Answer / a s nath

Local Breaker Backup (LBB) or Breaker Failure Pretection is
associated with Busbar Protection. If breaker fails to
operate due to its inoperable condition in spite of
operation of protective relays, there will be damage to the
system.This condition is being monitored by LBB relay or
BFR relay (Breaker Failure Relay)and will initiate the
Busbar protection and thus clears the bus.
The LBB protection will operate under the following
conditions:
(i) Lockout relay should operate
(ii)Current shall be more than 20% of normal current rating
(iii) The above currents shall persist after a time,
generally 200ms
When all the three conditions satisfy,it is considered that
the breaker is stuck and LBB protection will operate to
clear the bus.
By A S Nath

Answer / s@nz

LBB as ssaid above it means LOCAL BREAKER BACK UP RELAY is a
back up protection for local breaker (CIRCUIT BREAKER) a
predefined time set in the relay and when the circut breaker
for LBB is kept does not operate ( during fault conditions)
in the pre defined time the surrounding breakers are given
trip command by the LBB relay to restriced the fault..

Answer / manikandan.c

LBB means local breaker backup protection.This relays are
associated with some important main relays like
distance,differential and busbar relays.If main relays are
fail to open circuit breaker(or any mechanical problem in
breaker) under fault conditions,The LBB relay gives trip
command the same breaker for 100ms.If also not open means
next 200ms,It gives initiation for main busbar protection
and followed by busbar protection operated and direct trip
command send to the remote end.And finally protect the power
system.

Answer / selvakumar.j

LBB- local breaker backup protection. after issued the trip command by the relay ,the breaker should be open . if breaker not operate after received trip command ,LBB protection will operated and trip the upstream or downstream breaker to protect the circuit.

Answer / satya

None of these answers is precise, except ans 2 to large extent.

OK. LBB is Local Breaker Backup. (This is opposed to Remote Back up.)

What is LBB?

First of all here is the philospohy that must be met for LBB.
1)There must be a fault. ( Or more precisely, a protective relay has issued a command to trip the breaker)
2) But that breaker has failed to trip.
Then LBB scheme disconnects other breakers at that station ( Local).

If LBB fails to isolate ( assuming an elemnt is still connected while others have opened) , the remote end stations breakers connected to this station will trip ( Remote Backup)

An LBB scheme thus ensures
1) The relay commanded trip on fault. ( NO contacts of main trip relay used)
2) That there was a current of rasonable amount after some reasonable time. ( Breaker did not open for that much time)
eg we set 200ms time. If so it means that the breaker still has current flowing after 200ms means it failed.
Then the LBB relay will issue a trip signal to other breakers at that bus.
OK Explain well in interview.

OK just a supplement. Should LBB operate if the breaker fails to open on manual command ( not fault)? Think about it.

Answer / prasanna

LBB Is the Local Breaker Backup
relay.

Answer / anbarasan

LBB is nothing but local breaker backup.below condition are required
1.86 is operated
2.fault current still persist in our bay
Those two conditions are satisfied lbb relay will send trip command to all the bays.

Answer / prasanna

LBB IS THE LOCAL BREAKAR BACKUP
RELAY.
All the trip command are go via the
mastar trip relay. Suppose mastar
trip relay fail means lbb gives the
trip command... Commant ANSI
code of LBB is 96. It is energised by
67RYBN means overload relay

Answer / eashwar

LBB RELAYS ARE LOCAL BREAKER BACKUP RELAYS.THEY ARE USED TO
PROTECT THE CIRCUIT BREAKER .THE CONTACTS OF THE LBB RELAYS
GETS ENERGISED WHEN THE UPSTREAM OR DOWNSTREAM BREAKER GETS
TRIPPED ,AND THE MAIN BREAKER GETS TRIPPED.

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