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2004

IEEE Intemational Conference on

Electric

Utility Deregulation, Restructuring and Power Technologies (DRPT2004)

April

2004 Hong Kong

Generate new relay settings

Intelligent Method for Protection Coordination

C.W.

So,

Member,

IEEE,

K.K. Li, Senior Member, IEEE

Abstract:

This paper presents the application of

Artificial Intelligence in protection coordination. It can

substantially improve the coordination of protection

relay operations. The relay settings and coordination

requirements are formulated into a set of constraint

equations and an objective function is developed to

manage the relay settings by the Time Coordination

Method TCM). Modified Evolutionary Programming

MEP) is employed to search for the optimum relay

settings with maximum satisfaction of coordination

constraints. The results show that the intelligent

method for protection coordination can optimize the

protection relay settings, reduce relay mis-coordinated

operations, and increase supply reliability. The

efficiency of TCM taking the fault current changes

into consideration is also discussed in this paper.

Index Terms - Protection Relay Coordination, Time

Coordination Method, Power System Reliability.

I. INTRODUCTION

A modem protection system consists of various types

of protective relays, which functions

to

detect and isolate

system abnormalities swiftly. For various voltage level,

the various combinations of main and backup relays are

installed to provide complete protection to various power

apparatus. The main protection relay works in unit

protection principle and removes in-zone fault instantly.

The backup protection relay is designed to backup the

main protection relay in case it fails. The overcurrent relay

is

a major type of backup protection relay. As it is non-

unit protection, it is discriminated by their operating time,

which forms a sequence of backup relay operations for the

unclear system fault. Any incorrect operation of the

backup relays will result in a large area of supply

interruption

[11

as well as decreasing the supply reliability.

The backup protection relay coordination is thus necessary.

It ensures that the fault clearance actions are in correct

sequence and minimizes the supply interruption. As the

power system is changing from time to time, the

coordination work should be carried out upon any

significant change in power system configurations [2].

Based on the communication ability equipped in modem

digital relay, the coordinated relay settings can be

downloaded through the communication network. The

Time Coordination Method (TCM), which formulates the

coordination of relay settings into a set of constraint

equations and an objective function, is proposed in [3] to

The authors would like to thank The Hong Kong Polytechnic

University for supporting the research and publishing this work.

C.W.

So (e-mail: paulsot~~comnuter.or~)s currently working in

a PhD project with the Hong Kong Polytechnic University. Dr. K.K.

Li

(e-mail: cckkli@polwi.cdu,hk) is with the Dcpartment of Electrical

Engineering, Hong Kong Polytechnic University, Hong Kong.

manage the relay settings. In distribution network, the

major backup protections are Inverse Definite Minimum

Time Lag (LDMTL) overcurrent and earth fault relays.

Their operations depend on the fault current magnitude.

Thus, the relay operation is affected by the change

of

fault

current magnitude [7]. In fact, any unclear fault will be

cleared by the backup relay operations. Any circuit

breaker operation will result in changes in fault current

distribution and magnitude experienced by backup relays.

In order to boost the performance, the TCM must be able

to handle a reasonable number of fault current changes.

This paper shows how the TCM can significantly improve

the supply reliability and reduce relay mal-operations.

11. PRINCIPLES

OF

TIMECOORDINATION METHOD

(TCM)

Initialize relay settings

Objective value calculation I

E No

Fig. 1

Time Coordination Method

The process flow chart of the TCM is shown in Fig 1.

It formulates the power network and protection system

into an objective function and a set of constraint equations.

The objective function in the TCM is shown in equation

(1).

where

Ri

is each relay operation time and regulated by a

scale factor

a.

C y s the operation time difference for each pair of

relays and regulated by a scale factor p

CV,

is the number of coordination constraint

violations and regulated by scale factor

x

nd 6

Note: Variable

i,

j and

k

are iterated for all possible

system configurations.

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which will caused fault current changes. In the result

section, the efficiency of the TCM with different number

of fault current changes will be examined. The more

number of fault current changes to be handled, the larger

number of system configurations should be considered.

The possible system configurations are considered as

follows:

For a fault in a particular busbar, the number of

system configurations C to be studied due to the number

of linesN in the system is:

C=2N

The number of system configurations C' if r out of N

circuits will trip to isolate the fault is shown in equation

(4).

(3)

i O

In the sample system as shown in Fig 2, although the

number of configurations is C=2 =256, but some rare

system configurations may be ignored. If the maximum

allowable circuit outages

=

3, the number of system

configurations to process C' = C: +

C:

+C: +C:

=

93

The processing time reduction due to the minimized

system configurations is equal to 6 3 -36,3 . The

effect of the reduced number of system configuration in

constraint checking will be discussed in the result section.

