Date Code 20010515
Specifications
2-13
SEL-2BFR, -2/BFR Instruction Manual
Figure 2.1: A-Phase Failure to Trip for Fault Logic, Scheme 1
Scheme 2
Figure 2.2 shows the logic diagram for Scheme 2, A-phase breaker protection.
In a single breaker arrangement, fault current causes the 50FT element to assert immediately
following fault inception and just prior to trip signal arrival. If 50FT is asserted when the
SEL-2BFR Relay receives the trip signal, the AND 1 output goes high. The 62FC pickup timer
starts and the trip input signal is latched in. At this point, trip signal dropout does not affect the
breaker failure scheme. If the 50FT element remains asserted until the 62FC timer expires, the
Relay Word FBF bit asserts. If the breaker operates successfully, the 50FT element drops out
before the 62FC timer expires and FBF does not assert.
Although it is very simple and effective in single breaker arrangements, Scheme 2 is not
recommended when the protected breaker is part of a ring-bus or breaker-and-a-half installation.
Consider using Scheme 1, Scheme 4, or Scheme 5 in such breaker arrangements.
Figure 2.2: A-Phase Failure to Trip for Fault Logic, Scheme 2
Scheme 3
Figure 2.3 shows the logic diagram for Scheme 3, A-phase breaker protection.
Like Scheme 2, Scheme 3 is intended for use in a single breaker arrangement. When a fault
occurs, 50FT asserts and the line protective relay asserts the SEL-2BFR Relay trip input. The
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