Protection Presentation
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EXTERNAL FAULT
BB
Eng.Mohammad.A.Surrati
INTERNAL FAULT IF
BB i1
i2
i3
i4 ∑ i = if
Eng.Mohammad.A.Surrati
EXTERNAL FAULT
HV
LV I1/_0º
I2/_0º
Current difference is not equal to zero but it less than the setting value – due to CT .class error
|I1/_0º – I2 /_0º |
=0
Eng.Mohammad.A.Surrati
INTERNAL FAULT
I1/_0º
I2 /__180º
|I1/_0º – I2 /_180º |
=
|I1 +I2|
Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay
Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay A) Through-fault current under healthy conditions or on an external fault: • I2 reverses its direction (I2 = –I1) . • Both currents are equal in magnitude |I2| = |I1|. • IDiff = |I1 + I2| = |I1 – I1| = 0 . • IRest = |I1| + |I2| = |I1| + |I1| = 2·|I1| . • No tripping effect (IDiff = 0); restraint current (IRest) corresponds to twice the through flowing current. Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay B) Internal fault, fed from each end (with equal currents ): • In this case, I2 = I1 in direction . • In magnitude |I2| = |I1| . • IDiff = |I1 + I2| = |I1 + I1| = 2·|I1| . • IRest = |I1| + |I2| = |I1| + |I1| = 2·|I1| . • Tripping effect (IDiff) and restraining (IRest) quantities are equal and correspond to the total fault current. Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay C) Internal fault, fed from one end only: • In this case, I2 = 0 • IDiff = |I1 + I2| = |I1 + 0| = |I1| • IRest = |I1| + |I2| = |I1| + 0 = |I1| • Tripping effect (IDiff) and restraining (IRest) quantities are equal and correspond to the fault current fed from one side. Eng.Mohammad.A.Surrati
Metro cell
REF
REF
R
R
stabilizing
At Turn to turn occur , diff relay cannot operate due to low current . REF relay will operate by voltage according to the setting
Eng.Mohammad.A.Surrati
EXTERNAL FAULT
I2/_0º
I1/_0º
Current difference is not equal to zero but it less than the setting value – due to CT .class error
|I1/_0º – I2 /_0º |
=0
Eng.Mohammad.A.Surrati
INTERNAL FAULT
I1/_0º
I2 /__180º
|I1/_0º – I2 /_180º |
=
|I1 +I2|
Eng.Mohammad.A.Surrati
Problems in Diffrential Protection Saturate any one of the CT’s during fault- 1 For transformer , current from both CTs may not equal- 2 . due to changing tap changing position For cables , current from both CT’s may not equal due- 3 . to capacitive current
Mal - operation of the relay
Eng.Mohammad.A.Surrati
THE SOLUSION
Biased Differential Protection
I restrain
Idiff
SEESAW
Eng.Mohammad.A.Surrati
= I stabilizing
I diff
I restrain
SEESAW
Eng.Mohammad.A.Surrati
= I stabilizing
s
s
I2
I1
= I1| + |I2 | |IRESTRAIN
Eng.Mohammad.A.Surrati
s I2
s I1
= I1| + |I2 | |IRESTRAIN Eng.Mohammad.A.Surrati
I RESTRAIN is the algebraic sum of I1 and I2 . The current passing through restrain coil is DC . It is converted from AC to DC through bridge rectifier
Eng.Mohammad.A.Surrati
T = 2 sec T = 1.5 sec C
B
A T = 0 sec Z1 85%
T = 0.5 sec %Z2 120
T = 1 sec Z3 200%
21 Relay will not respond
Eng.Mohammad.A.Surrati
