coordination between conventional and wide area protection ... · abstract title: coordination...

Coordination between conventional and wide area protection for

electrical power systems

DIPLOMARBEIT

Institut für Elektrische Anlagen und Hochspannungstechnik

Abteilung Elektrische Anlagen an der

Technischen Universität Graz

Leiter der Abteilung: Univ.-Prof. Dipl.-Ing. Dr.techn. Lothar Fickert

Betreuung: o.Univ.-Prof. Dipl.-Ing. Dr.techn. Lothar Fickert Dr. Larsson Mats, ABB Privatdozent Dr.-Ing. Christian Rehtanz, ABB

Vorgelegt von: Georg Achleitner

Graz, im Mai 2003

Abstract Title: Coordination between conventional and wide area protection for electrical power systems Keywords: wide area protection system, protection devices, overcurrent protection, distance protection, Modelica, Dymola, simulation This diploma thesis reports an investigation on the coordination between conventional and wide area protection for electrical power systems. The interest was focused on distance and overcurrent protection devices. These two types were rebuilt as very detailed models in the simulation environment Dymola. Both models were included in different realistic network models. Various faults in the network were applied and the effect on the entire network and the relays were observed. Furthermore the interaction of a wide area protection system and the local protection devices were investigated and rules for the implementation of wide area protection systems were found. Kurzfassung: Titel: Koordination von konventionellem und Weitbereichsschutz für elektrische Netzwerke Schlüsselwörter: Weitbereichsschutz, Schutzeinrichtung, Überstromschutz, Distanzschutz, Modelica, Dymola, Simulation Diese Diplomarbeit untersucht die Koordinierung von konventionellem und Weitbereichsschutz für elektrische Netzwerke. Im Mittelpunkt der Untersuchung standen Überstrom- und Distanzschutzrelais. Diese beiden Typen wurden als detaillierte Modelle in der Simulationsumgebung Dymola nachgebildet und in verschiedene realistische Netzwerkmodelle inkludiert. Verschiedene Netzwerkfehler wurden getestet und die Auswirkung auf das gesamte Netzwerk und die Relais beobachtet. Weiters wurde das Zusammenwirken von Weitbereichsschutz und lokalen Schutzeinrichtungen untersucht und Richtlinien für die Implementierung von Weitbereichsschutzsystemen gefunden.

Acknowledgement

This thesis was written during my stay at ABB Corporate Research in Baden-Dättwil in

Switzerland. Many people assisted me with doing this thesis who I would like to thank,

especially the following persons:

Prof. Fickert has been my main supervisor at the Technical University of Graz. He supported

me in the preparation of my stay in Switzerland and produced a lot of good ideas during our

few, but very productive meetings. I also would like to thank him for his visit at Corporate

Research, which gave me the possibility to present my work and introduce him to my

supervisors in the department.

Christian Rehtanz who made this project possible. He arranged everything at ABB and was

my supervisor in the first 3 months. He introduced my to group C6, guided me through the

first and difficult period. Thanks to his happy and encouraged mood, for his readiness to

interrupt his work when I had a problem und to help me. Very often he just listened to me,

gave me an idea and brought me back on track of my work.

Mats Larsson who was willing to accept me as his diploma thesis student after Christian

Rehtanz left the department. He gave me the possibility to get to know a new simulation tool

and was already my „second supervisor“ in the first time beside Christian. In my last time at

ABB he supported me with many ideas, was always prepared to listen to me. Furthermore I

would like to thank him for the activities we joined together during my spare time.

Cherry and Petr, who have been perfect group members, for their help, when I had problems

and for some funny and long evenings, when a social group meeting was arranged.

I want to say thank you to Kirsi, who shared the office at ABB with me for 6 months. She was

a nice and busy colleague and I heard a lot of Finnish, but i was not able to learn a single

word. Peter Walti, who help me a lot to understand the basic of relay technology and for

supporting me, when I had problems due to practical and realistic use of protection devices.

Fatima and Jonas, two other trainees, for their time together in Kantonspital, skiing days and a

lot of fun.

I also would like to say thanks to Martin and Michi in Zürich for the nice hiking tours, dinners

and for showing me the social part of Zürich. Christian for the work he did for me when

something had to be arranged in Graz, Julia for correcting my thesis and Paul who was my

contact person in Linz.

I also say thanks to all my friends at home, who gave me the feeling that they did not forget

me in this time.

I also say thanks to my family for supporting me over the years and who gave me the

opportunity to study and encouraged me to go abroad to get to know also other countries and

people.

Table of Contents

Table of Contents

1 List of abbreviations and symbols..................................................3

2 Introduction ....................................................................................5

3 Protection of Power Systems ..........................................................7

3.1 Overview of protection equipment ......................................................................... 7

3.2 Basic considerations of short circuit faults ............................................................ 8

3.3 Different Types of Protection Relays...................................................................... 9

3.3.1 Overcurrent protection ....................................................................................... 9

3.3.2 Distance Protection .......................................................................................... 12

3.3.3 Thermal overload protection relays.................................................................. 25

3.3.4 Over/underfrequency protection relays ............................................................ 28

3.3.5 Over/undervoltage protection relays ................................................................ 29

3.3.6 Differential protection ...................................................................................... 29

3.4 Wide Area Measurement Systems ........................................................................ 29

3.5 Potential for Interaction WAMS – conventional relays ..................................... 33

4 Simulation tools and –models ......................................................35

4.1 Modelica – Dymola................................................................................................. 35

4.2 Relay model............................................................................................................. 36

4.2.1 The Breaker ...................................................................................................... 36

4.2.2 Overcurrent Relay ............................................................................................ 37

4.2.3 Distance Protection .......................................................................................... 39

4.2.4 Oscillation Detection........................................................................................ 40

4.2.5 Autoreclosing ................................................................................................... 41

4.2.6 Over/Under voltage relay model ...................................................................... 42

4.3 Network models ...................................................................................................... 42

Table of Contents

4.3.1 Line Model ....................................................................................................... 42

4.3.2 Cigrè Nordic 32................................................................................................ 45

4.3.3 A model from South-America.......................................................................... 47

4.3.4 Test Model........................................................................................................ 48

4.4 PSGuard system in Simulink ................................................................................ 48

5 Simulation results .........................................................................49

5.1 Nordic 32 system..................................................................................................... 49

5.1.1 Fault on Line 4021-4042 .................................................................................. 49

5.1.2 Fault on Line 4032-4044 .................................................................................. 53

5.2 South American Model .......................................................................................... 53

5.3 Test System ............................................................................................................. 56

5.3.1 Generator Tripping........................................................................................... 56

5.3.2 Line Fault on Line L1112................................................................................. 58

6 Conclusion and Discussion..........................................................61

Appendix A – Diagrams .....................................................................63

Cigrè Nordic 32 Test System............................................................................................. 63

Fault on Line 4021-4042 .................................................................................................. 63

Fault on Line 4032-4044 .................................................................................................. 69

Appendix B – Source Code.................................................................74

Bibliography......................................................................................114

List of Tables.....................................................................................118

List of Figures...................................................................................119

1 List of abbreviations and symbols Page 3

1 List of abbreviations and symbols

ABB Asea Brown Boveri

CIGRE Conférence Internationale des Grands Réseaux Electriques

DVG Deutsche Verbundgesellschaft e. V.

GPS Global Positioning System

PMU Phasor Measurement Unit

p.u. Per unit

SCADA Supervisory Control And Data Acquisition.

SCTF Study Committee Task Force

UCTE Union for the Coordination of Transmission of Electricity

UFLS Under Frequency Load Shedding

WAMS Wide Area Measurement System

WCSS Western Systems Coordinating Council

WECC Western Electricity Coordinating Council

α Thermal coefficient [K-1]

ρ0 Specific resistance @ ϑ0 [Ωmm2/m]

ϑ Temperature [K]

ϑ0 Reference temperature [K]

ϑ1 Starting temperature [K]

ϑ2 End temperature [K]

ϑU Ambient temperature [K]

ϑ∞ Stationary End Temperature [K]

τ Time constant

A Cross-section of the line [mm2]

a Index characterizing the algebraic function

A0 Line surface [m2]

b Constant characterizing the relay

B

c Specific heat [kJ/kgK]

C Capacity [C]

http://www.abb.com/

http://www.cigre.org/

http://www.dvg-heidelberg.de/

http://www.ucte.org/

http://www.wecc.biz/main.html

http://www.wecc.biz/main.html

1 List of abbreviations and symbols Page 4

d Density [kg/m3]

G Conductance [ Ω

= 1S Siemens]

I Current [A]

I> 1,2 x ILoad [A]

ILoad Maximum Load Current [A]

Ip Continuous load current before the current is increased to ITamb.

k Settable inverse time factor

l Length [m]

L Inductance [H]

m Mass [kg]

P Active Power [W]

p Ip/Ibase

Q Heat quantity [kJ]

R Resistance [Ω]

s = A0/l Line circumference [m]

SIL Surge Impedance Load

t Time [s]

Tamb Ambient temperature

Tbase Temperature under normal operation conditions

Tsc Duration of the short circuit [s]

Ttrip Max. Temperature

V Voltage [V]

X Reactance [Ω]

Z Impedance [Ω]

2 Introduction Page 5

2 Introduction Nowadays it becomes more and more important that electrical transmission lines can be in use

as long as possible and with maximum load. Due to the reason that faults are unavoidable in a

power system, the system has to be restored within the securely shortest time. Therefore

automatical protection systems are necessary, which operate securely, quickly and without the

influence of an operator. Since protection of transmission lines is more difficult than that of

busbars in most cases, transmission lines are in the interest of investigation.

Protection systems of transmission lines are traditionally equipped with protection relays,

which have different requirements. On one hand the relays have to protect the equipment

against physical damage, e.g. overcurrent over a long period, and on the other hand to react

responsibly with regard to the stability of the whole system. Both protective functions are

typically conflicting because long-term voltage instability can cause overcurrent and false

tripping of relays can cause stability problems. This and the different specification of various

networks make it difficult to tune a protection system and make it dependent on the

experience and idea of the planning technicians.

Because of the rapidly growing importance and availability of information technologies new

ways of protecting the power system need to be considered.

A new and interesting approach is using Phasor Measurement Units (PMU) to build up a

Wide Area Measurement System (WAMS). The advantage is to give better overall protection

instead of only local protection provided by traditional systems.

The main task of all these ideas is to protect a system from collapsing or equipment from

being damaged. However the basic principles should be the same for all [1]1:

Secure, selective and fast.

Secure means that the operator has to have the guarantee that a fault is detected and cleared.

The possibility of a failure should be minimized as much as possible.

1 Feier, Fickert „Störungen und Schutz in elektrischen Anlagen“, p3

2 Introduction Page 6

Fault detection and clearance have to be selective. A good protection system will fix the

problem without shutting down a whole system. Only the part concerned, has to be taken out

of service, the rest should be still working.

The idea behind an automated protection system is, that it can react much faster than an

operator. Furthermore it is able to make decisions, which would never or too late be done by

humans. The faster a relay, a machine works, the shorter the outage and the lower the costs of

such an outfall.

This thesis focuses on the coordination between a Wide Area Measurement System and the

traditional, local protection system. The overall theme is to explore the interaction between

distance- and overcurrent protection and the Wide Area Measurement System.

In Chapter 3 an overview of different types of power system protection is given and different

types are described. The emphasis is on the use of distance protection and on the problems,

which are related to distance relays.

The second part in this chapter is to introduce a Wide Area Measurement System (WAMS), in

particular the PSGuard of ABB and to show some possible interaction between conventional

protection systems and WAMS.

