Busbar Protection Philedelphia Edu Libre

8/10/2019 Busbar Protection Philedelphia Edu Libre

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PROTECTION 2

SUBSTATION

SOMPOL C.


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Busbar Protection


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Busbar ProtectionBus arrangement

1. Radial bus

2. Main and transfer

3. Double breaker double bus

4. Ring bus

5. Breaker and a half


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Busbar ProtectionMain Bus

DisconnectSwitch

Circuit Breaker

Circuit

Radial bus


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Busbar Protection

1. Radial busAdvantages

Lowest costSmall land area required

Easy to expand

Simple to operate

Simple protective relay


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Busbar Protection

1. Radial bus

Disadvantages

Low reliabilityLow flexibility of operation for maintenance

Bus fault and failure of breaker requires substation

be removed from service


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Busbar Protection

DisconnectSwitch

Circuit Breaker

Circuits

Main Bus

Transfer Bus

TransferCircuit

Breaker(N.O.)

Circuits

N . O .

N . O .

N . O . Transfer

Switch

Main and transfer


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Busbar Protection

2. Main and transfer Advantages

Small land area required

Easy to expand

Increased flexibility of operation over radial bus

Any breaker can be removed from service without

an outage


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Busbar Protection 2. Main and transfer Disadvantages

Increased cost over radial bus Increased complexity of operation over radial bus

Increased complexity of protection over radial bus Low reliability


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Disconnect

Switch

Circuit Breaker

Circuits

Bus No. 1

Bus No. 2

Circuits

Circuit Breaker

Busbar Protection

Double breaker double bus


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Busbar Protection

3. Double breaker double busAdvantages

Very high reliability

Very flexibility operation


an outage


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Busbar Protection 3. Double breaker double bus

Disadvantages

High costLarge land area required

Complex protective relaying and control


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Circuit Breaker

Source

Load

Source

Load

Line DisconnectSwitch

DisconnectSwitch

Busbar Protection

Ring bus


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Busbar Protection4. Ring bus

Advantages

High reliability

Flexibility operation

Low cost

Any breaker can be removed from service without outage

Expandable to breaker and a half configuration


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Busbar Protection

4. Ring bus Disadvantages

Complex protective relaying and control Failed breaker during fault caused outage of one additional circuit


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Line Disconnect

Switch

Main Bus No. 1

Main Bus No. 2

Circuit Breaker

Disconnect Switch

Circuits

Circuits

Busbar Protection

Breaker and a half


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Busbar Protection

5. Breaker and a half Advantages

Very high reliabilityVery flexibility operation


an outage


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Busbar Protection

5. Breaker and a half

Disadvantages

Large land area required High cost

Complex protective relaying and control


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Busbar Protection

Approximate per unit cost Reliability

Radial 1 5

Main and transfer 1.2 4

Ring bus 1.25 3Breaker and a half 1.45 2

Double breaker double bus 1.75 1


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Busbar Protection

Radial bus


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Busbar Protection

Main and transfer


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Busbar Protection

Double breaker double bus


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Busbar Protection

Breaker and a half


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- What kind of bus arrangement

in single line diagram 1 and 2 ?- Where is the zone of protection

of 87B1 and 87B2 ?

Practice 0


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Busbar Protection

Criteria of Bus Differential relay (87B)

Check the difference current betweenthe current flow in and out of the

protected bus ( vector summation at

relay = 0 )


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Busbar Protection

Bus differential has 2 types

1. High impedance

2. Low impedance


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Busbar Protection High impedance bus differential

1. Every bay must use same class and CT ratio

2. Suitable for non switching substation

3. Easy to expand

4. Easy to use


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Because of fault current at bus bar isvery high, so some CT may saturate

and make 87B misoperation onexternal fault..


