ABB ret650, Technical Manual

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en05000132.vsd
I> I>
A1 B1
Feeder
Time axis
t=0 t=t
1
t=t
2
t=t
3
IEC05000132 V1 EN
Figure 270: 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 start 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 504 135-UEN A
Section 21
Time inverse characteristics
627
Technical manual