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This document is the exclusive property of Alstom Grid and shall not betransmitted by any means, copied, reproduced or modified without the prior
written consent of Alstom Grid Technical Institute. All rights reserved.
GRID
Technical Institute
Breaker Fail Protection Considerations
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 2
Breaker Fail Protection Considerations - Agenda
Aims and Objectives Page 4
Types of Backup Protection Page 7
Typical Schemes Page 14
Single Phase Considerations Page 39
Non-conventional Techniques Page 44
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 3
Aims & Objectives
Duplicate:
Protective Relays
Trip Coils
DC Supplies Instrument Transformers
Not Duplicated:
Circuit Breakers Operating Mechanism
Hydraulic Systems
Pneumatic Systems
Dependability
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 4
Aims & Objectives
Objective:
To Clear the Fault with:
Minimal time delay
Minimum disruption to the Power System
Two forms of Backup Protection:
Remote Backup Local Backup
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 5
Breaker Fail Protection Considerations - Agenda
Aims and Objectives Page 4
Types of Backup Protection Page 7
Typical Schemes Page 14
Single Phase Considerations Page 39
Non-conventional Techniques Page 44
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 6
Remote Backup Protection
Advantages
Not affected by local station conditions
Contributes to both relay and CB failure
protection
21AA B C
Z3A
21B
Disadvantages
Slow
Sensitivity
Limited Discrimination
Z2AZ1A
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 7
Remote Backup Protection
Sensitivity Issue Affect of Fault Infeeds
Fault
Point
I
V
B
I1
A
21
I2R1 R2
B
R1
A
21
I1 I2R2
I3
Fault
Point
I
V
Effective
Fault
Point
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 8
Remote Backup Protection
Discrimination Issue Widespread Disruption
~
~
~
~
~
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 9
Local Backup Protection
Advantages
Faster
Improved sensitivity
Minimises network disruption
Disadvantages
May be affected by local conditions
Accidental Operations (finger trouble)
Security
No unwanted operations
Dependability
Guaranteed to operate when required
Why ?
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 10
Local Backup Protection
Two types of Local Backup can be considered
Relay Backup
Provision of duplicated main protection schemes
Breaker Backup
Cannot duplicate the circuit breakers (usually)
Can duplicate trip coils
Still common physical mechanism failures still possible
Breaker Failure Protection
Used to backtrip fault infeeds in case of local break failure
Only initiated when tripping has occurred
Sometimes called Stuck Breaker Protection or Backtripping Protection
Trip Circuit Supervision should be considered as part of the local backup facility
What is it?
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 11
Local Backup Protection
Duplicate Protection Schemes
CT
MAIN 2PROTECTION
MAIN 1PROTECTION
CT
CIRCUIT BREAKERMECHANISM
AUX. DCSUPPLY
VT
TCS1 TCS2
TRIP COILS
TRIP CIRCUITSUPERVISION RELAYS
CIRCUITBREAKER
TC1
TC2
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 12
Local Backup Protection
Duplicate Protection Additional Dependability
Circuit A
M2A
M1A
M1B
M2B
+ -TC1A
TC2BM2B
TC2A
TC1B
-M1A
M2A
M1B
Circuit B
Cct A Trip Supply Cct B Trip Supply
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 13
Local Backup Protection
Duplicate Protection Schemes
CT
MAIN 2PROTECTION
MAIN 1PROTECTION
CT
CIRCUIT BREAKERMECHANISM
AUX. DCSUPPLY
VT
TCS1 TCS2
TRIP COILS
TRIP CIRCUIT SUPERVISION RELAYS
CIRCUITBREAKER
TC1
TC2
CB FailProtectionScheme
Backtrip & Intertrip otherinfeeds
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 14
Local Backup Protection
If Breaker A fails to clear the fault,
Circuit Breakers B, C, D and E must be
simultaneously tripped to clear the fault
locally
Remote end Circuit Breaker should bedirectly tripped to prevent the fault being
fed (if it hasnt already been opened)
Consider Health & Safety!!
This is the responsibility of theCB Fail protection scheme
Backtripping and Intertripping
E
B A CTrip
Fault
MAINPROTECTION
Intertrip
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 15
Breaker Fail Protection Considerations - Agenda
Aims and Objectives Page 4
Types of Backup Protection Page 7
Typical Schemes Page 17
Single Phase Considerations Page 39
Non-conventional Techniques Page 44
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 16
Typical Schemes
Simplest Scheme No Current Check
+TC1
Main 2
-
86
Trip AdjacentCircuits & Intertrip
2
Main 1
TC2CB Time (Arc
Out)
Prot Op.
