6.1-Busbar protection.pdf

7/24/2019 6.1-Busbar protection.pdf

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6.1 BusBar protection


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Ref : APP14

Last Release : October 2010

Schneider Electric - Jean Marmonier - 20/01/2011

Pro ram

PART 1 : GENERALITY

PART 2 : OPERATING PRINCIPLES

PART 3 : OTHER SUBSTATION TOPOLOGIES

Advantages / Disadvantages

PART 4 : HIGH IMPEDANCE DIFFERENTIAL PROTECTION

PRINCIPLE

PART 5 : LOW IMPEDANCE PROTECTION PRINCIPLE

PART 6 : FRAME LEAKAGE PROTECTION - PRINCIPLE

PART 7 : BLOCKING SCHEME PROTECTION

2Schneider Electric - Jean Marmonier - 20/01/2011

PART 8 : OTHER APPLICATIONS


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PART 1 : Generality

PART 2 : Operating Principle


PART 4 : High Impedance Differential

Protection Princi le

PART 5 : Low Impedance Protection Principle

PART 6 : Frame Leakage Protection - PrinciplePART 7 : Blocking Scheme Protection


PART 8 : Other Applications

Busbar protection

Objective :

Clear a fault inside a substation as quickly as

possible

CA B

To Protect :

- The operator and workers

- HV equipment


-


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Differential Protection

The grading between overcurrent protections is difficult to guarantee

The max clearance time is critical for HV equipment or network

Applicable for :

Generators,

,

Overhead lines, Underground cables,

busbars,


Motors.

Busbar Faults Are Usually Permanent

Falling debris

Insulation failures Circuit breaker failures

Current transformer failures

Isolators switchs operated on load or outside their ratings

Safety earths left connected

Therefore :

Circuit breakers should be tripped and locked out by busbar protection


rec os ng mus e one a er ns a a on c ec


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Busbar Protection must be

Failure to trip could cause widespread damage to the substation

STABLE

False tripping can cause widespread interruption of supplies to

customers / ossible ower s stem instabilit

DISCRIMINATING

ou r p e m n mum num er o rea ers o c ear e au

FAST


To limit damage and possible power system instability

Protection Methods

High Impedance

Low Impedance

Medium Impedance with Bias Characteristic (no more used)

Directional Comparison Protection (Blocking Scheme)



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PART 1 : Generality





PART 6 : Frame Leakage Protection - Principle

PART 7 : Blockin Scheme Protection



Biased Differential Scheme

21

I1 - I2

21

I1 - I2

Differential

Current

Differential

CurrentHI LII1 - I2

Trip

I1 - I2

Trip

no Trip


Mean Through

CurrentI1

2

I2+Mean Through

CurrentI1

2

I2+


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Differential

I1 - I2

Trip

no Trip

Mean ThroughCurrent

I1 I2+


2


Differential

I1 - I2

Trip

no Trip

Differential Current

Mean Through Current

Mean Through

Current

I1 I2+I1 I2+

I1 I2+


2Differential Current = 2 X Mean Through Current


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Protective Zone definitions

BS

Bus Section / Bus Disconnector

one

Zone 3 Zone 4

Zone 2

BC1 BC2

F1 F2 F3 F4


No Busbar Protection

Advantages

There are fewer faults on busbars than on

other parts of the power system.

accidental operation of busbar protection.F2F1

Drawbacks

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 (Zone 2)


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With Busbar Protection

ZONE

breakers at the busbars F1

Fast Tripping but only for the

Cirscuit breakers of the selectied

ZONE 1

F2F1

ZONE 2

zone



1/2SS SS SS

87BB

87BB

1

2 3

21 21



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2/2

87BB

87BB

21 21


Without Busbar Protection

1/2

21 21 21

21 21



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Without Busbar Protection

2/2

21 21 21

21 21


With Busbar protection

87BB

87BB

21 21

Without Busbar protection

21 21 21


21 21


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PART 1 : Generality




Protection Princi le


PART 6 : Frame Leakage Protection - PrinciplePART 7 : Blocking Scheme Protection



Topology & Architecture of the HV

Most basic, simple andSingle breaker - Single bus

.

