ABB REC650 ANSI, Technical Manual

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en05000132_ansi.vsd
51 51
A1 B1
Feeder
Time axis
t=0 t=t
1
t=t
2
t=t
3
ANSI05000132 V1 EN
Figure 284: Selectivity steps for a fault on feeder B1
where:
t=0
is The fault occurs
t=t
1
is Protection B1 trips
t=t
2
is Breaker at B1 opens
t=t
3
is Protection A1 resets
In the case protection B1 shall operate without any intentional delay (instantaneous).
When the fault occurs the protections pickup to detect the fault current. After the time t
1
the 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 start before the trip is sent to the B1 circuit
breaker.
At the time t
2
the circuit breaker B1 has opened its primary contacts 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
2
the timer
of protection A1 is active.
At time t
3
the protection A1 is reset, i.e. the timer is stopped.
In most applications it is required that the delay 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:
1MRK 511 287-UUS A
Section 19
Time inverse characteristics
657
Technical manual