The simulation-tool used is presented in chapter 4. In this part the used models of the relays

are described and problems are illustrated. The used network models are explained.

The simulation results are discussed and solutions are given in chapter 5.

In chapter 6 the results will be discussed and some perspective for further work will be given.

3 Protection of Power Systems Page 7

3 Protection of Power Systems

3.1 Overview of protection equipment

Relay (possible time settings)

Generator • Differential protection: very fast (0.1-0.5 sec)

• Stator: overcurrent protection

• Rotor: excitation protection both winding protection

• Unbalanced protection (1-2000sec)

• Synchronism – check

• Over/undervoltage protection (0.05-2 sec)

• Power flow direction protection (Turbo generators can

work as motor)

• Earth fault (5 sec)

• Over/underfrequency protection (0.05-1sec) Busbar • Differential protection (0.05-1sec)

• Overcurrent protection (0.05-10sec)

• Voltage surge protection

Lines • Distance protection (0.05-5sec)

• Overcurrent protection (0.05-10sec)

• Earth fault protection (5sec)

• Overload protection (0.5 – 10sec)

Transformer • Differential protection (0.05-1sec)

• Overcurrent Protection (0.05-10sec)

• Overexcitation protection

Load

• Over/under voltage protection

• Overcurrent protection

• Overexcitation protection (0.2-10sec)

Table 1: Overview of Protection [2], [3], [4]


In the following parts the overcurrent, the over/undervoltage relay and especially the distance

protection are described more detailed.

3.2 Basic considerations of short circuit faults

There are different reasons for short circuits having to be cleared very quickly. One is

transient stability which requires rapid clearing in order to avoid unstable operation points,

another reason is that the lines and cables have only limited potential to absorb a lot of

energy. Because of the normally short duration of a fault it can be assumed that there exist

neither heat radiation nor heat conduction. The starting temperature will be set equal to the

maximum operation temperature. The following equations show the relation between current

and temperature. [5]1

( ) ϑdmcdtRtIdQ sc ⋅=⋅⋅⋅= −32 10 (3-1)

( )[ ]AlR 00 1 ϑϑαρ −+= (3-2)

dAlm ⋅⋅= (3-3)

When 3-3 and 3-2 are inserted in 3-1 the following expression is given:

( ) ( )( )∫ −+

−+=

sct

sc dcdtA

tI

0 01

02

0

2

11

lnϑϑαϑϑα

αρ (3-4)

Q Heat quantity [kJ] Isc Current [A] R Resistance [Ω] m Mass [kg] c Specific heat [kJ/kgK] ϑ Temperature [K] ρ0 Specific resistance @ ϑ0 [Ωmm2/m] α Thermal coefficient [K-1] l Length [m] A Cross-section of the line [mm2] d Density [kg/m3] ϑ0 Reference temperature [K]


ϑ2 End temperature [K] tsc Time of Short Circuit [sec]

1 Muckenhuber, ”Elektrische Anlagen“, p 1.2.3


The problem during a short circuit is that the energy, which is stored in a very short time,

cannot be delivered to the ambient air. The equipment will therefore be heated more and more

and will eventually be destroyed or will loose a lot of its lifetime.

3.3 Different Types of Protection Relays

3.3.1 Overcurrent protection

There are three different types of overcurrent protection relays; short circuit, earth fault and

overload. The operation principle for all three applications is based on the comparison of the

current seen by the relay with a pre-set value. [6]1

Overcurrent relays are the simplest and the least expensive but the most difficult to apply. It is

not easy to coordinate a large number of relays only by time settings. If also different relay

characteristics can be chosen the coordination can become a challenge. That is one of the

reasons why overcurrent relays are normally only used as a backup protection or in

distribution networks which have a radial structure in most cases.

Due to the fact that in this thesis only short circuit relays are used for simulations, only these

relays will be described in detail.

3.3.1.1 Short circuit overcurrent relays

The line current is the only input variable for these relays and such a relay works

independently of the direction of the current. If direction detection is necessary the voltage

has to be added as a second input.

One group of overcurrent relays has a constant time–current independent characteristic the

other one has a current-dependent trip characteristic.

The choice of a specific characteristic has more or less traditional reasons. In Europe a current

independent characteristic is widely used, in America it is more common with current

dependent characteristics. [7]2

1 Jonsson: „Line Protection and Power System Collapse”, p. 9 2 Gremmel Hennig: ”ABB Taschenbuch - Schaltanlagen”, p 714


Current dependent

Current independent

Operating

time [s]

Current [I]

Figure 1: Overcurrent Trip Characteristic

One problem is to choose the type of relay. The other one is to coordinate the relays in a

network.

R1 R2 R3

R1

R2

R3

Operation time [s]

Current [A]

Figure 2: Coordination of Overcurrent Relays


The operation current of the relays has to be larger than the maximum current during normal

conditions, to avoid unnecessary trips. The relays must have current settings which give a

secure tripping for the following station and at least such settings that the relay trips as a

backup protection for the next line if there is a short circuit at the end of the longest following

line. To get selectivity the tripping time is set shorter for relays located close to the load, and

longer for more distant loads. Short circuits with large fault currents will therefore exist

longer than ones with small currents. This is unsatisfactory because the settings have to be

done not only to protect the equipment from being damaged but also to keep the connected

network stable. [8]1

In case of meshed system configurations it may be impossible to find correct settings for

overcurrent protection that achieve selectivity in the network. In this case the overcurrent unit

has to be equipped with a directional element and is then called “directional overcurrent

protection”. Even with these relays it can be difficult to find a clever and good way to gain

selectivity in a network.

One possibility would be to use directional overcurrent protection with a current dependent

relay characteristic. If all relays have the same settings, the relay with the highest measured

fault current will trip first. It can be assumed that this is the right relay because the fault

current becomes higher the closer it is located to the fault.

However short circuit relays are rarely used on the transmission level and will therefore in

this theses only be used as a backup protection.

3.3.1.2 Earth fault protection relays

Under normal condition a power system is usually balanced and the residual currents are

small. During an earth fault the balance is disturbed and the residual currents increase

significantly. Thus the zero current can be used to detect this type of faults and it will also be

insensitive to the load current.

This type of protection in combination with overcurrent protection will be preferable in non-

solid grounded system, however in other networks distance protection will do this work.

1 Arnesen O., Faanes H.: „Elektriske Kraftsystemer Del2”, p. 194


3.3.2 Distance Protection

Distance protection is the most widely used protection system in transmission networks. The

most accurate form of comparison for relay quantities is to compare the current entering a

circuit with the current leaving it. For many transmission circuits, because of the line length, it

is costly to compare the currents at the two ends of the line since this requires communication

circuits that are at least as long as the transmission line. Therefore distance protection of

transmission lines is a reliable and selective form of protection for lines where the line

terminals are relatively far apart. [10]1 However in some applications communication lines are

used to speed up the fault clearing time [11], a progress becoming more and more common.

3.3.2.1 Operating principle of distance protection

Definition of distance protection [12]2:

“Distance protection is a time coordinated protection

system, which is dependent of the resistance and the direction

of the energy flow. The tripping time increases stepwise

with the increase of the distance between the relay and the fault location.”

Distance protection is working by measuring the impedance of the line. During normal

conditions the impedance seen by the relay is very large.

IUZ= (3-5)

Z Impedance [Ω] U Voltage [V] I Current [A] If a fault occurs, only the impedance of the line up to the fault point and the fault resistance

will limit the current. Both are very small in comparison to normal conditions and as a result

the current will increase. With the measured current and voltage the relay calculates the

resulting resistance and reactance. If these values are smaller than the known and stored data

of the line, the fault has to be in the protected area and the relay will work.

1 Anderson P.M: „Power System Protection”, chapter 11, p. 379 2 Siemens, „Elektronische Netzschutztechnik“, p. 5.1


Figure 3 shows the R-X diagram in principle. The area around the line impedance is

necessary, because the fault resistance is not known and can vary from failure to failure.

Line impedance

Zone1

jX

R

22

1

Figure 3: R-X diagram for a distance relay (MHO-Relay)

The normal operating point would be far to the right (point 1 in Figure 3) while during

disturbances this point moves to or into the tripping characteristic (point 2 in Figure 3).

One has to be aware that there is always an uncertainty in the measured parameters. The line

parameters are changing due to load conditions, environment influence and compensations

installations. The measuring transformers have a certain percentage of inaccuracy and

additionally the relay itself has some inexactness.

In Figure 4 a typical distance protection scheme is shown. It can easily be seen, that the relay

is working as the primary protection for “its own” zone, and as a backup for the next lines.

The coordination is achieved by different time delays.


R1 R2 R3

Length

Time

T1

T2

T3

T4

Zone 1 Zone 1 Zone 1

Zone 2 Zone 2 Zone 2

Zone 3

Zone 4

Zone 3

Figure 4: Principle of Distance Protection

The first zone of Relay 1 should cover about 80-85% of the first line without any time delay.

Due to the above-mentioned inaccuracy of the line parameters and an additional fault

resistance the first zone cannot protect the whole line length. The second zone has to work for

the remaining 20% of the line and as a backup for Relay 2. The third zone of Relay 1 has to

be the backup for Relay 2 and 3. Hence to a fault on Line 2, between Relay 2 and Relay 3, not

only R2 will see the fault but also R1. In this case R2 should trip the line, because it will

detect the failure in its first, at least second zone. Relay 1 also detects a fault, but in the

second or even third zone and has to wait too long to get the chance to take the line out of

operation.

In practice the second zone will cover 80-120% of the first line and is called overreach

protection zone. Its duty is to protect the end of the line and the connected busbar.

Zone 3 is typically set to cover about 120% of the longest adjacent line.

More than 3 zones are becoming very difficult to handle in a meshed network and are

therefore used very rarely However the fundamental idea of zone 3 is to provide 100% remote

back-up protection to all adjacent circuits and also to be discriminative in time with zone 2 of

all adjacent circuits. [6]1

1 Jonsson: „Line Protection and Power System Collapse”, p. 9


3.3.2.2 Overview over the basic types of distance relays

This section gives an overview of the 6 basic types of distance relays [13]1:

TRIP ZONE

NO TRIP ZONE

jX

R

jX

R

R

jX

R

jX

Zone 3

Zone 2

Zone 1

R

jX

Zone 3

Zone 2

Zone 1 R

jX

a) Impedance characteristic b) Mho characteristic

c) Offset mho characteristic d) Self-polarized mho and reactance characteristic

e) Quadrilateral f) Lenticular

Figure 5: Basic types of distance relays

a) Impedance. The disadvantage of this relay is that it is not directional. It is also very

sensitive to load encroachments and power swings.

b) MHO. To avoid the problems of the impedance relay the origin was moved to the

first quadrant to get a directional relay.

c) Offset MHO. This relay provides better protection for close-in faults.

d) Reactance. This relay measures only the reactive component of the impedance.

e) Quadrilateral. Numerical relays have a quadrilateral characteristic where the reach

can be set independently in resistive and reactive direction. An example is the ABB

REL 5xx relay group, or ABB REL 316*4.

f) Lenticular or Ellipse. To provide less sensitivity to load.

1 “IEEE Guide for Protective Relay Application to Transmission Lines”, p40-41


Figure 6 shows the relay characteristic of a state of the art distance relay. This relay has the

ability to fulfil different functions. It has not only a normal but also a reverse zone detection

to protect a certain part “behind” the relay and a characteristic which obstructs load

encroachment.

