220 kV Distance Protection

Backup To Busbar ProtectionWith

Numerical Distance Protection

Shashank Jewalikar; Dy.E.E, MSETCL

email id: shashank.jewalikar@gmail.com

TPF

��

FPT

Abstract

- An application idea for applying distance

protection to backup the busbar protection is presented

here. The proposed scheme is applicable to substations

with following bus configurations.

1) 2 Main + 1 transfer bus with bus coupler.

2) 1 Main + 1 Transfer bus with bus sectionalizer breaker

3) 1 Main bus with sectionalizer breaker.

The proposed scheme envisages use of reverse zone of

existing numerical distance protection relays in a different

way than conventionally used in utilities.

Index Terms

- Busbar protection, Numerical distance

protection, backup to busbar protection, reverse zone

I. INTRODUCTION

A bus differential protection is applied for protection

of busbar against bus faults. Looking at the various reports of

past occurrences in our network; there are many occurrences

involving non operation of bus bar protection schemes. Any

case of such non operation,

1. Always results into loss of complete bus as no selective

tripping are possible in present scheme.

2. Delays the fault clearance as the fault in such cases will be

cleared by remote Zone 2, Zone 3, T/F or generator backup

protections as the case may be.

3. Increases the spread of occurrence.

4. Many times results into a wide spread system disturbance.

This can lead to a cascade tripping condition.

Practices for enhancing reliability of Busbar protection:

For enhancing the reliability of busbar protection; following

practices are adopted.

1. Main and check zones in busbar protection.

ar protection schemes in 1 out of 2

erse zone is also said to act as a back

ication

1. T

zone

3. T opted in these cases is generally more

4. T

ackup to remote Zone 3 for the

e

ng bus

vided in two sections

3. 1 Mai

Author is working as Deputy Executive Engineer (Testing) at 400 kV

Girwali substation of MSETCL .

2. Replicated DR with check zone in RADSS

3. Main 1 and Main2 busb

or 2 out of two trip logic.

4. Distance protection rev

up for busbar protection.

First three of these practices are basically busbar repl

schemes with same differential operating principle.

Present practice for reverse Zone as back up to busbar:

he reverse zone of numerical line distance protection is

adopted to cover the bus at many places. The reverse

is generally set to cover 10% of the line impedance.

2. This is said to be a back up to the busbar protection.

he time setting ad

than Zone 3 time.

his makes the operating possibility of reverse zone

virtually remote. The bus fault; in case of non operation of

busbar protection is cleared from remote end Z2 & Z3 as

the case may be. The purpose of reverse zone backing up

bus bar protection is defeated. In a way the reverse zone in

this case is acting as a b

local bus coverage area.

The gravity of this situation can be reduced to a large extent

if bus coupler / bus sectionalizer breaker can be opened before

any Zone 2 operation takes place. This can be achieved by us

of reverse zone available with numerical distance protection

relays. The necessary configuration & settings are discussed

here. The sugges

Zone 2 Trip Zone 2 Trip

Reverse zone of

line

T > T Zone 3

ted scheme is applicable to followi

configurations.

1. 2 Main + 1 Aux. bus with bus coupler breaker.

2. 1 Main + 1 Aux. bus with Main bus di

with sectionalizer breaker.

n bus with sectionalizer breaker.

By way of opening the bus coupler before any Zone

2 operation; the bus fault will be limited the faulty bus section.

This fault will be eventually cleared by the remote Zone 2

Zone 2 Trip Zone 2 Trip

Zone 2 Trip Zone 2 Trip

Zone 2 Trip Zone 2 Trip

Fig 1: Non operation of busbar protection.

FAULT

Fig 2: Present practice of Z3 usage

Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

403

protections of the lines; transformer / generator backup

protections connected to that bus section only. (Ref. Fig 3)

Requirements of the scheme:

1. Time:

1. Bus coupler breaker should open before any remote Zone 2

operation.

2. Bus coupler trip should not be initiated before Zone 1 fault

clearance time.

3. The bus coupler trip should not initiate the LBB (50Z) of

d by the distance protection from which the

onnected to the bus.

4. A 20% of shortest line impedance can be used for

ments a two stage configuration of

Tw

2. T

fixed impedance so as to

l

onnected to the bus.

e

.

nce

g

e zone start continued. (Refer figure 4

00 kV lines as discussed

trip the

se Zone Stage 1 ---------- Trip Bus coupler.

section only. If any of the remote lines

fa

ulty bus section

stead of

up protection operation.

A logical representation of the scheme is shown in

line protecte

bus coupler trip is obtained.

2. Impedance:

1. The reverse zone always must cover the local bus

completely.

