investigation into the protection of microgrids using ... · source, calculate the pickup currents...

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INVESTIGATION INTO THE PROTECTION OF MICROGRIDS

USING ADAPTIVE RELAYS

Murdoch University School of Electrical Engineering, Energy

and Physics

Bachelor of Engineering Honours Degree

Prepared by: Joseph J. Dines

Academic Supervisor: Dr. Greg Crebbin

November 2016

Declaration Joseph J. Dines declares that he is the sole author of this thesis based on his own

research, except for where it has been appropriately acknowledged and referenced.

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Abstract Due to a proliferation of renewable power sources and a rise in distributed generators,

the transmission network is now able to split into smaller isolated sections. These

sections are often referred to as microgrids as they function similar to larger networks

with power production being sufficient to power the loads. Microgrids are hampered by

the lack of fault current being sufficiently high to operate traditional overcurrent

protection. The lack of fault current has resulted in a need to find newer methods to

provide fault protection. One such method is the use of modern relays that allow for the

trip settings to be changed as the network itself changes. Relays that allow for this

adaption are known as adaptive relays and provide a method to deal with the lower fault

current when the microgrid is isolated from the main network by reducing their pickup

current as appropriate.

The effectiveness of adaptive relays has been investigated by the use of DIgSILENT

PowerFactory simulation software to model two differing networks under varying

conditions. The networks chosen to be simulated, consist of a test network used in

previous research and a modelling of a physical network on Hailuoto Island. The networks

were simulated with the faults falling into one of the following four categories:

1. Faults occurring on the external grid

2. Faults occurring on the feeder connecting the external grid to the microgrid

3. Faults occurring on the feeders inside the microgrid

4. Faults occurring on the loads and connections inside the microgrid

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The adaptive relays were found to operate correctly having discrimination between

relays, once the pickup currents were calculated correctly. Each microgrid requires that a

microprocessor, being informed of the status of the grid and output of each power

source, calculate the pickup currents for each relay, and notify the relay of its new pickup

current.

The microprocessor’s calculations were simulated in MathWorks MATLAB via a script

which allows calculation of the current seen by a relay as the sum of the rated output

from each distributed generator. Then multiplied by the status of the generator and its

percentage contribution. This formula is an adaption from previous work by (Oudalov and

Fidigatti n.d.). The current calculated by the MATLAB script is found when compared to

the PowerFactory simulations as having a difference of less than 2.8 per cent and 8 per

cent on the test network and Hailuoto Island respectively. Providing proof that not only

does the MATLAB script and its associated formula work, so do adaptive relays for

protecting microgrids.

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Acknowledgements I would like to acknowledge my family: my father Dr Eric Dines for being a strong role

model, my mother, Kathy Dines for being supportive, my two sisters Ashlee and Natasha

for their help and friendship.

I would also like to acknowledge the faculty and my fellow students at Murdoch

University for their help and guidance.

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Table of Contents

Declaration .................................................................................................................. ii

Abstract ...................................................................................................................... iii

Acknowledgements ...................................................................................................... v

Table of Contents ........................................................................................................ vi

Table of Tables .......................................................................................................... viii

Table of Figure ............................................................................................................ ix

Chapter 1: Introduction ................................................................................................ 1 1.1 Microgrids ..................................................................................................................... 1 1.2 Limitations of Microgrids ............................................................................................... 2 1.3 Protection of Microgrids ................................................................................................ 3 1.4 Methods of Protection................................................................................................... 4 1.5 Purpose of Thesis .......................................................................................................... 5

Chapter 2: Review of the Literature .............................................................................. 7 2.1 MicroGrids .................................................................................................................... 7 2.2 Adaptive Network Protection in Microgrids ................................................................... 8 2.3 Fault Current Coefficient and Time Delay Assignment for Microgrid Protection System With Central Protection Unit ............................................................................................... 9 2.4 Adaptive Protection and Microgrid Control Design for Hailuoto Island ........................... 10

Chapter 3: Materials and Methods.............................................................................. 12 3.1 Networks ..................................................................................................................... 12 3.2 Wind Turbines .............................................................................................................. 17 3.3 Synchronous Machine and Diesel Generators ................................................................ 18 3.4 Transformers ................................................................................................................ 18 3.5 Cable Types .................................................................................................................. 19 3.6 Relays .......................................................................................................................... 20

3.6.1 Nominal Currents and MATLAB Network Table ............................................................. 20 3.6.2 Fault Currents and Relay Type ....................................................................................... 21 3.6.3 Relay Positions ............................................................................................................... 22 3.6.4 Relay Setting Calculations .............................................................................................. 23

3.7 Fault Currents .............................................................................................................. 24 3.8 Faults ........................................................................................................................... 25

Chapter 4: Experimental Chapter ................................................................................ 26 4.1 Introduction ................................................................................................................. 26 4.2 Experimental procedure ............................................................................................... 27

4.2.1 Simulating in PowerFactory ........................................................................................... 27 4.2.2 MATLAB Script ................................................................................................................ 28 4.2.3 Recalculating Pickup Currents ........................................................................................ 29

4.3 Results ......................................................................................................................... 30 4.3.1 PowerFactory Simulations .............................................................................................. 30 4.3.2 MATLAB Calculations...................................................................................................... 32

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4.3.3 PowerFactory Simulations with Adaptive Relays ........................................................... 33 4.3.4 PowerFactory Simulations with Adaptive Relays and Varying Output Power ............... 34

4.4 Discussion .................................................................................................................... 36 4.4.1 Overview ......................................................................................................................... 36 4.4.2 Difference in Fault Current ............................................................................................. 36 4.4.3 Issues due to Lower Fault Currents - Test Network ....................................................... 37 4.4.4 Issues due to Distributed Generators - Test Network .................................................... 38 4.4.5 Algorithm - Test Network ............................................................................................... 40 4.4.6 Hailuoto Island ................................................................................................................ 40 4.4.7 Issues due to Lower Fault Currents – Hailuoto Island Network ..................................... 41 4.4.8 Issues due to Distributed Generators (Diesel) – Hailuoto Island Network .................... 42 4.4.9 Algorithm– Hailuoto Island Network .............................................................................. 43 4.4.10 Issues Relating to Communication with Microprocessor and Distributed Generators 44 4.4.11 Issues Relating to Isolation ........................................................................................... 45 4.4.12 Issues due to Varying Output Distributed Generators when Grid Connected – Hailuoto Island ....................................................................................................................................... 45 4.4.13 Issues due to Varying Output Distributed Generators when Islanded – Hailuoto Island ................................................................................................................................................. 46 4.4.14 Issues Relating to Communication Methods ................................................................ 48

Chapter 5: Conclusions ............................................................................................... 50 5.1 Overview ............................................................................................................................ 50 5.2 Limitations of Microgrids ................................................................................................... 50 5.3 Adaption, Communication and Further Work ................................................................... 51 5.4 Updated Algorithm and Further Work .............................................................................. 51 5.5 Conclusion ......................................................................................................................... 53

References ................................................................................................................. 54

Appendix .................................................................................................................... 57 A: Test Network ................................................................................................................. 57

A.1 PowerFactory Single Line Diagram – Test Network showing Relay Positions................... 57 A.2 Relay Settings .................................................................................................................... 58 A.3 3-Phase Short Circuit Fault at Terminal(6) ........................................................................ 59 A.4 3-Phase Short Circuit Fault at Terminal(2) ........................................................................ 61 A.5 No Fault – Loads at Terminal(5) and Terminal(6) disconnected ....................................... 63

B: Hailuoto Island network ................................................................................................. 64 B.1 PowerFactory Single Line Diagram – Test Network showing Relay Positions ................... 64 B.2 Relay Settings .................................................................................................................... 65 B.3 Wind Output 100% ............................................................................................................ 66 B.4 Wind Output 0% ................................................................................................................ 80

C: MATLAB Script ............................................................................................................... 94

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Table of Tables Table 1. Test Network PowerFactory Specifications .......................................................... 15

Table 2. Hailuoto Island PowerFactory Specifications ........................................................ 16

Table 3. Hailuoto Island Network Cable Lengths ................................................................ 17

Table 4. MATLAB Network Table ........................................................................................ 21

Table 5. Test Network PowerFactory Current Simulations Grid Connected ...................... 30

Table 6. Hailuoto Island Network PowerFactory Current Simulations Grid Connected .... 31

Table 7. Test Network PowerFactory Time to Operate with Grid Connected Settings ...... 31

Table 8. Hailuoto Island Network PowerFactory Time to Operate with Grid Connected Settings ................................................................................................................................ 32

Table 9. Test Network Comparison Current MATLAB vs PowerFactory ............................. 32

Table 10. Hailuoto Network Comparison Current MATLAB vs PowerFactory .................... 33

Table 11. Test Network PowerFactory Time to Operate with Islanded Settings ............... 33

Table 12. Hailuoto Island Network PowerFactory Time to Operate with Islanded Settings............................................................................................................................................. 33

Table 13. Hailuoto Network Comparison Current MATLAB vs PowerFactory when Islanded Settings and with a Varying Output .................................................................................... 35

Table 14. Test Network Relay Settings Grid Connected ..................................................... 58

Table 15. Test Network Relay Settings Islanded ................................................................. 58

Table 16. Hailuoto Island Network Relay Settings Grid Connected ................................... 65

Table 17. Hailuoto Island Network Relay Settings Islanded ............................................... 65

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Table of Figure Figure 1. Typical Microgrid ................................................................................................................................ 2

Figure 2. Faults on a Microgrid .......................................................................................................................... 3

Figure 3. Test Network (Ustun, Ozansoy and Zayegh, Modeling of a Centralized Microgrid Protection System and Distributed Energy Resources According to IEC 61850-7-420 2012) ........................................................ 13

Figure 4. Hailuoto Island Network (Laaksonen, Ishchenko and Oudalov, Adaptive Protection and Microgrid Control Design for Hailuoto Island 2014) ........................................................................................................ 14

Figure 5. PowerFactory Single Line Diagram – Test Network showing Relay Positions .................................. 57

Figure 6. 3-Phase Short Circuit Fault at Terminal(6) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays.................................................................................................................. 59

Figure 7. 3-Phase Short Circuit Fault at Terminal(6) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays ......................................................................................................................... 59

Figure 8. 3-Phase Short Circuit Fault at Terminal(6) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays ............................................................................................................................................ 60

Figure 9. 3-Phase Short Circuit Fault at Terminal(2) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays.................................................................................................................. 61

Figure 10. 3-Phase Short Circuit Fault at Terminal(2) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays ......................................................................................................................... 61