Figure 6: Distance function characteristic [9]1

1 ABB, „Numerischer Leitungsschutz Type REL 316*4“, p. 3.5.2-36

Underimpedance Characteristic

Zone 3

Zone 2

Zone 1

RLoad

Reverse zone

Overreach zone

Load angle


3.3.2.3 Oscillation Detection

Figure 7: Oscillations in a 2-machine network [9]1

In large power systems it can happen that one part starts to swing against each other because

of large changes in load or changes in power system configuration caused by load changes or

clearance of faults. As the rotating masses try to find a stable point, they oscillate with

damped oscillation until they find a stable operating point. [15]2

These oscillations cause changes in phase and amplitude of voltage difference between the

different parts of the network and cause changes in the power flow between the swinging

parts.

If such an oscillation reaches an unfavourable operation point (high current, low voltage) the

tripping characteristic of the relay will be reached and can lead to unwanted trigger of the

relay because distance relays see such oscillation only as a swing of the measured impedance.

To avoid such problematic operation conditions, oscillation detection has been implemented

in most of the relays.

1 ABB, „Numerischer Leitungsschutz Type REL 316*4“, p. 4-40 2 ABB, “Application Manual Rel 511*2.3”, p. 125


The operating principle of the oscillation detection is very simple:

jX

R

Rout

Impedance locus at power swing

Rin

Xin

Xout

t

Figure 8: Oscillation Detection

The method uses the feature that the change of the impedance is slow in comparison during a

short circuit fault. If the speed of the change is lower than a 6-Hz-power swing, the detection

logic decides that it has to be a power swing, and the relay will not operate.

Two limits are introduced. The time it takes to cross the area between the outer and the inner

line is measured. If the timer exceeds the pre-set value, the tripping function will be blocked

for a certain time (normally a few seconds). Due to the reason that the first swing is normally

slower than the following ones, the time is set to 45ms. [15]1

Another possibility to detect oscillations is described in [9]2. As can be seen in Figure 7 the

voltage changes and therefore also the angle between U and I. This feature is used to detect

oscillations. If there are several changes of U x cos(ϕ) in a short time period the relay will

receive a block signal. Oscillations up to 6 Hz will be detected.

1 ABB, “Application Manual Rel 511*2.3”, p. 133 2 ABB, „Numerischer Leitungsschutz Type REL 316*4“, p. 4-41


3.3.2.4 Theoretical background of distance protection

New relays measure the failure impedance in the positive system independent of the type of

the short circuit. The positive (+) and negative (-) sequence impedance are considered to be

the same for the line. [8]1

A detailed introduction to symmetrical components can be found in [10].

32πj

ea = (3-6)

( )3210 31 UUUU ++= (3-7)

( )32

2131 UaUaUU ⋅+⋅+=+ (3-8)

( )322

131 UaUaUU ⋅+⋅+=− (3-9)

−+ ++= UUUU 01 (3-10)

−+ ⋅+⋅+= UaUaUU 202 (3-11)

−+ ⋅+⋅+= UaUaUU 203 (3-12)

In the following, one, two and three pole short-circuits are described

1 Arnesen O., Faanes H.: „Elektriske Kraftsystemer Del 2”, p. 200


Relay

1

2

3

Z+ , Z- , Z0

I1I2I3

U1U2U3

Figure 9: In principle the connection of a distance relay

The next equations and considerations refer to Figure 9

a) Three pole short circuit:

+++

===ZUI

ZUI

ZUI 3

32

21

1 ,, (3-13)

13

13

32

32

21

21

3

3

2

2

1

1

IIUU

IIUU

IIUU

IU

IU

IUZ

−−

=−−

=−−

====+ (3-14)

b) Two pole short circuit

+−+

−=

+−

=−=Z

UUZZUUII

22121

21 (3-15)

21

21

1

21

2 IIUU

IUUZ

−−

=−

=+ (3-16)

c) One pole short circuit (grounded in starpoint)

( )0

11

31 ZZZ

UI++

=−+

(3-17)

01 333 IIII === −+ (3-18)

−+ = ZZ ; +≠ ZZ0 (3-19)


( ) ( )++−+−−++ −+++=++= ZZIZIIIZIZIZIU 000001 (3-20)

−+=

+

+++ Z

ZZZIZIU 0

011 (3-21)

kZ

ZZ30 =

−

+

+ (3-22)

01

1

3IkIUZ+

=+ (3-23)

+→= XX )52(0 ; +→= RR )65.1(0 ; ++ →= RX )202(

Parameter k varies from 1/3 to 4/3 depending on the tower-configuration.

For all fault scenarios the fault resistance has to be taken into account. Warrington gives the

following formula for the resistance of an arcing fault [14]:

305.08750

4.1arcl

IR = (3-24)

larc Length [m] of fault I Current [A]


3.3.2.5 Examples which can cause problems to distance relays

In this section 3 examples will be given which illustrate problems related to distance relays

and their settings.

3.3.2.5.1 Current infeed

It can cause problems for the measurement of the relay, if an infeed exists on the following

bus. This will increase the measured impedance of the relay.

ZAB ZBC

R1

A BC

IAB IBC

IDB

D

ZBF

F

Figure 10: Current infeed

( )BF

AB

DBAB

AB

BFABDBABAB

AB

R ZIIZ

IZIIIZ

IUZ

++=++== 11 (3-25)

The impedance will increase with the term AB

DB

II

. The bigger the infeed the bigger the

aberration.


3.3.2.5.2 Current outfeed

ZAB ZBC

R1

A BC

IAB IBC

IBD

D

Figure 11: Current outfeed

( )BF

AB

BDAB

AB

BFBDABABAB

AB

BFBFABAB

AB

R ZIIZ

IZIIIZ

IZIIZ

IUZ

−+=−+=+== 11 (3-26)

The impedance will decrease with the term AB

BD

II

. The bigger the outfeed the smaller the

measured impedance.

3.3.2.5.3 Double lines

ZAB ZBC

R1

A B C

IAB1 IBC1

ZBF

F

IBC2

D

ZCD

IAB2

R2

Figure 12: Double line


a) IAB2 = 0

BF

BFBC

BC

BC

ZZZ

II −

=2

2

1 (3-27)

12 BCABBC III −= (3-28)

With equation 3-27 and equation 3-28 follows:

−=

BC

BFABBC Z

ZII2

11 (3-29)

BC

BFABBC Z

ZII22 = (3-30)

BC

BFBFAB

ABR Z

ZZZIUZ

2

1 2 −+== (3-31)

The problems start with the settings of Zone2. The relay should cover 120% of the first

line, thus 20% of the following line, the measured impedance in the case that the fault is at

20% of the Line BC (ZBF = 0.2 x ZBC) will be:

BCABR ZZZ 36.01 +=

Therefore the settings of Zone 2 and 3 have to be chosen very carefully, so that there is no

interaction with other relays, specially, if there are more lines than the double line

connected to e.g. Bus B in Figure 12.

b) Assumption that the two Lines AB are identical and therefore IAB2 = IAB1

12 BCABBC III −= (3-32)

BC

BFBFAB

ABR Z

ZZZIUZ

2

12

4 −+== (3-33)

In comparison with equation 3-31 and the example given above, it can easily be seen that

the measured impedance will increase much more because of the infeed from the parallel

Line AB.


A short example:

We assume that all lines are identical and have a resistance of 10 Ω and there is a fault at

busbar C which has a very small impedance in relation to the line impedance and

therefore it is neglected. We look at the Relay R1.

Scenario1 – Line AB2 is out of operation:

The Relay would measure a fault resistance of 15 Ω.

Scenario2 – All lines are in operation:


Scenario3 – Line BC2 is out of operation:


The example is meant to show that it is difficult to find a good solution for the settings of

a distance relay in meshed networks when the relay should be used as reserve protection

for the adjacent lines.

3.3.3 Thermal overload protection relays

Overload protection relays have to protect the equipment from overcurrent for too long.

Overcurrent over a certain period can exceed the limits. The heat dissipation of overhead lines

is so good that overload protection is rarely used. Under normal conditions it would not be

possible to run the line at the heat limit with respect to the ensuing voltage drop.

Overload of lines is not a matter of seconds but minutes or hours. Therefore all mechanisms

cooling and heating the line are working: radiation and conduction respective the loss of the

line and sun radiation.

If the radiation is neglected, the heat balance is [5]1:

( ) dtAkdcmdtRIdQ Uϑϑϑ −⋅+⋅⋅=⋅= 02 (3-34)

1 Muckenhuber, ”Elektrische Anlagen“, p 1.2.1


From (3-34) follows:

∞=+ ϑϑϑτdtd (3-35)

with:

20

2

IkAsAdcαρ

τ−

⋅⋅= (3-36)

( )2

0

200 1

IkAsIkAs U

αραϑρϑϑ

−−+

=∞ (3-37)

the general solution is:

τϑϑt

ec−

∞ ⋅−= (3-38)

and the particular one:

( )

−−+=

−

∞τϑϑϑϑt

e111 (3-39)

The relation for the end temperature is:

( )( )00 1 ϑϑα

ϑϑρ −+

−=

∞

∞ UkAsI (3-40)

and the equation for the time is:

1

lnϑϑϑϑτ

−−−=

∞

∞t (3-41)

Q Heat quantity [kJ] R Resistance [Ω] ρ0 Specific resistance @ ϑ0 [Ωmm2/m] I Current [A] m Mass [kg] A Cross-section of the line [mm2] c Specific heat [kJ/kgK] α Thermal coefficient [K-1] l Length [m] d Density [kg/m3] ϑ Temperature [K] ϑ0 Reference temperature [K]


ϑ2 End temperature [K] ϑU Ambient temperature [K] ϑ∞ Stationary End Temperature [K] τ Time constant s = A0/l Line circumference [m]


The maximum load current may not be higher than the maximal allowed operation current.

(The maximum operation temperature must not be higher than the maximum allowed

temperature ϑ∞ ≤ ϑB)

( )( )00 1 ϑϑα

ϑϑρ −+

−=≤B

UBall

kAsII (3-42)

The overload protection works similar to the overcurrent relay. It has also the current as input

and waits a certain time until it trips the line.

For example the ABB-Relay 5111 uses the following equation, which is very similar to 3-41.

base

ambTrip

base

base

TTT

II

pI

I

t−

−

−

= 2

22

lnτ (3-43)

p is Ip/Ibase Ip is continuous load current before the current is increased to I Tamb. [A] Tamb is ambient temperature [K]. TTrip max. temperature [K] Tbase temperature under normal operation conditions [K]

The ambient temperature influences the conductor and insulation temperature. Since it is the

actual temperature and not the temperature rise, that damages the equipment, ambient

temperature compensation is used with most thermal protection relays. In addition the settings

of the relay have to be adapted continuously because of changing weather conditions.

Therefore it can become necessary to equip some parts of the line with additional sensors to

get actual reference points. [5]

Overload relays have to operate correctly under all conditions. Their time settings will set so

long that there is no problem due to transient stability but they may operate during long-term

voltage stability.

However it could be important to have the possibility to overload a line for a longer period to

avoid a total blackout because some damages on the line could be cheaper than to have a total 1 ABB, “Application Manual Rel 511*2.3”, p. 294


breakdown of the network. This could be done by external signals or adaptive relaying. If

investigations show that problems due to overload relays can cause major problems, one

should abstain from using such relays.

3.3.4 Over/underfrequency protection relays

The frequency of a power system will change if the load-generation equilibrium is disturbed.

If the state of imbalance is caused by a deficiency of generation, the frequency will decrease

until a new balance between load and generation is established. If there is too much

generation in comparison to the load, the frequency will increase.

To avoid damage to the generation-equipment and to avoid frequency instability, certain

protection mechanisms are included in power systems.