Protection ResetTime (Max) Error In
TimerSafety Margin
Setting Of Timer
Backtrip
Disadvantages of this simple scheme
Long total fault clearance times due to
long timer setting
Security of scheme
Risk of initiation during testing causing
widespread system disruption
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 17
Typical Schemes
Simple Scheme Use of CB Auxiliary Contact
+TC1
Main 2
-
86
Trip AdjacentCircuits & Intertrip
2
Main 1
TC2CB Time (Arc
Out)
Prot Op.
Error InTimer
Safety Margin
Setting Of Timer
Backtrip
Advantage of this scheme is that we dont need to considerthe main protection reset time so fault clearance time ismuch reduced
Disadvantages of this simple scheme
Security of scheme Risk of initiation during testing causing
widespread system disruption
52a
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 18
Typical Schemes
Simple Scheme Use of CB Auxiliary Contact
+TC1
Main 2
-
86
Trip AdjacentCircuits & Intertrip
2
Main 1
TC2CB Time (Arc
Out)
Prot Op.
Safety Margin
Setting Of Timer
Backtrip
Additional improvement by including the CB
auxiliary contact in the back tripping path
Removes timer overshoot
Increased security of trippingBut, consider is it rational or proper to consider the
breaker status in a CB failure protection scheme?
52a
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 19
Typical Schemes
Simple Scheme Use of BF Current Detector
+TC1
Main 2
-
86
Trip AdjacentCircuits & Intertrip
2
Main 1
TC2CB Time (Arc
Out)
Prot Op.
50BF ResetTime Safety Margin
Setting Of Timer
Backtrip
Advantages of this scheme are:
50BF designed for fast reset so improved total faultclearance times
Security enhanced by two elements being required tooperate for timer initiation
Disadvantages of this scheme
50BF must be set greater than maximum load current(if security is to be maintained)
50BF
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 20
Desirable Features
Sensitive
Secure
Dependable
Fast
Selective
Minimise Additional Cabling
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 21
Desirable Features
Minimum Plant Conditions
Fault Position
Operation Factor (or whats instantaneous!)
Relay Drop Off / Pick Up Ratio
Generator Circuits
Large Inductive Circuits
We NEED to achieve a setting of less than full load current
Sensitivity
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 22
Desirable Features
For Large Inductive Loads special circuit breakers are
applied, utilising dual breakers:
Main CB contacts opens first
The resistor is used to reduce the switching
overvoltages The auxiliary CB opens 1 or 2 cycles
later
BF current detector should NOT remainoperated for the resistor current IR, but
The minimum fault level MUST takepriority (in which case the timer settingwould need to allow for auxiliary CB
operation)
Switching Large Inductive Loads CB Resistor Current
LARGEINDUCTIVE
LOAD
IR
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 23
Desirable Features
If the Breaker Fail Current check is to be set below
full load, it must only be switched into service when
required:
Inhibited during normal conditions
For static type relays:
Control application of auxiliary power to
the 50BF relay
For numerical relays:
Software control
Exact operation depends upon relay
Current Settings below Full Load Current
+ -
2
86
MAIN B.F.
B/F
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 24
Typical UK Current Settings
Applies to transmission levels (400/275kV)
In general, 20% (minimum IF of 55%)
Generator Circuits, 5%
Inductive Loads, 80% (20% if IF
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Breaker Fail Protection Considerations - P 25
Breaker Fail Timer settings
Theoretically, in order to set the BF timer we should consider:
CB Trip Time
Main contact seperation time (Arc Out)
Or Resistor contact seperation time
Current Detector
Operation time, and
Reset time
Main Protection
Reset time
Discriminating (Safety) Margin
Maximum permitted fault clearance times
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 26
Timer Setting Example
Simple Scheme Current Check before Timer
+TC1
Main 2
-
86
Trip AdjacentCircuits & Intertrip
50BF
Main 1
TC2
2
MainProt
FaultOn
ArcOut Safety
MarginFaultCleared
(40) (50) (10) (50)(10) (50)
86OP
BFResetTimerStarted
(5)B
BFInit
A C D
Breaker Fail Timer setting:
A+C+D-B = 105msecs
Total Fault Clearance time (of CB Fail)
210msecs
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 27
Timer Setting Example
Alternative Arrangement Timer before Current Check
+TC1
Main 2
-
86
Trip AdjacentCircuits & Intertrip
2
Main 1
TC2
50BF
FaultCleared
MainProt
FaultOn
ArcOut Safety
Margin
(40) (50) (50)(10) (50)
86OP
BFOp.
