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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
Any breaker can be removed from service without
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
Any breaker can be removed from service without
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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Transmission line protection
Basic operation of distance relay
Operating condition :
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Transmission line protection
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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Transmission line protection
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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Transmission line protection
We use R-X diagram to represent the line
impedance:
Z = R + jX
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Transmission line protection
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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Transmission line protection
Plain impedance
R
jX
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Transmission line protection
Plain
impedancehas no
direction !
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Transmission line protection
Plain
impedance
with direction
i i li i
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Transmission line protection jX
Mho
R
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Transmission line protection
Offset mho
R
jX
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Transmission line protection
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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Transmission line protection
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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From single line diagram 2
- 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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Transmission line protection
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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Transmission line protection
Teleprotection scheme
1. Permissive underreach transfer trip ( PUTT )
2. Permissive overreach transfer trip ( POTT )
T i i li t ti
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Transmission line protection
- 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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Transmission line protection
- 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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Transmission line protection
- clear fault 100% line as fast as zone 1
Benefit of teleprotection
- on more over trip
- also initiate recloser as zone 1
Transmission line protection
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Transmission line protection
Other functions in distance relay
* Power swing blocking
* Fuse failure
* Switch onto fault ( SOTF )
Transmission line protection
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Transmission line protection
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!
Transmission line protection
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Transmission line protection
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
Transmission line protection
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Transmission line protection
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.
Transmission line protection
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Transmission line protection
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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Transmission line protection
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Transmission line protection
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
Transmission line protection
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Transmission line protection
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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From single line diagram 2
- If circuit breaker 80722 fail to trip, which circuit
breakers should be tripped?
From single line diagram 1
- 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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The end