Overfrequency relays will be used for generator shedding in case of too much generation.

The settings vary from network to network. (e.g.: WECC .: 61,7 Hz @ 60 Hz normal).

Underfrequency load shedding (UFLS) will be necessary to restore a network from low

frequency. It will stepwise increase the amount of shed load. For smaller disturbances, the

amount will be smaller and the time delay from recognition to trip will become shorter than

for larger ones.

The recommendations for the relay’s settings differ from network to network. In Europe for

example the first actions have to be taken at 49 Hz, before other regulations should work.

[16]1

Network (country) Nom. Frequency [Hz] First action [Hz] Minimal Frequency [Hz]

UCTE 50 49 47.5

WECC 60 59.4 56.4

Brazil 60 58.5 57.3

Australia 50 49 46.7

Thailand 50 49 47.9

Canada 60 58.5 56

1 UCPTE, “Summary of the current operating principles of the UCPTE”, p. 24


Tasmania 50 47 44.8

Ireland 50 48.5 48

Table 2: UFLS in different networks [16], [17], [18], [19]

For security reasons power plants will automatically disconnect at 47,5 Hz. Operation below

this frequency is endangered (vibration, loss of capacity in the auxiliary gear, …). [20]1

3.3.5 Over/undervoltage protection relays

Over/under voltage protection systems are very similar to over/under frequency protection.

The voltage at the line end depends on the voltage drop on the line and therefore on the load.

The voltage has to be kept in certain limits. Overstepping these limits can be caused by an

abnormal operation situation or faults. Overvoltage is mainly a reason of problems with

voltage regulations of generators or bad reactive power control. Undervoltages are caused by

short circuits or high demand for reactive power.

3.3.6 Differential protection

The idea of the differential protection is to measure the sum of the currents flowing in a point

and the current leaving this one. If the balance is ok, the protection system will not react. If a

fault occurs, the protection unit detects that the sum of all currents is not zero any more and

will therefore open all the connections to the protected part. Normally this system is used to

protect short line or busbars where communication lines are short and affordable.

3.4 Wide Area Measurement Systems

The WAMS is a new possibility to monitor the network by using Phasor Measurement Units.

The PMUs measure the amplitude of the voltage, the current and the angle. These data are

transferred to a central computer, the so-called “PSGuard” System.2 The big advantage of this

system is, that all measurements get a time stamp by a GPS (Global Positioning System)-

Signal. Therefore the System knows which data belong to which dataset even if the

transmission time of one signal is longer than the other one (See Figure 13).

1 9th Meeting of the European Electricity Regulatory Forum, UCTE Paper, p. A1-22 2 http://www.abb.com/global/abbzh/abbzh254.nsf/viewUNID/E3091E26E4DC972EC1256B98002BB004


Wide Area Measurement Systems can increase [21]

• the power transmission

• the system reliability, or

• both in combination.

p

ABB

PSGuard

System

Protection

Center (SPC)

High Voltage

Transmission Network

PMU

Re

U2

I2

U1

U3

I1I3

Im

Re

U2

I2

U1

U3

I1I3

Im

Re

U2

I2

U1

U3

I1I3

Im

Re

U2

I2

U1

U3

I1I3

Im

PMU PMU PMU

PMU

Re

U2

I2

U1

U3

I1I3

Im GPS

Satellite

PSGuard

System

Protection

Center (SPC)

Figure 13: PSGuard

Furthermore the requirements for a wide area protection system are [21]:

• Dynamic measurement and representation of events

• Wide area system view

• Coordinated and optimized stabilizing actions

• Handling of cascaded outages.

The big advantage of PSGuard is, that it provides a very simple state estimation.

For the state calculation the weighted least squares algorithm (WLS-algorithm) using phasor

measurement units is used. [22], [23]

Assume an electrical network with N busses and K connections between the nodes. For each

connection which connects the bus i and j, the following equation holds: KK ,,2,1 K∈


( ) ( )( ) ( ) ikjjkkijkjjkjk

jkiikkjikiikik

UYUYYUUYUYIUYUYYUUYUYI

−+=−+=

−+=−+= (3-44)

h( )X z

v

Figure 14: Model for state calculation

( ) vxhz += (3-45)

The measurement relationship between the voltages (state of the system) and the connection

currents is linear when PMUs are used. This yields:

vxHz += (3-46)

The mathematical formula of the optimisation problem is:

( ) ( ) ( )xHzWxHzxJ T

x−−=

21min (3-47)

W is the inverted covariance matrix. All measurements are assumed to be independent.

The solution of equation 3-46 can easily be derived as:

( ) zWHGzWHHWHx TTT 11 −−== (3-48)

with

[ ]TNi IIIIUUUz 11111 γδβα LLL= (3-49)

The Greek letters denote the starting and ending point of the connection. And H can be

written as

=

BI

H (3-50)

I identity matrix of dimensions [NxN]

B build out of equation 3-44 with respect of ordering of currents and voltages, and the

admittance parameters of the connection.


The advantage of this calculation:

• Solution is only a simple matrix equation

• Matrix G can be computed offline

Furthermore PSGuard provides the possibility for

• Topology detection of the network

• Transient voltage stability prediction

• Frequency stability

• ….


3.5 Potential for Interaction WAMS – conventional relays

Table 3: Possible Interaction WAMS - relays
Fewer problems Possible problems


In Table 3 dark grey areas symbolize possible problem areas. Light grey parts should not

cause any problematic interaction between the protection relay and the WAMS.

In the Table a short explanation of the reasons for some interactions and also the time are

given.

Overload protection was considered as not so important because of the reasons described at

the end of section 3.3.3.

Frequency relays have been already included in the simulations in the context of load

shedding.

The simulations in this thesis are focusing on overcurrent and distance protection. These two

protection systems are the most widely used types of protection for transmission lines.

Therefore the interest was to focus on problems which can be caused by local protection.

Furthermore interferences between PSGuard Protection System and local protection should be

detected and solutions for avoiding such problems should be found.

4 Simulation tools and –models Page 35

4 Simulation tools and –models This chapter gives a short introduction to the simulation tool, explains the simulation models

and presents the used network models.

4.1 Modelica – Dymola

The used simulation tool in this thesis is Dymola (Dymosim AB, Lund, Sweden). Dymola is a

graphical editor and translator for the object oriented language Modelica.

Modelica is an object-oriented language for modelling of large, complex and heterogeneous

physical systems. Models are described by using differential, discrete or algebraic

equations. [24]

It supports also non causal modelling which makes it in addition to the object oriented

concept very powerful to simulate for example power lines that are very cumbersome to

model using block-orientated languages as Simulink (Mathworks Inc., Natick, USA). [25]

Dymola was chosen because it was much easier to simulate breaker actions, than in Matlab

(Mathworks Inc., Natick, USA) or Simulink. The breaker logic was very easy to implement

by using state-machines and the possibility of object-orientated programming made it simple

to combine different modules.

In power system models of the simulation tool all voltages and currents are described with

their phasors:

ba jiiI += (4-1)

ba jvvV ++= 1 (4-2)

The connection pin (one node in the network) is defined as followed:

01

=∑=

j

kkI (4-3)

jVVV === .......21 (4-4)

For a more detailed description of the parts of the network models see:

Online Documentation of the Library “ObjectStab” or [25].

http://www.dynasim.com/

http://www.modelica.org/

http://www.mathworks.com/

http://www.modelica.org/library/ObjectStab/docu/ObjectStab.html


The power system represents a star grounded, three phase balanced network. The faults are

three-phase low impedance earth fault.

The influence of the measuring transformers on the Relays is neglected.

4.2 Relay model

Figure 15: Distance Relay (Screenshot)

In the simulation environment a relay model was developed. It includes an overcurrent

protection, a distance protection, an oscillation detection and has the possibility for

Autoreclosing. In the following each part is presented separately.

Additionally, when a trip signal arrives from one part of the protection system, a short time

delay is included, which should simulate the opening time of the circuit breaker. The opening

time was set to be 50msec.

An oscillation signal from Oscillation Detection only blocks the tripping signal from the

distance protection, but not from the overcurrent protection. [9]

Overcurrent protection exists also as a standalone relay model. Furthermore an

over/undervoltage protection relay exists, which is described in 4.2.6.

4.2.1 The Breaker

It was not possible to set the current over the breaker to zero, when the breaker should be

open. This would lead to an unsolvable Jacobian Matrix. Therefore the current over the

breaker was set to be very small. 1e-5 p.u. was small enough to get acceptable simulation

results.


4.2.2 Overcurrent Relay

In the overcurrent relay time inverse and time constant trip characteristic were applied.

The relay has the current as input, the measured impedance and a so-called “direction” signal,

which gives information about the direction of the power flow.

The direction of the power flow is calculated as follows:

jX

R

A

V

*V*A

Figure 16: Powerflow direction detection

0)cos( >− VA ϑϑ (4-5)

If equation 4-5 is greater than 0, the power flow is in the direction, the relay should protect,

otherwise it is the opposite direction.

a) Time-constant

If the current is over a preset value, the timer is started. If the timer reaches the trip-time a trip

signal is given to an output variable and can be used in the main part of the relay for starting

the breaker opening process. The time constant has to be set longer than the longest time of

the Zone detection to avoid interferences with the impedance measuring system. [15]1

b) Time-inverse

The principle is the same as described above, but the calculation of the tripping time is

different. Now the time is depended on the value of the current. A larger current results in

faster trigger. [26]2 1 ABB, “Application Manual Rel 511*2.3”, p. 217 2 ABB, “RAIDK, RAIDG, RAPDK and RACIK Phase overcurrent and earth fault protection, User’s Guide”, p7


1−

=

>

a

II

kbt (4-6)

As long as I is greater than I>, the relay will trigger when the following equation is fulfilled.

( )

dtkb

ItI

t

a

∫−

= >

0

11 (4-7)

Figure 17: Example for normal inverse [26]

The values for the different characteristics [26]:

Characteristic a b

Normal inverse 0.02 0.14

Very inverse 1 13.5

Extremely inverse 2 80

Long-time inverse 1 120

Table 4: Overcurrent characteristics

If there was a short activation of the time-inverse overcurrent protection and afterward the

starting signal for the protection system is reset the value will not be set to 0 at once, however

it will be slowly set back to 0 to simulate some fall-back process.


The overcurrent function was built in as a reserve overcurrent protection and will not react if

the Zone-detection is working.

4.2.3 Distance Protection

Zone 1

Zone 2

Zone 3

LinejX

R

R1 R2 R3

X3

X2

X1

Figure 18: Distance relay characteristic

The distance characteristic was programmed as seen in Figure 18. This model is based on the

ABB-Relay 511*2.3 [15]1. The point R1-R3 and X1-X3 are the setting points for Zone1-

Zone3. The time settings were chosen as 0.1 sec for Zone1, 0.4 sec for Zone 2 and 0.8 sec for

Zone3.

If the impedance enters Zone3, the timer is started. When the impedance stays too long in one

of the zones, corresponding to the preset trip times, the distance protection sets a trip signal to

true.

The impedances were calculated as followed:

( )22ba

bbaaa ii

iuiuz

++

= (4-8)

( )22ba

baabb ii

iuiuz

++

= (4-9)

The following tripping conditions have to be fulfilled:

• Overcurrent (1,4 x In) or Undervoltage (0,7 x Un) and

• The Zone Detection.

1 ABB, “Application Manual Rel 511*2.3”, p. 56


The undervoltage condition is necessary, because sometimes there is a very low infeed and

then the fault current will not reach the required amplitude, however the voltage can then be

used as an indicator for deciding whether it is a fault or not.

