Date Code 20010515
Applications
5-19
SEL-2BFR, -2/BFR Instruction Manual
62UF and 62UP Timer Settings
When you set failure and pending failure time delays, consider the disruptive effects of breaker
phase discordance on load or generation equipment and system stability. There may be a limit to
the amount of time the system can withstand single phasing when the breaker carries maximum
load. Use a pending failure timer setting, 62UP, shorter than 62UF.
For the example protected breaker:
62UP = 50 cycles
62UF = 60 cycles
Select MOD Trip Logic Setting
Motor-operated disconnect switches are used to isolate a circuit breaker for maintenance or in the
event of a failure. You can set the SEL-2BFR Relay to operate an MOD following a breaker
failure. The protection scheme must meet several requirements before the MOD Trip logic is
useful.
The relay must be able to measure all current flowing in the MOD.
The MOD must be equipped with a form “a” auxiliary contact to indicate status.
Logic Description
in
Section 2: Specifications
provides operational descriptions of SEL-2BFR
Relay MOD Trip logic. If you want the relay to operate a motor-operated disconnect switch
automatically to isolate a failed breaker, set ModTrip to Y.
If you do not use an MOD on the protected breaker, consider using this logic to indicate a “Safe
to Disconnect” condition for station personnel.
If you do not wish to use the MOD Trip logic, set ModTrip to N. Overcurrent and timer setting
considerations for both schemes appear below.
MOD Trip Logic Enabled, ModTrip Equals Y
50MD Overcurrent Element Setting
Set the 50MD element to pick up when protected breaker current exceeds the MOD current break
rating. If you use this logic to indicate a ‘Safe to Disconnect’ condition, set 50MD below the
level appropriate for the application.
In the example application, we do not attempt to operate the MOD as long as current can be
detected in the protected breaker. We select the minimum setting for 50MD.
50MD = 0.10 A secondary
The 50MD element accuracy specification is ±0.025 A secondary ±5% of setting. Thus, the
maximum error for a setting of 0.10 A secondary is ±0.030 A secondary.
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