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Assume one CT saturate on external fault

Rct 87B

Voltage > 0at 87B

E C l l ti f 87B


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Ex Calculation of 87BData

- 3 phase fault current at bus = 25000 A ( If - 3phase )

- 1 phase fault current at bus = 23600 A ( If - 1phase )

- CT ratio 2000/5 ( N )

- Rct = 1.2

- RL = 1.5

( lead resistance between relay and CT )

- Relay setting range ; 175, 225, 275, 325 v

- Vk = 800 v


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Vs3 >= ( If / N )* ( Rct + RL ) ; 3 phase fault

Vs1 >= ( If / N )* ( Rct + 2RL ) ; 1phase fault

Setting of 87B ( Vs )

Vs1 = 249.6 v

Vs3 = 169.8 v

So set Vs = 325 v;

( Vk >= 2Vs )


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- From single line diagram 2, if

- 3phase fault =17000 A- 1phase fault = 13000 A

What is the setting of Vs ?

Practice 1


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Busbar Protection Low impedance bus differential

1. Can use difference CT ratio for each bay

2. Suitable for switching substation

3. Not easy to expand


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Busbar ProtectionFunction of bus differential

Trip all circuit breakers that connected

to the fault bus via 86B ( bus differential

lockout relay ) and interlock all circuit

breakers also.


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From single line diagram 2

- Which circuit breaker should be tripped if 87B1

operated?

- What is the operating time of 87B?

Practice 2


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Transmission line Protection


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Transmission line protection

Impedance seen by relay Zr = Zline + Zload

Z loadZrVr

Z lineZS

Vs

Ir

Relay point


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Basic operation of distance relay

Operating condition :


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Since the relay see current via CT and voltage

via VT, so actual impedance that relay seen is :

Z relay = Zr * CT ratio / PT ratio


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We use R-X diagram to represent the line

impedance:

Z = R + jX


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Relation between rectangular and polar form

R = P cos

Polar form

Rectangular form Z = R + jX

X = P sin

P

P = R 2 + X2

= tan-1 X/R


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We use R-X diagram to represent the line

impedance:

Z = R + jX


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R-X diagram

R

jX

Z1=R1+ jX1 Z2=R2+ jX2

Load area

P 1 1 P 2 2

1 2


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Plain impedance

R

jX


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Plain

impedancehas no

direction !


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Plain

impedance

with direction

i i li i


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Transmission line protection jX

Mho

R


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Offset mho

R

jX


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Quadrilateral


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Transmission line protection Stepped distance protection - 3 zone of protection, zone1, zone2, zone3

- 3 difference tripping time

A B CZ1A

Z2A Z3A

Z1B

Z1B

Z1C Z2C

Z3C

T2A

T3A

T2C

T2B

T2B

T3C


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Zone1 = 85 % line , instantaneous trip

Zone2 = 120 % line , delay trip T2

Zone3 = 100 % line+120 % next line delay trip T3

Example criteria

f


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Ex Calculation of 21Data

- Base voltage =115 kV

- Base MVA = 100 MVA

- CT ratio = 800/5

- PT ratio 115/115 kV/V

- Conductor type : 477 MCM AAC 590 A


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Data

- Length of line AB = 70 km, line BC = 30 km, line BD = 50 km

- Impedance data :

AB : z1= z2 = 9.7 + j29.1 p , z0 = 25.4 + j101 p

BC : z1= z2 = 5.8 + j16.9 p

BD : z1= z2 = 8 + j25 p

C

A B21 D


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Multiply by 0.16, so

AB : z1= z2 = 1.55 + j4.65 s , z0 = 4 + j16.1 s= 4.91 71.5 s

BC : z1= z2 = 0.92 + j2.7 s

BD : z1= z2 = 1.28 + j4 s

Setting

Zone 1 = 85% line AB = 4.17 71.5 s

Zone2 = 120% line AB = 5 71.5 s , 0.5 sec

Zone3 = 100% line AB + 120% line AB = 9.17 71.5 s ,1 sec


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R

jX

A

B

71.5

zone1

zone2

zone3


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Earth fault compensate

Kn = ( z0 z1 ) / 3z1

= 2.51 + j11.51 = 11.78 77.6

4.67 + j13.97 14.73 71.5

= 0.799 6.15

P ti 3


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- Which circuit breaker should be tripped if 21

line 1 operated ( both primary and back up )?

