Checking coordination with relay 67 for fault 2 – Basler Electric BE1-51/27C User Manual
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9137200998 Rev E
(2)
Relay 51 time at 7.6 multiples (from B6 curves) @ 08 time dial: 0.31 s.
(3)
Set 51/27 pickup:
(
)
(
)
Primary
A
97
1.73
11
3700
0.5
=
(
)
A
1.6
300/5
97
=
(4)
Set the 51/27 time to provide 0.3 s coordinating interval:
A
776
@
s
0.61
0.3
31
.
0
=
+
(5)
51/27 voltage equals 0, so the time element is operative.
(6)
51/27 multiples:
0
.
8
97
776 =
(7)
51/27 TIME DIAL (from B6 curve, @ 8.0 multiple): 22.
(8)
Multiples of pickup in the 51 relay at steady-state level:
(
)
2
.
6
6
800/5
5961
=
(9)
51/27 relay time at 6.2 multiples: 0.37 s.
(10) 51/27 multiples at 129 A:
3
.
1
97
129 =
(11) 51/27 time at 1.3 multiples: 13.0 s (approx.).
(12) Relay 51/27 coordinates with relay 51 over the full range of fault currents with transformer T2 out of
service. With both T1 and T2 in service, relay 51 sees more current and operates faster than the
above times. If the fault is not interrupted by the feeder breaker, the generators will be tripped at
time falling between 0.61 s and 13.0 s.
Checking Coordination with Relay 67 for Fault 2
(1)
67 multiples at transient level with T2 in service:
(
)
24
3000/5
5
.
0
7256
=
(2)
67 time at 24 multiples (B3 curve, TIME DIAL 02): 0.15 s.
(3)
67 multiples at transient level with T2 out of service:
3
300
1552 =
(4)
67 time at 3 multiples: 0.23 s.
(5)
Note that a failure of the differential protection (87T) for fault 2 with T2 out of service is a double
contingency. Coordination of 51/27 relays with 67 relays does occur at the transient level (0.61 vs.
0.35 s). As the current decays, the times converge and cross because the 67 Relay pickup is 300
amperes vs. 97 amperes for 51/27 relays (see calculation below for steady-state multiple of 0.86 for
the 67 relays). So coordination may not be achieved for this double contingency with the generator
regulators out of service. Boosting by the regulators will partially arrest the decay of current. In
addition, the decay will be less for a phase-phase fault.
(6)
67 multiples at steady-state level with T2 out:
86
.
0
300
258 =
Tests and Adjustments
BE1-51/27C