ABB RELION 670 Series Applications Manual page 168

Section 7
Current protection
t=0
The fault
occurs
IEC05000205 V1 EN-US
Figure 84: Sequence of events during fault
where:
t=0
t=t
1
t=t
2
t=t
3
To ensure that the overcurrent protection at IED A1, is selective to the overcurrent protection at
IED B1, the minimum time difference must be larger that the time t3. There are uncertainties in the
values of protection operation time, breaker opening time and protection resetting time. Therefor
a safety margin has to be included. With normal values the needed time difference can be
calculated according to equation 38.
D ³
t 40
EQUATION1266 V1 EN-US
where it is considered that:
the operation time of overcurrent protection B1 is 40 ms
the breaker open time
the resetting time of protection A1
the additional margin
162
A1
I>
t=t t=t
1
Protection Breaker at
B1 trips B1 opens
is the fault occurs,
is the trip signal from the overcurrent protection at IED B1 is sent. Operation time of this protection is t1,
is the circuit breaker at IED B1 opens. The circuit breaker opening time is t2 - t1 and
is the overcurrent protection at IED A1 resets. The protection resetting time is t3 - t2.
+ + +
ms 100 ms 40 ms
B1
I>
t=t
2 3
Protection
A1 resets
=
40 ms 220 ms
is 100 ms
is 40 ms and
is 40 ms
1MRK 505 337-UUS A
Feeder
Time axis
en05000205.vsd
(Equation 38)
Application manual