2 Busbar Protection

7/28/2019 2 Busbar Protection

1/79

1 1> Busbar Protection

Busbar Protect ion

Busbar Protection:Including High Impedance,

Frame Leakage andDirectional Comparison

Principles

GRID

Technical Institute

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.


2/79


Busbar Protect ion

There are fewer faults

on busbars than on

other parts of the

power system

F2F1

Without Busbar Protection

No dislocation of system due to accidental operation of busbar

protection

Slow Fault Clearance

Busbar faults at F1 and F2 are cleared by remote time delayed

protection on circuits feeding the faults:

Time Delayed Overcurrent or

Time Delayed Distance Protection


3/79


Busbar Protect ion

F2F1

Busbar

Zone

With Busbar Protection

Fast clearance by Breakers at the Busbars

Where Busbars are sectionalised, protection can limit the amount ofsystem disruption for a Busbar fault


4/79


Busbar protect ion must be

ReliableFailure could cause widespread damage to the substation

Stable

False tripping can cause widespread interruption of

supplies to customers

Discriminating

Should trip the minimum number of breakers to clear the

fault

Fast

To limit damage and possible power system instability


5/79


Busbar faul ts are usual ly permanent

CAUSES

Insulation failures

Circuit breaker failures

Falling debris

Isolators operated outside their ratings

Safety earths left connected

Current transformer failures

THEREFORE:CIRCUIT BREAKERS SHOULD BE TRIPPED AND

LOCKED OUT BY BUSBAR PROTECTION


6/79


Methods of p rovid ing Busbar protect ion

1. Remote Time Delayed Protection

2. Frame to Earth (Leakage) Protection

3. Directional Comparison Protection

4. Phase Comparison Protection

5. Differential Protection: High Impedance

Low Impedance


7/797 7> Busbar Protection

Frame leakage pro tect ion

ADVANTAGES

1. Simple and economic form of protection

2. Ideal for the protection of phase segregated switchgear where

earth fault protection only is required

DISADVANTAGES

1. Insulation is required between switchgear sections

2. It is not possible to discriminate between faults on two sets of

busbars running through common switchgear frames

3. Care must be taken in construction of the substation in order to

ensure that the fixing bolts do not come in to contact with thesteel reinforcing of the concrete



Frame earth pro tect ion scheme

Only an earth fault system

Involves measuring fault current from switchgear frame to

earth

Switchgear insulated by standing on concrete plinth

Only one earthing point allowed on switchgear

C.T. mounted on single earth conductor used to energise

instantaneous relay

All cable glands must be insulated



Sing le Zone Frame - Earth Protectio n

64

G

Frame-earth

fault relay

H J K

+Trip all circuit breakers

Switchgear frame



Current Distr ibu t ion fo r External Fault

Generator

Frame-leakage current

transformer

Switchgear frame

Switchgear frame

bonding bar

Outgoing feeder

System earthing resistor

Earth bar

Earthing electrode

resistance

Frame insulation

resistance to earth

I1 + I2

I2I1I1

IF= I1 + I2



Frame leakage Busbar protect ion

External Fault

I1

I1

>10 I2



Frame leakage Busbar protect ion

INTERNAL FAULT

Suitable for phase segregated indoor metalclad

switchgear. Only E/F protection required.

I1

I2

Frame

Insulation

>10I2

I1+ I2

IF=

I1 +

I2

Frame

System

Earthing

Resistance

Substation

Earthing

Electrode 0.1 IF(Max)

Disadvantages:

Insulation of switchgear frame and between sections

Insulation of cable glands to prevent spurious currents

during through faults



Frame leakage scheme

w ith doub le insulat ion barr ier

64

Z1

Trip A

BA

Insulation Barrier

Zone 1 Zone 2

C

Trip B

96

CTrip C

Zone 3

96

A

96

B1

64

Z2

96

B2



Frame leakage scheme

w ith sing le insulat ion barr ier

64

Z1

Trip A

BA

Insulation Barrier

Zone 1 Zone 2

C

A

Trip B

B1 B2

T

C Trip C

0.2 -1 SEC.

64

Z2



Frame leakage scheme for dup l icate Busbars

64Z1

BA

Insulation Barrier

Zone 1 Zone 2

c

Zone 3

+

64Z3

RM1

a b

Dd

C

96

Aa

b

96D1

96

D296

B196

B296

C

c

d

M1 M2 R

M2

-



Frame leakage pro tect ion

Check feature

To differentiate between a genuine busbar fault and a fault

in the secondary winding of a c.t.