Z4
Z5
T = 2 sec B T = 0.5 sec
A Z5
T = 0 sec Z1 85%
%Z2 120
T = 1.5 sec C T = 1 sec Z3 200%
21
Eng.Mohammad.A.Surrati
Z4
)Permissive under – reach zone 1 extension ( PUR Z1X A
21
B
SEND
Z1 85% Z1 85%
%Z2 120
Both relays will not respond
21
C
Z1X
Z2 = Z1X Both breakers will trip instantaneously with no effect of SEND signal :Summary : The distance relay will operate at Z1 time if . Fault occur at Z1- 1 Fault occur out of Z1 and inside Z1X (DISTANCE PICK UP) + Receive SEND- 2 .signal from remote end distance relay Eng.Mohammad.A.Surrati
)Permissive under – reach zone 1 extension ( PUR Z1X DISADVANTAGE 1
It is used with over head lines (OHL) for more than 20 km , and it is not advisable to be used in short distances of over head lines (less than 20 km )
S/S B
S/S A ARCING RESISTANCE
Eng.Mohammad.A.Surrati
)Permissive under – reach zone 1 extension ( PUR Z1X
B
A
Z1X
Z1 85%
21
C
21
Arcing resistance is added to line impedance when fault is in the middle of the line which cause increase in line impedance . So then both relays .will see the fault as Z2 and give delay tripping Eng.Mohammad.A.Surrati
DISADVANTAGE 2
A
Z1 85%
21
B
NO SEND
T = 0.5 sec
%Z2 120
21
Eng.Mohammad.A.Surrati
C
Z1X
)Permissive under reach Transfer trip ( PUTT A
21
B
SEND
Z1 85% Z1 85%
%Z2 120
Both relays will not respond
21
C
Both breakers will trip instantaneously with no effect of SEND signal :Summary : The distance relay will operate at Z1 time if . Fault occur at Z1- 1 Fault occur out of Z1 (DISTANCE PICK UP) + Receive SEND signal from- 2 .remote end distance relay Eng.Mohammad.A.Surrati
)Permissive over reach Transfer trip ( POTT A
SEND
B
C
ZOR %Z2 120 Z1 85% Z1 85%
Both relays will 21 not respond and relay A will trip at Z2 will trip instantaneously with no effect of Both breakers SEND signal :Summary : The distance relay will operate at Z1 time if 21
. Fault occur at Z1- 1 Fault occur out of Z1 and inside ZOR (DISTANCE PICK UP) + Receive SEND- 2 .signal from remote end distance relay Eng.Mohammad.A.Surrati
)Permissive over reach Transfer trip ( POTT ECHO FEATURE A
Z1 85%
21
B
ECHO SEND ZOR
%Z2 120
21
Z2 = ZOR
Eng.Mohammad.A.Surrati
C
)Permissive over reach Transfer trip ( POTT WEEK INFEED FEATURE KV 110 KV KV KV 80 90 77
KV 110 A
B
SEND
Z1 85%
G
21 Z2 = ZOR
ZOR
%Z2 120
21 WEEK INFEED UNIT OPERATED
Eng.Mohammad.A.Surrati
C
Pelec
Generator Out of Step due to prolong of fault without WEEK END FEED function
Pmech
δ Eng.Mohammad.A.Surrati
Blocking Over Reach
Blocking Signal
A
B
ZOR %Z2 120 Z1 85% Z1 85%
21 Z2 Z1 = ZOR
21 21 Z1 = ZOR
Eng.Mohammad.A.Surrati
C
NO EVOLVING FAULT OCCURE
)Auto Reclosure (AR A
B
Z1 85%
+ + +
+ Dist trip
TC _
+
Action
Dead
Reclaim
Time
Time
Time
+
AR AR STARTING
AR CB cycleTRIP CC starting _
Eng.Mohammad.A.Surrati
Reclosing command
Reclaim time expired
EVOLVING FAULT OCCURE
)Auto Reclosure (AR A
B
Z1 85%
+ + +
+ Dist trip
TC _
+
Action
Dead
Reclaim
Time
Time
Time
+
AR AR STARTING
AR CB cycleTRIP CC starting _
Eng.Mohammad.A.Surrati
