine to Ground fault, this quantity assumes a larger value and can be compared to a setthreshold.


Figure 3.20: Two Phase Fault Identification

Figure 3.21: Single Phase to Ground Fault

The block that contains these elements is as shown below. Since the identification is donebased on current, current is given as input to the block and F4, the output serves to tellif fault has occurred or not. The output is in the form of an integer where, integer 1-specifies Single Phase to Ground Fault, integer 2 specifies Line to Line fault and integer3 specifies Symmetrical 3 Phase to ground fault. Once the fault is identified the outputF is then given to a Multi-Agent based Fault Localization and Phase Selection block.

3.4.2 Fault Localization and Phase Selection

Fault Localization and Phase selection is done to identify the location of fault by dis-tributed algorithm and to identify suitable breaker to be opened to isolate the faultedsection. Each bus is considered as an Agent, with current, voltage and power as itscomponents.

Each bus contains number of controllers based on number of adjacent buses it is connectedto. The relevant controller is operated when conditions set in it are met, opening therelevant breaker. The first task for the controller is to localize the fault. Controller isfed type of fault in the network. Based on nature of fault i.e. Single phase, 2 Phase orSymmetrical different approaches are considered.


Figure 3.22: Multi-Agent based controller for Breaker46

Figure 3.23: Multi-Agent based controller for Breaker42

3.4.2.1 Single Phase Fault

Localization of single phase fault is done by comparing difference of RMS values of sumof adjacent line currents as shown in the figure below-


Figure 3.24: Localization of Single Phase to Ground Fault

Based on the comparison, location of 1 phase to ground fault is determined. The faulted

Figure 3.25: Single Phase Fault- Phase Selection

phase on selection will give output equal to 0 which could be used to isolate the breakerrelevant to the phase.

3.4.2.2 Line to Line Fault and Three Phase to Ground Fault

As mentioned in the algorithm, Line to Line fault phases and 3 phase faults are localizedbased on direction of active power flowing in the line connecting two buses. Identicalblocks are used for this purpose. The blocks are as shown in the figure below-


Figure 3.26: Two Phase Fault Localization

All 3 outputs of the block are constant equal to 1 when there is no fault. As a fault isreported, the switch connects the output to terminal 1. Details of the block connectedat terminal 1 are as follows-

Figure 3.27: Fault Localization Algorithm for Phase A

Based on reversal of active power among buses, respective breakers are sent outputsignal equal to zero, isolating the faulty phases. The same procedure is applied forall buses,except the terminal ones. For the terminal buses, in case of fault, the powerflowing through the bus becomes zero. In that case it is not possible to apply thismethod. Instead breaker of terminal buses is coupled with breaker connecting the sameline to adjacent pre-terminal bus.

Chapter 4

Results

In this chapter the results that obtained with the methods described in the previous chap-ter are compiled, and compared with the theory presented in the Related Work chapter.

Two scenarios are considered for the case study. In first case fault is introduced atthe farthest point of the network, on Bus 10. In scenario two, fault is simulated at Bus4. In both cases fault was introduced at 0.15 seconds, the simulation running time was0.25 sec.

4.1 Scenario 1- Fault at Bus 10

Fault introduced on Line 6 connecting Bus 6 and Bus 10.

4.1.1 Three Phase fault

Fault identification in case of fault on Line 6.

50

Chapter 4.Results 51

Figure 4.1: Three Phase Fault Identification on Line 6

The trip signal issued to isolate faulted region.

Figure 4.2: Trip Signal for Fault on Line 6

Breakers corresponding to Line 6 are issued trip signal. Opening of the breakers willlead to fault being isolated. Interruption of fault current in this case verifies isolation offaulted line.


Figure 4.3: Fault current after issuing trip signal

Response at various buses, bus 6 and 10 respectively-

Figure 4.4: Voltage, Current and PQ at Bus 6



The current, voltage and PQ responses show that Line 6 has been isolated bringing thesequantities to zero at bus 10.