The check feature provides a second line of defence

The check relays pick up for both internal and external faults

Both check and discriminating relays must operate beforetripping can occur

The various methods of obtaining the check feature are:-

a) Neutral check provided by a relay energised from a single c.t.in the power system neutral

b) Residual check provided by a relay energised from a residually

connected c.t. on the busbar incomersc) Residual voltage check provided by a voltage relay energised

from a broken delta v.t. supply

Check relays are normally self-reset in order to avoid havingto reset the relay after each external fault

Si l Z F E th P t t i



Single Zone Frame Earth Protect ionWith Neutral Check

64

+

G H

64

CH

Neutral check relay

Trip all circuit

breakers

Frame-earthfault relay

J K

Switchgear frame

T i l T i A d A l Ci i t F F L k



Typical Trip And A larm Circuits For Frame Leakage

With Double Insulat ion Barr ier And Check Feature

CSS-Z1

+-

96

A

In Out64Z1-1

In Out

CSS-Z2

64Z2-1

96

B1

96

B2

96

C

Trip Supply

Supervision

64CH-1

AlarmRelay

7464CH-2 64Z1-2

64Z2-2

74-1

74-2

Lamp

Lamp

Lamp

Lamp

Buzzer

In Out

In Out

CSS-Z1

CSS-Z2Alarm

SupplySupervision

Lamp

Di t i l C i S h



Direct ional Comparison Scheme

R

+ (a) Trip

R

R

+(b)

Trip

R

BR

Load

current

Phase to earth external

fault, scheme (a)

Di t i l C i S h



Direct ional Comparison Scheme

R

+ (a) Trip

R

R

+(b)

Trip

R

BR

Load

current

Phase to earth external

fault, scheme (b)



Phase Comparison Scheme - External Fault

Positive Half Cycle Negative Half Cycle

A

B

A

B

B A B

Feeder X

A B A

Feeder Y

Relay Operation

Current Transformer

Secondary Current

+Trip

+Trip

X Y X Y

Ph C i S h I t l F l t



Phase Comparison Scheme - Internal Fault

A

+

B

A

BTrip

Trip

A B A

Feeder X

A B A

Feeder YRelay Operation

Current Transformer

Secondary Current

X YX Y

Positive Half Cycle Negative Half Cycle

+

Basic Circ lating C rrent Scheme


23/79


Basic Circulating Current Scheme

External Fault

R

R

Internal Fault

Differential Protect ion


24/79


Differential Protect ion

Uses Merz-Price circulating current principle. All currents

entering and leaving Busbar are compared

One set of CTs for each circuit associated with a particularzone are all connected to a relay

A single element relay gives earth fault protection only

A three element relay gives phase and earth fault protection


25/79


Basic Circul t ing Current Scheme

Earth Fault Pro tect ion Only

G H J K

87

Differential

relay

C C


26/79


Phase And Earth Fault Circu lat ing Current

Scheme Using Three-Element Relay

G H

AB

C

N

Differentialrelay

87A 87B 87C

High Impedance Protect ion


27/79


High Impedance Protect ion

This is a versatile and reliable protection system applied to

many different Busbar configurations

If CT requirements are met, scheme performance may be

predicted by calculation without heavy current conjunctive

tests

High Impedance Busbar Protect ion


28/79



Simple system to apply and extend

High Sensitivity for phase and earth faults

Extremely stable for external faults

Hi h I d B b P t t i


29/79



RST

87

Metrosil

CT Requirements: Equal ratios

Class X

May require stabilising resistors, RST

May require non-linear resistors (Metrosils)

High Impedance Differential Pro tect ion


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High Impedance Differential Pro tect ion

Uses equal ratio CTs

Scheme assumes that with heaviest through fault, one CT

saturates, the other not

To ensure stability, voltage setting of relay circuit made

higher than voltage developed across relay circuit. To

achieve this an extra relay circuit resistance is required.

This is known as the stabilising resistance

E i l t Ci i t


31/79


Equivalent Circu i t

Y ZM

RCT RLY RLX RCT

RST

RR

R ZM X

Hi h I d Th


32/79


High Impedance Theory

RS

IF

RCT

Assume one CT saturates

Assume relay resistance is high

V = IF (2RL + RCT)VS > V

RL IF

RL

RCT

RL RL

V



33/79



Choose IS from min fault current ( 30%)

VS = ISRS + ISRR

ISRS = VS ISRR

RS = - RR

RS =

IS

RS

RR

VS

S

S

I

V

2

SS

S

I

VA-

I

V

Thus we can choose a value of RS:-

Knowing 1) Max. & Min Fault Levels,

2) C.T. Circuit Impedances,

3) Relay Information,

4) C.T. Ratio,

Primary Operating Current (P O C )


34/79


Primary Operating Current (P.O.C.)