TimerStarted
(5)BBFInit
A D
Breaker Fail Timer setting:
A+D-B = 95msecs
Total Fault Clearance time (of CB Fail)
200msecs
Considerations versus Current Check first
No Fast Reset on 50BF
2 stage schemes more difficult to implement
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 28
Typical 2 stage scheme
Start Verifier or 2-stage (re-trip & backtrip) Scheme
Advantages of 2-stage approach
With lack of use, circuit breakers will become
sticky
Start verifier, re-strikes the trip coil and may
overcome the initial reluctance of the CB to open
First stage may be time-delayed (if preferred) but
will extend overall fault clearance
Disadvantages
Breaker fail timer setting must be set longer and
overall fault clearance time is longer
-
SV
+
TC1
Main 1
TC2
SV
50BF
50BF
Main 2
Timer
86
52a
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 29
Typical 2 stage scheme
Start Verifier or 2-stage (re-trip & backtrip) Scheme
FaultOn
SVOp.
(10)
10)
(50)
40)
(50)
D
SVInit.
AE(5)
MainProt
BFInit.
BFRESET
86OP.
FaultCleared
TimerStarted
Timer Setting=A+C+D=110msec
Total BF Clearance Time = 225msec
(10) (50)C
B
ArcOut Safety
Margin
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 30
Desirable Features
Security
Duplication with Series connections
For example, duplicate current detectors & timers
AND logic: 2 out of 2 Dependability
Duplication with Parallel connections
OR logic: 1 out of 2
Cater for single contingency failure
These may often be contradictory requirements so consider the scheme carefully
Security & Dependability
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 31
Desirable Features
Security & Dependability-+
50BFMainProt
86T1B
50BF
T2BT1AT2A
-T1AT1B
+Unit DC Supply No 1
T2AT2B
-Unit DC Supply No 2
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 32
Desirable Features
Selectivity & Cabling
Breaker fail scheme needs to:-
Intertrip remote infeed
Backtrip all local feeds
Problems:
Cabling cost Cabling complexity for all but the simplest
schemes
Easy to make an error
It may be acceptable to integrate the backtripping into the
local busbar protection
BF BF BF
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 33
Desirable Features
Selectivity & Cabling Double Bus Systems
As can be seen, lots of auxiliary contacts will be required for
a segregated backtrip system
Is it more secure?
Do we duplicate the breaker fail protection scheme to
increase dependability & security?ct A
50BF
MI(A)
RI(A)
50BF
MI(C)
RI(C)
Cct C
MI(B)
RI(B)
50BF
Cct B
TCB
50BF(A)MI(A) MI(B)
RI(A) RI(B)
MI(A)
etc.
RI(A)
MI(C)
RI(C) TCC
P ti l S h E l
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Breaker Fail Protection Considerations - P 34
Practical Scheme Examples
Single Busbar Scheme
+
BBDA
50BF(A)
50BF(B)
B C
50BF(B)
50BF(C)
BBCH
50BF(A)50BFT
(A)-1
50BF(C)50BFT
(B)-150BFT(C)-1
B.B. ProtectionBuswiresNT(C)
50BFT(C)-2
BBTR(C)INT
(B)
BBTR(B)INT
(A)
BBTR(A)
50BFT(A)-2
50BFT(B)-2
P ti l S h E l
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 35
Practical Scheme Examples
Main & Reserve Bar Scheme
Main Bar
BF
(B)
BF
(A)+
MI
BB
M
BF
(C)
MIReserve Bar RI RIMI RIA B
BB
R C
50BF(A)
50BFT(A)
50BF(B)50BFT
(B)
50BF(C)50BFT(C)
MI
BBTR(A)
INT(A)
RI
MI RI INT(B)BB
TR(B)MTR
RTR
MTR RTRMII
50BFT(A)
50BFT(B)
50BFT(C)-
MI RI
BB
CH
MIRI
Practical Scheme E amples
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Breaker Fail Protection Considerations - P 36
Practical Scheme Examples
Existing 275kV Breaker Fail Scheme
+Supply 1
TRMain 1 TC1
TC2
+ T
BF1 BF2
BF1BF2
+
T1AT1B
Main 2
Supply 2TR T2A
T2BAlarmSupply
B.F. Defective+ T1AT2A 29M
M R
29R
INT
TR
B.B. Prot TripBuswires
29L
52a
T1B
T2B
CH
-
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Breaker Fail Protection Considerations - P 37
Breaker Fail Protection Considerations - Agenda
Aims and Objectives Page 4
Types of Backup Protection Page 7
Typical Schemes Page 17
Single Phase Considerations Page 39
Non-conventional Techniques Page 44
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 38
Single Phase Considerations
Standard 3 phase CB Failure Scheme
Trip AdjacentCircuits & Intertrip
Breaker Fail Timer setting:
A+E+C+D-B = 145msecs
Total Fault Clearance time (of CB Fail)
250msecs
With Common BF initiation during single phase trpis, loadcurrent will prevent fast reset of the CB Fail current check device
-
86
+
50BFABC
MainProtA
Timer
BC
FaultOn Safety
Margin
(10)50) (40)
ArcOut
(40)
MainProtReset
BFAReset86OP
FaultCleared
(10)(50) (50)
D
TimerStart
BFABCInit.