Figure 11. 3-Phase Short Circuit Fault at Terminal(2) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays ............................................................................................................................. 62

Figure 12. No Fault – Loads at Terminal(5) and Terminal(6) disconnected Time-Overcurrent Plot - Grid Connected Network with Islanded Settings on Relays .................................................................................... 63

Figure 13. PowerFactory Single Line Diagram – Hailuoto Island Network showing Relay Positions ............... 64

Figure 14. Wind Output 100% No Fault Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays ......................................................................................................................... 66

Figure 15. Wind Output 100% No Fault Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays ............................................................................................................................................ 66

Figure 16. Wind Output 100% No Fault Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays .............................................................................................................................................................. 67

Figure 17. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault ............................................ 68

Figure 18. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault ....................... 68

Figure 19. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault ............................................... 69

Figure 20. F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Diesel Generator Side of Fault................................................................. 69

Figure 21. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Grid Side of Fault ........................................................... 70

Figure 22. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault ....................................... 70

Figure 23. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault ............................................ 71

Figure 24. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault ....................... 71

Figure 25. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault ............................................... 72

Figure 26. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Diesel Generator Side of Fault ...................................... 72

Figure 27. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays Grid Side of Fault ........................................................... 73

Figure 28. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault ....................................... 73

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Figure 31. Wind Output 100% F2 - 3-Phase Short Circuit Fault Middle of Line(8) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault ................................................ 75

Figure 32. Wind Output 100% F2 - 3-Phase Short Circuit Fault Middle of Line(8) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Diesel Generator Side of Fault ........................... 75



Figure 35. Wind Output 100% F3 - 3-Phase Short Circuit Fault Middle of Line(10) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault .................................... 77

Figure 36. Wind Output 100% F3 - 3-Phase Short Circuit Fault Middle of Line(10) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault ................ 77





Figure 41. Wind Output 0% No Fault Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays ............................................................................................................................................ 80

Figure 42. Wind Output 0% No Fault Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays ............................................................................................................................................ 80

Figure 43. Wind Output 0% No Fault Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays ............................................................................................................................................................... 81

Figure 44. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault ............................................ 82

Figure 45. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault ....................... 82

Figure 46. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault .............................................................. 83

Figure 47. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Diesel Generator Side of Fault .......................................... 83

Figure 48. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Grid Side of Fault .......................................................................... 84

Figure 49. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault ..................................................... 84







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Figure 66. Wind Output 0% F3 - 3-Phase Short Circuit Fault Middle of Line(10) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Grid Side of Fault ........................................................... 93

Figure 67. Wind Output 0% F3 - 3-Phase Short Circuit Fault Middle of Line(10) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault ....................................... 93

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Chapter 1: Introduction

1.1 Microgrids

Due to changing societal expectations and advancements in small scale power generation

and storage technology, the distribution networks for power transmission have been

forced to adapt to a new and shifting paradigm (Colson and Nehrir 2009). This paradigm

shift manifested in the fact that renewable power supplies have increased in production

so much that they have outstripped the traditional generation of electricity by large coal

burning power stations in 2015 (International Energy Agency 2016). The rise in the

number of small-scale power generation systems has allowed for the creation of localised

pockets of self-contained power balances, where the generated power is being used by

local loads causing networks to become less interconnected and more modular. This

more compartmentalised supply has the additional benefit of reducing the problems

routinely experienced at the end of the transmission line, such as significant fluctuations

in voltage and blackouts caused by the operation of relays. These end of line problems

cause a reduction in the overall reliability of the network and increase both the

maintenance costs and outage payments. The West Australian state-run network

provider Western Power has highlighted the end of the line problems as occurring at the

town of Kalbarri (Western Power 2016). As a result of the supply problems that are

experienced at Kalbarri, Western Power has investigated the feasibility of converting or

modifying the town into a grid connected network that is self-sufficient. The state of

South Australia has recently experienced the perfect storm of events that lead to a state-

wide blackout. This blackout was precipitated in part by the lack of suitable protection

methods which could enable the network to split into smaller independent networks. A

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typical example of this type of network is shown in Figure 1. These localised pockets have

the inherent ability to disconnect from the main grid into small self-contained networks,

often called microgrids (MG), and continue to function in what has become known as an

islanded state (Lasseter 2002). This ability has in turn necessitated changes to the

protection of the local and interconnected distribution networks.

Figure 1. Typical Microgrid

1.2 Limitations of Microgrids

From as early as 2002, it was raised as a serious issue that the existing network’s current

protective devices may fail to detect faults in the event of islanding when disconnected

from the main grid (Lasseter 2002). This failure is due to the inability to provide large

fault current from the small-scale generators and the protection devices, using the

presence of excessive current flows to detect faults. The absence of large fault currents

arising from the use of small-scale generators resulted in the unfortunate situation where

the overcurrent protection devices, either failed to respond, or whose operation is

delayed to the point of being ineffectual (Wang, et al. 2016).

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1.3 Protection of Microgrids

There are three main areas where faults can occur that affect a microgrid installation

requiring particular attention, shown in Error! Reference source not found.. The first (F1)

is a fault on the transmission line connecting the transmission network to the microgrid

while the microgrid is connected to the grid. As mentioned, if connected to the grid the

overcurrent protection will operate on the grid side (R1) to clear the fault (F1); yet the

micro side will not provide enough overcurrent for the relay to clear (R2). The second (F2)

is a fault on the feeders inside the microgrid. Thirdly (F3) the fault occurs in the load. If

the external grid is isolated from the rest of the microgrid, the relays R2-R5 will not

operate due to the absence of a sufficiently high fault current.

Figure 2. Faults on a Microgrid

Several methods of protection for a microgrid against these types of faults have been

discussed and investigated by other researchers (Colson and Nehrir 2009) (H. Laaksonen

2010). These proposals include the use of devices such as capacitor banks and flywheels

to provide the fault currents needed for existing protection devices to operate without

modification (Olivares, et al. 2014). Other methods include using differential relays, both

current and voltage, instead of overcurrent relays and by doing so detect the conditions

present during the period of the fault, rather than the effect of faults expressed by large

currents (Zarei and Parniani 2016). Another method is to utilise the computing power

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that is available, the existing communications infrastructure, and the use of adaptive

relays to create a network connected relay system (Han, Hu and Zhang 2010). Such a

system requires a central processor to be continuously supplied information on the state

of the network, for the processor to make decisions based on that information, and then

to signal the individual adaptive relays in the network with the settings needed.

1.4 Methods of Protection

Even though each of the proposed methods has at least one distinct advantage,

unfortunately, each method also has some associated shortcomings. While it is beyond

the scope of this project to consider the cost and practical applications of each of these

methods, it is still worth noting that they exist. The installation of devices whose primary

role is to provide large fault currents is costly and may also present a significant hazard

due to the presence of the stored energy. The use of differential relays requires

communication with the sensors which are potentially placed considerable distances

apart from each other, at a not insignificant cost and risk of failure. Adaptive relays

require a connection to a central processor via a high-speed interface. However, an

advantage of adaptive relays is that under fault conditions, when they are no longer in

communication with the processor, they can fall back on a range of predetermined

settings (Oudalov and Fidigatti n.d.). In the worst case scenario, the adaptive relays fall

back on these predetermined settings and continue to operate until the fault is fixed and

communication restored. Based on the adaptive relay method, a protection system has

been implemented in Hailuoto Island in Finland as a test case (Laaksonen, Ishchenko and

Oudalov 2014). Research has also been undertaken at the University of Victoria (Ustun,

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Ozansoy and Zayegh 2011) into an algorithm that can be used to determine the settings

of a relay. The settings are based on; the current network conditions, the number

generator devices and their power flow, the state of relays, whether or not the relays

have operated, and what values have been set on the relays.

1.5 Purpose of Thesis

The goal of this project is to investigate the performance and the levels of protection

provided by a system based on adaptive relays. The changing value of fault currents

provided under the various network arrangements being the primary focus of this

project. The chief concern is the changing nature of the network and the need for some

method to be able to quickly and reliably calculate the prospective fault currents for each

of the adaptive relays, and to respond in real-time. Preliminary research work has been

undertaken previously by Oudalov and Fidigatti into establishing an algorithm to calculate

the fault current. This work has been subsequently expanded upon by Ustun, Ozansoy

and Zayegh at the Univerity of Victoria.

In this project, the preliminary findings of these researchers are to be investigated and

assessed under various conditions so that the strengths and limitations of each

methodology can be identified.

As Ustun, Ozansoy and Zayegh’s algorithm provides an effective means for calculating the

fault currents for each relay in a microgrid; our goal is to develop further the algorithm to

extend its capability by building on the findings of this other research work. It is

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proposed in this work that adaptive relays using high-speed communications and a

central microprocessor be simultated and investigated as the basis of providing an

effective method for the protection of microgrids. It is proposed that Ustun, Ozansoy and

Zayegh’s algorithm be implemented in a comprehensive MATLAB deployment utilising

matrices and tables to extend the capability of the algorithm by improving its

responsiveness and robustness. The results of the MATLAB implementation are then to

be evaluated against a detailed comparison against a PowerFactory simulation of the

network.

The outcome of this report is to find a simple method of calculating fault currents and to

prove the effectiveness of using adaptive relays. With the aim of being able to provide a

method for protection of microgrids that will allow for protection when grid connected

and islanded.

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Chapter 2: Review of the Literature

2.1 MicroGrids

R. H. Lasseter wrote in 2002 about clusters of loads and micro sources operating as a

small-scale grid, calling this arrangement a microgrid (Lasseter 2002). He then went on to

identify and specify certain characteristics of the microgrid. For example: have power

sources with less than 100 kW capacity and electronic power interfaces, have the ability

to be able to provide an uninterruptible power supply, have a microprocessor for control

and protection, and be self-contained. While for the most part, this has been the case,

modern microgrids are found to be supplied with power sources that greatly exceed the

100 kW rating that was proposed along with the need for the sources to have electronic

power interfaces. Systems are now being built with either existing infrastructure or as

part of the microgrids construction that includes energy sources 5-10 times the 100 kW

rating and often including more traditional sources of energy like diesel generators

lacking power electronic interfaces. These changes highlight the infancy of the

understanding around microgrids and what they have evolved into, yet the identifiers

proposed by Lasseter of the microgrid providing voltage stability and independence are

still important and relevant. Along with his assessment that microgrids are going to have

certain problems to overcome. Chief among these being the lower level of fault current

as evidenced when he states:

Micro sources may only be capable of supplying twice load current or less to

a fault. Some overcurrent sensing devices will not even respond to this level

of overcurrent, and those that do respond will take many seconds to

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respond, rather than the fraction of a second that is required. (Lasseter

2002)

This highlighting of the lack of fault current is still relevant as it is the primary problem

surrounding the establishment of microgrids as part of the wider network. While Lasseter

puts forward a number of potential solutions, many, including developing a real-time

fault location technique, are costly and impractical.