Main use :

- distribution,- lower transmission voltages

Drawback :

- Lack of flexibilit for bus

faults

- maintenance

enera y no pro ec e y a

busbar protection if one or

two infeeds exist.



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Topology & Architecture of the HV

Sin le buses connected with bus tie number of circuits exist.

Main use :

- Distribution networks,

- Industrial substations with or

without co-generation.

Advantages :

- Flexibility, specially when the

substation is fed by two

separa e power supp es

(generators).

- A bus fault only causes the

loss of half a bar


Double breaker - Double bus2 Busbars ; 2 Circuit Breakers

X

kV)

Advantage :- Increased operating flexibility,

- Both busbars are independent,

specially from a protection point of

X X X X

.

- All switch disconectors are normally

closed and no bus couplor is used.

- The loss of one bus dos not affect

e ransm e power.

Drawback :

- The line rotection must be


connected to both CTs.


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Main and transfer buses with single

Main

Reserve / Transfer

By-passIsolator

By-passIsolator


Main and transfer buses with single

Main

Transfer

Reserve

TransferCB

rans er

Be carefull to the CT ocation on the Bus Transfer in order to


clearly defined the protected zone


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Breaker and a half bus arrangementWidely used for larger multicircuit and higher voltage systems

Advantage :

- ,- Line faults trip two circuit breakers but does not cause loss of

services of other lines and busbars.

87

Zone to

protect

separately


87

Other Busbar TopologiesRing Bus

OHL FEEDER

No busbar

Advantage :X

X- One circuit breaker for two lines,

- No busbar is required (not

applicable) as the bus protection is

XX XX

X

protection themselves.

- The ring can be opened without loss

of power.

Drawback :

- If the ring is opened, a fault on a line

ma se arate the other lines and the


TRANSF. FEEDERbus.


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Mesh Busbar

T1 T3


F4 F2

Mesh Busbar ProtectionF1 F3

87R1

87R3

T1 T3

T4 T2


F4 F2R4 R2


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and Number


Effect of CT location on the global

ro ec on er ormanceBus

Feeder

FeederProtection

Protection

Feeder

BusProtection

BusProtection

BusProtection

51


CT Overlap s on ne s e

Feeder


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PART 1 : Generality


PART 3 : Other Substation To olo iesAdvantages / Disadvantages


ro ec on r nc p e





Single Bus Substation

P1 S1 P1 S1 P1 S1

P2 S2 P2 S2 P2 S2



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Double Bus Substation



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Bus A

Bus B

P1 S1 P1 S1 P1 S1

P1

P2

S1

S2

P2 S2

P2 S2 P2 S2 P2 S2 P1 S1

ab

Current



Bus A

Bus B

ab



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Bus A

Bus B

ab

Current



Bus A

Bus B

ab

Current



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Bus A

Bus B

ab

Current



Bus A

Bus B

ab

Current



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Double Bus SubstationBus A

Bus B

a

Tripping ab



Interposing CTs are not acceptableMain CT must be identical urren sw c ng v a aux ary re ay s no accep a e.Requirement of number of position contact (Disconnector switch) is

high



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No auxiliary contact must be used

for current switchinSupplementary delay on current switching

Reliabiliby

Auxiliary relays must be designed

so that :