T1: in Zone 3 T2: in Zone 2

T6:not in Zone 3

wait Zone 2T5: not in Zone 2 T4: not in Zone 1

Zone 1Zone 3

T3: in Zone 1

Figure 19: Distance protection logic

In Figure 19 the logic of the distance protection is shown. Zone 2 can only be detected, when

zone 3 was detected before.

4.2.4 Oscillation Detection

T1: OutzoneT3: inzone

T4: not outzone

T2: not outzone

waitStart

Timer

Stop

Timer

Figure 20: Oscillation detection logic

For the oscillation detection the same trip characteristic was implemented as presented in

Figure 8. The “ring” is laid outside Zone 3, to protect all zones from unwanted tripping.

The oscillation signal is active as long as the impedance is located in Zone 3.

.

The timer is started when the outzone (the outer part of the “ring”) is entered. If it is left, the

timer is stopped and reset, if it enters the inner zone, the timer will be stopped and the time is

compared to the pre-set value.

The pre-set value for the first swing is 45msec and for the following 15msec.


4.2.5 Autoreclosing

Statistically 80% of all failures in transmission networks will disappear, when the line is

cleared. They are mostly transient faults like arcs, trees or similar. If the line is taken out of

operation, the normal situation will be restored and the line can be reclosed. This is the reason

why autoreclosing is implemented in most protection relays.

After opening the breaker the relay will wait a certain time, for example 600msec, and will

then reclose the breaker. If this action is successful, the line is in operation again and the fault

is removed. If the Autoreclosing process was not successful, the relay will open the breaker

again and take the line out of operation until a service team fixes the problem and resets the

relay manually. Reclosing more than 2 times is considered too dangerous and only allowable

in areas where it can be assumed that this second try of reclosure will lead to success and not

to damage of life or equipment.

The Autoreclosing function will however only work when the fault detection logic was started

as the primary protection system (the fault is located in the first zone, and the tripping is not

due to overcurrent). In all other cases it has to be assumed that the fault is more complex or

has a bigger problem as reason that a reclosing should be avoided.

The functionality was implemented in the simulation model. If the breaker opens, a timer is

started. After a time period of 600ms the breaker will be closed again. If the failure still exits,

the relay will work and open the breaker otherwise the breaker will stay closed and the relay

will continue working.

The input variable from the higher-ranked relay is the variable breaker-open. Due to the

reason that the breaker could be closed externally, the condition T3 was necessary in the state

machine model. (see Figure 21).


T1: Breaker openT2: Timer > Autoreclosing Time

T4: Breaker close

T3: Breaker close

waitStart

Autoreclose

Reclose

breaker

Figure 21: Autoreclosing logic

4.2.6 Over/Under voltage relay model

This model is very simple. It will trigger with a preset time delay if the voltage is over (for

example 1,1 x Un) or under (for example 0,9 x Un) a certain limit.

Additionally there is a possibility for Autoreclosing.

4.3 Network models

4.3.1 Line Model

Figure 22: Line model

The line model in Figure 22 is composed of one PiLink model as it can be seen in Figure 23

and 2 relay models. Both relay models are directional relays, which means that they “look”

only in one direction. The two relays are connected via a “transmission channel”. If one relay

opens the breaker, the breaker on the other side will also be opened with a time delay of

20ms.


Figure 23: Line model (PiLink)

The line is described with the following equations (1 is the left node, 2 the right one) and with

equation 4-1 and 4-2:

( )

−−

−+

+

+

−

=

bb

aa

b

a

b

a

vvvv

RXXR

XRvv

GBBG

ii

21

2122

1

1

1

1 1121 (4-10)

( )

−−

−+

+

+

−

=

bb

aa

b

a

b

a

vvvv

RXXR

XRvv

GBBG

ii

21

2122

2

2

2

2 1121 (4-11)

The line model was also built in a version with a fault. At any position on the line a fault can

be simulated. If the fault current becomes very small (the breaker does not set the current to

zero) the fault is assumed to be cleared. With the length of the fault duration, the fault type

can be chosen. (short and transient faults to permanent faults).

The base for the per unit (p.u.) system is 100 MVA. However with generators it is possible to

use another base (for example: 1000 MVA). The voltage is 1 p.u. as rated voltage in the

network, but for the current this is not true. The value has a range of 20 p.u. or more. It was

necessary to find a possibility to get all the currents to a comparable base because the relays

use the current as input.

Therefore the SIL (Surge Impedance Load) was used to level all the calculated currents at the

different lines. At rated line voltage, the real power delivered, or SIL, is [27]1

CL

VSIL rated2

= (4-12)

1 Glover J. D., Sarma M.: ”Power System Analysis & Design”,


To get the length of the line the impedance which is in p.u, has to be recalculated to real

values. The resistance is then divided through 0.03 Ω/km [28], which is a reasonable value for

high voltage transmission lines.

The maximum possible line load depends on the line length. For shorter lines much higher

load is possible than for longer ones where voltage-stability limits the maximum load.

The “St. Clair curves” [29] show the correlation between the line length and the line load in

SIL. These curves have been implemented in the line model.

The current is divided by the SIL and a factor that comes from the St. Clair curves.

In this line model it was not taken care of the mutual coupling of the three phases.


4.3.2 Cigrè Nordic 32

Figure 24:The Cigrè Nordic32 test system. Bold lines represent 400 kV and

thin lines represent 220 kV and 130 kV.


The Nordic 32 test system is a system which is constructed in order to study transient and

voltage stability and long-term dynamics. [30] The system consists of four major parts:

“North” with a large hydro production and some load, “Central” with a heavy load and

substantial thermal generation, “South-west” with thermal generation and some load and

“External” with a high load and generation. The “North” may be seen as the northern part of

Sweden, “Central” the central and southern part of Sweden, South-west the Danish island

Zealand and “External” Finland. The system consists of 32 nodes and 29 generators on the

voltage levels 400, 220 and 130 kV. [31]1

For the simulation the CIGRÈ Nordic 32 with the flow case lf28 was used. [32]2

Two different fault scenarios have been simulated with the Nordic 32 test system. The first

one was fault at bus 4045 and the second was a line fault in the area around bus 4042.

1 Agneholm E.: “The Restoration Process following a major Breakdown in a Power System”, p35 2 Larsson, Mats: “Coordinated Voltage Control in Electric Power Systems”, p 151


4.3.3 A model from South-America

14

6

25

13

11

12

10

15

7

8

24

2316

27

22

19

18

9

21

1

3

2

4

20

26

5

17

load with fixed power

load with explicit load model

neighboring model

Substation which is observed with PMUs

(not all lines must be observed)

1

2

6

5

4

3

shunt element

Figure 25: Model from South-America

The model presented above has a very large amount of generation in the “north”, or upper

part, and large loads in the “south”, or lower part. Therefore it is very interesting for

simulating problems with the transmission corridors.


4.3.4 Test Model

The test model is the same as in 4.4. (see Figure 26). The only difference is, that in this

model an UFLS – protection is integrated, whereas in 4.4 the protection task is done by a

PSGuard System, which is included in the Simulink model.

4.4 PSGuard system in Simulink

Figure 26: Test system

A two-area test system was used to have a look on interactions between the PSGuard System

and local protection. It is based on data given in reference [33].

The test system was set together using Modelica. All the settings were done in this simulation

environment. Inputs and Outputs were defined to get a communication between Modelica and

Simulink. The model was then exported from Modelica and imported as a Simulink block to

Simulink.

The rest of the PSGuard simulation was already implemented in Simulink. This system uses a

frequency prediction algorithm which was presented in [34].

For the test of the protection system a fault on the line N10-N11 was simulated.

5 Simulation results Page 49

5 Simulation results In this chapter the simulation results are presented. The goal of chapter 5.1 and 5.2 is, to show

how quickly the local protection needs to finish working.

In part 5.3 the interest of study was to look at the interaction between PSGuard and the

protection relays.

The impedance characteristic of the relays shows the 3 zones, as they were set in the

simulations and also shows the line impedance as a straight line.

In these simulations the relay settings were chosen to be as realistic as possible because real

values were not available for these investigations.

5.1 Nordic 32 system

Two test scenarios were used in the Cigrè Nordic 32 model (see page 45). In the first one a

fault on the Line 4021-4042 and in the second one a fault on the Line 4032-4044 was

simulated.

Both cases were simulated. “Case A” used current independent characteristics and “Case B”

reserve overcurrent protection with current depend trip characteristics. (inverse time

characteristic).

The inverse time characteristic should simulate an overload protection.

The comparison of the two simulations shows that the system will not collapse in the first 500

seconds if the relays have an inverse time overcurrent characteristic or a current independent

overcurrent protection could be blocked.

As a third possibility a successful reclosing was shown. In this “Case C” the system stabilizes

itself after the disturbance quite quickly.

5.1.1 Fault on Line 4021-4042

In this test case a fault on the Line 4021-4042 was applied. The fault was of the type that can

not be cleared by disconnecting the line. Therefore the reclosing was not successful.

The first figure (see Figure 27) shows the voltage at one of the most interesting buses of the

system whereas Figure 28 shows the current on Line 4032-4042. The beginning of a voltage

collapse can be observed.


0 20 40 60 80 100 120 1400.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05Voltage at Bus 4045

Time [sec]

Vol

tage

[p.u

.]

7

6

5

4

3

2

1

Figure 27: Voltage at Bus 4045

0 20 40 60 80 100 120 1400

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Time [sec]

Cur

rent

[I/Im

ax lo

ad]

Current on Line 4032−4042

1

2

3

4

5

Figure 28: Current on Line 4032-4044

In Figure 29 and Figure 30 the measured impedance of Relay 4032 on Line 4032-4042 and

Relay 4032 on Line 4032-4044 are shown.


−0.15 −0.1 −0.05 0 0.05 0.1 0.15

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]

Impedance of Relay 4032 on Line4032−4042

1

2 4 3

Figure 29: Impedance of Relay 4032 on Line 4032-4042

−0.1 −0.05 0 0.05 0.1

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]

Impedance of Relay 4032 on Line 4032−4044

1

2

6 5 4

3


Point 1 shows the operation point up to 1. In Figure 30 point 1 is far outside the plot range.


Event Time [sec] Description

1 0-1 Normal operation

2 1-1,15 Fault on Line 4021-4042

1,15-1,75 Line 4021-4042 is tripped

3 1,75-1,9 Reclose trial, unsuccessful and final trip at 1,9sec

4 125,54 Trip of Line 4032-4042 due to overcurrent

5 125,55 Shortly after action 4

6 127,12 Trip of Line 4032-4044 because of zone 3

Table 5: Time-table for the Fault on Line 4021-4042 in Case A

At the time of 1 second the fault was applied. The operation point 2 shows that the voltage

decreases and the current increases. The measured impedance in Figure 29 and Figure 30

“jumps” near to the tripping characteristic. After 150 msec the line is tripped and the voltage

begins to recover. Because of the reclosing mechanism the relays bring the line back into

operation after 600msec. (Time: 1,75 sec) however the fault is still existing and the breaker

open again at 1,9 sec and will not try an autoreclose again.

The system starts to swing and will be damped after 20 sec. Due to the system conditions the

voltage will steadily decrease and the current increase. After crossing the limit of 1.4 p.u. of

the current the overcurrent protection (see Figure 28) is activated and will therefore trip the

line (point 4 at 125,54 sec). The outage of the Line 4032-4044 leads to a voltage drop and a

sudden increase of the current on line 4032-4044. The impedance moves quickly (the

oscillation detection will not work) into Zone 3 which results in a tripping at 127,12 sec. After

this trip the system starts to collapse because three of the important transmission lines are

taken out of operation.