2.2 Adaptive Network Protection in Microgrids

In 2009 Alexandre Oudalov and Antonio Fidigatti expanded on the work previously done

and suggested a new novel approach (Oudalov and Fidigatti n.d.). Their novel approach

consisted of using relays that can be changed as the network changes via a

communication network that allows the relays to be informed of the current network

status. This changing network has been enlarged to include not only the ability to

disconnect from the external grid but also to split into smaller and smaller microgrids.

The smaller grids are limited only by the size and number of the power sources with the

cause for splitting being faults that occur on the network. Oudalov and Fidigatti detailed

four main classes of faults on the network concerning microgrids and certain methods to

protect against them. The faults being: a fault on the external grid, a fault on the

distribution transformer, a fault inside the microgrid on a feeder and a fault on the load.

These faults are shown to require a specific type of relay that can be adjusted and be

directional along with a feature set that allows for communication interfacing with a

central microprocessor. Not only is the relay to be adaptive but must also be sensitive,

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selective and fast. To fulfil the requirements of sensitive and selective the relay must be

set with an accurate knowledge of maximum fault current that will be seen by the relay.

Oudalov and Fidigatti have put forward the following formula ( 1 ) to enable the pickup

current to be calculated.

∑

( 1 )

Where is a rated output current of a particular distributed energy resource (DER)

and is a fault current contribution coefficient shown below ( 2 ).

( 2 )

This formula served as the basis for future refinement by others and by this report. The

current values outputted from this equation are the summation of the current outputted

by each power source with the only concession to the network topology being the

coefficient which needs to be calculated for every output rating. This formula does

not allow for the output of the generator to be less than its rated output or even to be

not contributing current that is seen by the relay.

2.3 Fault Current Coefficient and Time Delay Assignment for Microgrid Protection

System With Central Protection Unit

In 2013 IEEE published an article (Ustun, Ozansoy and Zayegh 2013) which built upon the

formula of Oudalov and Fidigatti and put forward a very different method for

discrimination of the relays. Their version of the formula becomes quite complex in

comparison, and much is left to the microprocessor to adapt to the network and calculate

10

the required settings based on results from sensors measuring impedances of the

network at each relay and using this information to calculate the fault currents seen.

They also put forward the argument that as the microgrid is much smaller than the main

grid, the relay discrimination can be done via a simple 200 ms delay between relays. This

fixed delay between relays allows for the relays to be easily adjusted by the

microprocessor as all that is required to be known prior is the hierarchy of relay control.

The microprocessor can then calculate the current expected, tell the primary relay its trip

current and its back up the same current along with a wait time of 200 ms. The flat

overcurrent limit has some unfortunate side effects namely the incapacity to allow small

overcurrent fluctuations caused by electric machines at start up and its validity of use in a

microgrid with multiple sources is in question. However, the concept of fully automating

the process of adaption with the relays inside of a microgrid is a worthwhile goal that

should be investigated and to some extent is with this report using the network

suggested in this paper as a test network to verify the operation of the system proposed.

2.4 Adaptive Protection and Microgrid Control Design for Hailuoto Island

Hailuoto Island is showcased in research done by (Laaksonen, Ishchenko and Oudalov

2014) as an example of adaptive relays in use using high-speed communications and a

central microprocessor to control the relays. This example is a prime case of the

distributed generators found in microgrids today, being more than the 100 kW power

rating first proposed by Lasseter twelve years earlier. This microgrid also showcases the

very clear reasons for needing adaptive relays to cope with the islanding that may occur

and a high-speed communications network between the microprocessor, the relays, and

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the distributed generators to allow for the correct settings to be selected on the relays.

The system installed is the basis of the one used in this report in that the microprocessor

will calculate the fault current based on the information regarding status and output of

the distributed generators and subsequently inform the relays. The relay will individually

select the settings that have been pre-set and loaded in the relay as part of the

commissioning of the system using the values calculated during the design of the system.

This network also forms part of this project as it is simulated from data made available in

this paper and used to check the hypothesis.

12

Chapter 3: Materials and Methods

3.1 Networks

Studying the effects of islanding on the protection capabilities of a network under various

fault conditions requires that the network is studied in a theoretical setting. Due in part

to the large and potentially dangerous fault currents that are to be investigated and the

impractical nature of experimental study on large networks. These simulated networks

consist of a theoretical test network and a modelling of an existing network currently in

use. Both networks include wind turbines and diesel generators. The networks were

modelled using DIgSILENT PowerFactory. The research at the University of Victoria done

by Ustun, Ozansoy and Zayegh used a test network (Ustun, Ozansoy and Zayegh 2012)

that consisted of four loads and four generators shown in Figure 3. This test network has,

as part of this project, been simulated in PowerFactory along with the Hailuoto Island

microgrid network (Laaksonen, Ishchenko and Oudalov 2014) shown in Figure 4.

13

Figure 3. Test Network (Ustun, Ozansoy and Zayegh, Modeling of a Centralized Microgrid Protection System and

Distributed Energy Resources According to IEC 61850-7-420 2012)

14

Figure 4. Hailuoto Island Network (Laaksonen, Ishchenko and Oudalov, Adaptive Protection and Microgrid Control

Design for Hailuoto Island 2014)

15

The particulars of each network can be seen earlier in Figure 3 and Figure 4. The

specifications of each equipment model are shown below in Table 1 and Table 2, with

Hailuoto Island Cable lengths in Table 3.

Table 1. Test Network PowerFactory Specifications

Rated Voltage

Rated Current

AC-Resistance

Reactance

Aerial Cable 20 kV 194 A 0.323 Ω/km 0.259 Ω/km

Active Power Reactive Power

Load 1 MW 0 Mvar

Rated Output Max Output R/X Ratio Short-Circuit Current Ik”max

Diesel Generator

1 MW 1.2 MVA 0.1 0.115 kA

Rated Power

High Voltage

Low Voltage Impedance

Transformer 1 10 MVA 110 kV 6 kV 3%

Rated Power

High Voltage

Low Voltage Positive Sequence Impedance

Copper Losses

Zero Sequence Impedance

Wind Turbine Transformer

2.5 MVA 6 kV 0.69 kV 6% 22 kW 3%


Wind Turbine 1 1 MVA 1.5 MVA 0.1 0.144 kA

16

Table 2. Hailuoto Island PowerFactory Specifications

Rated Voltage

Rated Current

AC-Resistance

Reactance Inductance Capacitance

Aerial Cable 20 kV 194 A 0.323 Ω/km 0.259 Ω/km

XLPE Submarine Cable

20 kV 180 A 0 Ω/km - 0.41 mH/km 0.23 uF/km

Active Power Reactive Power

Load 0.628 MW 0.01956 Mvar


Diesel Generator

1.4 MW 2.1 MVA 0.1 0.061 kA

Rated Power

High Voltage

Low Voltage Impedance



Rated Power

High Voltage

Low Voltage Positive Sequence Impedance

Copper Losses

Zero Sequence Impedance

Wind Turbine Transformer

2.5 MVA 20 kV 0.69 kV 6% 22 kW 3%

Rated Output Max Output R/X Ratio Subtransient Short-Circuit Level

Wind Turbine 1 0.6 MVA 0.72 MVA 0.1 0.72 MVA




17

Table 3. Hailuoto Island Network Cable Lengths

From To Cable Length

Transformer 1 Transformer 2 23.1 km

Siikajoki Substation Mainland Wind Turbines 8.8 km

Mainland Hailuoto Island 7.4 km

Hailuoto Island Marjaniemi 3 5.2 km

Marjaniemi 3 Junction Marjaniemi 3 17.4 km

Marjaniemi 3 Junction Viinikantie (Recloser Station) 2.9 km

Viinikantie (Recloser Station) Marjaniemi 1 & 2 20.2 km

Viinikantie (Recloser Station) Keskikylä (Disconnector Station) 1.7 km

Keskikylä (Disconnector Station) Potti (Disconnector Station) 8.7 km

Potti (Disconnector Station) Huikku (Diesel Generator) 9.7 km

Huikku (Diesel Generator) Huikku (Wind Turbine) 0.8 km

The simulated networks were chosen to be modelled in DIgSILENT PowerFactory due to

its robustness as a simulating tool. PowerFactory’s robustness is best evidenced by the

state network authority Western Power requiring all new large scale loads and

generations to be modelled in PowerFactory both as part of and before connection

(Systems Analysis & Solutions 2016).

3.2 Wind Turbines

Each wind turbine was modelled using PowerFactory’s built-in models that are based on

the IEC61400-27-1 standard (DIgSILENT GmbH 2015). The 4A type turbine was chosen

due to its ability to; sustain low voltage ride through events, its interface being an AC/DC-

DC/AC inverter-rectifier configuration common to turbines that are installed in Western

Australia, and for its lack of needing reactive power from the grid (DIgSILENT GmbH

18

2015). The turbines used in the Hailuoto Island simulation are grouped into one turbine

at each location. Representing two actual turbines by increasing the single simulated

turbine power output to the combined output of the actual turbines at locations on the

mainland and Marjaniemi.

3.3 Synchronous Machine and Diesel Generators

Another type of distributed generator that was used was a synchronous machine.

PowerFactory uses certain models and methodologies in it simulations, and it requires

that there be some form of a synchronous generator connected to the simulated network

so as to perform its load flow calculations. PowerFactory’s requirement of having a

synchronous generator connected required the adoption of simulating small-scale diesel

generators in the case of the Hailuoto Island network as synchronous machines and the

two of the non-specific generators in the test network so that the microgrid could be

islanded from the external grid during load flow analysis. Use of the synchronous

machines was hamstrung by the higher than expected fault currents being provided in

PowerFactory during fault events. The synchronous generators models were then

substituted out for fault current limited external grid models for use in circuit breaker

discrimination testing.

3.4 Transformers

The networks utilised a double wound transformer model in PowerFactory for the high

voltage to low voltage transformer. In the test network, this is part of the connection for

the external grid to the microgrid. The Hailuoto Island has two double wound as part of

19

its connection to the local distribution network to the transmission network and external

grid. In the absence of more accurate information regarding the manufacturer and

specifications, the parameters of the model in PowerFactory were set to the defaults

except for the power ratings.