2. The reverse zone should never encroach into Zone 2 of any

of the lines c

3. The reverse zone can be set to cover 10% of protected line

impedance.

setting of

all lines where a short and a long line are connected to the

same bus.

Considering these require

reverse zone is suggested.

o stage reverse zone

1. Numerical distance relays are having separately settable

impedance zones for reach as well as direction.

he reverse zone impedance to be set to cover the bus fault.

The impedance setting to be adopted as per the

requirements discussed above. A

cover the bus can also be thought over in this case for al

the lines c

3. A two stage trip is to be obtained from this reverse zon

element

4. Stage 1: The reverse zone stage 1 will be obtained as

below.

The reverse zone start signal will be used to start an internal

timer. The timer will be set to less than Zone2 time setting of

remote end protections and more than Zone1 fault cleara

time of local end. Considering currently adopted time settin

on 400 kV level (T Z2 =300 mS & T Z1 =0 so Z1 fault

clearance = 100 mS), a time of 200 mS can be set for the

timer. An output contact will pick up on operation of timer

with presence of revers

& 5) This output contact will be used to trip bus coupler /

sectionalizer breaker.

Stage 2:

The stage 2 will be from the operation of the reverse

zone element set to a time delay of more than zone2 time.

Zone 2 Trip

With currently adopted timings for 4

above; it can be set to 400 mS. This will be used to Reverse zone of

line own breaker of the protected line.

Rever

T = 200 mS

Reverse Zone Stage 2 ---------- Trip line breaker of protected

line.

T

he stage 1 will trip the bus coupler breaker and isolate the

faulty section. The fault will now be cleared by the remote end

distance protections in Zone 2 or the T/F and generators

connected to the faulty

Zone 2 Trip

ils to trip till the stage 2 operation; stage 2 will trip the line

breakers at local end.

If the fault remains till the time of stage 2 operation a

thought can be given to initiate tripping of fa

totally(i.e. along with transformers and generators) in

waiting for their back

following diagram.

The reverse zone stage1 operation logic is like creating a

new zone of operation inside the relay.

Logic Verification & testing:

The suggested scheme logic is verified on Micom P442

relay (ref fig.6). The logic testing was carried by using the

automatic relay testing kit Omicron CMC 256-6. The method

Figure 3: Reverse zone suggested usage

Timer

(200 mS)

Reverse Zone Start

AND

LOGIC

Reverse Zone

Stage 1 trip

Reverse Zone Trip (T=400mS) Reverse Zone Stage 2 trip

Figure 4: Reverse zone 2 stage operation logic.

OR

LOGIC

Any forward zone trip Trip protected line

Reverse Zone Stage 2 trip

breaker

Start LBB of

protected line

Reverse Zone Stage 1 trip Trip bus coupler

breaker

Start LBB of Bus

Coupler

Figure 5: Reverse zone 2 stage trip logic

Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

404

included applying faults through the kit and replaying of

actual fault records. The relay was set to real line settings of

one of the lines in the MSETCL 400 kV network.

DDB #195

Z4 Pick-Up

200

0

DDB #195

Z4 & Pick-Up

0

0

Relay Label 08

DDB #007

Rev Zone Start Trip Bus Coupler

Rev Zone Start Timer T=200mS

sent protection

(M provided on all lines.

F o

1. B

and stage 2 tripping can be

at the reverse zone stage 1 trip should not

i

ections can be used for a two stage

.

stance protection:

tion will be used for two stage

r

3. Su 00 kV

o 1 S

zone stage1 operating time. As

the V lines is 400 mS, the

stag be taken to 300 mS for tripping

of bu

1 or 220 kV

ne 1 fault in 30% of line section the fault

tion in service should

e

onfigured in the relay to achieve the same functional

below.

am (Fig.4

& 5

reve

1. N e 1 & Reverse Zone = Stage 2

& 5) and

recommended

2. N tage 1

In

a

b

re internal LBB is

dition.

ed to the general

3. R

a cility for creation

b

or external LBB of the feeder. The necessary care

4. R

S

possible to configure the reverse

b

cable here.

the general

The possibility of having similar configuration with REL

521 relay is also verified.

Implementation:

The possibilities of configuration and

checks required are discussed in view of pre

practice of 400 kV & 220 kV lines.