Reclosing command
BB
Eng.Mohammad.A.Surrati
INTERNAL FAULT IF
BB i1
i2
i3
i4 ∑ i = if
Eng.Mohammad.A.Surrati
EXTERNAL FAULT
HV
LV I1/_0º
I2/_0º
Current difference is not equal to zero but it less than the setting value – due to CT .class error
|I1/_0º – I2 /_0º |
=0
Eng.Mohammad.A.Surrati
INTERNAL FAULT
I1/_0º
I2 /__180º
|I1/_0º – I2 /_180º |
=
|I1 +I2|
Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay
Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay A) Through-fault current under healthy conditions or on an external fault: • I2 reverses its direction (I2 = –I1) . • Both currents are equal in magnitude |I2| = |I1|. • IDiff = |I1 + I2| = |I1 – I1| = 0 . • IRest = |I1| + |I2| = |I1| + |I1| = 2·|I1| . • No tripping effect (IDiff = 0); restraint current (IRest) corresponds to twice the through flowing current. Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay B) Internal fault, fed from each end (with equal currents ): • In this case, I2 = I1 in direction . • In magnitude |I2| = |I1| . • IDiff = |I1 + I2| = |I1 + I1| = 2·|I1| . • IRest = |I1| + |I2| = |I1| + |I1| = 2·|I1| . • Tripping effect (IDiff) and restraining (IRest) quantities are equal and correspond to the total fault current. Eng.Mohammad.A.Surrati
Operating conditions of transformer Diff relay C) Internal fault, fed from one end only: • In this case, I2 = 0 • IDiff = |I1 + I2| = |I1 + 0| = |I1| • IRest = |I1| + |I2| = |I1| + 0 = |I1| • Tripping effect (IDiff) and restraining (IRest) quantities are equal and correspond to the fault current fed from one side. Eng.Mohammad.A.Surrati
Metro cell
REF
REF
R
R
stabilizing
At Turn to turn occur , diff relay cannot operate due to low current . REF relay will operate by voltage according to the setting
Eng.Mohammad.A.Surrati
EXTERNAL FAULT
I2/_0º
I1/_0º
Current difference is not equal to zero but it less than the setting value – due to CT .class error
|I1/_0º – I2 /_0º |
=0
Eng.Mohammad.A.Surrati
INTERNAL FAULT
I1/_0º
I2 /__180º
|I1/_0º – I2 /_180º |
=
|I1 +I2|
Eng.Mohammad.A.Surrati
Problems in Diffrential Protection Saturate any one of the CT’s during fault- 1 For transformer , current from both CTs may not equal- 2 . due to changing tap changing position For cables , current from both CT’s may not equal due- 3 . to capacitive current
Mal - operation of the relay
Eng.Mohammad.A.Surrati
THE SOLUSION
Biased Differential Protection
I restrain
Idiff
SEESAW
Eng.Mohammad.A.Surrati
= I stabilizing
I diff
I restrain
SEESAW
Eng.Mohammad.A.Surrati
= I stabilizing
s
s
I2
I1
= I1| + |I2 | |IRESTRAIN
Eng.Mohammad.A.Surrati
s I2
s I1
= I1| + |I2 | |IRESTRAIN Eng.Mohammad.A.Surrati
I RESTRAIN is the algebraic sum of I1 and I2 . The current passing through restrain coil is DC . It is converted from AC to DC through bridge rectifier
Eng.Mohammad.A.Surrati
T = 2 sec T = 1.5 sec C
B
A T = 0 sec Z1 85%
T = 0.5 sec %Z2 120
T = 1 sec Z3 200%
21 Relay will not respond
Eng.Mohammad.A.Surrati
Z4
Z5
T = 2 sec B T = 0.5 sec
A Z5
T = 0 sec Z1 85%
%Z2 120