3.5 Cable Types

The Hailuoto Island network was implemented using publicly available information made

primarily in (Laaksonen, Ishchenko and Oudalov 2014). Due to the lack of some non-vital

information, several assumptions were made as to the types of cable used and generator

types and specifications. The cables specifications were selected based on the amperage

and the usage requirements. The aerial cables were simulated using the specifications

from manufacturer Olex as they are an archetype and are, in the absence of clearer

information, a firm practical choice (Nexans 2012). The undersea cables were simulated

using the specifications from ABB and the justification to use ABB cable specification

based on the use of submersible ABB cables in the undersea regions of similar nearby

projects (ABB, Inc. 2016). The test network in Ustun, Ozansoy and Zayegh’s research has

also been recreated in PowerFactory using the Olex cables for consistency with the cable

distance between buses as one kilometre for simplicity.

20

3.6 Relays

3.6.1 Nominal Currents and MATLAB Network Table

Upon being created in PowerFactory, the networks were used to calculate nominal

current and load flows of both the generators and lines. This information gained was then

used to populate a Comma Separated Values (CSV) file in the format shown below in

Table 4, with the nominal currents filling out column A. The file is broken into three

sections. The first section is the leading row, which provides the MATLAB script (See

Appendix C) information on the state of the grid (islanded '0' or grid connected '1'), the

number of relays, and the number generators in the network. The second section consists

of relay data and extends from row 3 to row 3+#relays. Column A as previously

mentioned is nominal current. Column B is pre-set pickup current values for grid

connected state. Column C is the calculated values of maximum fault currents calculated

by the MATLAB script. Column D is the status of the relay, 0 for offline and 1 for online.

Column's E to E+#generators are for stating which generator is contributing to the

current seen by that relay. The third and last section is regarding the generators. Starting

at row 5+#relays column A is for nominal current, column B is for maximum fault current,

and column C is for the status of generator inputted as a fraction of the nominal output

ranging from 0-1. See Appendix C for a copy of the MATLAB script.

21

Table 4. MATLAB Network Table

A B C D E F G H (E+#generators)

1 1 12 4

2

3 385 3900 0 1 0 0 0 0

4 385 3900 512 1 1 1 1 1

5 95 130 114 1 1 0 0 0

6 95 7710 512 1 1 1 1 1

7 95 143 142 1 0 1 0 0

8 95 7710 512 1 1 1 1 1

9 95 124 114 1 0 0 1 0

10 95 4384 512 1 1 1 1 1

11 95 4384 512 1 1 1 1 1

12 95 139 142 1 0 0 0 1

13 192 4000 256 1 1 1 0 0

14 (3+#relays) 192 650 256 1 0 0 1 1

15

16 (5+#relays) 95 114 1

17 95 142 1

18 95 114 1

19 95 142 1

3.6.2 Fault Currents and Relay Type

After simulating the load flows, the two networks were then simulated with various faults

to obtain fault current values. As mentioned earlier, the Column B maximum fault

currents are set as 1.5 times the nominal current values for wind turbines and 1.5 times

the nominal for synchronous generators. The pickup and fault current values enabled the

subsequent creation of relays. The relays were modelled using the ABB/Westinghouse

C07 – 288B716A24 type prebuilt into PowerFactory. The relay has a characteristic

moderate inverse overcurrent curve found in electromechanical relays (ABB, Inc. 1990),

and newer equipment can replicate its tripping characteristics via programmable relays

(ABB, Inc. 2015). Electromagnetic relays are still found in networks, and due to their

22

prevalence, the choice was made to use this relay type in PowerFactory to allow the test

conditions to be similar to real-life conditions as possible. The settings on the relays were

chosen based on the need for time discrimination of at least a 0.3 of a second delay

between relays (See Appendix A.2 and B.2). The discrimination being to give the closest

relay time to operate to ensure selectivity. To minimise the loss of power and contain the

losses to small sections of the network. The time to operate being calculated using the

formula given in IEC 60255-3 and as shown in ( 3 ) where is the time delay setting,

is the expected fault current, and is the current required to operate the

relay.

(

)

( 3 )

3.6.3 Relay Positions

For the test network, the relay positions were determined by the need to protect the

equipment and lines from excessive current flows. The protection of equipment and lines

predilected the need to install relays at the connection point of any line whereby

excessive currents may enter. Resulting in the 12 relays being simulated. The relays are

placed anywhere a line is connected to a busbar or terminal that is fed from another line.

Relays are simulated at each of the disrupted generators even though most generators

with a rectifier-inverter control system have an existing protection system already in

place (See Appendix A.1). For the Hailuoto island network the locations were chosen to

mimic the placements indicated in the literature. This resulted in the simulation of eight

relays installed in the flowing locations: one on the main feeder for the island at the

connection to the MV grid at the Siikajoki Substation, one at the Viinikantie recloser

23

station, two at the Keskikylä disconnector station, two at the Potti disconnector station,

and then one on each of the Huikku distributed generators (See Appendix B.1). The relays

at the Keskikylä and Potti disconnector stations are in pairs with the relays being

somewhat directional and one operating in the forward direction with the other in

reverse. The assumption being that each of the existing distribution generators (wind

turbines) have their own over current protection systems.

3.6.4 Relay Setting Calculations

The assumption is also made that the settings needed for the relays will have already

been prior calculated using a combination of PowerFactory and formula (3) (See

Appendix A.2 and B.2) and that the relays will adapt to the right settings based on the

current levels sent via the script. The timing of when the configuration for the relays has

been calculated differs from Ustun, Ozansoy and Zayegh’s system in that the

microprocessor, in this case, will not calculate any settings other than the expected fault

currents. Unlike Ustun, Ozansoy and Zayegh’s algorithm that also calculates the trip

settings and time delay values. Ustun, Ozansoy and Zayegh’s system is designed for relays

that work by measuring the current and if found to be exceeding pre-set overcurrent

levels, cause the relay to operate without the time delay intrinsic to electromagnetic

devices. With the required discrimination coming from the microprocessor setting the

backup relay to operate after 200 ms when it detects an overcurrent in the event of a

fault occurring. Contrast this with the proposed algorithm in this report that aims to allow

for a time delay to operate to limit nuisance tripping by using relays modelled on the

inverse time to operate curve. In practice, the relay may calculate itself, its required

24

settings and adapt to them based on the expected fault current levels predicted by the

microprocessor yet it assumed that for the moment that they will select from pre-set

values. These pre-set relay values and settings involved were calculated using the

aforementioned formula ( 3 ) and not using the MATLAB script. Rather the current values

calculated by the MATLAB script were used as the basis for the calculations. The

networks in PowerFactory were simulated with the relays setup to handle the

appropriate settings allowing for investigation on the effectiveness of having adaptive

relays.

3.7 Fault Currents

The fault current in the islanded state was calculated based on the following formula

Error! Reference source not found.. The state of the generator variable also allows the

output of the generator to be simulated as if it has a reduced output by inputting a

decimal fraction as the multiplier . Using a decimal fraction for output variation

is especially useful for wind turbines that are notorious for being a variable output

generator given how they dependent on wind speed for production. The generators'

contribution variable ( ) allows for the specific addition of each generator

current to the pickup current of the relay. The contribution variable can also be a decimal

fraction ranging from 0-1 allowing for the loss of current due to cable reactance and

equipment resistance.

∑( )

( 4 )

25

The faults to be inspected are 3 phase short circuit faults using the IEC60909

methodology in PowerFactory. The use of 3 phase short circuit faults is because this class

of fault are the worst-case scenario in terms of fault current levels when compared to

single phase to ground or phase to phase faults.

3.8 Faults

The faults simulated on the test network are short circuits on:

The low voltage side of the coupling transformer. Simulated in PowerFactory

by a fault at Terminal(1)

Line(4). End closest to Feeder (T1)


Line. End closest to Feeder (T2)




The faults simulated on the Hailuoto Island network are short circuits on:

Line(6). End closest to Terminal(7) - F0

Line(6). Middle - F1

Line(8). End closest to Terminal(12) - F2

Line(10). Middle - F3

26

Chapter 4: Simulation Analysis

4.1 Introduction

Adaptive relays provide a way for the protection of microgrids that traditional methods

have been unable to provide. The lack of significant fault current means that traditional

over current protection methods of fuses and directional electromagnetic relays fail to

operate when the microgrid is islanded. The adaptive nature of adaptive relays means

that they can be set for both islanded and grid connected networks. They are not limited

to just being able to respond to the presence or absence of the grid but also to the

changing outputs of the distributed generators. The distributed generators are primarily

in microgrids a renewable source with a diesel generator backup. The renewable source

of power for the generators often results in an unpredictable and varying source of

power. The Hailuoto Island and the University of Victoria test networks are to be used to

firstly highlight the need or limitations of the traditional method for protection on grids

that become islanded. Secondly, they are to be used to test the proposed algorithm's

ability to calculate the current values in the microgrids islanded state correctly. Thirdly

they are to be used to verify the effectiveness of having relays adapt different settings

based on the reduced pickup currents. The effectiveness of the relays is to be gauged by

the presence of discrimination whereby allowing for the closest relays to operate but also

for the backup of relays as appropriate and by their ability to respond to the each of the

faults without the contribution afforded by the external grid. The algorithm will be

deemed successful if it can match the current output values calculated by the

PowerFactory simulation in a statistically significant way under a variety of varying

27

outputs on the generator. The limitations that are to be investigated is the failure of the

relays to operate in a network when islanded and experiencing a fault. Along with the

over sensitive nature of the network caused by trying to provide protection without the

use of adaptive relays resulting in parts of the network to be isolated needlessly and

potentially causing blackouts on customer’s homes.

4.2 Simulation Procedure

4.2.1 Simulating in PowerFactory

The first part is simulating the test networks and recording the current data in both

islanded state and grid connected. Obtaining the current data is done as prior mentioned

by first calculating the nominal current values in PowerFactory in both grid connected

and an islanded state. Secondly calculating the maximum currents caused by various

faults, again both grid connected and islanded. Recording the data and using this

information to pick suitable values for the relays. After adding the relay models to

PowerFactory, the relays operating times were recorded. The circuits were then tested

with faults at various locations to determine the effect on operating times the relay

settings had. Once all this preliminary testing was done the results were inspected to

highlight areas where the grid connected relay settings failed to operate and need to be

adapted.

28

4.2.2 MATLAB Script

The second part of the procedure is to create a MATLAB script that will use the formula

Error! Reference source not found. mentioned earlier to calculate the current seen by

each relay. Testing will then be done to see how the algorithm performs using the both

the test and Hailuoto Island networks. Seeing how the calculated maximum currents,

when islanded, compare to the results of the PowerFactory simulations. Testing using the

Hailuoto Island network, the algorithms ability to adapt to changing load flows by

modifying the outputs of the wind turbine generators at several settings: 0%, 25%, 50%,

75%, and 100% of total capacity. Then to test the calculation operation against the

PowerFactory simulations results. These generators outputs can be modified by changing

the maximum output in PowerFactory of each wind turbine generator. See Appendix A.1

and B.1 for single line diagrams of both networks.

