BUSBAR PROTECTION
AMIT LOHIYA
BUSBAR PROTECTION WITH REB670 RELAY
Busbars have often been left without specific
protection. The damage resulting from one un-
cleared fault, may be very extensive leading to
the complete loss of the station by fire.
Unit busbar protection or busbar differential
protection is based on Merz-Price principle
and is a direct application of
Kirchhoff's First Law.
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REB670 Relay Hardware
Transformer Module
Binary Input Module
Binary Output Module
Communication Module
Power Source Module
Analog to Digital Converter
Central Processing Unit
Functions in REB670 Relay
FUNCTION
Busbar Differential Protection
Discriminating & Check Zone
Zone Selection or CT Switching
Open CT Detection
Blind Spot Protection
End Fault Protection
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Bus Bar Protection Requirement
STABILITY Must be ABSOLUTELY STABLE during all external faults.
Must have as short tripping time SPEED
SPEED Must be SENSITIVE enough to detect and securely operate for
internal faults with minimum fault current and even with heavy
CT saturation.
SENSITIVITY
Must be able to SELECTIVELY detect faults and trip only the
faulty part of the busbar system.
SELECTIVITY Must be SECURE against mal-operation
Must be RELIABLE, because protection systems can stay un-
SECURITY operative for years.
RELIABILITY
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Busbar Differential Protection 87B
The basic concept for any differential IED is
that the sum of all currents, which flow to and
from the protection zone, must be equal to
zero. If this is not the case, an internal fault
has occurred.
The busbar differential IED is unique in this
respect, that usually quite a few CTs with
very different ratios are connected to the
same differential protection zone.
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Busbar Differential
Discriminating Zone Characteristics
Centralized Busbar Protection
Low Impedance Protection
Restrained Differential Protection
Phase Segregated Protection
Simple algorithm based on
a) Incoming current
b) Outgoing Current
c) Differential Current
Stable for Heavy External Fault
Very Fast Tripping Time, down to 10 msec
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Busbar Differential
Check Zone Characteristics
To improve overall security of busbar
protection, CHECK ZONE is employed along
with DISCRIMINATING ZONE.
All outgoing circuits’ CTs except bus section &
bus coupler CTs are connected to check
zone.
This function detects faults anywhere in the
substation and gives a release signal to
discriminating zones.
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Busbar Differential Zone Selection/CT Switching
CT Switching (Zone Selection) is required in
situation when one particular circuit can be
connected to different busbars by individual
isolators.
Traditionally, the CT switching has been done
in CT secondary circuits. However, with
REB670, all necessary zone selection done
in software based on isolator position.
Therefore, the CT secondary circuits are
always intact and without any auxiliary relay
contacts.
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Open CT Detection
REB670 relay provides stability for open or
short-circuited main CT secondary circuits.
At detection of problems in CT secondary
circuits, the differential protection can be
instantly blocked and an alarm is given.
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End Fault Protection
.When only one CT is available in a
feeder, it leads to a blind spot in
protection (B & C) because of
physical separation b/w CT & CB.
End Fault Protection takes care of
this blind spot.
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End Fault Protection
CONDITION B
Some time after feeder CB opening due
to BBP, a fast OC protection is enabled
to detect fault within end fault region (1).
Operation of this OC protection will issue
inter-trip command to the remote feeder
end CB.
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End Fault Protection
CONDITION C
The current measurement is
disconnected from the BBP zone some
time after feeder CB opening(due to
feeder protection).
This measure will insure fast busbar
protection tripping for faults within end
fault region (1) in that feeder bay
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Blind Zone Protection
Two sets of main CTs, which are located
on both sides of the bus section/bus
coupler breaker
NO BLIND ZONE
Two differential zones overlapping
For Fault in ZA only Left circuit tripped
For Fault in ZB only Right circuit tripped
For Fault b/w ZA & ZB both circuits tripped
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Blind Zone Protection
No zones overlapping
For Fault in blind zone only Left circuit
tripped unnecessarily but fault not cleared
The current measurement is disconnected
from both zones after CB opening due to
fault detection in either ZA or ZB.
Later ZB trips if fault is in BLIND ZONE
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QUESTIONS
CONTACT INFORMATION
AMIT LOHIYA
PROTECTION ENGINEER
IPM / MFCL PANAGARH / ELECTRICAL
Mobile 1: +91 83 72 80 88 39
E-mail: [email protected]
THANK YOU & HAVE A GREAT DAY
siemens.com
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