INTEGRATED SUPPORT SYSTEM FOR PROTECTIVE RELAY SETTING AND COORDINATION

Ryozo Ichie, Fusao Hirata, Sigeaki Ogawa

Chubu Electric Power Co.

Nagoya, Aichi, JAPAN

Chihiro Fukui, Hiroyuki Kudo, Yuji Nakata

Hitachi, Ltd.

Hitachi, Ibaraki, JAPAN

Keywords : Protection, Coordination, Contingency evaluation

ABSTRACT

This paper presents a newly developed integrated support system for setting and coordination of protective relays . The system aim is

to automate coordination tasks for large scale power systems. Its

advanced fault analysis module have a contingency evaluation

mechanism on network configuration and fault states. As well as

normal fault analyses such as short and ground faults, it can

calculate the circulating zero phase sequence current that may cause miss-operation of a ground fault relay. Its setting and coordination modules deal with 10 types of relay schemes.

1. INTRODUCTION

The setting and coordination of protective relays are essential

procedures to maintain power system reliability. Relay engineers

must determine suitable setting values to meet requirements of

sensitivity, selectivity, and reliability to clear faults . Thus, setting

and coordination are tedious and time consuming tasks. To determine reliable setting values , relay engineers should know critical fault conditions for various possible network configurations.

However, tremendous numbers of relays and the complex configurations of power systems have made this difficult. Therefore

automation of setting and coordination have been long awaited.[ l )[2)

Recently, much work has been done to develop computer-aided

coordination system s to help in setting and coordination.[3]-[15) In

these studies, however, only three-phase short faults and one-phase

ground faults were considered. And, most focused on coordination

problems of over-current relays and distance relays.

Today, increasing size and complexities of modern power systems and new relay schemes require more precise studies of

faults and coordination calculations. Besides, a large scale database

that stores all the necessary relay data is needed to automate the

whole relay setting process.

In order to meet these needs, Chubu Electric Power Company and

Hitachi, Ltd. have developed an integrated support system for

protective relay setting and coordination. The aim of this system is to

automate the whole coordination task for large scale power systems.

The support system includes not only the setting and coordination

system, but also a large scale database system that stores all

necessary relay data on the power systems. The database can store

data on over 10000 relays, and over 10000 buses, transformers, and tran smission lines. It can cover from 33kV to 500kV voltage

systems. Therefore relay engineers can easily specify any setting

points and relays in the whole power system. The second feature of this support system is its advanced fault

analysis functions. Beside normal fault analysis functions such as a

three-phase short fault and one-phase ground fault, the fault analysis

module provides a circulating zero-phase sequence current analysis.

This current is observed at parallel circuit transmission lines and may cause miss-operation of a ground fault relay. The fault analysis module has a contingency evaluation function . on network

configuration that automatically generates possible networks for the

most critical situation of various relays . The setting and coordination modules can execute setting

calculation of over,current relay, distance relay, current balance

relay, direction comparison relay, PCM and FM carrier differential

relays, and etc.

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In this paper, we describe the system configuration of the support

system first. Then, we explain the features of the fault analysis module. Finally, the setting and coordination modules ai:e explained.

2. CONFIGURATION OF THE SYSTEM

This support system for setting and coordination of protective relays was developed with several other power system operation

support systems[l6]. As shown in Fig. 1, the system shares the

network database with the operation scheduling and line dispatching

support systems. Besides the database, these systems share

simulating programs such as the fault a_nalysis program. The fundamental calculation modules and database are shown in

Fig. 2. They are explained below.