The value of primary operating current should be around

30% of minimum fault current available. This ensures

sufficient relay current during internal fault conditions for

high speed operation

Differential Relays


35/79


Differential Relays

Relays used for high impedance protection are high

stability, unbiased and tuned to nominal frequency.

Two modular types are available:-

MCAG14/34

Current calibrated with external stabilising resistor

MFAC14/34

Voltage calibrated with internal high impedance

Knee Poin t Voltage Definit ion


36/79


Knee-Poin t Voltage Definit ion

For High Impedance Protection Choose VK

such that:

VK2VSThis ensures fast operation for all faults greater than the setting

current.

VK is thus dependent on setting voltage and hence on maximum

through fault current.

ICK

Exciting

Voltage

(VS

)

VK

Exciting Current (Ie)

+10% VK

+50% IeK

In ternal faul t on high impedance scheme


37/79


In ternal faul t on high impedance scheme

Zm

RST

VF = IF.R

= IF.

Effective setting

IS

= IR

+ 2Ie

with 2 circuits

= IR + nIe with n circuits

Primary effective setting

IP = T.(IR+nIe)

Or IP = T.(IR+ nIe+IM+ISR+IV)

RCT

VF

RLY RLX RCT

R

ZmX

IF

)R+(RI

ILXCT

R

Y

F

Y

Use of faul t sett ing resisto r


38/79


Use of faul t sett ing resisto r

I0P = IR + ISR

I0P

ISR

RSR

IR

RST

RR

Metros i l l im itat ion of relay vol tage


39/79


Metros i l l im itat ion of relay voltage

IR

RR

For heavy internal faults large voltages may develop across relay +Stab. Resistor.

>3kV Voltages must use Metrosil

VP =

VK = Knee point voltage

VF= Max. RMS voltage if C.T. didnt saturate= IF(RCT + 2RL + RST + RR)

For Metrosil:

V = CI (D.C.)

= C (A.C.)

VS

RST

Im

V

IOP

)V-(V2V2 KFK

52.0

IRMS

VM

SV2

Use of Non L inear Resis tors


40/79


Use of Non L inear Resis tors

Under in zone fault conditions it is possible for voltages above the

relay withstand of 3kV peak to be produced. Metrosil non linearresistors may be necessary to limit the peak voltage below thislevel

Approx peak volts =

Metrosil characteristic:- V = CIwhere:- V and I are peak values

C = constant depending on metrosilconstruction

= constant in range of 0.2 to 0.25

The values of C and are chosen to limit metrosil voltage to less

than 3kV peak at maximum fault current

)V-(V2V2 KFK

Metros i l L im itat ion Of Relay Voltage


41/79


Metros i l Lim itat ion Of Relay Voltage

IR

RR

To ensure primary operating current not adversely affected,

metrosil constant C must be sufficiently high to restrict metrosilcurrent at relay setting voltage VS.

Typical currents:-

30mA for use with 1 amp CTs

100mA for use with 5 amp CTs

VS

RST

INLR

IOP

VMLRR

CT Wir ing Supervision


42/79


g p

Open circuit connections between CTs and relay circuit result inunbalance currents which may operate the protection.

Supervision is applied by a voltage relay across differential relay

circuit

Supervision relay is time delayed, gives alarm and also shorts out

bus wires to protect differential relay circuit

Typical effective setting is 25 primary amps or 10% of lowest

circuit rating, which ever is greater.

Healthy Cond it ion


43/79


Healthy Cond it ion

ZM4

CT4

I4

ZM3

CT3

ZM2

CT2

I2 I3

Super

VisionRelayRR

RST

ZM1

CT1

I1

I1 = I2 + I3 + I4

Supervision Against Open Circuit C T s


44/79


Supervision Against Open Circuit C.T. s

I4

ZM2

I1

Super

Vision

RelayRR

RST

CT1 open circuit, I1 flows through magnetising impedance and relay circuit

in parallel

Voltage measured by supervision relay

V = I1 (RZM2 ZM3 ZM4)If Supervision relay setting = VSPOut-of-balance current to operate the supervision relay

VR

ZM4 ZM3

I1

I3I2

M4

SP

M3

SP

M2

SPSP

Z

V+

Z

V+

Z

V+

R

V=I

Differential Relay Circu it


45/79


y

A

Metrosil

resistors

BCN

87

V

87

V

87

V

95X

95X

95X

Stabilising

resistors

95 Supervisionrelay

Bus wire shorting contacts

Zone bus

wires

Current Trans form ers


46/79


Current transformers must be of low reactance type (classx) and

have identical turns ratio (1 in 100)