4.2.2.1 Explanation of MATLAB Script

The MATLAB script is designed around the concept that information on the status of the

generator will be fed to a central processor that will update the relays on the expected

pickup currents. The relays will then adapt to the changed current and adjust the setting

so as to be able to operate appropriately. The MATLAB script (See Appendix C) is

designed to act as the microprocessor, and it receives the information in the form of a

CSV file. The CSV file notifies the script the status of the networks connection and if grid

connected it will output the pickup currents set from the initial designing of the network

done before connection to the grid as per the utility stipulations. The file also states the

generator output values which the script then reads and calculates the current before

29

writing it back into the CSV file. It does this based on the assumption that when the

circuit is designed the information regarding the current flows in the network through a

particular relay will be entered into the script in the form of a table. Essentially the

hierarchy of control for the various relays and highlighting which relays back up each

other and what discrimination needs to apply. This table will be such that it allows the

script to sum the generator currents for each relay based on the binary value/decimal

fraction stipulated in the table. The script cycles through each relay and summing the

current generator output via its pre-set max output value multiplied via its status

variable. The script has been designed and optimised for speed as the changes in the

network will require updating of the relays as quickly as possible to minimise the

problems caused by having relays either over or under sensitive. Under sensitive relays

will result in faults not tripping the relays causing the damage to equipment or personal.

Whereas the over sensitive will result in the relays operating under conditions that are

not faults causing homes and business to lose power needlessly and could potentially

open the utilities operate to economic costs. Not the mention the likelihood of ‘the boy

who cried wolf’ syndrome in that the breaker is reset without further investigation after

several false positives. Which in turn could lead to circumstances where faults are left

unattended for example a power line on the ground drawing full current but seen as just

a load when the network is in islanded mode.

4.2.3 Recalculating Pickup Currents

The third part is to recalculate, based on the islanded networks new pickup currents,

settings for the relays. The new relay settings will be tested to see the new operating

30

times and will then be inspected for improvement over the relays time to operate using

grid-connected settings.

4.3 Results

4.3.1 PowerFactory Simulations

The results for the first part are the results from the PowerFactory simulations and are

outlined below in Table 5 and Table 6. These results include the nominal currents and

fault currents for faults at various locations for both networks.

Table 5. Test Network PowerFactory Current Simulations Grid Connected

Fault Location R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12

Gri

d C

on

nec

ted

(A

)

Coupling Transformer (LV Side) / Terminal(1)

181 115 118 113 116 229 229

Line(4) Feeder (T1) 1769 113 115 113 116 32893 229

Line(4) Feeder (T4) 422 27 27 115 118 7782 233

Line Feeder (T2) 416 27 7726 27 26 27 53 53

Line(1) Feeder (T3) 416 27 27 7726 26 27 53 53

Line(2) Feeder (T5) 226 14 15 62 4275 64 4171 4171

Line(3) Feeder (T6) 226 14 15 62 4275 64 4171 4171

Isla

nd

ed (

A)

Coupling Transformer (LV Side) / Terminal(1)

463 115 118 113 116 229 229

Line(4) Feeder (T1) 0 115 118 113 116 233 229

Line(4) Feeder (T4) 0 113 116 115 118 229 233

Line Feeder (T2) 0 111 446 114 109 112 221 221

Line(1) Feeder (T3) 0 111 114 446 109 112 221 221

Line(2) Feeder (T5) 0 109 112 111 446 114 221 221

Line(3) Feeder (T6) 0 109 112 111 446 114 221 221

Nominal Currents (A) R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12

Grid Connected 23 384 96 97 96 97 96 97 97 96 192 192

Islanded 0 0 97 97 96 97 96 97 97 96 192 192

31

Table 6. Hailuoto Island Network PowerFactory Current Simulations Grid Connected

Fault Location R1 R2 R3 R4 R5 R6 G

rid

Co

nn

ecte

d

(A)

F0 line(6) 887 922 76 76 58 17

F1 line(6) mid 852 901 76 76 59 17

F2 line(8) 746 789 789 77 59 17

F3 line(10) mid 552 584 584 584 6 18

Nominal 54 35 34 46 49 14

Isla

nd

ed (

A)

F0 line(6) 0 6 76 76 58 17

F1 line(6) mid 0 6 76 76 59 17

F2 line(8) 0 6 6 77 59 17

F3 line(10) mid 0 59 59 58 61 18

Nominal 0 48 31 13 9 14

Table 7 and Table 8 show the relays time to operate for both networks when they are

grid connected and islanded but using the relay settings that meet the requirements

when grid connected. See Appendix A and B for more information about relays settings

used and the Time-Overcurrent Plots.

Table 7. Test Network PowerFactory Time to Operate with Grid Connected Settings


Gri

d C

on

nec

ted

Set

tin

gs

(s)

Line Feeder (T2) Grid Connected

0.715 N/A DNO (Did Not

Operate)

0.02 DNO N/A DNO N/A N/A DNO N/A DNO

Line Feeder (T2) Islanded

N/A N/A 0.572 0.168 0.572 N/A 0.572 N/A N/A 0.572 N/A DNO

Line(3) Feeder (T6) Grid Connected

1.195 N/A DNO N/A DNO N/A DNO N/A 0.02 DNO 0.317 N/A

Line(3) Feeder (T6) Islanded

N/A N/A 0.596 N/A 0.596 N/A 0.596 N/A 0.168 0.596 DNO N/A

32

Table 8. Hailuoto Island Network PowerFactory Time to Operate with Grid Connected Settings

Fault Location R1 R2 R3 R4 R5 R6

Gri

d

Co

nn

ecte

d

(s)

F0 line(6) 0.922 0.606 0.205 0.699 3.172 3.028

F1 line(6) mid 0.934 0.613 0.205 0.697 3.163 3.016

F2 line(8) 1.008 0.653 0.143 0.688 3.109 2.941

F3 line(10) mid 1.249 0.776 0.160 0.02 2.992 2.760

Isla

nd

ed (

s) F0 line(6) N/A DNO 0.195 0.635 2.889 2.724

F1 line(6) mid N/A DNO 0.195 0.634 2.879 2.725

F2 line(8) N/A DNO DNO 0.626 2.820 2.760

F3 line(10) mid N/A DNO DNO 0.360 2.676 2.760

4.3.2 MATLAB Calculations

Table 9 and Table 10 show the MATLAB predicted fault currents seen by each relay and

the comparison with the current results from PowerFactory for both networks when

islanded.

Table 9. Test Network Comparison Current MATLAB vs PowerFactory

MATLAB current (A)

PowerFactory current (A)

% difference

R1 0 0 0.0

R2 512 511 -0.2

R3 114 115 0.9

R4 512 498 -2.8

R5 142 141 -0.7

R6 512 498 -2.8

R7 114 115 0.9

R8 512 498 -2.8

R9 512 498 -2.8

R10 142 141 -0.7

R11 256 257 0.4

R12 256 257 0.4

33

Table 10. Hailuoto Network Comparison Current MATLAB vs PowerFactory

MATLAB current (A)

PowerFactory current (A)

% difference

R1 0 0 0.0

R2 57 60 5.0

R3 75 76 1.3

R4 75 77 2.6

R5 60 61 1.6

R6 17 18 5.6

4.3.3 PowerFactory Simulations with Adaptive Relays

The results of the second PowerFactory simulations after the relays have had their

settings adapted for the islanded configuration are shown in Table 11 and Table 12 for

both networks. See Appendix A and B for more information about relays settings used

and the Time-Overcurrent Plots.

Table 11. Test Network PowerFactory Time to Operate with Islanded Settings


Isla

nd

ed (

s)

Line Feeder (T2) N/A N/A 1.321 0.168 1.321 N/A 1.321 N/A N/A 1.321 N/A 0.513

Line(3) Feeder (T6) N/A N/A 1.321 N/A 1.321 N/A 1.321 N/A 0.168 1.321 0.513 N/A

Table 12. Hailuoto Island Network PowerFactory Time to Operate with Islanded Settings

Fault Location R1 R2 R3 R4 R5 R6

Isla

nd

ed (

s) F0 line(6) N/A 2.617 0.297 0.635 4.308 3.512

F1 line(6) mid N/A 2.618 0.296 0.634 4.285 3.514

F2 line(8) N/A 2.621 1.357 0.626 4.152 3.526

F3 line(10) mid N/A 2.629 1.390 0.360 3.832 3.560

34

4.3.4 PowerFactory Simulations with Adaptive Relays and Varying Output Power

The results of the third part with the settings on the relays tested with the power outputs

of the wind turbines at several settings 0%, 25%, 50%, 75% and 100% of rated output can

be seen in Table 13. See Appendix B for more information about relays settings used and

the Time-Overcurrent Plots.