Mainframe

Operation Scheduling System

Line Dispatching Support System

Workstation

Database

.Network atabase

Local Area Network

Integrated Support System · for Relay Setting and Coordination ·

Workstation

Fig. 1 Relay setting and coordination system and other operation suppo1t system

Equipment Data User Interface

Relay Characteristic Editor

~Equipment Data

Relay

Network ---1.,._1Data

Editor

Characteristic ~ Data

Relay Scheme Editor

Network N t k1....,.,...__-1.,._1Analysis

D~t:or ' ,u_s_e_r_In_t_erf_ac_e~

data

~ Setting and Coordination User Interface

Network Analysis Module

Setting Module

Coordination Module

Fig. 2 System configuration (database and module architecture)

2.1 Database

Basically, the database is divided into the following sections.

1. Equipment database

2. Network configuration database

3. Relay characteristic database

4. Relay scheme database

S. Fault current database

6. Relay setting database

(1) Equipment database

Various attributes of lines and transformers are stored. These

include the shape, height, and phase disposition of towers, cable

types and sizes, and etc. By using these parameters, usual branch

data such as impedance, capacitance, and mutual impedance are

automatically calculated. Beside line data, transformer data such as

winding connections and earthing methods are also stored. In

particular the neutral earthing method at the transformer is important

to calculate the ground fault current.

(2) Network configuration database

The network configuration data of the power system are stored in

this database. Generator data, on/off states of circuit breakers, and

connection (topology)· data are also kept. The positive, negative, and

zero phase sequence impedance including mutual coupling

impedance data are stored here.

One of the features of this support system is that the network

database contains parallel line data. These data are used to calculate

the circulating zero sequence current that may cause miss-operation

of a ground fault relays. A mechanism of circulating zero sequence

current is shown schematically in Fig. 3. In Japan, two or more

lines are sometimes installed at the same tower as shown in Fig.3(a) .

When one circuit of Line-B is disconnected from the system ,

unbalance of the electromagnetic induction between Line-B and

Line-A generates the circulating zero sequence current in Line-A. In

order to deal with this problem, several types of ground fault relays

with countermeasures for circulating zero sequence current have

been developed and are in use. Therefore, calculating the circulating

current is an important function for modem relay coordinations.

The circulating zero sequence current Ico is calculated with the

following equations.

Ico = k1_L_IR + kzLL lo (1) Lk k

where, lR: Max:imum load current of Line-B

la: Max:imum one-phase ground fault current ofLine-B

L: Line length of Line-A

Lk: Line length of joint use of Line-A and Line-B at the

same towers

k 1, k2 : Induction parameters.

Unbalance electromagnetic induction

Line-Al

Line-A2

(a) Line dispositions (b) Induction of circulating zero-sequence current

Fig. 3 Zero sequence circulating current on multi-lines at the same tower

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(3) Relay characteristic database

In this database, various attributes of each relay are stored

including relay type, manufactures' type number, and other

parameters such as inverse time characteristic of over-current relays.

(4) Relay scheme database

A relay scheme including primary and backup relays, consists of

several relay units. At every point of the network, these scheme

configuration data are necessary and stored in this database.

(5) Fault current database

Results of fault analysis are stored in this database.

(6) Relay setting database

All the setting values of each relay are stored here. The setting and

coordination modules refer to this database. The final results of

coordination are also stored here, and are outputted to the laser beam

printer in the fonn of setting tables, coordination tables, etc.

2.2 User interfaces

This support system was built on an engineering workstation with high definition graphic display. All the user int~rface modules use

this graphic library. The individual databases described in section

2.1, have a user interface to edit these data. All data can be easily

modified with these interfaces.

Several hardcopies are shown in Fig. 4 as examples from a user

interface. Figure 4(a) is a example of invoking fault analysis. The

user can use an editor to create and modify the network

configuration, and invoke any fault analysis program as desired.

Figure 4(b) is an example of distance relay coordination .

2.3 Network analysis module

The network analysis module provides the following calculation

programs.

1. Fault analysis including

Three-phase short fault analysis

One-phase ground fault analysis

Voltage drop analysis at faults

2. Load flow calculation

3. Circulating zero sequence current

4. Cable melting condition by over-cunent

Voltage drop calculation is necessary for setting the under-voltage

relay.