C 256

During the constraint checking, the constraint

violations are checked against whether the operation time

difference between the upstream and downstream relays is

smaller than the coordination margin [3,4]. The objective

value is also calculated during constraint checking. One of

the major objective of the TCM is the minimization of the

number of constraint violations.

V . RELIABILITYVALUATION

The benefits of the TCM may be measured by the

supply reliability indices. The basic principle of the supply

reliability is presented by Billinton and Allan [9,10]. The

effectiveness of protection relay operations contributed to

the supply reliability [I

11

may be computed by the three

classic calculations. The first class of reliability

calculation is the stuck breaker and is shown in equations

4) and 5).

us b )

= b rb

4)

(b)

=

b 5)

Where

A

is the failure rate of stuck breaker.

rb is the switching time to restore system due to stuck

(b) is the supply b failure rate due to stuck breaker.

Uv(b) s the supply b restoring time.

The second class of reliability calculation is the

breaker.

busbar fault and is shown in equations 6) and (7).

Where

Afis the failure rate of busbar.

rf

is the repair time of busbar.

(b) is the supply b failure rate due to busbar fault.

Ub(b) is the supply

b

repair time.

The third class of reliability calculation is the

protection fault and is shown in equations

8)

and (9).

U ,

b)= f , r , 8)

(9)

Where

A s the failure rate of the cable.

r is the switching time of the cable.

f

s the probability of protection failure.

AJb) is the supply b failure rate due to protection

U,(b) is the supply

b

restoring time.

fault.

The resultant reliability of the supply b due to

protection operation is shown in equations (lo),

1 1)

and

(12).

A b) = As@ + + ,(b) (10)

[E]

@)= Us@) Ub(b>4 Up@)

r(b) =

U(b)/A (b)

Where

(b)

is the failure rate of supply

b.

U(b) is the repair time of supply b.

r(b) is the mean duration of supply b interruption.

The supply reliability for every supply busbar may be

evaluated by simulating the busbar fault, stuck breaker

and protection failure in each busbar. For instance, a

single-phase-to-earth fault occurs at busbar bi, the

protection relay operates according to the fault current

distribution and resulting in busbar

bj

loss of supply

(bifbj). The supply reliability of busbar bj should be

updated according to equations (6) and (7).The protection

failure and stuck breaker cases are also simulated by

applying busbar fault on the circuit connected

to

the

busbar and update the reliability indices by equations

(4),

9, 8) and 91). The resultant reliability indices will be

the sum of all individual simulated reliability indices

according to equations

lo),

(1 1) and

(12).

VI. SIMULATION RESULT N D DISCUSSION

The relay information and system parameters of the

sample distribution system are shown in Table

1

and 2

respectively.

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2004

IEEE

Intemational Conference on

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Technologies DRPT2004)

April

2004

Hong Kong

Note: All per-unit (pu) values are based on 100MVA.

Table 3: Si1

The TCM can be set of different population size,

number of generations and number of fault current

changes. The results shown

in

Table

3

are used to

determine the case for the best TCM performance.

The contribution of constraint violations in objective

value is proportional to the number of system

configurations. Moreover, from the results, the number of

constraint violations depends on the number of fault

current changes, the comparison of the objective value is

only valid for those cases with the same number of fault

current changes, i.e. case 1 to 3 , 4 to 6, 7 to 9, 10 to 12, 13

to 15 and 16 to 18. For cases 1 to 3, they have been

checked based on no fault current change. The TCM then

only checks the relay operations with single and three

phase busbar faults at E31 to B7, i.e. 12 fault cases are

being studied. In cases 16 to 18, the number of system

configurations based on equation (2) for a fault in either

busbar is

c

=

2 c

p

= 219

As there are six

busbars in the system and two types of fault are simulated,

a total of 219 x

6

x

2

= 2628 fault cases are to be studied.

Thus, the number of constraint violations for cases 16 to

18 are considerable larger than cases 1 to 13.

When a busbar fault occurred, two or more tripping

should be carried out by OC relay to isolate the fault

completely. For cases 1 to 6, since the number

of

fault

current changes is less than 2, they are impractical to

implement. The number of constraint violations and the

processing time per generation

of

cases 7 to 9 are less than

cases 10 to 18. Case

8

has the smallest number of

constraint violations. Case 14 has better reliability indices

with 0.6160 f/yr and 1.2016 hr/yr. It implies that case 13

to 15 has less chance in loss of supply due to relay mis-

coordination. As the roll of distribution

is

to provide a

reliable power network

to

customers, relay settings of case

14 should be the best for retaining the supply reliability.