C
MainProt Op
B(5)
BFBC Reset
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 39
Single Phase Considerations
Alternative 3 phase CB Failure Scheme
Trip AdjacentCircuits & Intertrip
Breaker Fail Timer setting:
A+C+D-B = 135msecs
Total Fault Clearance time (of CB Fail)
240msecs
With Common BF initiation during single phase trpis, loadcurrent will prevent fast reset of the CB Fail current check device
FaultOn Safety
Margin
(50) (40)
ArcOut
(40)
MainProtReset
BFABCOp86OP
FaultCleared
(10)
(50) (50)
D
TimerStart BFABCInit.
C
MainProt Op
B(5)
-
86
+Timer
Main ProtA
50BFABC
BC
ABC
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 40
Single Phase Considerations
Single Phase control of current check devices required
Breaker Fail Timer setting:
A+C+D-B = 105msecs
Total Fault Clearance time (of CB Fail)
210msecs
Phase segregated control of CB fail current check relay requiredto remove main protection reset time from setting consideration
-
Timer
+BF(A)
MainProtA
86
BC
BF(B)
BF(C)
FaultOn Safety
Margin
(10)50)
ArcOut
(40)
86OP
FaultCleared
(10)(50) (50)
D
TimerStart
BFAInit.
C
MainProt Op
B(5)
BFA Reset
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 41
Single Phase Considerations
2-stage, Single Phase Control using a Modern 3 Phase Relay
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 42
Breaker Fail Protection Considerations - Agenda
Aims and Objectives Page 4
Types of Backup Protection Page 7
Typical Schemes Page 17
Single Phase Considerations Page 39
Non-conventional Techniques Page 44
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 43
Non-Conventional Techniques
Traditional CB Fail protection schemes utilise overcurrent technology Control inputs to energise the detection unit under appropriate conditions only i.e during a
fault. This permits:
Low current thresholds good sensitivity & speed
Allow for good thermal withstand Need to be designed correctly to ensure:
Fast energisation Fast resetting and very close to pick-up setting
Can suffer extended reset times during fast fault clearance due to a decaying DC current in thesecondary circuit.
Modern relays can achieve the same goals using different methods:
Software control prevent operation except during fault situation, negating traditional issuesassociated with low current settings & thermal capacity
Use of undercurrent type elements, or sampling relies on fast operation, not resetting Can account for or filter the DC currents preventing fast resetting on traditional overcurrent
based technologies
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 44
Non-Conventional Techniques
At fault clearance, the flux within the core will still be at somevalue but this suggests that there is a magnetising current
Since the primary circuit is open, this magnetising current canonly be present in the secondary circuit but it is not a sustainablestate
The CT will attempt to reach a stable state with no magnetisingcurrent
The transition from the point on the flux curve to the point withno magnetising current (CT remenance) will cause a decaying DCcomponent on the secondary circuit
Due to low current settings, this may be enough to preventresetting of overcurrent elements (or operation of undercurrent
elements)
Decaying DC Current after Fast Fault Clearance
A
C
B
E
D
F
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 45
Non-Conventional Techniques
The algorithm looks for successive positive going and negative going excursions above a positive and
negative current threshold. If they are both above the current threshold and of oposite sign, current
flow is still present i.e the CB has not opened.
Sampling Method of Current Check in CB Fail Schemes
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 46
Non-Conventional Techniques
In this case, the breaker fail timer is completed but the current check still indicates that the CB is
closed. Therefore, a CB Fail condition is given.
Sampling Method of Current Check in CB Fail Schemes
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ALSTOM 2010. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representationor warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, isstrictly prohibited.
Breaker Fail Protection Considerations - P 47
Non-Conventional Techniques
In this case, the breaker fail timer is completed and the current check indicates that the CB is open,
even in the presence of the decaying DC component due to the CB opening.
Sampling Method of Current Check in CB Fail Schemes
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