They get closed before

the bus disconnector is closed

The et o en after

the bus disconnection is open


Check Zone Supervision

Bus A

A B

TripBus

TripBus

Zone AZone B



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Bus A

A B

TripBus

TripBusurren

switching

failure

Zone AZone B


False

Tripping


Bus A

A B

TripBus

TripBus

Zone AZone B


Check

Zone


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Bus A

A B

TripBus

TripBus

Zone AZone B



Bus A

A B

TripBus

TripBus


Check

Zone


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Protection Sensitivity


Stability for External Faults

RCT RCT2RL 2RLM

ZM A ZM

2RL

RCT


MRCT

2RL


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Requirements


CT Wiring Supervision (2)I1

CT1

Super

vision

V

RST

R

RZM2 ZM3 ZM4

relaynsupervisiobymeasuredVoltage

reay

I1

relansu ervisiotheo eratecurrent tobalance-of-Out

VsettingrelaynsupervisioIf

)// Z// Z// Z(RV

SP

M4M3M21

Z

V

Z

V

Z

V

R

V

M3

SP

M3

SP

M2

SPSP


..


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Differential Relay CircuitB

C

N

Zone bus wires

95X

95X

95X

Bus wire short contacts

Supervision relay95

Stabilising resistors

87 87 87

v v vresistors


High Impedance Protection

Stability is entirely due to a stabilising resistor in the circuit..

,

The CTs must have the same ratio & must be of high

accuracy (low magnetizing current) - class X

The CT knee point voltage needs to be relatively high

The magnetising current can desensitise the scheme

The scheme can be very fast

Isolator contacts are needed to switch the full CT secondary

current between the zones.

There are risks to o en the secondar side of CTs

Extending the scheme is quite simple (if CTs not too old)

Metrosil and Buswire supervision is required


a n enance ru es are s r c


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One Breaker and a Half

Substation


One and Half Circuit Breaker

P1

P2

S1

Bus A Bus

B

P1 P2 P1P2

S1 S2 S1S2

Use of one additional

Protection

High Impedance

Differential rela

Low Impedance

Differential relay (3

windin transformer


relay)


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Bus A Bus

B



Bus A Bus

B



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Bus A Bus

B



Bus A Bus

B



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Bus A Bus

B



Bus A Bus

B

P1 P2 P1P2

S1 S2 S1S2

P1 P2 P1P2

S1 S2 S1S2



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PART 1 : Generality

: pera ng r nc p e

PART 3 : Other Substation Topologies

van ages sa van ages

PART 4 : High Impedance Differential Protection

r n c p e

Principle

: rame ea age ro ec on - r nc p ePART 7 : Blocking Scheme Protection



GENERAL SCHEME

BB1bBB1a

Peripheral

Unit

Peripheral

Unit

Peripheral

Unit

Peripheral

Unit

Peripheral

Unit

Peripheral

Unit

Peripheral

Unit

Peripheral

Unit

Unit

Centralle

Peripheral UnitsOptical Fibres Optical Fibres

Peripheral Units



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Bias Characteristic Principle

idiff (t)

Tri in Area

X X1

X XX

I >2 Blocking Area

2

ISID>1

ni 3

Differentail Current: idiffnoeud (t) = i1 + i2 + i3 + + inO eratin Quantit : i t = i t = i

bias


Bias Quantity: ibias(t) = |i1|+ |i2|+ | i3| + + |in| = |in|

INTEGRATED FUNCTIONS

Peripheral Units Objective

Local Signal Processing (magnitude, angle, saturation detection )

Local Back-up Protections (Max I)

Central Unit objective

Automatic Ada tation of zone number

Differential Calculation Element for each zone

Differential Calculation Element Check Zone

--

Circuitry Fault Control for each Differential Element



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OTHER INTEGRATED FUNCTIONS

Pole Discrepency Supervision, for circuit breakers and bus

disconnectors

uperv s on

Inter-Tripping management in case of Internal Bus Fault

Circuit Breaker Failure : ReTrip order (stage 1) or Zone Tripping

(stage 2)

Circuit Breaker Failure Definition of zones to be tripped

Maintenance modes management (per zone differential blocking)


Current Circuitry Fault Supervision

iidiff= 0= 0

Under normal operating conditionsUnder normal operating conditions

iidiff 00

=> use of a circuitry fault alarm threshold so that :=> use of a circuitry fault alarm threshold so that :

1.2 x1.2 x ii II >1>1 0.8 x I0.8 x I .

