
Date Code 20010515
Applications
5-13
SEL-2BFR, -2/BFR Instruction Manual
In our example application, 10 cycles are allowed to clear faults with current duties below 5456 A
primary. Local and remote breaker operating times are considered identical to those used in
selecting the 62FC delay setting. Operating time of line protective relay, Tpr, is two cycles.
Specified reset time of the 50LD overcurrent element, T50, is less than 1.55 cycles. Safety
margin time is defined Ts and calculated below.
Ts
= Tt – (Tpr + Tbl + T50 + Tbr + Tc) cycles
Ts
= 10.0 – (2.0 + 2.0 + 1.55 + 2.0 + 0.5) cycles
Ts =
1.95
cycles
62LD = Tbl + T50 + Ts = 5.5 cycles
We set the pending failure timer, 62LP, to retrip the protected breaker more than two cycles
before tripping the lockout relay:
62LP = 3.25 cycles
Select 52A Supervised Breaker Failure Protection Settings
If there are conditions under which the protected breaker could be called to trip while current is
below the 50LD overcurrent element setting, you may wish to enable the 52A supervised breaker
failure timers 62AP and 62AF. An application where this function might be required is when the
protected circuit breaker is connected to a generator-transformer unit.
In this instance, the circuit breaker could be issued a trip signal while the generator is idling.
Under these conditions, current through the protected breaker is nearly zero. You can set the
SEL-2BFR Relay to operate the 86 lockout relay if the relay 52A input is not deasserted after a
settable time delay.
In our example application, this logic is not used. The E62A setting is set equal to N.
The time delay settings should be selected based upon the maximum time permissible to operate
the protected equipment under low- or zero-current conditions. A slightly larger safety margin
should be considered for this logic than is allowed for the breaker failure timers described above.
The longer safety margin can allow for possible differences in expected and actual breaker
auxiliary contact operating times.
Select Time-Delayed Retrip Settings
In some applications, you may wish to retrip the protected breaker through a second trip coil,
perhaps using a backup dc tripping supply. The SEL-2BFR Relay can issue the retrip signal
instantaneously or with a short time delay. The time delay may be desirable to allow external
sequential events recorders or SCADA remote terminal units to distinguish between issue of the
initial trip and retrip signals.
To enable time-delayed retripping, set DRTE equal to Y. With this setting, the relay supervises
assertion of the Relay Word trip bits TA, TB, and TC with each phase 50LD overcurrent element
and a settable time delay, RTTD. The programmable logic mask settings used to control the relay
outputs providing the retrip function are described near the end of this section.
Select an RTTD time delay long enough to allow your external event logging equipment to
distinguish between the trip and retrip signals, but short enough to allow the breaker time to
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