bus bar protection basics

7/25/2019 Bus bar protection basics

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r Technology and

Solutions

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Protection and Substation Automation

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Topic:

BUSBAR

PROTECTION

APPLICATION

BASICS 1BASICS 1


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Topic Objectives

rMeasurement

- Differential Current Measurement

- Stabilized Differential Current Measurement

- Fault Conditions

r Differential Current Supervision

r Intertripping

Objectives


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Measuring Principle

Who knows

Mr. Kirchhoff ?


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Measuring Principle

Kirchhoffs 1st Law: Node Rule

I1 + I2 + I3 =

I = 0

The summe of all

currents must be zero


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Measuring Principle

Kirchhoffs 1st Law: Node Rule

I1 + I2 + I3 = I

0 Fault on the busbar

Trip circuit breaker

If


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Measuring Principle

Differential current measurement

I = I1 + I2 + I3

If

I > differential current setting

Trip Busbar Protection


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Measuring Principle

Stabilised differential current measurement

Differe

ntia

lcurrentIdiff=

|

I|

Restraint current IRest = | I |

intern

alfault

no fault

Ikmin

k= 0,85

k= 1

0

Low impedance

measuring

principle !!!

If I > Ikmin ; and

( I / I ) > k Trip Busbar

Protection


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Measuring Principle


Advantage:

load depending tripping value

as more (load / fault) current is flowing on the

busbar

as more differential current is required to generate

a tripping signal

system is very stable in case of

CT failure

CT saturation


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Measuring Principle load depending tripping value


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Busbar fault condition

Measuring Principle

I1 =

1000A

single injection



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What would be thedifferential and

restrained current in thatsituation

???



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I = + I1

= + 1

= 1 kA

l = + + I1

= + 1 kA

= 1 kA




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Differen

tialcurren

tId

iff=|

I|


internalf

ault

no fault

Ikmin

k= 0,85

k= 1

0

trip measurement system !!!

( if I > Ikmin)



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Busbar fault condition

Measuring Principle

I1 = I2 = I3 = I4 =

1000A 2500A 1500A 2000A

multiple injection



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???



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I = + I1 + I2 + I3 + I4

= + 1 kA + 2.5 kA + 1.5 kA + 2 kA

= 7 kA

l = + + I1+ + I2 + + I3 + + I4

= + 1 kA + 2.5 kA + 1.5 kA + 2 kA

= 7 kA




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Differen

tialcurren

tId

iff=|

I|


internalf

ault

no fault

Ikmin

k= 0,85

k= 1

0

trip measurement system !!!



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Measuring Principle

e.g. line fault

External fault condition

I2 = I3 = I4 =

2500A 1500A 2000A

I1 =

6000A


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???

Measuring Principle External fault condition


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I = + I1 + I2 + I3 + I4

= - 6 kA + 2.5 kA + 1.5 kA + 2 kA

= 0 kA

l = + + I1+ + I2 + + I3 + + I4

= + 6 kA + 2.5 kA + 1.5 kA + 2 kA

= 12 kA




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Differen

tialcurren

tId

iff=|

I|


intern

alfault

no fault

Ikmin

k= 0,85

k= 1

0

measurement system stable !!!



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Measuring Principle

during fault condition ()

Current transformer failure

I2 = I3 = I4 =

2500A 1500A 2000A

I1 =

6000ACT shorted !!!


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???

Measuring Principle Current transformer failure


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I = + I1 + I2 + I3 + I4

=

=

l = + + I1+ + I2 + + I3 + + I4

=

=




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Differentia

lcurren

tId

iff=|

I|


intern

alfault

no fault

Ikmin

k= 0,85

k= 1

0



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Measuring Principle

during fault condition ()


I2 = I3 = I4 =

2500A 1500A 2000A

I1 =

6000A

CT shorted !!!


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???



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I = + I1 + I2 + I3 + I4

=

=

l = + + I1+ + I2 + + I3 + + I4

=

=




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Differentia

lcurren

tId

iff=

|

I|

Restraint current IRest =

| I |

intern

alfault

no fault

Ikmin

k= 0,85

k= 1

0



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Measuring Principle

during load condition


I2 = I3 = I4 =250A 150A 200A

I1 =

600A

CT shorted !!!


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???



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I = + I1 + I2 + I3 + I4

=

=

l = + + I1+ + I2 + + I3 + + I4

=

=




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Differentia

lcurren

tId

iff=

|

I|

Restraint current IRest =

| I |

intern

alfault

no fault

Ikmin

k= 0,85

k= 1

0



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How is it possible to detectfailures in the CT circuits

???


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Differential Current Supervision

Differential Current Alarm

A differential current for a longer time is

the consequence of a failure in the

system (intern / extern)

Differential current alarm

Option to block the system


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Which failures in the CT circuitscan the Differential current

supervision detect???



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The differential current

supervision can detect

a missing CT input (e.g. CT circuitnot connected to the system)

a wrong CT ratio

a wrong current direction


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the di f ferent ial current su perv is ion is ableto detect a missing / wrong CT input

therefore the differential current alarm isvery important and must not be ignored by the

operating personal

If not, there is a risk of maloperation !!!


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Intertripping

Tripping flow chart

trip all CBs

connected

to zone x

TRIP BBPzone x

TRIP CB

TRIP CB

TRIP CB

Measurement

system

Intertripping

system

just the Intertripping system can send a trippingsignal to the CB because it knows which CB

to trip (the measurement systems are only

responsible for measuring !)


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bus bar protection basics

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