2 breaker fail protection ms

8/22/2019 2 Breaker Fail Protection MS

1/48

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


2/48

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


3/48



Aims & Objectives

Duplicate:

Protective Relays

Trip Coils

DC Supplies Instrument Transformers

Not Duplicated:

Circuit Breakers Operating Mechanism

Hydraulic Systems

Pneumatic Systems

Dependability


4/48



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


5/48










6/48



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


7/48




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


8/48




Discrimination Issue Widespread Disruption

~

~

~

~

~


9/48



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 ?


10/48




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?


11/48




Duplicate Protection Schemes

CT

MAIN 2PROTECTION

MAIN 1PROTECTION

CT

CIRCUIT BREAKERMECHANISM

AUX. DCSUPPLY

VT

TCS1 TCS2

TRIP COILS

TRIP CIRCUITSUPERVISION RELAYS

CIRCUITBREAKER

TC1

TC2


12/48




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


13/48




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


14/48




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


15/48










16/48



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


17/48



Typical Schemes

Simple Scheme Use of CB Auxiliary Contact

+TC1

Main 2

-

86


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


18/48



Typical Schemes

Simple Scheme Use of CB Auxiliary Contact

+TC1

Main 2

-

86


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


19/48



Typical Schemes

Simple Scheme Use of BF Current Detector

+TC1

Main 2

-

86


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


20/48



Desirable Features

Sensitive

Secure

Dependable

Fast

Selective

Minimise Additional Cabling


21/48



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


22/48



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


23/48



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


24/48



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


25/48



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


26/48



Timer Setting Example

Simple Scheme Current Check before Timer

+TC1

Main 2

-

86


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


27/48



Timer Setting Example

Alternative Arrangement Timer before Current Check

+TC1

Main 2

-

86


2

Main 1

TC2

50BF

FaultCleared

MainProt

FaultOn

ArcOut Safety

Margin

(40) (50) (50)(10) (50)

86OP

BFOp.

TimerStarted

(5)BBFInit

A D


A+D-B = 95msecs


200msecs

Considerations versus Current Check first

No Fast Reset on 50BF

2 stage schemes more difficult to implement


28/48



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


29/48



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


30/48



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


31/48



Desirable Features

Security & Dependability-+

50BFMainProt

86T1B

50BF

T2BT1AT2A

-T1AT1B

+Unit DC Supply No 1

T2AT2B

-Unit DC Supply No 2


32/48



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


33/48



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


34/48



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


35/48




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


36/48




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

-


37/48










38/48



Single Phase Considerations

Standard 3 phase CB Failure Scheme



A+E+C+D-B = 145msecs


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


39/48




Alternative 3 phase CB Failure Scheme



A+C+D-B = 135msecs


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


40/48




Single Phase control of current check devices required


A+C+D-B = 105msecs


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


41/48




2-stage, Single Phase Control using a Modern 3 Phase Relay


42/48










43/48



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


44/48




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


45/48




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


46/48




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.



47/48




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.



48/48

This document is the exclusive property of Alstom Grid and shall not be

GRID

Technical Institute

2 breaker fail protection ms

Documents