The performance of MEP depends on the population

size, the number of generations and the number of fault

current changes. For cases 13

to

15, a better objective

value occurs in case 14 for population size of 50 rather

than case 13 or 15, similar behaviors occur in every three

consecutive cases. It implies that population size of 100

may be over-crowed, in which better protection settings

are not easily to be selected to survive during the selection

process in

MEP.

VII. CONCLUSION

r O

The TCM can make relays more intelligent and adapt

to the system configuration. The supply reliability can be

improved by reducing the number of mis-coordinated

relay operations. The setting of the TCM with different

number of fault current changes is examined. The result

shows that better improvement of supply reliability do not

occur in larger number of fault current changes. It implies

that the unrealistic number of fault current changes will

cause the TCM to over-test the system and the TCM force

the protection relays to handle those unrealistic system

configurations.

VIII. REFERENCE

[l ]

R.P.

Graziano,

V.J.

Kruse, G.L. Rankin,

Systems Analysis of Protection System Coordination:

A

Strategic Problem for Transmission and Distribution

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2 0 0 4 IEEE I n t e ma t i ona l Conf e r e nc e o n E l e c tr i c U t il i t y D e re gu l a ti on , Re s t r uct u r i ng a nd P ow e r T e c hn o l og i e s ( D RP T 2 004)

April

2 0 0 4 H o n g K o n g

Reliability, IEEE Transactions on Power Delivery, Vol.

7, NO. 2, pp 720-724, April 1992.

[2] William J. Ackerman, Substation Automation

nd the EMS, I999 IEEE Transmission and Distribution

Conference, April 1999,

Los

Angeles, USA, Vol.

1,

pp.

[3] C.W.

So,

K.K. Li, Time Coordination Method

for Power System Protection by Evolutionary Algorithm,

IEEE Transactions in Industry Application,

Vol. 36, No. 5,

[4] C.W. So, K.K. Li, K.T. Lai, K.Y. Fung,

Application of Genetic Algorithm for Overcurrent Relay

Coordination, IEE Ih International Conference on

Developments in Power System Protection, Nottingham,

UK, March 1997, pp. 66-69.

[5 ]

R. Salomon, Evolutionary Algorithms and

Gradient Search

:

Similarities and Differences, IEEE

Transactions on Evolutionary Computation,Volume 2, pp

[6] C.W.

So,

K.K. Li, K.T. Lai, K.Y. Fung,

Overcurrent Relay Grading Coordination Using Genetic

Algorithm, IEE APSCOM-9 7 International Conference,

Hong Kong, Vol.

1,

pp. 283-287, November 11-14, 1997.

[7] C W

So,

K K Li, Overcurrent Relay

Coordination by Evolutionary Programming, Journal of

Electric Power System Research,

Volume 53, pp 83-90,

2000.

[8] A. E. Eiben, R. Hinterding, and

Z.

michalewicz,

Parameter Control in Evolutionary Algorithms,

IEEE

Transactions on Evolutionary Computation,Volume

3 ,

pp

[9] R. Billinton, and R.N. Allan, Reliability

Evaluation of Engineering Systems: Concepts and

Techniques, Plenum Press, New York, USA, 2dEdition,

1992.

[101R. Billinton, and R.N. Allan, Reliability

Evaluation of Power Systems, Plenum Press, New York,

USA,

2d

Edition, 1996.

274-279.

Sqt/ Oc t 2000, pp. 1235-1240.

45-55, July 1998.

124-141, July 1999.

C11lJ.J. Meeuwsen,

W.L

Kling, S.P.J. Rombouts

The influence of protective relay schemes on the

reliability indices of load points in meshed operated mv

networks,

I rH International Conference and Exhibition

on Electricity Distribution, Part

1:

Contributions, Congres

International des RCseaux Electriques de Distribution

(CIRED), June 1997, IEE Publication

No.

438, Vol;. 4, pp.

14/1-14/5.

IX.

BIOGRAPHIES

C.W.

So

rcceived the BEng and PhD degree from

the Hong Kong Polytechnic University in 1996

and

2001

respectively. He is working as an

Engineer in CLP Power Ltd. in Hong Kong,

responsible for Protection and Substation

Automation. His rescarch interest is power

system protection, the applicahon of artificial

intelligent, substation automation and power

system computer programming

K. K. Li received the M.Sc. and the Ph.D degree

from the University of Manchester Institute of

Science and Technology, Manchester, U.K., and

City University, London, U.K. He is currently an

Associate Professor in the Department of

Electrical Engineering, Hong Kong Polytechnic

University, Hong Kong. His research interests

are power systcm protection and I applications

in power systems.

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