Date Code 20010515
Applications
5-11
SEL-2BFR, -2/BFR Instruction Manual
Table 5.3: Scheme Timing Considerations
Scheme Considerations
Schemes 1, 4, 5, and 6
In these schemes, the breaker failure timer starts independently from
50FT assertion. This independence allows scheme usage in bus
configurations where the 50FT element may assert after trip input
assertion, such as ring-bus and breaker-and-a-half bus arrangements.
Scheme 2
In Scheme 2, the 62FC timer does not start until both the trip input and
50FT element are asserted. This feature allows definite, predictable
scheme timing in single-breaker configurations where the 50FT
element asserts before the trip input.
Scheme 3
You can set the 62FC timer for this scheme independently of the 50FT
element reset time if the trip input deasserts when current stops
flowing in the protected breaker. The 62FC timer does not start until
the phase trip input is asserted and the phase 50FT element asserts.
Scheme 4
The 62TTdo timer setting defines duration of the 62TT timer output
pulse. The FBF bit asserts if the timer output is high and the phase
50FT element is asserted. The FBF bit deasserts when the 62TTdo
timer expires, regardless of 50FT element state.
Scheme 6
The 50FT element reset (dropout) time is the sum of:
the front-end analog filter dropout time (less than a quarter-cycle)
the First Order Difference (FOD) digital filter dropout time (vast
majority of the reset time)
The digital filter is disabled while the 62TT or 62FC pickup timers are
timing in Scheme 6. Thus, 50FT element reset time does not have to
be taken into account as part of the safety margin incorporated into the
62TT and 62FC pickup time delay settings. Technically, the front-end
analog filter dropout time should be taken into account in the safety
margin, but this is less than a quarter-cycle. (See Figure 2.7 and
accompanying note in
Section 2: Specifications
.)
Note:
50FT element pickup and dropout time curves are found in the back of
Section 2:
Specifications
.
For the example application, all Zone 1, three-phase faults must be cleared within 8.5 cycles to
maintain system stability. Thus, total fault clearing time, Tt, is 8.5 cycles. Nominal operating
time of local breakers, Tbl, and remote breakers, Tbr, is two cycles. Transfer trip channel time to
the remote breaker, Tc, is 0.5 cycles. Operating time of the line protective relay, Tpr, for a three-
phase fault near the Zone 1 boundary is two cycles. Specified reset time of the 50FT overcurrent
element, T50, is less than 1.10 cycles. Safety margin time, Ts, is defined:
Ts =
Tt – (Tpr + Tbl + T50 + Tbr + Tc) cycles
Ts =
8.5 – (2.0 + 2.0 + 1.10 + 2.0 + 0.5) cycles
Ts =
0.90 cycles
You can now calculate 62FC using the following equation:
62FC
= Tbl + T50 + Ts = 4.0 cycles
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Страница 234: ...C 8 Appendix C Date Code 990714 SEL 2BFR 2 BFR Instruction Manual Figure C 2 Horizontal Front and Real Panel Drawings ...
Страница 235: ...Date Code 990714 Appendix C C 9 SEL 2BFR 2 BFR Instruction Manual Figure C 3 Vertical Front and Rear Panel Drawings ...
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