4.1.2 Line to Line Fault

Results of fault identification process for Line to Line fault on Line 6 are-

Figure 4.6: Fault Identification for Line to Line Fault at Bus 6


Bus 4 and 6 identify the two phase fault that lies downstream to them. With the help offault localizing agents, the exact location of faulted line is located and relevant breakersare opened. The trip signal issued are presented in the figure below- Trip signals are

Figure 4.7: Trip Signal issued for Line to Line Fault at Bus 6

issued to breakers B610 and B106 which isolate Line 6. As the faulted phases are cutoff, the fault current can be shown as-

Figure 4.8: Fault Current for Line to Line Fault at Bus 6


Plots of voltage, current and PQ waveforms during Line to Line fault at bus 6 are-

Figure 4.9: Voltage, Current and PQ at Bus 6 for Line to Line fault




The operation at Bus 4 remains unaffected after opening of breakers on Line 6.

4.1.3 Single Phase Fault

Fault Identification in case of single phase fault-

Figure 4.12: Fault Identification for Line to Ground Fault at Bus 6


Buses 4, 6 and 10 identify the single phase fault. With the help of fault localizing agents,the exact location of faulted line is located and relevant breakers are opened. The tripsignal issued are presented in the figure below- Trip signals are issued to relevant breakers

Figure 4.13: Trip Signal issued for Line to Ground Fault at Bus 6

on Line 6. As the faulted phases are cut off, the fault current can be shown as-

Figure 4.14: Fault Current for Line to Ground Fault at Bus 6


Plots of voltage, current and PQ waveforms during Line to Ground fault at bus 6 are-

Figure 4.15: Voltage, Current and PQ at Bus 6 for Line to Ground fault




4.2 Fault on Line 4

Fault is introduced at Bus 6 on line 4 connecting Bus 4 and 6.

Figure 4.18: Network Simulation for fault on Line 4


Figure 4.19: Three Phase Fault Identification on Line 4

4.2.1 Three Phase fault

Fault identification in case of fault on Line 4. The trip signal issued to isolate faultedregion.

Figure 4.20: Trip Signal for Fault on Line 4




The current, voltage and PQ responses show that Line 4 has been isolated.


Figure 4.24: Line to Line Fault Identification on Line 4

4.2.2 Line to Line fault

Fault identification in case of Line to Line fault on Line 4. The trip signal issued toisolate faulted region.

Figure 4.25: Trip Signal for Line to Line Fault on Line 4




4.2.3 Line to Ground Fault

Fault identification in case of Line to Ground fault on Line 4.

Figure 4.29: Line to Line Fault Identification on Line 4


The trip signal issued to isolate faulted region.

Figure 4.30: Trip Signal for Line to Ground Fault on Line 4


Chapter 5

Discussion and Conclusion

Fault localization and selection of phase was implemented as shown in the flowchart in3.16. The simulations are carried out in SimPowerSystems. The multi-agent approach tothe task of fault localization and phase selection worked as required in the two scenariosconsidered. The scenarios considered could be repeated anywhere on the network andthe system will yield similar results. The scenarios considered are of fault at farthest endof a network and another being somewhere in the middle of network. It was observedthat system was able to identify faults and isolate the faulty phases. This resulted ininterrupting of fault currents as included in the preceding section. Multi-agent approachhas helped in identifying exact locations of fault.It was observed that at the far end of the distribution line the same approach couldnot be applied. Hence controlling of breaker connecting the farthest bus to rest of thenetwork was institute with its adjacent bus.Use of sequence quantities was appropriate in identifying faults. Along with, principleof Magnitude Relay of comparing RMS value of current flowing through a line with apreset value to determine health of the network.The multi-agent approach has been applied in power systems studies before and in thesimilar fashion this approach could be applied to real life distribution network for dis-tributed protection.