In Case B1 the overcurrent protection will not react in the first 500msec. In this time no

problem with the zone detection could be observed. A phenomenon of this power system can

be seen in Figure 40 and Figure 41: Voltage Instability. We can see that there are no adverse

interactions between different protection systems even though the system will end up in a

voltage collapse.

1 Appendix A page 64


Case C1 shall show, that there is no problem with the system, if the reclosing is successful.

5.1.2 Fault on Line 4032-4044

Case A2 and Case B3 are very similar to the scenario described in section 5.1.1.

In Case A the collapse is much faster after the tripping of Line 4032-4044 than in Case A of

5.1.1. (1.04sec than 1.57sec)

Remark to Case A: Relay 4021 trips because of the action of the overcurrent protection. Point

6 seems to hit zone 3, but the measured impedance does not reach the outer zone.

The time table for the fault in Case A (1-3 are the same for Case B):



2 1-1,15 Fault on Line 4032-4044

1,15-1,75 Line 4032-4044 is tripped

3 1,75-1,9 Reclose trial, unsuccessful and final trip at 1,9sec

4 137,48 Trip of Line 4032-4042 due to overcurrent

5 137,49 Shortly after action 4

6 138,53 Trip of Line 4021-4042 because of overcurrent

Table 6: Time-table for the Fault on Line 4032-4044

With this simulation it should be proven, that the general simulation results in 5.1.1 are not

changing with the location of the fault.

5.2 South American Model

In the South American Test System (see Figure 25) the fault was applied on the double Line

9_16. One the first of both lines (Line 9_16) the fault was generated after 2 seconds, 0.4

seconds later a fault was generated on the second line 9_16_2.

This test system is employed to investigate, if an unplanned tripping of the relays occurs.

1 Appendix A page 66 et seq. 2 Appendix A page 69 et seq. 3 Appendix A page 72 et seq.


0 20 40 60 80 100 120 140

0.4

0.5

0.6

0.7

0.8

0.9

1


Vol

tage

[p.u

.]

Time [sec]

1

2,3 4,5

9

6

7

8


0 20 40 60 80 100 120 1400.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75Current on Line 8−24

Time [sec]

Cur

rent

[I/Im

ax lo

ad]

1

2

3

9

4

5

6

7

8


Figure 31 and Figure 32 show a voltage instability after the tripping of the double line due to

the high production in the upper and the high consumption in the lower part of the network.

No problem could be found with Relay 24 on Line 16-24.


−0.08 −0.06 −0.04 −0.02 0 0.02 0.04 0.06 0.08

−0.1

−0.05

0

0.05

0.1

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]

Impedance at Relay 24 on Line 16−24

2 3,4, 5

9

8 7 6

Figure 33: Impedance at Relay 24 on Line 16-24

Relay 14 on Line 8-14 sees a Zone 3 detection. But before the impedance had to cross the

oscillation detection. The time to cross this area (Resistance: 0.0008 p.u. and Reactance:

0.0016 p.u.) was 0.3 sec, much higher than the maximal allowed 0.045sec. (see chapter 4.2.4).

−0.15 −0.1 −0.05 0 0.05 0.1 0.15

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


9

outer line

inner line

5 4

3

2

6 7 8

Figure 34: Impedance on Relay 14 on Line 8-14

The oscillation flag was set and blocked a tripping of the Relay due to distance protection.


Even if there was no oscillation detection, the time from entering zone3 to the collapse of the

whole system was only 0.2sec, which is much too slow for this zone.



2 2-2,15 Fault on Line 9_16

3 2,4-2,55 Fault on Line 9_16_2

2,15-2,75 Line9_16 is tripped

2,55-3,15 Line9_16_2 is tripped

4 2,75-2,9 Reclose trial, unsuccessful and final trip at 2,9sec of Line 9_16

5 3,15-3,3 Reclose trial, unsuccessful and final trip at 3.3sec of Line 9_16

6 115.44 Enter outer area of oscillation detection

7 115.74 Enter inner area of oscillation detection

8 120,45 Enter zone 3

9 120,65 System collapse

Table 7: Time-table for Fault on double Line 9_16

The oscillation detection could help blocking the relays in such a case and avoid unplanned

tripping. Together with other security arrangements this could help stabilizing the system.

5.3 Test System

This test system is a combination of the system showed in Figure 26 and a Matlab model built

by ABB that includes the PSGuard System.

In this simulation two test cases are shown:

The first one has already been tested and described in [34]. The second case shows a fault on

Line L1112. Both simulations were used to find possible interactions.

It has to be mentioned that the system of test case two was not built to test line faults and

therefore it has taken care of transient voltage instability. Setting the clearing time of the relay

as low as possible could minimize this problem.

5.3.1 Generator Tripping

In this simulation generators are tripped at three different times. The first tripping is at 10.1

seconds of G5, at 85.2 seconds of G4 and at 160seconds of G2.


In Figure 35 the current over the TieLine is presented, because this bottleneck is the most

critical line in this test system. Additionally the voltage on Bus 10 is presented.

No problems in the interaction of the relays and PSGuard could be found.


1 10,1 Generator 5 is tripped

2 85,2 Generator 4 is tripped

3 160 Generator 2 is tripped

Table 8: Time-table of Generator Tripping

0 20 40 60 80 100 120 140 160 180 2000.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

Cur

rent

[p.u

.]

Time [sec]

Current on TieLine

1

2

3

Figure 35: Current at TieLine


0 20 40 60 80 100 120 140 160 180 2000.94

0.95

0.96

0.97

0.98

0.99

1

1.01

1.02

1.03

Time [sec]

Vol

tage

[p.u

.]

Voltage at Bus 10

1 2

3


5.3.2 Line Fault on Line L1112

A fault was applied on L1112 at 10seconds. The fault was not clearable therefore the

reclosing was not successful.

The system will be stabilized very fast with the help of PSGuard. One thing that has to be

mentioned in this case is that the relays have to be much faster than the first action of

PSGuard. Otherwise this would lead to a system collapse because these two protection

mechanisms are working against each other.


1 10 Fault on Line L1112

2 10,05-10,65 L1112 is out of operation

3 10.65-10.7 Reclose, unsuccessful and L1112 is finally out of operation

Table 9: Time-table of Line Fault on Line L1112


0 10 20 30 40 50 600

0.5

1

1.5

2

2.5

3

3.5

Time[sec]

Cur

rent

[p.u

.]

Current on TieLine

1

2 3

Figure 37: Current on Tie Line

0 10 20 30 40 50 60

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2


Vol

tage

[p.u

.]

Time [sec]

1

2 3

Figure 38: Voltage on Bus 10

However also in this test case no major problem could be detected. The clearing time was set

very fast and therefore the overshot of the voltage due to possible transient voltage instability

was very low.


This simulation shows that under very strange transient instability conditions neither PSGuard

nor the local protection units can detect the problem properly. A solution might be to use Out-

of-Step relays to avoid unexpected triggering of the relays.

A better approach might be to combine Out-of-Step Protection together with PMUs, which is

described more detailed in [35]. This could help to prevent relays from working in the right

way at the wrong time.

6 Conclusion and Discussion Page 61

6 Conclusion and Discussion

This thesis shows the functionality and interaction of protection systems in a power system. The used programming language provides the possibility to model different types of relays in a simple way and applies different types of complexity. The objective was to detect potential problems related to the simultaneous usage of the local protection relays and the PSGuard Wide Area Protection System. It is important to mention that in order to find a common base for all the line currents the use of SIL was essential because otherwise it would not have been possible to use the currents as an input variable for the relays. The currents of the simulation are normally not of interest and will have various levels depending on the base of the power. SIL was chosen because it represents the natural loading of the line that is an unique parameter for each line. Together with the “St. Clair’s” curves the maximum allowable loading could be calculated which gives realistic values for each line. These new loading was used as a new power base for each line and the current was calculated out of these parameters. The results were now comparable on the idea that every line has a certain limit of maximum transportable power and the result could be used for the relays. The simulation results show that the local protection relays should have done their work after 2-3 seconds if all relays are working and that they will, under not too abstruse conditions, do their work properly and without any surprising actions. For all systems it has to be assumed that the local protection system is set properly and that there are normally no faults due to hidden failures or false settings of the protection system. [36] We should also take into consideration that there will always be situations, when relays or breakers do not work because of several reasons: mechanical problems, maintenance, and failure settings. It can easily be seen, that a Wide-Area Measurement System should not start too early with the action because from the appearance of a fault to the clearance, if a reclosing is successful, it takes about 1-3 seconds, which depends on the settings and other circumstances. If a Wide Area Measurement System would react in this time too early it can cause problems even if the detected problems have already been removed. Today the relay settings are normally calculated from short circuit studies including a wide variety of system configurations, generations schedules and reasonable voltages.

6 Conclusion and Discussion Page 62

However due to the opportunities of transmission lines and protection relays ways of influence and communication with local protection equipment should be found. This could help to detect failures by starting self-tests of the units and could make the protection process more accurate and faster by adapting relay settings. Several papers describe different approaches to find the best settings of a relay. One approach could be to use PMUs to find the proper settings as described in [36], [37] and [38]. This could be a new area where PSGuard may be useful. Furthermore adaptive relaying will become more and more important with the use of FACTS-devices. This changes the measured impedance of the distance relay and can lead to unwanted operation of the protection systems. To avoid these problems it will be necessary to manipulate the characteristics of the protection units in order to achieve on the one hand a fast and controllable network on the other hand to maintain the availability and selectivity of the protection units. All the ideas mentioned above are only possibly if the protection units are relatively new with built in “intelligent” micro controlled operation systems that allow an external operator to change settings over some communication channels. The problem today is, that in fact about 70% of all relays are still electro-mechanical. [6]1 These relays can only be adjusted by hand and do not allow remote controlled changing of the settings. Due to the lifetime of such protection equipment these parts will be in service for at least 40 years or longer. Therefore this thesis should show, that no adjustments need to be applied to existing protection systems and that WAMS can be used additionally. One possibility offered by most of the “old” relays is to send a blocking signal and hinder the relay from tripping. This is easy to implement and gives the Wide Area Protection System the necessary flexibility to work together with local protection relays in cases of voltage instability or at times when some overload is needed to stabilize the system. However one should take care that this blocking does not block the relay from working when a “real” fault occurs independently from the worse system conditions. As presented in the thesis no large problems should be expected combining WAMS and local protection, provided that PSGuard has a delay time > 1.5sec. It has to be taken care, that the existing system is well planned and works fine without any major disturbances. With the change from old to new protection relays the possible fields of applications of WAMS will increase and allow more precise, faster and better protection of electrical power systems.

1 Jonsson: „Line Protection and Power System Collapse”, p. 36

Appendix A – Diagrams Page 63

Appendix A – Diagrams

Cigrè Nordic 32 Test System

Fault on Line 4021-4042

Case A

0 20 40 60 80 100 120 1400

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8Current at Line 4032−4044

Time [sec]

Cur

rent

[I/Im

ax lo

ad]

1

2

3

5

6

7



Case B

0 50 100 150 200 250 300 350 400 450 5000.8

0.85

0.9

0.95

1


Time [sec]

Vol

tage

[p.u

.]