35

Table 13. Hailuoto Network Comparison Current MATLAB vs PowerFactory when Islanded Settings and with a Varying Output

R1 R2 R3 R4 R5 R6

MA

TLA

B

curr

ent

(A)

Po

wer

Fact

ory

curr

ent

(A)

MA

TLA

B

curr

ent

(A

Po

wer

Fact

ory

curr

ent

(A)

MA

TLA

B

curr

ent

(A)

Po

wer

Fact

ory

curr

ent

(A)

MA

TLA

B

curr

ent

(A)

Po

wer

Fact

ory

curr

ent

(A)

MA

TLA

B

curr

ent

(A)

Po

wer

Fact

ory

curr

ent

(A)

MA

TLA

B

curr

ent

(A)

Po

wer

Fact

ory

curr

ent

(A)

Turb

ine

Ou

tpu

t 1

00

% F0 line(6) 0 0 57 60 75 76 75 76 60 58 17 17

F1 line(6) mid 0 0 57 60 75 76 75 76 60 59 17 17

F2 line(8) 0 0 57 60 57 60 75 77 60 59 17 17

F3 line(10) mid 0 0 57 59 57 59 57 58 60 61 17 18

Nominal 0 48 31 13 9 14

Turb

ine

Ou

tpu

t 7

5%

F0 line(6) 0 0 42.75 46 71.75 72 71.75 72 60 59 12.75 13

F1 line(6) mid 0 0 42.75 45 71.75 72 71.75 72 60 59 12.75 13

F2 line(8) 0 0 42.75 45 42.75 45 71.75 72 60 59 12.75 13

F3 line(10) mid 0 0 42.75 45 42.75 45 42.75 45 60 61 12.75 13

Nominal 0 37 19 4 8 11

Turb

ine

Ou

tpu

t 5

0%

F0 line(6) 0 0 28.5 31 68.5 67 68.5 67 60 59 8.5 9

F1 line(6) mid 0 0 28.5 30 68.5 68 68.5 68 60 59 8.5 9

F2 line(8) 0 0 28.5 30 28.5 30 68.5 68 60 59 8.5 9

F3 line(10) mid 0 0 28.5 30 28.5 30 28.5 30 60 61 8.5 9

Nominal 0 25 8 13 23 7

Turb

ine

Ou

tpu

t 2

5%

F0 line(6) 0 0 14.25 15 64.25 63 64.25 63 60 59 4.25 4

F1 line(6) mid 0 0 14.25 15 64.25 63 64.25 63 60 59 4.25 4

F2 line(8) 0 0 14.25 15 14.25 15 64.25 64 60 59 4.25 4

F3 line(10) mid 0 0 14.25 15 14.25 15 14.25 15 60 61 4.25 5

Nominal 0 14 8 25 39 4

Turb

ine

Ou

tpu

t 0

%

F0 line(6) 0 0 0 0 60 59 60 59 60 59 0 0

F1 line(6) mid 0 0 0 0 60 59 60 59 60 59 0 0

F2 line(8) 0 0 0 0 0 0 60 59 60 59 0 0

F3 line(10) mid 0 0 0 0 0 0 0 0 60 61 0 0

Nominal 0 0 19 37 55 0

36

4.4 Discussion

4.4.1 Overview

The results of the experiments revealed several main things. First, the test networks fault

current as expected from the grid are orders of magnitude bigger than the fault currents

produced by the distributed generators, however on the larger Hailuoto Island the fault

current is not as excessively bigger. The second is the inability to set the relays so as only

to trip when experiencing faults and using the same settings for both grid connected and

islanded. Thirdly the selectiveness required of the relays requires more discrimination

than is possible without lots of errors in the primary relays. Errors in this case being false

positives where the relay operates in the absence of a fault.

4.4.2 Difference in Fault Current

The fault current, using the test network in this example, from the grid provided up to

7000 amps on a near to connection fault. This value of fault current is in comparison with

the 380 amps provided from the distributed generators (Table 5) and it should be noted

that this requires that the renewable sources to be operating at maximum capacity. The

Hailuoto Island network while not as severe has a similar response in that the grid can

provide up to 887 amperes when experiencing a fault compared to the reduced 68

amperes provided by the distributed generators (Table 6). This lack of fault current in and

of itself is not new information. Rather a confirmation of the fact that distributed

generators cannot provide the fault currents external grids are able, which is the basis for

this research. Serving to reinforce the notion that traditional pickup current values are

37

not viable and that they need to be adaptive in the case of microgrids with the ability to

be islanded.

4.4.3 Issues due to Lower Fault Currents - Test Network

The lower fault currents, however, resulting in lower pickup currents for the relays

present a new set of problems. The pickup currents required for islanded fault detection

can be lower than nominal current flows under circumstances that are to be expected as

part of normal operation. For example in the test network when grid connected and no

load’s connected to Terminal(5) and Terminal(6) but the distributed generators are

providing full rated output power. The current flowing in the feeder line connecting the

distributed generators to Terminal(1) and Terminal(2), is more than what would be

flowing in the event of a fault on Terminal(1) and Terminal(2). Lower pickup currents

cause the relays operate even in the absence of a fault causing network outages.

Assuming that the relays are set to operate using settings that work under islanded

conditions on a grid connected network as shown in Appendix A.5. If the settings are not

adjusted for the lower fault currents and maintain the traditional settings used on grid

connected systems the relays will not operate if the microgrid is islanded as shown in

Appendix A.3.2 and A.4.2. If they do operate using the grid connected settings certain

relays will operate before they should, causing a need for the relays to have their time

delay setting increased to the point at which they are no longer effective. A simpler

solution is as proposed to have the relays adapt to the network configuration.

38

4.4.4 Issues due to Distributed Generators - Test Network

The changing network, due to the type of distributed generators, places an ever changing

amount of adaption required depending on the fault current seen by the relay and its

subsequent pickup current and settings. The feeder, for example, depending on the

amount of fault current running through it can result in circumstances where the fault

current contribution is less than the max nominal current that can potentially flow

through it. The same goes for the relay 2 at the transformer, the maximum current that it

will normally see is three hundred and eighty amps when grid connected and with no

load. If a fault occurs, the current contribution will be much less as the transformer will

draw a significant amount of current from the external grid causing relay 1 to operate

and disconnect the external grid. Resulting in the relay 2 having a nominal current flow

from the microgrid through relay 2 of zero amps. Thus, reinforcing the notion that the

relays must be able to adapt as quickly as possible and potentially be communicated with

a differing method than over the wire communications as already in place on networks.

As what would be ideal would be the ability of the grid to split into smaller grids to keep a

supply to unaffected areas but would require the microprocessor to be able to update

the relays continually. The updating of the relays is shown to be effective in its ability to

adjust the relays to operate in an appropriate manner. This effectiveness is demonstrated

by contrasting the time to operate seen by the relays when a fault occurs at Terminal(6).

The relays R1, R11, and R9 with settings set for grid connection, when the grid is

connected, operate with the required backup, and discrimination that is necessary see

Appendix A.3.1. However, when the same relays, with the same settings, with the same

fault conditions, but an islanded grid, relay R11 fails to provide backup protection to the

39

primary relay see Appendix A.3.2. The assumption as previously mentioned is that the

Relays R7 and R10 will trip on their overcurrent settings. When setting the relays to

islanded settings for the islanded network the protection provided is much more readily

apparent as seen in Appendix A.3.3. A fault on Terminal(2) illustrates another

circumstance where the use of adaptive relays and the algorithm to provide the specified

pickup currents works. When grid-connected the relay R1 provides back up to R4 as seen

in Appendix A.4.1. When using the grid connected relay settings, and the network is

islanded, the result is that not only does R4 operate but also R12 see Appendix A.4.2. The

operation of R4 and R12 is a favourable outcome with the faulty part of the network

being disconnected to provide protection. The same settings on the relays but without a

fault and the back two distributed generators providing power to the front two loads

cause the relay to trip. Granted this is not a usual occurrence but the adaptive settings on

the relays will cover for it as seen in Appendix A.5. When there is a fault on the

transformer or the line connecting the grid an unusual circumstance arises. If the grid is

connected at the time of the fault, then R1 will operate to disconnect the external grid

from the fault. R1 operating, however, will cause the fault to receive current flow from

the distributed grids and if the relay has been set for the maximum potential current to

allow for power export from the distributed generators, then the current flowing into the

fault will not cause the relay to operate. The high levels of fault current required to

operate the relay are exacerbated more by the fact the generators may not be able to

output their maximum.

40

4.4.5 Algorithm - Test Network

The algorithm predicted the maximum current flows in the test network under islanding

to within 2.8 per cent, with an average difference of 1.4 per cent. Indicating that the

algorithm can make reliable predictions on the state of the network, in relation to the

current flows and generator settings. The data does suggest that if there is an error in the

calculation, it is more likely to be overstating what the maximum current flow is rather

than understating. While this is well within the range of what would be needed to

calculate the settings on the relays, properly, it is difficult to tell which is preferable. As

the increase in higher required pickup current levels, due to the erroneously higher

calculated current levels results in the relays to be delayed in operating. The decrease in

the pickup current required to operate will have the effect of causing the relays to

operate earlier. With the difference in the current levels from normal operating

conditions to fault conditions being so small the likelihood is that the relays will operate

without faults causing widespread blackouts. The very thing the adaptive relay is

designed to help protect the network against. At this stage, it would seem to be

preferable for the algorithm to be slightly over reporting how much current is to be

expected. For as long as the relays will operate, the delay in time to operate is likely to be

of less consequence compared to the disconnection to customers from pickup current

levels being too low.

4.4.6 Hailuoto Island

The discussion has been about primarily the test network thus far, and focus has been on

the way the network reacts, and the relays need to adapt to it. The Hailuoto Island due to

41

its larger size and increased resistance due to the long cable runs, along with its more

linear layout has a different set of problems to face and overcome. The first being that

the fault currents provided by the external grid are much lower than those provided in

the test network. Secondly, the spread-out locations of the wind turbines also increase

the complexity in conjunction with the locations of the relays. Thirdly the linear layout of

the network results in changes in the direction of current flows depending on where the

fault is.

4.4.7 Issues due to Lower Fault Currents – Hailuoto Island Network

The fault currents provided by the external grid as mentioned are reduced due to the

significant length and therefore resistance of the cables feeding the network. Increased

length has a dampening effect on the pickup currents because of copper losses in the

wire. The low levels of fault current from the external grid require that the discrimination

between the relays be made more precise. This increase in precision also has

ramifications for the setting of the relays for islanding as the fault currents from the

previously established wind farms is, when they are running at maximum output,

significantly less than the fault current provided by the external grid. In this instance, the

problem is that setting the relays based on the grid connected settings will cause the

pickup current required for the relay to operate to be higher than the fault current that

can be provided by the wind turbines see Appendix B.3.1.1 and B3.1.2. A large pickup

current setting on the relay will result in the relays failing to function due to insufficient

pickup current. The relays protecting the lines closest to the external grid are therefore

the most in need of adaptive settings as they are the ones most affected by the changing

42

from grid connected to islanded. Relays 3 and 4 must be able to discriminate current

direction along with overcurrent as the external grid provides current through them to

the faults occurring in locations F2 and F3 see Appendix B.3.3 and B.3.4. Directional

protection is functionally able to be furnished by the same relay with differing settings for

forward and reverse. It is also able to be done, as it has been in this project, by having

separate forward and reverse relays. The choice to have separate relays being done for

convenience, as the effect of the either design choice is not seen to have any impact on

the system in question. These relays still need to be able to adapt as the current flows

from the wind turbines when islanded is not to the same level of output as when the

external grid is providing fault current see Appendix B.3.3.1 and B.3.3.2. As seen during

external grid connected faults in locations F2 and F3 relays 2, 3 and 4 are going to be

receiving fault currents from the external grid. During islanded faults at F0 and F1 with

the wind turbines not operating the currents will be coming from the other direction and

in this circumstance, current is being provided by the diesel generator see Appendix B.4.

The relays are shown to need to adapt when experiencing changing outputs from the

wind turbines when islanded. The changing outputs are not required for circumstances

when the external grid is connected to the network as the lack of production by the wind

turbines is made up by being able to draw extra current from the external grid.