(a) Fault analysis user-interface

3. NETWORK ANAL YSlS

Fault analysis is the essential task in determining suitable and well

coordinated relay setting values. Usually, the maxim um and

minimum fault current values are necessary to obtain the critical

situation for each relay.

In this section, we explain the new features of this support

system's contingency evaluation functions

3.1 Generation of the maximum and minimum networks

In normal setting steps, we must calculate the fault current of

every node where relays are installed. Usually, the maximum fault

current is necessary to determine instantaneous trip units, and the

minimum fault current is necessary to decide pickup current values.

Fault current ·values depend on power system conditions

including network configurations and the number of operating

generators. In order to obtain the possible maximum and minimum

fault currents, we introduced an automatic network generation

mechanism . This function generates the maximum and the minimum

size networks.

In the maximum network, all the generators are in service, and all

the transmission lines and transformers are used. In this situation,

the fault current at every node will reach the maximum value. In the

network database, all necessary data are stored. Therefore, it it quite

easy to get the maximum network.

The minimum network is introduced by considering the

contingency condition where some generators or lines are out of

service

Figure 5 describes generation of the minimum network. The basic

procedures are executed in the following order.

1. Disconnect all the generators that are connected to 77kV or

lower voltage systems.

2. Disconnect at leas t half the generators in 154kV power

stations. For example, if there are three generators in a

power station, two generators are disconnected.

3. Disconnect the transformer which has the smallest impedance

in the substations between upper and lower voltage systems.

4. Multiply the back impedance for upper voltage systems by

1.0/0. 7.

These procedures are executed rn the network generation

l'.lftlGit ( l 5~) .i r. tli'ill ll (154) 2.L

(b) Coordination user-interface

Fig. 4 Examples of graphical user-interface

791

'!54kV System ; Gcncralors

Back Impedance to upper voltage network

Zb-..l.f-

Generators undcr77kV

l1 54kV System Generators I Fig. 5 Generation of the minimum size network

function. To do this task, a network search is carried out in the depth first.

3.2 Fault analysis

The fault analysis module provides the following fault types.

1. Three-phase short fault

2. One-phase ground fault

3. Voltage drop All types of faults are calculated in each node (bus) in the

maximum and minimum networks. All the values are stored in the

database and are used in setting and coordination steps.

(1) Three-phase short fault

The results of the three-phase short fault calculation are used to

generate the equivalent back impedance for the relay setting points.

With these back impedance values, the fault current in the "remote

bus fault'', "close-in fault", and "line-end fault" are calculated.

Figure 6 shows an example of the fault calculation. The maximum

fault current is calculated with the back impedance of the maximum

network and the fault is found to be the close-in fault. The minimum

fault current is the two-phase short fault at the remote bus. (Two

phase short current is simply calculating by multiplying fJ/2 by the

three-phase fault) If this line has a multi-terminal end and there is a

transformer in an end terminal, the two-phase short fault current at

the lower voltage bus of the transformer is also calculated as the

remote-bus fault.

(2) One-phase ground fault

The one-phase fault current at every bus is used for setting

ground fault relays. In a ground fault, the fault current value

strongly depends on the earthing register of neutral point.

Therefore, the fault analysis module asks a user about the on/off

states of earthing register in calculating the one-phase ground fault.

(3) Voltage drop

Under-voltage relays are used in some relay schemes. The

calculation of voltage drop at faults is necessary for special under­

voltage relays with a load current compensation mechanism. In this

case, line-end faults or multi-te1minal end faults are considered

792

3.3 Cable melting check

In rather old transmission lines, the melting problems caused by

insufficient current capacities of cables must also be considered. In

the worst cases, cables may melt due to a fault current that is smaller

than the maximum fault cmTent. Therefore, a melting check is

important and melting current can be a constraint that is used in setting over-current relays.