1 2

Figure 40: Voltage on Bus 4045

0 50 100 150 200 250 300 350 400 450 5000.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15Current on Line4032−4044

Cur

rent

[I/Im

ax lo

ad]

Time [sec]



−0.1 −0.05 0 0.05 0.1

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


2 3


−0.15 −0.1 −0.05 0 0.05 0.1 0.15

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


1

2

3



Case C

0 5 10 15 20 25 30 35 40 45 500.8

0.85

0.9

0.95

1

1.05

Time [sec]

Vol

tage

[p.u

.]Voltage at Bus 4045

1

2


0 5 10 15 20 25 30 35 40 45 500.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Time [sec]

Cur

rent

[I/Im

ax lo

ad]


1

2

Figure 45: Current on Line4032-4044


−0.25 −0.2 −0.15 −0.1 −0.05 0 0.05 0.1 0.15 0.2 0.25

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


1

2


−0.1 −0.05 0 0.05 0.1

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


1

2



−0.15 −0.1 −0.05 0 0.05 0.1 0.15

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


2

1



Fault on Line 4032-4044

Case A

0 20 40 60 80 100 120 1400.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Time [sec]

Vol

tage

[p.u

.]

Voltage at Bus 4045

2

3

4

5

6



0 20 40 60 80 100 120 1400

0.5

1

1.5

Time [sec]

Cur

rent

[I/Im

ax lo

ad]


2

3

4

5


0 20 40 60 80 100 120 1400

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Time [sec]

Cur

rent

[I/Im

ax lo

ad]


4

5

6

7

2

3



−0.15 −0.1 −0.05 0 0.05 0.1 0.15

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


1

2 3

4


−0.15 −0.1 −0.05 0 0.05 0.1 0.15−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


1

2

3

4

5 6



Case B

0 100 200 300 400 500 6000.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Time [sec]

Vol

tage

[p.u

.]Voltage at Bus 4045

2 3


0 100 200 300 400 500 6000.9

1

1.1

1.2

1.3

1.4

1.5

1.6

Time [sec]

Cur

rent

[I/Im

ax lo

ad]


1

2

3



−0.15 −0.1 −0.05 0 0.05 0.1 0.15

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


1

2 3


−0.15 −0.1 −0.05 0 0.05 0.1 0.15−0.25

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

0.25

Resitance R [p.u.]

Rea

ctan

ce X

[p.u

.]


3

2

1


Appendix B – Source Code Page 74

Appendix B – Source Code

Relays

Protection Test

Relays.Buswithselfexpiredfault Busbar model with shunt fault

Information

The shunt fault is modelled as an impedance connected to ground through

a breaker. The fault is applied at simulation time FaultTime and stays

active as long as the fault current is not smaller than the variable small.

For numerical reasons, the fault impedance must not be exactly equal

to zero.

Parameters

Name Default Description

FaultTime 10 Time of fault occurence [s]

FaultDuration 0.05 Duration of fault [s]


FaultR 0.1 Fault Resistance [p.u.]

FaultX 0 Fault Reactance [p.u.]

iFaultmin 1e-4 min Fault Current [p.u.]

Relays.Relay.Basic Relay Basic Components

Types and constants

type CurrentAngle = ObjectStab.Base.Angle;

Relays.Relay.Basic.BreakerAndMeasurement

Breaker with external trigger and measurement

Information

Power, Voltage and Current Measurement unit. The values are forwarded to the

out ports. The breaker has an external trigger input.

This model has to be series connected

Parameters


small 1e-6

Relays.Relay.Basic.PowerMeasurement Power Measurement


Information

Power Measurement for Electrical Cuts.

Should be connected in series.

Relays.Relay.Basic.CurrentMeasurement Current Measurement

Information

Current Measurement for Electrical Cuts.

Should be connected in series.

Relays.Relay.Basic.VoltageMeasurement Voltage Measurement for Electrical Cuts

Information

Voltage Measurement for Electric Cuts.

Should be connected to one pin

Relays.Relay.Basic.TakeTimer

Information

Timer model. If the 'run' input is true, the timer will

start counting and gives the time, which has elapsed to the output 'Time'. With


the input 'reset', the timer can be reset, whether it is in running or

stop-state.

Relays.Relay.Basic.TransmissionDelay

Information

This transmission delay is used for simulating the tripping signal which is sent from a relay at

one

side of the line to the other side. It will send a trip signal after a delay time to both sides back.

Parameters


DataDelay 0.01 Time to transfer the data


Relays.Relay.OvercurrentRelay Over Current Relays

Relays.Relay.OvercurrentRelay.OvercurrentRelayconstanttime

withReclosing Over Current Relay which time constant trip characteristic and has the possibility

for auto reclosing

Information

This overcurrent Relay has a constant time characteristic and the possibility for Autoreclosing

Also in this model it is necessary to set the line parameters to get the maximum allowable

load current. (see SIL Table)

Parameters


imax 1.3 i>> [p.u.]


vmin 0.8 Minimum Voltage [p.u]

tfast 0.5 Time for i> [s]

ReclosingTime 0.6 Auto Reclosing Time [s]

NumberofReclosing 2 Number of Reclosings

breakeropen 0.05 Time for open the breaker [s]

small 1e-4

R 0.0 Series Resistance [p.u.]

X 0.1 Series Reactance [p.u.]

B 0.1 Shunt Susceptance [p.u.]

G 0.0 Shunt Conductance [p.u.]

Voltagebase 400 Voltage Base in kV [p.u]

Resistancebase 0.03 Ohm per km

SIL 1/(sqrt(X/B)) SIL

Relays.Relay.OvercurrentRelay.OvercurrentRelayconstanttime Overcurrent Relay which detects a shortcut

Information

This overcurrent Relay has a constant time characteristic.




Parameters


imax 1.3 i>> [p.u.]

tfast 0.5 Time for i> [s]

breakeropen 0.05 Time for open the breaker [s]

small 1e-4









Relays.Relay.OvercurrentRelay.OvercurrentRelay Over Current Relay which trip time depends on the current

Information

This Relay has different tripping characteristics (settings see OvercurrentRelayTable):

Normal inverse

Very inverse

Extremely inverse

Long-time inverse



Parameters


ild 1.2 I> (1.2 *Iload) [p.u.]

imax 1.5 I>> (0.7 *Ishort cut) [p.u.]

tfast 0.5 time for I>> - time for opening breaker [s]

k 0.7 settable inverse time factor

breakeropen 0.05 time for opening the breaker [s]


small 1e-4

i 3 1 normal inverse, 4 long time inverse








Relays.Relay.OvercurrentRelay.OvercurrentRelayTable Table look-up in one dimension (matrix/file)

Information

The different trip characteristics: (see ABB Relay RAID)

Normal inverse: 1

Very inverse: 2

Extremely inverse: 3

Long-time inverse: 4

Parameters




Relays.Relay.OvercurrentRelay.OvercurrentRelaywithReclosing Over Current Relay which trip time depends on the current with Auto Reclosing

Information

This Relay has different tripping characteristics (settings see OvercurrentRelayTable):

Normal inverse

Very inverse

Extremely inverse

Long-time inverse

and the possibility for Autoreclosing.



Parameters


ild 1.2 I> (1.2 * I load) [p.u.]

imax 1.5 I>> (0.7 * I short cut) [p.u.]



tfast 0.5 time for I>> - time for opening breaker [s]

k 0.7 settable inverse time factor




small 1e-4










Relays.Relay.VoltageRelay Over / Under Voltage Relays

Relays.Relay.VoltageRelay.VoltageRelay Over / Under Voltage Relay

Information

Voltage Relays use as input the voltage. If this parameter is lower a certain value, the breaker

will open.

Parameters


vmax 1.3 V>> [p.u]

vmin 0.7 V>> [p.u]

twait 0.5 Time to wait to trip (to avoid voltage tips) [s]


small 1e-4


Relays.Relay.VoltageRelay.VoltageRelaywithReclosing Over/Under Voltage Relay with Reclosing

Information

Voltage Relays use as input the voltage. If this parameter is lower a certain value, the breaker

will open.

This model has the possibility for autoreclosing.

Parameters


vmax 1.3 V>> [p.u]

vmin 0.7 V>> [p.u]

twait 0.5 Time to wait to trip (to avoid voltage tips) [s]

ReclosingTime 2 Auto Reclosing Time [s]



small 1e-4


Relays.Relay.DistanceRelay

Relays.Relay.DistanceRelay.Autoreclosing

Information

The Autoreclosing function tries to reconnect the line after a trip related to zone1. If this

process is successful, all timers will be reset. If this fails, the breaker will stay open and the

line will be out of operation.

Parameters


imax 1.4 I> [p.u.]




resettime 10 Time to wait that AR is reset


Relays.Relay.DistanceRelay.OscillationDetection

Information

The Oscillation Detection should prevent the distance relay from tripping during power

oscillations.

^

|

|

_______________________|______________________

| | |

| ____________________|___________________ |

| | | | |

| | | | |

| | | | |

| | | | |

| | |------------------------------------->

| | | |

| | | |

| | | |

| | | |

| | | |

| |________________________________________| |

| |

|______________________________________________|


The time crossing the part between the outer and inner boarder is measured. If this value is

higher than a preset value, an oscillation is detected and the variable oscillation is set to true.

If it is lower, nothing will happen.

Parameters


inOsciR 0.02892 Oscillation Detection Resistance innerZone [p.u.]

inOsciX 0.2892 Oscillation Detection Reactance innerZone [p.u.]

OsciR 0.001 Oscillation Detection Resistance Zone1 + .. [p.u.]

OsciX 0.01 Oscillation Detection Reactance Zone1+... [p.u.]

osci1 0.025 Time for first Oscillation [s]

osci 0.015 Time for the following Oscillations [s]

ArgDir 15 ArgDir

ArgNegRes 25 ArgNegRes



resetoscillationtime 5 Time that have to pass before oscillation is reset [s]

Relays.Relay.DistanceRelay.OvercurrentDetectionwithDirection

Information

This Overcurrent Protection is the backup protection for the distance Relay.

The characteristic is time-constant. For more Information have a look at the Overcurrent

Relay Models.

Parameters



imax 1.4 I> [p.u.]

R3 0.02892 Resistance Zone3 [p.u.]

X3 0.2892 Reactance Zone3 [p.u.]

timeimax 0.5 Trip time for I>> [s]

ArgDir 15 ArgDir




Relays.Relay.DistanceRelay.ZoneDetectionwithDirection

Information

Zone Detection for Distance Relays


The relay has the following characteristic: The crossings with the x- and y-axis are the values

which can be set.

jX

^

_____¦__________

\ ¦ /

\ ¦ /

\ ¦ /----right line

\ ¦ /

/\¦---------------> R

/ /'. /

/ / '

ArgNegRes /

/

ArgDir

The right line is parallel to the line characteristic.

A more detailed description can be found in the manual of the Relay ABB 511

http://www.abb.com/substations

Parameters



imax 1.4 I> [p.u.]



timezone1 0.5 Time for Zone 1 [s]




timezone2 1 Time for Zone 2 [s]



timezone3 2 Time for Zone 3 [s]

ArgDir 15 ArgDir




Relays.Relay.DistanceRelay.DistanceRelaywithDirection Distance Relay

Information

Distance Relay

The original for this model is the ABB Relay 511


In the model are included:

a possibility for Autoreclosing


an oscillation detection

an time-constant overcurrent protection as backup protection and

a zone detection

It is necessary to combine this model with a line. It is not possible to use it as a stand alone

model. (use PilinkwithDistanceRelay)

Parameters


imax 1.4 I> [p.u.]


timeimax 1 Trip time for I>> [s]










ArgDir 15 ArgDir


R 0.001 Series Resistance of the Line [p.u.]

X 0.1 Series Reactance of the Line [p.u.]

inOsciR R3 Oscillation Detection Resistance innerZone [p.u.]

inOsciX X3 Oscillation Detection Reactance innerZone [p.u.]

OsciR 0.1*R3 Oscillation Detection Resistance innerZone + .. [p.u.]