4.4.8 Issues due to Distributed Generators (Diesel) – Hailuoto Island Network

It can also be seen that the output of the new distributed generator is not safely capable

of producing enough power to provide power to the entire island as required during a

situation where the external grid is disconnected, and the wind drops see Appendix

43

B.4.0.2. Over-reliance on the diesel generator will force some load shedding to be done

to reduce the burden on the generator and stop it from being disconnected due to

overload protection. However, load shedding is a function that the microprocessor could

perform by its operating of controlled relays. It has not been investigated, but

preliminary observations/work would indicate that it is a distinct possibility.

4.4.9 Algorithm– Hailuoto Island Network

The network was simulated in various states to provide an understanding of how the

network responds to the changing current draw. As seen in Table 13 the output reduction

in the wind turbine power results in an increase in current from the generator and the

external grid. The settings on the relays were tested with the power outputs of the wind

turbines at several settings 0%, 25%, 50%, 75% and 100% output with the algorithm

tested to see if its current calculations are close to what PowerFactory simulates them as

being results can be seen in Table 13. The algorithm predicted the current flows to a

difference of less than 8 percent (disregarding outliers) which allows for confidence in the

algorithm as the percentage difference is so small. The average difference taken across

the entire data is 2.88 per cent. With the large percentage differences coming from low

values of current compared to another low value of current. For example, the MATLAB

script calculated the 25% output from the wind turbine at Hikkuo as being 4.25 amperes

while PowerFactory simulated it as being 4 amperes resulting in a percentage difference

of 15% but an actual difference of ¼ ampere. Compare this to the effect of the diesel

generator’s output being calculated in MATLAB as being 60 amperes and PowerFactory

simulating it as being 59 amperes. The percentage difference being 1.7 per cent while the

44

actual difference is 1 ampere. The largest actual difference in amperes when comparing

the PowerFactory simulations to MATLAB calculations being 3 amperes.

4.4.10 Issues Relating to Communication with Microprocessor and Distributed Generators

When the settings for the relays were assessed, there was a definite problem of a lack of

fault current. This fault current being required to operate traditional breakers. However,

the use of adaptive relays allowed for the issue to be overcome. The relays R2, R3 and R4,

have a distinct need to have their pickup currents reduced not only because of the lack of

fault current from the external grid but from the lack of fault current due to the lack of

power wind turbines can provide caused by the reduction in wind. The effect of wind has

more of an effect on the networks fault current and in turn on the settings for the relays

than the lack of the external grid. The effect varying wind production has, illustrates the

need for information regarding the distributed generators power outputs to be available

for the microprocessor and the diesel generator to be brought online immediately in the

event of isolation from the external grid. As the time taken to bring the diesel generator

online will cause blackouts if the wind drops suddenly. The effect on the time to operate

based on the four faults expected and the change in power outputs of the wind turbines

can be seen in Appendix B.4. Where the effect on the relays, if they are not changed, is

that they fail to operate under islanded conditions and reduced power outputs from the

wind turbines. Adapting the relays using the fault currents calculated from the algorithm

in MATLAB showcases the effect of causing the relays to become operational. Once again

it is worth noting that while preliminary work has gone into the calculation and

discrimination of the relay settings, this is done not using the microprocessor but a more

45

traditional method of calculating each setting before implementation as part of the

design process. Allowing for the configuration for each relay to be pre-set and to be

selected by the individual relay based on the amount of pickup current the

microprocessor calculates that the relay will be experiencing. The calculation of which is

in turn based on the output of the generators and the state of the network if it is

connected to the external grid or islanded. This can be seen in the Table 4.

4.4.11 Issues Relating to Isolation

The relay forming part of the isolation point would not need to be part of the

microprocessor controls as it will not receive any fault current except when the entire

network is connected to the external grid. There may be times however where a fault

occurs past the relay in the external grid that may cause fault currents to flow from the

wind turbines and diesels generator. Resulting in a need for the relay to operate to

disconnect the Hailuoto microgrid and protect it from having a blackout. This current

flowing from the microgrid will not be anywhere near the amount that is typically seen by

the relay and so will require a forward and a reverse setting on the said relay.

4.4.12 Issues due to Varying Output Distributed Generators when Grid Connected – Hailuoto

Island

The effect on the network relay settings when grid connected by the wind turbines is

marginal at best. So much so that whether the wind turbines be at 100% power output or

0% power output the relay settings for pickup currents do not change see Appendix B.2.

46

The relay times to operate, do not vary significantly if at all when simulated at 100% or

0% of wind turbine power output. This is not the case when the network is islanded. The

wind turbines have a decisive impact on the fault current levels and subsequently the

settings that are needed for the relays to operate properly. The effect of power output

becomes most notable when comparing the effect on fault currents when the wind

turbines are set to 100% power output to 0% production. When running at full power the

turbines provide up to 60 amperes under fault conditions, yet when at zero percent or

switched off that number unsurprisingly drops to zero amperes. Between these two

extremes lies a gulf of variance caused by combinations of the six different wind turbines

that operate independently and may experience differing wind conditions or

maintenance programs. Due to this effect care has to be made to make sure any output is

communicated to the microprocessor so as to be able to provide accurate calculations.

4.4.13 Issues due to Varying Output Distributed Generators when Islanded – Hailuoto Island

The difference between the maximum fault current and the nominal current is severely

reduced in absolute terms the less the output of each turbine is. For example, the

difference between the fault current seen by relay 2 during fault conditions with the

nominal current and the wind turbines at 100% is 12 amperes. While under the same

faults but with the wind turbines providing 50% power the difference between the

nominal and any fault currents seen by relay 2 is six amperes as seen in Table 13. The

algorithm has proven itself to be able to calculate sufficiently the maximum currents seen

by each relay, but the relays now need to be able to respond suitably well to be able to

protect the microgrid. The relays need to be able to react to smaller and smaller

47

variances in maximum current flows, and this is only possible if the relays can have

settings that can be updated. This has been simulated by changing the settings on the

relays between the simulations. The settings on at least one of the relays needed to be

changed every time there was a change in the network. Whether that be changing from

grid connected to islanded or from 100% power output to some fraction of. This only

highlights the effectiveness of the technique of adaptive relays as they can be adjusted

and operate with efficacy. The need to be able to distinguish between fault current and

nominal current is even more apparent when considering the effect of reducing the

power output to 0 per cent and islanding the network. The nominal current flow in a

circumstance not unreasonable (faults occur at inopportune moments) exceeds the

current flow in certain fault conditions. This can be seen when the diesel generator is

required to provide current to the loads when the system is islanded; the wind turbines

are disconnected, and the current is drawn only from the generator for all the connected

loads. This current being drawn is higher than the current seen by relays 3 and 4 when

the current is drawn from the diesel generator under fault conditions at F0 and F1.

Indicative of the fact that the relays must be set with regard to the load flows of the

network and not just the current when the system is running at full capacity or islanded.

When the network is islanded and the wind turbines are not generating any power the

relays are notified by the microprocessor that the maximum current that can be flowing

through them is zero amperes. This may present a situation during fault conditions where

the current is increased as the wind turbine increases its power production. The need

would be for the relay to be updated faster than the relay’s time to operate, for the level

of overcurrent it is experiencing. Another issue this raises is during circumstances where

48

a fault has occurred and the wind turbines are slowly ramping up power output from not

producing power, but are now providing power into a fault. A fault that may have been

disconnected from the rest of the microgrid by virtue of the diesel generator being on the

other side of the fault providing fault current but the breakers on the other side not

having any current did not trip. Circumstances like this and the disconnection of the

microgrid via incoming relay operating, show the need for the relays to be isolated and

operated with the microprocessor ensuring that the relay on both sides of a fault is

operating. To make sure that the fault is not fed current as the network topology

changes.

4.4.14 Issues Relating to Communication Methods

The communication methods required have not been investigated yet some inferences

about the type of communication needed can be found. The first being communications

would need to be of a kind that enables the relay to poll the microprocessor continually

and if it does not receive a reply to switch to pre-set conditions. This requires that the

relay has as part of its programming a failsafe state. The second is that power line

communication, along with wired cabling like high performance copper twisted pair or

optical fibre bundled with the power cables, may not be sufficient or desirable. This being

most profoundly obvious when considering the effect of a line going down or nearly any

other type of fault as any disruption to the line results in a loss of communication. To

achieve this would lead to a secondary network of wiring for communications which

would further increase the cost. The use of wireless technologies may provide a cheaper

solution to installing more cabling but would need further investigation. The higher cost

49

in the cabling may be offset in the increased reliability of the network causing lower

economic losses due to outages.

50

Chapter 5: Conclusions

5.1 Overview

The understanding of microgrids and by extension has changed over the previous decade

and a half, but the primary problem of a lack of overcurrent protection has remained

largely unresolved. The solutions put forward in 2002 have not aged well, but this is not

to be cause for concern as technology has advanced now to the point where relays are no

longer limited to electromechanical devices. Modern relays are now ‘smart’ devices

having the capacity to be software controlled allowing for greater functionality including

the capability to be adjusted to suit certain circumstances. However, unlike more

traditional overcurrent protection methods the awareness in how an adaptive relay

would work in a network is not as fully developed nor is the overall knowledge of

microgrids exhaustive.

5.2 Limitations of Microgrids

As networks, have developed to consist of microgrids the requirement to protect the

microgrid and the rest of the grid is imperative. The problem is that as the microgrid is

disconnected from the grid the level of fault current needed to operate traditional relays

is lacking. This is in part a function of the lower power outputs of the smaller sources of

energy, but also the limited number of them. As seen the fault current may be as low as

0.25 of an ampere higher than the nominal current outputted by the wind turbine when

the wind speed is low. These types of low currents and the variation in the output mean

that the relays cannot be set for one current level, as differing values of current will cause

them to fail to operate correctly.

51

5.3 Adaption, Communication and Further Work

The lower fault current requires that differing methods be adopted to allow the correct

operation of the microgrid and that they are protected. Several competing methods have

been suggested in the past but the creation of adaptive relays shows the most promise

and at Hailuoto Island is proved to be a functional system. The adoption of adaptive

relays is not without its problems and shortcomings. Adaption to the lower fault current

is only possible if the lower fault current is known. This may be done by being calculated

beforehand during the design of the system or calculated based on the network in real

time. Whatever way is chosen the relay must be communicating with a central processor

that is updated with every change as it happens so as to be able to be informed about the

status of the network and the distributed generators allowing for the right fault current

level to be set on the relay. High-speed communication is most important when

considering the effect of intermittent, unpredictable and varying power sources that

primarily are renewables like wind and solar have on contributions to fault current.