Equivalent back impedance of the maximum and minimum network Note: ZBmaJ<(max .. network) < ZBmin(min. network)

Relay setting point

l3dls Maximum current in close-in fault (three phase short)

13cj>s = Wbase

1/3 v l2ct>s = Wbase

1/3 v

Ze

_lQQ_

ZBmax

100 ZBmin + ZL

ZL

Minimum current in remote-bus fault (two phase shon)

xll 2

Fig. 6 Examples of fault current calculation in close-in fault and remote bus fault

Table 1 Protective relay schemes to be set and coordinated

Status Classification Scheme type

Over-current relay (OC) Instantaneous over-current relay (HOC) Ground over-current relay (OCG)

Developed Line Phase short distance relay (DZ) Protection Ground distance relay (DG)

Current balance relay ( Short & Ground) (HSS, HSG) Pilot wire relay (PW) Directional comparison relay (DC) FM carrier differential relay (FM) PCM carrier differential (PCM)

Under Bus Protection Differential relay, Overvoltage, etc.

Development Transformer. Differential relay, Overvoltage, etc. Protection

Backward zone

Bus-A

Bus-M

Zone2 (next zone)

Bus-D

Bus-B

Zone2 (next zone)

H----~...-----U Bus-F

------1.11 Bus-G

Bus-C

Bus-H ._ __ __, Zone 2

(next zone)

Bus-I

Bus-K Bus-J

Fig.7 Topological search of primary, next, and backward protective zones

4. SETTING AND COORDINATION

4.1 Relay types Table 1 shows the relay scheme types that the setting and

coordination modules can handle. Currently, line protection· schemes are available. Other schemes such as bus protection, transformer protection are under development.

Most previous work on relay setting and coordination automation [3]-[15] focused on ~he setting procedure on over-current or distance relays . Besides these relays, this support system. provides various other relay schemes; curreht balance relay for parallel circuits, phase distance relay, pilot wire relay, direction comparison relay, and FM and PCM carrier differential relays, etc.

4.2 Protective zone search Searching the protective zone is necessary for setting distance

relays and over-current relays. For coordination calculation, information on the relays which are installed in the forward and backward directions is needed. And, there are many multi-terminal ends transmission lines in the power system that this support system handles.

793

In order to automate the setting and coordination procedure as much as possible, we developed a topological protective zone searching function that checks .all the connections stored in the network database. A search example is explained with Fig.7 . In Fig.7, the primary protective zone includes the multi-terminal ends and the transformer at Bus-D. The parallel line between Bus-A and Bus-B is also recognized as the next zone (next zone), and there are other next zones such as the line between Bus-Band Bus-E.

4.3 Setting Before building setting module, we analyzed the training manuals

for relay engineers that are used in Chubu Electric Power Company. All the setting procedures are based on them.

The setting calculation is executed in the following steps. At each step, the relay engineer can interactively edit or change the calculation values:

(1) When a relay scheme is specified, the setting module retrieves the corresponding data from relay characteristic and device data.

(2) Calculate the maximum and minimum fault current as described in Fig. 6.

Pickup current point Time j (s) 1

Inverse current relay

(Inver/se time characte1:::::taneous

high-set elay

lpickup

Back Impedance

Maximum current at close-in faull

0Time dial setting point Imax ~ !3<1>5

Time dial setting point

--- / -----o

Minimum current al remote-bus faul t

'

Imax I(A)

at next zone's emote-bus Faull

(3) Obtain the circulating zero sequence current from the

database, if necessary.

(4) With these data, determine the setting values according to

each relay's defined algorithm.

A setting example for over-current relay is shown in Fig.8. The

time dial setting value for an instantaneous over-current relay is

determined by the maximum current at the close-in fault. The pickup

fault current should meet the following conditions (constraints).

l. 9 IL :5: Ipickup

(2)

lpickup :5: l ~S I'2$S

where Ipickup is a pickup fault current,

IL is the load current at the setting point,

I2$5 is the minimum fault current at remote bus fault,

1'2<1> 5 is the minimum fault current at the next zone's

remote bus fault.