They should be of similar design, or if not, of reasonably matched

magnetic characteristics

It is common practice to use CTs having 1 amp secondaries

Current Transfo rmer Wir ing


47/79


g

Lead burdens between various sets of CTs must be kept low.Usually buswires are run in closed ring between breaker control

panels. Typical route:-

CTs to marshalling kiosk

Marshalling kiosk to isolator auxiliaries

Loop between marshalling kiosks Conductor size:-

Normally 2.5mm2

Effect of C.T. Lo cation


48/79


Effect of C.T. Lo cation

on Busbar Protect ion Performance

(a)Overlapping C.T.s

Circuit

Protection

F1

Busbar

Protection

F3

F4

F2

(b)All C.T.s on line side of

circuit breaker

F1

Circuit

Protection

F3

F2

Busbar

Protection

Interlocked

Overcurrent

Relay

(c)All C.T.s on Busbar side of

circuit breaker

F1Interlocked

Overcurrent

Relay

F3

F2

Circuit

Protection

Busbar

Protection

Zones of Protect ion fo r Doub le Bu s Stat ion


49/79


Zones of Protect ion fo r Doub le Bus Stat ion

BC

Zone G

Typical feeder circuits

Zone H

BS

Zone J

BC

Check Featu re


50/79


Check Featu re

Zone B

Usually provided by duplication of primary protection using second set of CTs on

all circuits other than bus section and coupler units. Check system forms one

zone only, covering whole of busbar systems and not discriminating betweenfaults on various sections.

87B

87

CK

Check Zone

87A

Zone A

Iso lator Aux i l iary Sw itches


51/79


y

R

Auxiliary Switches Should:

1) Close before the isolator closes

2) Open after the isolator opens

in order to maintain stability on switching

A

Buswires

M

B C D

m

r

a b c d

Busbar Auxi l iary Sw itches Requ irements


52/79


y q

Reserve Bar

Normal Operating Condition

R

RMain Bar

Busbar Auxi l iary Sw itches Requ irements


53/79


y q

On-Load Transfer

R

R

Main & reserve zones

Ultimately paralleled by

reserve busbar selector

auxiliary switches

Circui t Breaker Bypass


54/79


yp

M

R

A.C.Buswires

M

c1

b1 a1

c2

b2 a2

a1

b1

c1

R

N

CH

N

a2

b2

c2a

1b1

Circui t B reaker and CT Bypass


55/79


yp

M

R

M

b1 a1

R

N

CH

N

Check

Zone

CTs

Normally

Shorted

AC

Buswires

a1

b1

Tripping Circui ts


56/79


One tripping relay (device 96) is required for each feeder

breaker and 2 for each bus section or bus coupler breakers

Both main and check relays must be energised before

tripping relays trip all breakers associated with zone

Typical Trip Relay ArrangementDouble Busbar System


57/79


Double Busbar System

-+

CSS M1

CSS M2

CSS - R

In Out87M1 - 1

87M2 - 1

87R - 1

96

D1

M1M2R

a1

c1

96

D2

96E

96

F196

F2

96G

b1

c2 96H196

H2

87CH - 1

80T

D.C. Buswires

Through Fault Stabi l i ty


58/79


Busbar protection stability is based on maximum through fault

current

Generally this value is derived from the rating of the associated

switchgear irrespective of existing fault level, since it can beexpected that system will develop up to limit of rating

Earth-fau l t p rotect ion for bu sbars and o ther pr imary plant


59/79


connect ions (one relay per zone)

T

A A A

D

G H K

Relay

Circuit

G KH

E F

B B B

T

T

C C C

Vs

Rated stabi l i ty l imit ph ase

to earth external fault

Vs > TxIFx(2H+2K+F+C)

OR: -

IF


i ( l )


60/79



T

A A A

D

G H K

Relay

Circuit

G KH

E F

B B B

T

T

C C C

Vs



Vs > TxIFx(A+D+2G)

OR: -

IF


t i ( l )


61/79



T

A A A

D

G H K

Relay

Circuit

G KH

E F

B B B

T

T

C C C

Vs



Vs > TxIFx(B+E+2H)

whichever is the

greatest.