Further work needs to be done on the type of network technologies used for high-speed

communications with a particular focus on optical fibre, high-performance copper

twisted pair, powerline transmission and wireless technologies gauging their reliability

and cost.

5.4 Updated Algorithm and Further Work

If the state of the network is known, the central microprocessor can then calculate the

prospective fault current allowing the relays to adjust. There are existing methods for

doing this however they were either overly complex or don’t account for variation in the

52

power sources. This report modified a version of the formula proposed by Alexandre

Oudalov and Antonio Fidigatti to allow for the change in load and to create a MATLAB

script that enabled the microprocessor to calculate the fault current. The modified

formula Error! Reference source not found. and the subsequent MATLAB script were

designed to be quick and efficient. Forgoing the extra precision and less reliance on

multiple data points from external sensors for lower latency and speed. The relays being

adaptive allows for the adjustment to the lower current levels in a network during

islanding to provide protection. This report has looked at the relays being a direct

replacement for existing electromagnetic devices and model the time to operate on an

inverse protection curve. However, further investigation could be done on the use of a

more linear response time for relays rather than an exponential decay followed by a step.

Rather more broadly what type of response curve or shape is optimal for modern relay

protection. Investigation could also be done on the mixing of differential relays with

adaptive and even using the current and voltage sensors in the new models of relays to

provide differential protection. Utilising the microprocessor and the communication

network to identify fault locations via the differences between relays in current and

voltage. The formula created and the methodology employed in this report allowed the

current to be calculated to within 2.8 – 8 percent of the simulated value found by using

PowerFactory. Apart from contextual outliers whose actual values of fault current are

significantly lower than other simulated values. In these circumstance the currents

calculated by the formula and methodology were still considered valid as the actual value

difference was deemed insignificant. This was done on two different networks that were

showcased in research done by the University of Victoria and by the real life example on

53

Hailuoto Island. Preliminary work has been done to develop the microprocessor to be

able to calculate the current transform ratio and the time delay setting for each relay as

well as being mindful of the discrimination needed in the network. This future work

would result in the microprocessor being able to adjust the relays completely on the fly

without needing to be pre-calculated settings and allow for new plug and play relays and

power sources.

5.5 Conclusion

Simulating these two networks in PowerFactory enabled the investigation into how well

traditional methods are for protecting the microgrids and unsurprisingly they were found

to be quite poor. The setup for the relays was done allowing for discrimination and based

in the first instance on the grid being connected. When the grid was disconnected from

the microgrid, the relays in some circumstances failed to operate. Allowing the relays

settings to be recalculated using the MATLAB script and adjusting the relays meant that

under all fault conditions the relays would operate with appropriate sensitivity and

discrimination providing proof that not only does the MATLAB script and its associated

formula work so does the adaptive relays for protecting microgrids.

54

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57

Appendix

A: Test Network

A.1 PowerFactory Single Line Diagram – Test Network showing Relay Positions

Figure 5. PowerFactory Single Line Diagram – Test Network showing Relay Positions

R2

R11

R12

R3 R4 R5 R6

R7 R8 R9 R10

R1

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A.2 Relay Settings

A.2.1 Grid Connected

Table 14. Test Network Relay Settings Grid Connected

CTR TDS CS

R1 100:5 2 5

R2 400:5 0.5 5

R3 95:5 0.5 4

R4 100:5 0.5 5

R5 95:5 0.5 4

R6 100:5 0.5 5

R7 95:5 0.5 4

R8 100:5 0.5 5

R9 100:5 0.5 5

R10 95:5 0.5 4

R11 2000:5 0.5 5

R12 200:5 9 5

A.2.2 Islanded

Table 15. Test Network Relay Settings Islanded

CTR TDS CS

R1

R2

R3 95:5 1 4

R4 100:5 0.5 5

R5 95:5 1 4

R6 100:5 0.5 5

R7 95:5 1 4

R8 100:5 0.5 5

R9 100:5 0.5 5

R10 95:5 1 4

R11 200:5 0.5 4

R12 200:5 0.5 4

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A.3 3-Phase Short Circuit Fault at Terminal(6)

A.3.1 Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on

Relays

Figure 6. 3-Phase Short Circuit Fault at Terminal(6) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays

A.3.2 Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

Figure 7. 3-Phase Short Circuit Fault at Terminal(6) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

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A.3.3 Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

Figure 8. 3-Phase Short Circuit Fault at Terminal(6) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

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A.4 3-Phase Short Circuit Fault at Terminal(2)

A.4.1 Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on

Relays

Figure 9. 3-Phase Short Circuit Fault at Terminal(2) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays

A.4.2 Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

Figure 10. 3-Phase Short Circuit Fault at Terminal(2) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

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A.4.3 Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

Figure 11. 3-Phase Short Circuit Fault at Terminal(2) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

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A.5 No Fault – Loads at Terminal(5) and Terminal(6) disconnected

A.5.1 Time-Overcurrent Plot - Grid Connected Network with Islanded Settings on Relays

Figure 12. No Fault – Loads at Terminal(5) and Terminal(6) disconnected Time-Overcurrent Plot - Grid Connected

Network with Islanded Settings on Relays

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B: Hailuoto Island network

B.1 PowerFactory Single Line Diagram – Test Network showing Relay Positions

Figure 13. PowerFactory Single Line Diagram – Hailuoto Island Network showing Relay Positions

R1 R2

R3 R4 R5 R6

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B.2 Relay Settings

B.2.1 Grid Connected

Table 16. Hailuoto Island Network Relay Settings Grid Connected

Relay CTR TDS

R1 150 3

R2 150 2

R3 18 0.5

R3 (rev) 97 0.5

R4 30 1

R4 (rev) 30 0.5

R5 30 3

R6 12 2

B.2.2 Islanded

Table 17. Hailuoto Island Network Relay Settings Islanded

Wind Turbine Output 100%

Wind Turbine Output 0%

Relay CTR TDS CTR TDS

R1 150 3

R2 40 2

R3 30 0.5 30 0.5

R3 (rev) 40 1

R4 30 1 30 1

R4 (rev) 30 0.5

R5 35 3 50 3

R6 13 2

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B.3 Wind Output 100%

B.3.0 No Fault

B.3.0.1 Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays

Figure 14. Wind Output 100% No Fault Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays

B.3.0.2 Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

Figure 15. Wind Output 100% No Fault Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

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B.3.0.3 Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

Figure 16. Wind Output 100% No Fault Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

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B.3.1 F0 - 3-Phase Short Circuit Fault at Terminal(7)


B3.1.1a Relays Grid Side of Fault

Figure 17. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault

B3.1.1b Relays Diesel Generator Side of Fault

Figure 18. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault

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B.3.1.2a Relays Grid Side of Fault

Figure 19. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault

B.3.1.1b Relays Diesel Generator Side of Fault

Figure 20. F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Diesel Generator Side of Fault

70

B.3.1.3 Time-Overcurrent Plot – Islanded Network with Islanded Settings on Relays


Figure 21. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Grid Side of Fault


Figure 22. Wind Output 100% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault

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B.3.2 F1 - 3-Phase Short Circuit Fault Middle of Line(6)



Figure 23. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault


Figure 24. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault

72



Figure 25. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault


Figure 26. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Diesel Generator Side of Fault

73



Figure 27. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays Grid Side of Fault


Figure 28. Wind Output 100% F1 - 3-Phase Short Circuit Fault Middle of Line(6) Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault

74







75





Figure 32. Wind Output 100% F2 - 3-Phase Short Circuit Fault Middle of Line(8) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Diesel Generator Side of Fault

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77







78






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B.4 Wind Output 0%

B.4.0 No Fault


Figure 41. Wind Output 0% No Fault Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays


Figure 42. Wind Output 0% No Fault Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays

81

B.4.0.3 Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

Figure 43. Wind Output 0% No Fault Time-Overcurrent Plot - Islanded Network with Islanded Settings on Relays

82

B.4.1 F0 - 3-Phase Short Circuit Fault at Terminal(7)



Figure 44. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Grid Side of Fault


Figure 45. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Grid Connected Network with Grid Connected Settings on Relays Diesel Generator Side of Fault

83



Figure 46. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Grid Side of Fault


Figure 47. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot - Islanded Network with Grid Connected Settings on Relays Diesel Generator Side of Fault

84



Figure 48. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Grid Side of Fault


Figure 49. Wind Output 0% F0 - 3-Phase Short Circuit Fault at Terminal(7) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault

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92






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Figure 66. Wind Output 0% F3 - 3-Phase Short Circuit Fault Middle of Line(10) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Grid Side of Fault


Figure 67. Wind Output 0% F3 - 3-Phase Short Circuit Fault Middle of Line(10) Time-Overcurrent Plot Islanded Network with Islanded Settings on Relays Diesel Generator Side of Fault

94

C: MATLAB Script

%Call the file named GridRelayState.dat and create an array of the data

called M filename = 'GridRelayState.dat'; M = csvread(filename);

%Set number of relays RelayNum = M(1,2); %Set number of distributed generators DisGenNum = M(1,3); %Set value to begin reading distributed generator current Read_DisGen_Current = 3 + RelayNum; %Set value for loop RelayLoopCount = 1;

%check the boolean condition of the system state GridConnect = M(1,1); if GridConnect == 1 %if Grid is connected disp('Grid is connected, pre-set values used')

else %if Grid is NOT connected while RelayLoopCount <= (RelayNum-1) %Calculate fault current contribution from distributed

generation RelayLoopCount2 = 1; while RelayLoopCount2 <= (RelayNum) DisGenLoopCount = 1; FaultDisGen = 0; while DisGenLoopCount <= (DisGenNum) FaultDisGen = FaultDisGen +

M(Read_DisGen_Current + DisGenLoopCount,2) * M(Read_DisGen_Current +

DisGenLoopCount,3) * M(2+RelayLoopCount2,4+DisGenLoopCount); %add the

current from the current DisGen to the total M(2 + RelayLoopCount2,3) = FaultDisGen; %add

the relay fault current to the array DisGenLoopCount = DisGenLoopCount + 1;

%advance the loop counter by one end RelayLoopCount2 = RelayLoopCount2 + 1; %advance the

loop counter by one end %terminate the loop RelayLoopCount = RelayLoopCount + 1 ; %advance the loop

counter by one end %terminate the loop disp('MircoGrid is islanded, current fault values calculated') end %terminate the if/else

M %display M array to check values csvwrite(filename, M) %write M array to csv file to be used by

PowerFactory

investigation into the protection of microgrids using ... · source, calculate the pickup currents...

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