- Which circuit breaker should be reclosed?

- Where is the zone of protection of 21?

Practice 3

l


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Zone1 can over trip due to :

- CT, PT error

- Impedance data and calculation error

- Relay error

So zone1 should not set 100 % line

Tele Protection


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Tele Protection


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T i i li i


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Teleprotection scheme

1. Permissive underreach transfer trip ( PUTT )

2. Permissive overreach transfer trip ( POTT )

T i i li t ti


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- Send carrier by zone 1

1. Permissive underreach transfer trip ( PUTT )

- High speed trip ( by pass T2 ) when

zone 2 start and carrier received

T i i li t ti


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- Send carrier by zone 2

2. Permissive overreach transfer trip ( POTT )

- High speed trip ( bypass T2 ) when

zone 2 start and carrier received

T i i li t ti


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- clear fault 100% line as fast as zone 1

Benefit of teleprotection

- on more over trip

- also initiate recloser as zone 1



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Other functions in distance relay

* Power swing blocking

* Fuse failure

* Switch onto fault ( SOTF )



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Power Swing Blocking

distance relay operate by detect impedance in its

zone, and sometime voltage and current in the

system are disturb by fault. System impedance

also change and if impedance move into relays

zone, Its trip. Wrong operation!



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To prevent this situation, relay use PSB. By

detect rate of change of the impedance, relay will

know which one is fault which one is power swing

and block itself to trip



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Fuse failure

Distance relay calculate impedance by the

ratio of voltage to current. If voltage goes to zero,

impedance will be zero also. Zero impedance

means fault is very close to distance relay and

should trip the transmission line.



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PT fuse blows can make distance relay see

zero impedance in spite of no fault in high

voltage system. Distance relay use zero sequence

concept to protect itself from misoperation


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Auto recloser relay ( 79 ) - Close circuit breaker after tripped by distance relay

( only trip by high speed zone ) - Single or multi shots

- Single or three poles

- Dead time and reclaim time should be set properly

- Helpful for temporary fault

Trip & reclose


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Dead time



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Synchrocheck relay ( 25 ) - Supervise recloser relay befor close circuit breaker

by check voltage level, frequency, and phase angle

at both sides of circuit breaker ( sync. Function ,

BH-LH or LL-LB) - Only check voltage level for charge line function

( voltage check Function, BH-LD or DL-LB )


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Back up Protection

Back up Protection


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Back up Protection

In protection system, each equipment

should have 2 sets of protective relay. One

set we call primary protection and the

another is call back up protection.

Back up Protection


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Back up Protection

Example :Transformer

Primary 87K, self protection, Back up 51T, BF

Feeder

Primary 51/51G, Back up 51T, BF


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Back up Protection


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p

Bus bar Primary 87B, Back up zone2, zone3 of

others distance relay at remote endsubstation ( 115 kV ), BF

Back up Protection


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p

Principle of Breaker failure

Measure the duration of fault current from theinstance at which any relay operates to trip

circuit breaker. If current is still flowing after

preselected time delay, it is considered that thecircuit breaker has failed to trip.

Back up Protection


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p

Principle of Breaker failure

Normally breaker failure timer should less thanzone 2 timer of distance relay at remote end

substation to limit the tripping area only in

substation that breaker fail.

Back up Protection


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p

Element of Breaker failure

1. Main protection operate 2. Current detector operate ( 50BF) 3. Breaker fail timer operate ( 62BF) 4. On this function by cut off switch ( BFCO)


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Practice 4


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- If circuit breaker 80722 fail to trip, which circuit

breakers should be tripped?


- If circuit breaker 7052 fail to trip, which circuit breakers should be tripped?

Question ?


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Question ?

Have a nice day!


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Busbar Protection Philedelphia Edu Libre

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