IF

Phase and earth-fault pro tect ion fo r bus bars and other

i l t t i ( l )


62/79


prim ary plant conn ect ions (one relay per zone)

G H

Relay

Circuit

G H

E F

T

T

A A A

D

K

K

B B B

TC C C

K

KG

G

H

H

Relay

CircuitRelay

Circuit

IF

Rated stabi l i ty l im it phase

to p hase external fault

Vs

VsVs > TxIFx(H+K+C)

OR: -


i l t t i ( l )


63/79



G H

Relay

Circuit

G H

E F

T

T

A A A

D

K

K

B B B

TC C C

K

KG

G

H

H

Relay

CircuitRelay

Circuit

IF



Vs > TxIFx(A+G)

OR: -

Vs

Vs


i l t t i ( l )


64/79



G H

Relay

Circuit

G H

E F

T

T

A A A

D

K

K

B B B

TC C C

K

KG

G

H

H

Relay

CircuitRelay

Circuit



Vs > TxIFx(B+H)

whichever is the

greatest

IF

Vs

Vs

Busbar Protect ion With Separate Relays Per Circuit

Breaker Basic Scheme


65/79


Breaker Basic Scheme

12

TR

+

+1

+

+

2

+

2

D

CH

21

D

CH

TR

+ 1


Breaker Basic Scheme With Addi t ional Tr ipp ing Route


66/79


Breaker Basic Scheme With Addi t ional Tr ipp ing Route

1

2

TR

+

+2

+

+

1

+2

D

CH

21

D

CH

TR

+ 1

+

+

2

1

TR

+

+

TR

1

2

STN+


Breaker Basic Scheme With Addit ion al Relays Per Zone


67/79


Breaker Basic Scheme With Addit ion al Relays Per ZoneAnd B ack Tr ipp ing Faci l i t ies

1

2

TR

+

+2

+

+

1

+2

D

CH

21

D

CH

TR

+ 1 STN

2+

CH

BT BT

+1

D

+


Breaker Basic Scheme With Addit ion al Relays Per Zone


68/79


Breaker Basic Scheme With Addit ion al Relays Per ZoneAnd Back Trippin g Faci l i t ies With Separate Trip Relays

1 2

TR

+

+2

+

+

1

+2

D

CH

D

CH

TR

+ 1 + STN

2

CH

BT BT

D

+

+2

1+

+1

2

TR TR

+1

Double Busbar With Trans fer Faci l i t ies


69/79


Main

By-Pass

Isolator

Reserve/ Transfer

By-Pass

Isolator

Triple Busbar


70/79


Main

Transfer

CB.

Reserve

Transfer

Transfer

CB.

1 Breaker Scheme


71/79


1 Breaker Bus Pro tec tion


72/79


87

87

Mesh BusbarF1 F3


73/79


F4

T1

F1

T4

F3

T3

F2

T2

Mesh Busbar Protect ion


74/79


F4

T1

F1

T4

F3

T3

F2

T2

87

R187

R3

87

R4

87

R2

Busbar Protect ion and Breaker Fai l


75/79


Where breaker fail protection is applied to a system, backtripping of associated breakers is required in the event of abreaker failure

Often, breaker fail protection is arranged in conjunction withbusbar protection tripping circuits to initiate tripping of

breakers on a busbar zone associated with the failedbreaker

Midos Relays for High Impedance Protect ion


76/79


Differential Relay MCAG34 or MFAC34

Supervision Relay MVTP31

Tripping Relay (Hand Reset) MVAJ13 No Volt Relay MVAX12

Zone Indication Relay MVAA13

Modern Low Impedance Busbar Protect ion


77/79


Fast

Modular scheme design allows relays to relate to each circuit and

function of the protection. This enables the user to easily

understand the principles of application

High sensitivity for phase and earth faults. Protection for each

phase can be relatively independent

Earlier schemes were less stable than high impedance schemes.

Modern schemes incorporate saturation detectors and are

extremely stable

Duplicate measuring circuits are included

Current transformers can be:

Of different ratio

Of relatively small output

Shared with other protections

Current transformer secondary circuits are not switched

Continuous supervision of CT circuits and constant monitoring of

vital circuits are included

MBCZ 10 Single Bus Protect ion


78/79


F1

FM1

Z1

Z1

ZCK

Z1

FM2 BSM

BS

FM3

Z2

FM4

Z2

ZCK

Z2

F2 F3 F4

ZCK

MBCZ 10 Double Bus Protect ionBS


79/79

Z1

Z1

FM1 BSM

BS

Z1

ZCK

Z3

ZCK

BC1

BCM

1

Z3

Z3

FM2

Z2

F2F1

Z4

F3

FM3

Z2

Z4

FM4

F4BC2

BCM

2

Z2

Z4

ZCK

2 Busbar Protection

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Transcript of 2 Busbar Protection