OsciX 0.1*X3 Oscillation Detection Reactance innerZone+... [p.u.]




breakeropen 0.05 Time for opening the breaker [s]




SIL SIL


Relays.Relay.DistanceRelay.DistanceRelaywithDirection1 Distance Relay

Information

Distance Relay

The original for this model is the ABB Relay 511


In the model are included:

a possibility for Autoreclosing


an oscillation detection

an overcurrent protection with various trip characteristics (see Overcurrent Relay) as backup

protection and

a zone detection

It is necessary to combine this model with a line. It is not possible to use it as a stand alone

model. (use PilinkwithDistanceRelay)Distance Relay

Parameters


imax 1.4 I> [p.u.]


timeimax 1 Trip time for I>> [s]










ArgDir 15 ArgDir



X 0.1 Series Reactance of the Line [p.u.]

inOsciR R3 Oscillation Detection Resistance innerZone [p.u.]

inOsciX X3 Oscillation Detection Reactance innerZone [p.u.]

OsciR 0.1*R3 Oscillation Detection Resistance innerZone + .. [p.u.]


OsciX 0.1*X3 Oscillation Detection Reactance innerZone+... [p.u.]



breakeropen 0.05 Time for opening the breaker [s]




SIL SIL


Relays.Relay.DistanceRelay.OvercurrentDetectionwithDirection

timeinvers

Information

This Overcurrent Protection is the backup protection for the distance Relay.

The characteristic has an inverse trip characteristic. For more Information have a look at the

Overcurrent Relay Models.

Parameters


imax 1.4 I> [p.u.]



timeimax 0.5 Trip time for I>> [s]

ArgDir 15 ArgDir





k1 0.7 settable inverse time factor



Relays.Relay Protection Relays

Relays.Relay.PilinkwithDistanceRelay

Information

This model combines two Relays with a Line element.

The maximum load current is calculated with the SIL and the St. Clairs Curves.

Both Relays are directional Relays and "look" into the line.

The transmission line connects both units and trips the second breaker if one detects a failure.

Parameters


imax1 1.4 I> Relay1 [p.u.]

vmin1 0.8 Minimum Voltage Relay1 [p.u]

timeimax1 1 Trip time for I>> Relay1 [s]

R11 0.8*X11 Resistance Zone1 Relay1 [p.u.]

X11 0.9*X Reactance Zone1 Relay1 [p.u.]

timezone11 0.1 Time for Zone 1 Relay1 [s]





R31 1.2*R21 Resistance Zone3 Relay1 [p.u.]

X31 0.2892 Reactance Zone3 Relay1 [p.u.]


ArgDir1 15 ArgDir

ArgNegRes1 25 ArgNegRes

inOsciR1 R31 Oscillation Detection Resistance innerZone Relay1 [p.u.]

inOsciX1 X31 Oscillation Detection Reactance innerZone Relay1 [p.u.]

OsciR1 0.01*R31 Oscillation Detection Resistance Zone1 + .. Relay1 [p.u.]

OsciX1 0.01*X31 Oscillation Detection Reactance Zone1+... Relay1 [p.u.]

osci11 0.045 Time for first Oscillation Relay1 [s]

osci1 0.015 Time for the following Oscillations Relay1 [s]

breakeropen1 0.05 Time for opening the breaker Relay1 [s]

ReclosingTime1 0.6 Auto Reclosing Time Relay1 [s]

NumberofReclosing1 1 Number of Reclosings Relay1







R22 0.8*X22 Resistance Zone2v [p.u.]







ArgDir2 15 ArgDir




OsciR2 0.01*R32 Oscillation Detection Resistance Zone1 22+ .. Relay2

[p.u.]

OsciX2 0.01*X32 Oscillation Detection Reactance Zone1+2... Relay2 [p.u.]
















Relays.Relay.Pilinkwithselfexpiredfault Pilink with shunt fault model

Information

The model of the Pilink with a shunt fault is realised using the Pilink

models and the ideal breaker models.

At time FaultTime, the breaker B3 closes and the ground fault becomes active

for the duration of FaultDuration seconds, after which the line is disconnected

at both ends. The ground fault location is determined by alpha, where alpha=0

corresponds to a fault located at T1 and alpha=1 to a fault location at T2.

For numerical reasons the fault and pilink impedance may not be exactly zero,

and alpha not be equal to 0 or 1.

Parameters






FaultTime 1 Time of fault occurrence [s] [s]



alpha 0.5 Position of Fault

FaultR 1e-5 Fault Resistance [p.u.]


Relays.Relay.FaultedPilinkwithDistanceRelay

Information

The fault in this model can be controlled. The start and stop time can be adjusted.

The rest is the same as in "PilnkwithDistanceRelay".

Parameters















ArgDir1 15 ArgDir























ArgDir2 15 ArgDir






[p.u.]












ClearTime 0.07 Fault Clearing Time [s] [s]

RecloseTime 1e60 Time of Reclosing [s] [s]










Relays.Relay.PilinkwithselfexpiredfaultwithDistanceRelay

Information

This model is a combination of PilinkwithDistanceRelay and Pilinkwithselfexpiredfault.

Parameters














ArgDir1 15 ArgDir
























ArgDir2 15 ArgDir





[p.u.]












FaultTime 1 Time of fault occurence [s] [s]










Relays.Relay.SILTable Table look-up in one dimension (matrix/file)

Information

The base for this data set are the "St. Clairs" Curves. More Information:

Dunlop R. D., Gutman R.: ?Analytical Development Of Loadability Characteristics For EHV

And UHV Transmission Lines?, IEEE Transaction on Power Apparatus and Systems, VOL.

PAS-98, No. 2 March/April 1979, p.606-613


Parameters


tableName "NoName" table name on file or in

function usertab(optional)

fileName "NoName" file where matrix is stored

(optional)

icol[:] 2 columns of table to be

interpolated

table[:, :]

[0.0, 3; 80.0, 3; 97, 2.7; 112, 2.5; 130, 2.3; 180, 2;

225, 1.7; 290, 1.4; 354, 1.25; 420, 1.1; 480, 1; 515,

0.9; 645, 0.8; 740, 0.7; 960, 0.65]

table matrix (grid = first

column)

Relays.Relay.PilinkwithDistanceRelay1

Information

This model combines two Relays with a Line element.

The maximum load current is calculated with the SIL and the St. Clairs Curves.

Both Relays are directional Relays and "look" into the line.

The transmission line connects both units and trips the second breaker if one detects a failure.

The difference between PilinkwithDistanceRelay and PilinkwithDistanceRelay1 is, that the

overcurrent protection in PilinkwithDistanceRelay1 uses a current depended trip characteristic

(see Overcurrent Relays).


Parameters














ArgDir1 15 ArgDir
























ArgDir2 15 ArgDir





[p.u.]

















Relays.Relay.PilinkwithselfexpiredfaultwithDistanceRelay1

Information

This model is a combination of PilinkwithDistanceRelay and Pilinkwithselfexpiredfault.

Parameters















ArgDir1 15 ArgDir























ArgDir2 15 ArgDir






[p.u.]





















Documentation generated by Dymola

http://www.dynasim.se/

Bibliography Page 114

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[1] Feier B, Dr. Fickert L.: Störungen und Schutz in elektrischen Anlagen, Laborunterlagen, TU-GRAZ, Austria 2002

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[4] Datasheets of Relay ABB RXEDK, 316*4, 521, RAGIK, SPCD 3D53, 509

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[14] Warrington, C.: “Protective Relays, Vol. 1”, Chapman & Hall Ltd., 1968, 380 p.

[15] ABB, Application Manual Rel 511*2.3, Line distance protection terminal, ABB

Automation Products AB, Substation Automation Division, Västeräs, Sweden, 2001

http://www.abb.com/substationautomation

[16] UCPTE, “Summary of the current operating principles of the UCPTE”, 2000,

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[17] “WECC Coordinated Off-Nominal Frequency Load Shedding and Restoration Plan”,

Underfrequency Issues Work Group, 1997,

http://www.wecc.biz/documents/policy/OFFNOMLOAD&RESTORATION.pdf

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EHV And UHV Transmission Lines”, IEEE Transaction on Power Apparatus and

Systems, VOL. PAS-98, No. 2 March/April 1979, p.606-613

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List of Tables Page 118

List of Tables Table 1: Overview of Protection [2], [3], [4] ............................................................................. 7

Table 2: UFLS in different networks [16], [17], [18], [19]...................................................... 29

Table 3: Possible Interaction WAMS - relays.......................................................................... 33

Table 4: Overcurrent characteristics ........................................................................................ 38

Table 5: Time-table for the Fault on Line 4021-4042 in Case A............................................. 52

Table 6: Time-table for the Fault on Line 4032-4044.............................................................. 53

Table 7: Time-table for Fault on double Line 9_16 ................................................................. 56

Table 8: Time-table of Generator Tripping.............................................................................. 57

Table 9: Time-table of Line Fault on Line L1112 ................................................................... 58

List of Figures Page 119

List of Figures Figure 1: Overcurrent Trip Characteristic ................................................................................ 10

Figure 2: Coordination of Overcurrent Relays......................................................................... 10

Figure 3: R-X diagram for a distance relay (MHO-Relay) ...................................................... 13

Figure 4: Principle of Distance Protection ............................................................................... 14

Figure 5: Basic types of distance relays ................................................................................... 15

Figure 6: Distance function characteristic [9] .......................................................................... 16

Figure 7: Oscillations in a 2-machine network [9]................................................................... 17

Figure 8: Oscillation Detection ................................................................................................ 18

Figure 9: In principle the connection of a distance relay ......................................................... 20

Figure 10: Current infeed ......................................................................................................... 22

Figure 11: Current outfeed ....................................................................................................... 23

Figure 12: Double line.............................................................................................................. 23

Figure 13: PSGuard.................................................................................................................. 30

Figure 14: Model for state calculation ..................................................................................... 31

Figure 15: Distance Relay (Screenshot)................................................................................... 36

Figure 16: Powerflow direction detection................................................................................ 37

Figure 17: Example for normal inverse [26] ............................................................................ 38

Figure 18: Distance relay characteristic ................................................................................... 39

Figure 19: Distance protection logic ........................................................................................ 40

Figure 20: Oscillation detection logic ...................................................................................... 40

Figure 21: Autoreclosing logic................................................................................................. 42

Figure 22: Line model .............................................................................................................. 42

Figure 23: Line model (PiLink) ............................................................................................... 43

Figure 24:The Cigrè Nordic32 test system. Bold lines represent 400 kV and......................... 45

Figure 25: Model from South-America.................................................................................... 47

Figure 26: Test system ............................................................................................................. 48

Figure 27: Voltage at Bus 4045................................................................................................ 50

Figure 28: Current on Line 4032-4044 .................................................................................... 50

Figure 29: Impedance of Relay 4032 on Line 4032-4042 ....................................................... 51


Figure 31: Voltage at Bus 24.................................................................................................... 54

Figure 32: Current on Line 8-14 .............................................................................................. 54

List of Figures Page 120

Figure 33: Impedance at Relay 24 on Line 16-24.................................................................... 55

Figure 34: Impedance on Relay 14 on Line 8-14..................................................................... 55

Figure 35: Current at TieLine................................................................................................... 57

Figure 36: Voltage at Bus 10.................................................................................................... 58

Figure 37: Current on Tie Line ................................................................................................ 59

Figure 38: Voltage on Bus 10 .................................................................................................. 59


Figure 40: Voltage on Bus 4045 .............................................................................................. 64





Figure 45: Current on Line4032-4044 ..................................................................................... 66













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