The setting value is determined considering these conditions.

When the coordination module or a relay engineer changes the

setting value, the coordination user interface checks these

conditions. ·

The setting procedures are also outputted in the form of

calculation tables as shown in Fig.9 where all the corresponding

0Pickup current point

(I) IL x 1.9 :5: lpickup

(II) lpickup~ t 12<1> 5 I

., data are displayed.

_ .. _ ..... ~"""'~'""'""~~""""""'""'----=!-,,,-- 4.4 Coordination

...

(ll) (III) The setting values of over-current relays (including short and

-¥2<1>s / 5 I2.<1>s ground relay) and distance relays should be coordinated to ensure (III) lpickup~ /5

I2<1>s

(I)

l.91L

Fig.8 An example of over-current relay setting

DZI lell (CUI (UUl-101 IA~I

a••lE ·um tHlf' .. , 151181. • IOMU

ftftllQ'Jl,..(:.>~-t:.n, •I.HU l'H·D• I I ':17°'~ !01

•:A:ll : l.H • •lolA : I.SI lhf I 1'

C T l!;: JDOI/ I

. "' P Tlt. :

U40U I 111 • 1411,

•TA!t- • taAI

z.~o • (I . Un+ !DI) x (JU' + U} • I . ll Q

z.,a . z~n 11 1.u • l. tU QQ'1

l.,.,a • Z.,O x ICTJt + PTJtl • '·'" x (Ill + 1411} • ! .10 0 lit"f

z., 0 ,l• 1•1'• 1'1':111 + l.,-.,.Ol x 100 •(I. It + 1. 11 ) )I IH •1J. 1t'IEU:.

J:-,T [) 'Jl,1..:llE

· -IJ:f:liJfillCl'))t.111

Y,n • 1.u +tu+ 1011 x ouo + •aa) . !JI] 0

z,.,o • D.H + 114 +JOO) . [ft] [I

.,. 1.H D

-~··ill '·" n

Fig. 9 Printer output of setting calculation procedure (Example of a distance relay)

the consistent operation order. In the coordination step, the

coordination module provides the graphical user interface as shown

in Fig.4(b). The user can easily change the setting values, and the

coordination module checks these new setting values.

In some radial networks, a distance relay and an over-current

relay may be installed in series as shown in Fig. 10. The

coordination module of this system can deal with this situation . In

this case, the operation times of the distance relay (DZ2 in Fig.10 )

and the instantaneous over-current relay (HOC in Fig.10) are

compared and coordinated.

Distance relay Over-current relay

~ f .. DZ2

Time °'7'' ~~~ (S~~ 2)

Instantaneous qver-current relay

794

D,Zl(step 1) HOC

Backward Zone l Primary Zone Next Zone Distance

Fig.10 Coordination between a distance relay and an over-current relay

4.6 Relay simulation

The operation simulation of each relay are also available to check

the final setting values . The simplified sequence of each relay is

used to simulate the operation with the results of fault analysis.

CONCLUSION

An integrated support system for setting and coordination of

protective relays was presented. This system has the following features.

(1) This system has a large scale database system that stores all

necessary relay data of the power systems. This database can

store data on over 10000 relays, 10000 buses, etc.

(2) This system is equipped with advanced fault analysis module.

It has a contingency evaluation mechanism on network

configuration and fault states . Beside the normal fault analysis

such as three-phase short fault and one-phase ground fault, the

fault analysis module provides the circulating zero phase

sequence current analysis. This current causes miss-operation of the ground fault relay.

(3) The setting and coordination modules can execute the setting

calculation of various types of relays such as over-current relay, distance relay, current balance relay, direction comparison relay,

and PCM and FM carrier differential relays.

(4) The entire system is built on an engineering workstation, and it

works in cooperation with other power operation support

systems. Its graphical user inte1face is easy to use, and relay

engineers can specify the setting values as desired.

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