Case 1: 400 kV Substation where two distance protections

ain1 & Main2) are

oll wing situations are considered for this case.

oth numerical protections on line: Following possibilities

exists in this case.

a. The reverse zone stage 1

separately obtained from each of the relays. It is essential

in this case th

in tiate the LBB protection.

b. Only one of the prot

reverse zone.

c. A series combination of stage1 reverse zone from both

is also possible

2. One numerical and one static di

a. Only numerical protec

everse zone.

ggested timings for 4

a. Present Zone timings

i. Zone1 = 0 mS

ii. Zone 2= 300 mS

iii. Zone 3 = 500 mS t

b. Reverse Zone timings suggested

i. Stage 1 = 200 mS

ii. Stage 2 = 400 mS

Case2: 220 kV substations where the main protection is

distance and back up is IDMT O/C & E/F

In such condition the scheme can be applied safely as far as

all of the distance protection relays connected to the

concerned bus is in service and functioning correctly.

The scheme can also be safely applied when the Zone1 fault

clearance time on the overlapping area of reverse zones and

Zone1 with only back up protection operation can be

coordinated with the reverse

Zone 2 operating time for 220 k

e 1 reverse Zone time can

s couplers in this case.

. Suggested timings f

a. Present Zone timings

i. Zone1 = 0 mS

ii. Zone 2= 400 mS

iii. Zone 3 = 700 mS to 1 S

b. Reverse Zone timings suggested

i. Stage 1 = 250/300 mS

ii. Stage 2 = 500/600 mS

Check:

For a Zo

clearance time with only back up protec

b less than the stage1 trip time of reverse zone used to trip

the bus coupler.

Configuration possibilities and LBB:

The numerical relays are providing lot of flexibility for

their configuration. Different logical formations can be

possibly c

behavior. The functional behavior of the numerical relays is

always a combination of its logic configuration and settings

adopted.

Some possibilities while configuring & setting the relay for

adoption of this busbar backup scheme are discussed

In this the logical formation shown in the logic diagr

) above to initiate the stage 1 is referred as 'new zone' and

rse zone of the relay is referred as 'reverse zone'.

ew Zone = Stag

a. This is as shown in the logic diagram (Fig.4

described already. This is the

configuration.

ew Zone = Stage 2 & Reverse Zone = S

this case following precautions are essential.

. The stage 1 trip needs to be disconnected from all

general trip conditions inside the relay.

. The stage 1 trip should not initiate the internal or

external LBB of the feeder. The external LBB initiation

can be avoided in wiring. In cases whe

used; a configuration change becomes essential. A check

should be made with the relay logic for possibility of

separation of such initiation con

c. The stage 2 here needs to be connect

trip conditions initiated from the relay. The stage2 will

initiate the LBB of the feeder.

everse Zone = Stage 1 and No stage 2

. If any of the relay is not providing fa

of new zones this configuration can be used.

. The stage 1 trip needs to be disconnected from all

general trip conditions inside the relay.

c. Here also the stage 1 trip should not initiate the

internal

as discussed in 2 above is applicable here.

ev Zone of Main1 = Stage 1 and Rev Zone of Main2 =

tage 2

a. When both main1 and main2 both numerical distance

relays are provided; it is

zones of one for stage1 and the other for stage2.

. The stage1 trip needs to be disconnected from all

general trip conditions.

c. Here also the stage 1 trip should not initiate the

internal or external LBB of the feeder. The necessary care

as discussed in 2 above is appli

d. The stage 2 here needs to be connected to

trip conditions initiated from the relay. The stage2 will

initiate the LBB of the feeder.

Figure 6: Reverse Zone stage 1 logic as implemented

in Micom P442

Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

405

5. U

tage2 comes up. This may not

guration becomes possible; the zone

eparated from the general trip conditions.

T

con

ic and timing modifications.

time check zone in combination with distance

ves

rotection

reverse zone to trip the bus coupler / sectionalizer breaker will

serve this purpose and limit th the disturbance.

r

t

se of multiple reverse zones from one relay.

a. Some of the numerical relays are providing facility to

have more than one reverse zone from one relay.

b. In such cases a possibility of configuring one for

stage1 and the other for s

be used unless it is possible to configure the relay for

continued measurement by other zones even after tripping

is issued by one of them.

c. If such confi

configured for stage1 should never initiate LBB of feeder

and be s

Extending the idea:

he idea can be extended. Following variations can be

sidered.

1) The scheme can be used to isolate the auxiliary bus faults

(i.e. by tripping the TBC breaker only) before stage2 trip

by some log

2) A definite

reverse zone can be considered for increasing the stability

of scheme.

Conclusion:

Non operation of busbar protection always increases the

spread of the disturbance. Applying relaying with different

operating principle to backup the busbar protection will be a

good practice. The present practice of utilizing reverse zone

with operating time more than Zone3 as busbar backup ser

no purpose. The suggested usage of distance p

e spread of

Shashank Jewalika

400 kV Testing Uni

MSETCL

Girwali -431 519

Ref

1. Micom P442 technical manual.

2. REL 521 technical manual.

3. Protection relay application guide- AREVA

erences:

Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

406