ABB RES670 Technical Manual page 887

1MRK 511 408-UUS A
Phasor measurement unit RES670 2.2 ANSI
Technical manual
A1
51
t=0 t=t
1
ANSI05000132 V1 EN-US
Figure 345: Selectivity steps for a fault on feeder B1
where:
t=0 is The fault occurs
t=t is Protection B1 trips
1
t=t is Breaker at B1 opens
2
t=t is Protection A1 resets
3
In the case protection B1 shall trip without any intentional delay (instantaneous). When
the fault occurs the protections pickup to detect the fault current. After the time t
protection B1 send a trip signal to the circuit breaker. The protection A1 starts its delay
timer at the same time, with some deviation in time due to differences between the two
protections. There is a possibility that A1 will pickup before the trip is sent to the B1
circuit breaker. At the time t
and thus the fault current is interrupted. The breaker time (t2 - t1) can differ between
different faults. The maximum opening time can be given from manuals and test
protocols. Still at t the timer of protection A1 is active. At time t
2
reset, that is the timer is stopped.
In most applications it is required that the times shall reset as fast as possible when the
current fed to the protection drops below the set current level, the reset time shall be
minimized. In some applications it is however beneficial to have some type of delayed
reset time of the overcurrent function. This can be the case in the following
applications:
Inverse time characteristics
B1
51
t=t t=t
2 3
the circuit breaker B1 has opened its primary contacts
2
Section 26
Feeder
Time axis
en05000132_ansi.vsd
1
the protection A1 is
3
the
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