69

Chapter 6

Future Work

For future work it will be interesting to run the system in Real Time and have Multi-Agent System implemented in JADE/ JACK. It will be interesting to have a Real TimeMulti-Agent system communicating with Real Time simulation over UDP. Along withthat, communication network modeling and including delay in communication time willbring the setup close to reality.Dynamic settings of thresholds in fault identification process could be another interestingtask. Also the thresholds used for identification are current thresholds, there is observeddrop in voltages during the fault; hence an algorithm based on voltage thresholds couldbe another interesting task. Restoration of the network will be a logical step forward.

70

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[19] Doug F Joens, The Utility Edge, Power Systems Engineering, Published Winter2013.

[20] H. Wan, K.P.Wong, C.Y.Chung, Multi-agent application in Protection Coordinationof Power System with Distributed Generations, Power and Energy Society GeneralMeeting - Conversion and Delivery of Electrical Energy in the 21st Century, 20-24July 2008.

[21] L.R. Phillips, H Link, R. Smith, L. Weiland, Agent-Based Control of DistributedInfrastructure Resources, Sandia National Laboratories, Jan 2006.

[22] Fenghui Ren, Minjie Zhang, and Danny Sutanto, A Multi-Agent Solution to Distri-bution System Management by Considering Distributed Generators, IEEE Trans-actions on Power Systems.

The Appendix 73

[23] Jignesh M. Solanki, Sarika Khushalani, and Noel N. Schulz, A Multi-Agent Solutionto Distribution Systems Restoration, IEEE Transactions on Power Systems, vol. 22,no. 3, August 2007.

[24] Three Phase VI Block, description available athttp://www.mathworks.se/help/physmod/sps/powersys/ref/threephasevimeasurement.html

[25] Three Phase Breaker Description, available athttp://www.mathworks.se/help/physmod/sps/powersys/ref/threephasebreaker.html

[26] Magnus Ohrstrom, Fast Fault Detection for Power Distribution Systems, LicenciateThesis, Royal Institute of Technology, Stockholm, 2003.

Appendix A

Network, Line and TransformerParameters

Table A.1: Network Parameters

Sl No DERs P (MW) Q(MVAR) Power Factor

1 L1 4.86 2.36 0.8995492 L2 3.04 1.47 0.90027013 L3 0.4 0.19 0.9032774 L4 0.3 0.15 0.8944275 L5 4.26 2.06 0.9002666 L6 2.99 1.05 0.8997787 L7 0.4 0.19 0.9032778 L8 2.2 1.06 0.9008839 G1 1010 G2 511 Total 18.45 8.83 0.900109

Table A.2: Line Parameters

Line Type Length(km) Start End

1 Overhead 0.1 SS1 SS22 Overhead 0.1 SS1 SS33 Overhead 2.1 SS2 SS84 Overhead 0.8 SS2 SS45 Overhead 1.4 SS3 SS76 Overhead 0.3 SS4 SS57 Overhead 0.5 SS5 SS68 Overhead 0.3 SS7 SS69 Overhead 1 SS8 SS610 Overhead 1 SS9 SS711 Overhead 2.4 SS8 SS1012 Overhead 1.9 SS10 SS9

74

The Appendix 75

Table A.3: Line Resistance, Inductance and Capacitance

Line Parameters R(Ohm/km) L(H/km) C(F/km)

1 Overhead+ 0.63 1.3e-3 1e-82 Overhead0 0.72 5.1e-3 1e-73 Cable+ 0.16 3.2e-3 3e-64 Cable0 0.16 2.87e-3 5e-6

Table A.4: Transformer Parameters

Type Yg-D11 60 kV 10kV*1.1Rated Power 50 MVA

Rs(p.u) 0.01If (p.u) 0.01Ploss 0.2625 kW

Xsc(pu) 0.06

Table A.5: External Grid

Capacity 10 MVANominal Voltage 60 kVX/R ratio 10

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