=> Affected zone blocking (option depending on manufacturer)=> Affected zone blocking (option depending on manufacturer)



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The Check Zone Element does not take into account the status

of busbar disconnections (assignment to bus A or B)

Total ITotal Idiffdiff= Sum of current node i= Sum of current node idiffdiff

diffdiff == diffdiff ==

Under pole discrepency condition on a circuit breaker or a bus

,

nil, preventing any maloperation of the busbar protection,

=> A trip will be issued only if the differential current measured

b the check zone has reached the tri in threshold.


Tripping Threshold Conditions

Differential Current detected by the Check Zone ElementDifferential Current detected by the Check Zone Element

Differential Current above the Tripping Threshold,Differential Current above the Tripping Threshold,generaly set so that :generaly set so that :

1,2 x1,2 x I_highest loaded feederI_highest loaded feeder (ID>2)(ID>2) 0.8 x I0.8 x I Min. shortMin. short--

Fault point inside the Characteristic Operating AreaFault point inside the Characteristic Operating Area



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Low Impedance Protection Synthesis

Stability is entirely due to the bias characteristic of the

scheme. Metrosils and Stabilizing resistors are not required,

CTs can have different ratios

Scheme bias characteristic can cater for lesser accuracy

CTs (class 5P), instead of Class X CTs,

,

can manage the saturation effects,

CTs can be shared with other protection, due to low burden,

Number of // circuits does not affect he primary operating

current

Fast Tri in time Decision between 3 to 5 ms

Isolator contact are not needed to switch heavy currents,

Extending the scheme is simple,


Self supervision and breaker fail protection is easier to

integrate,

PART 1 : Generality

: pera ng r nc p e

PART 3 : Other Substation Topologies

van ages sa van ages

PART 4 : High Impedance Differential Protection

r n c p e


PART 6 : Frame Leakage Protection

PART 7 : Blocking Scheme Protection




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Frame Leakage Busbar Protection

Principle and Limitations

Limited to Medium Voltage BusBar applications

Can detect only earth faults

Means that the fault current betwwen circuit breaker cells and earth

must be measured :

=> Switchgear must be insulated from earth (by standing on concrete

p n ,

=> Only one single earth conductor allowed on switchgear,

=> All cable glands must be insulated from the cells earth,

=> n y one s ng e p ase s use , e ween ear con uc or an an

instantaneous overcurrent relay. In case of several sections (with couplers), Switchgear sections must

be insulated.



>I

Insulation



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>I



>I



49/54


>I >I


Frame Leakage Busbar ProtectionConfirmation by Transformer Neutral protection

False Operation

because induced

loop

>I

>I

Fault)


Tripping is confirmed by the

relay, to avoid false trip


50/54


Confirmation by Transformer Neutral protection

>I

>I



Confirmation by Transformer Neutral protection

>I

>I



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Blocking Scheme Busbar ProtectionBUSBAR

PROTECTION

LOGIC>I >I >I >I>I


PART 1 : Generality



Protection Principle

: ow mpe ance ro ec on r nc p e






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Busbar Blocking Protection

Tripping of the Feeder Relay Only

Blocking of the Incommer RelayIncomer

BLOCK

No Blocking of the Incomer Relay

Time Delayed tripping of the

and Fault Clearance IF2

O/C Relay O/C Relay O/C RelayO/C Relay


F1

PART 1 : Generality



Protection Principle





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Bus Protection - other application

Other Application commonly used for Oil & Gas

The 51Relay is limited

to the load current of eachhalf section

I_pilote=I_incomer-I_coupler

Advantage

if TA is in maintenance


Bus Protection - other application

Can be used in case of 4 feeders max

No Bus Coupler or Bus Disconnector

87T

Documents

6.1-Busbar protection.pdf