T = 1.5 sec C T = 1 sec Z3 200%
21
Eng.Mohammad.A.Surrati
Z4
)Permissive under – reach zone 1 extension ( PUR Z1X A
21
B
SEND
Z1 85% Z1 85%
%Z2 120
Both relays will not respond
21
C
Z1X
Z2 = Z1X Both breakers will trip instantaneously with no effect of SEND signal :Summary : The distance relay will operate at Z1 time if . Fault occur at Z1- 1 Fault occur out of Z1 and inside Z1X (DISTANCE PICK UP) + Receive SEND- 2 .signal from remote end distance relay Eng.Mohammad.A.Surrati
)Permissive under – reach zone 1 extension ( PUR Z1X DISADVANTAGE 1
It is used with over head lines (OHL) for more than 20 km , and it is not advisable to be used in short distances of over head lines (less than 20 km )
S/S B
S/S A ARCING RESISTANCE
Eng.Mohammad.A.Surrati
)Permissive under – reach zone 1 extension ( PUR Z1X
B
A
Z1X
Z1 85%
21
C
21
Arcing resistance is added to line impedance when fault is in the middle of the line which cause increase in line impedance . So then both relays .will see the fault as Z2 and give delay tripping Eng.Mohammad.A.Surrati
DISADVANTAGE 2
A
Z1 85%
21
B
NO SEND
T = 0.5 sec
%Z2 120
21
Eng.Mohammad.A.Surrati
C
Z1X
)Permissive under reach Transfer trip ( PUTT A
21
B
SEND
Z1 85% Z1 85%
%Z2 120
Both relays will not respond
21
C
Both breakers will trip instantaneously with no effect of SEND signal :Summary : The distance relay will operate at Z1 time if . Fault occur at Z1- 1 Fault occur out of Z1 (DISTANCE PICK UP) + Receive SEND signal from- 2 .remote end distance relay Eng.Mohammad.A.Surrati
)Permissive over reach Transfer trip ( POTT A
SEND
B
C
ZOR %Z2 120 Z1 85% Z1 85%
Both relays will 21 not respond and relay A will trip at Z2 will trip instantaneously with no effect of Both breakers SEND signal :Summary : The distance relay will operate at Z1 time if 21
. Fault occur at Z1- 1 Fault occur out of Z1 and inside ZOR (DISTANCE PICK UP) + Receive SEND- 2 .signal from remote end distance relay Eng.Mohammad.A.Surrati
)Permissive over reach Transfer trip ( POTT ECHO FEATURE A
Z1 85%
21
B
ECHO SEND ZOR
%Z2 120
21
Z2 = ZOR
Eng.Mohammad.A.Surrati
C
)Permissive over reach Transfer trip ( POTT WEEK INFEED FEATURE KV 110 KV KV KV 80 90 77
KV 110 A
B
SEND
Z1 85%
G
21 Z2 = ZOR
ZOR
%Z2 120
21 WEEK INFEED UNIT OPERATED
Eng.Mohammad.A.Surrati
C
Pelec
Generator Out of Step due to prolong of fault without WEEK END FEED function
Pmech
δ Eng.Mohammad.A.Surrati
Blocking Over Reach
Blocking Signal
A
B
ZOR %Z2 120 Z1 85% Z1 85%
21 Z2 Z1 = ZOR
21 21 Z1 = ZOR
Eng.Mohammad.A.Surrati
C
NO EVOLVING FAULT OCCURE
)Auto Reclosure (AR A
B
Z1 85%
+ + +
+ Dist trip
TC _
+
Action
Dead
Reclaim
Time
Time
Time
+
AR AR STARTING
AR CB cycleTRIP CC starting _
Eng.Mohammad.A.Surrati
Reclosing command
Reclaim time expired
EVOLVING FAULT OCCURE
)Auto Reclosure (AR A
B
Z1 85%
+ + +
+ Dist trip
TC _
+
Action
Dead
Reclaim
Time
Time
Time
+
AR AR STARTING
AR CB cycleTRIP CC starting _
Eng.Mohammad.A.Surrati
Reclosing command
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