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r Technology and
Solutions
ABB
Protection and Substation Automation
ABBSw
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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
Stabilised differential current measurement
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
load depending tripping value
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What would be thedifferential and
restrained current in thatsituation
???
Measuring Principle load depending tripping value
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I = + I1
= + 1
= 1 kA
l = + + I1
= + 1 kA
= 1 kA
Stabilised differential current measurement
Measuring Principle load depending tripping value
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Differen
tialcurren
tId
iff=|
I|
Restraint current IRest = | I |
internalf
ault
no fault
Ikmin
k= 0,85
k= 1
0
trip measurement system !!!
( if I > Ikmin)
Measuring Principle load depending tripping value
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Busbar fault condition
Measuring Principle
I1 = I2 = I3 = I4 =
1000A 2500A 1500A 2000A
multiple injection
load depending tripping value
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What would be thedifferential and
restrained current in thatsituation
???
Measuring Principle load depending tripping value
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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
Stabilised differential current measurement
Measuring Principle load depending tripping value
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Differen
tialcurren
tId
iff=|
I|
Restraint current IRest = | I |
internalf
ault
no fault
Ikmin
k= 0,85
k= 1
0
trip measurement system !!!
Measuring Principle load depending tripping value
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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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What would be thedifferential and
restrained current in thatsituation
???
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
Stabilised differential current measurement
Measuring Principle External fault condition
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Differen
tialcurren
tId
iff=|
I|
Restraint current IRest = | I |
intern
alfault
no fault
Ikmin
k= 0,85
k= 1
0
measurement system stable !!!
Measuring Principle External fault condition
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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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What would be thedifferential and
restrained current in thatsituation
???
Measuring Principle Current transformer failure
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I = + I1 + I2 + I3 + I4
=
=
l = + + I1+ + I2 + + I3 + + I4
=
=
Stabilised differential current measurement
Measuring Principle Current transformer failure
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Differentia
lcurren
tId
iff=|
I|
Restraint current IRest = | I |
intern
alfault
no fault
Ikmin
k= 0,85
k= 1
0
Measuring Principle Current transformer failure
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Measuring Principle
during fault condition ()
Current transformer failure
I2 = I3 = I4 =
2500A 1500A 2000A
I1 =
6000A
CT shorted !!!
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What would be thedifferential and
restrained current in thatsituation
???
Measuring Principle Current transformer failure
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I = + I1 + I2 + I3 + I4
=
=
l = + + I1+ + I2 + + I3 + + I4
=
=
Stabilised differential current measurement
Measuring Principle Current transformer failure
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Differentia
lcurren
tId
iff=
|
I|
Restraint current IRest =
| I |
intern
alfault
no fault
Ikmin
k= 0,85
k= 1
0
Measuring Principle Current transformer failure
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Measuring Principle
during load condition
Current transformer failure
I2 = I3 = I4 =250A 150A 200A
I1 =
600A
CT shorted !!!
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What would be thedifferential and
restrained current in thatsituation
???
Measuring Principle Current transformer failure
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I = + I1 + I2 + I3 + I4
=
=
l = + + I1+ + I2 + + I3 + + I4
=
=
Stabilised differential current measurement
Measuring Principle Current transformer failure
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Differentia
lcurren
tId
iff=
|
I|
Restraint current IRest =
| I |
intern
alfault
no fault
Ikmin
k= 0,85
k= 1
0
Measuring Principle Current transformer failure
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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???
Differential Current Supervision
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Differential Current Supervision
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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Differential Current Supervision
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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