ABB Relion Technical Manual page 741

1MRK 502 048-UUS A
Technical manual
A1
51
t=0 t=t
1
ANSI05000132 V1 EN
Figure 318: 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 operate without any intentional delay (instantaneous).
When the fault occurs the protections pickup to detect the fault current. After the time t
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 the circuit breaker B1 has opened its primary contacts and thus the fault
2
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
of protection A1 is active.
At time t the protection A1 is reset, i.e. the timer is stopped.
3
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:
Time inverse characteristics
B1
51
t=t t=t
2 3
Section 21
Feeder
Time axis
en05000132_ansi.vsd
the timer
2
1
735