ABB Relion 670 Series Applications Manual page 149

1MRK 511 401-UUS F
A1
t=0
The fault
occurs
ANSI05000205 V1 EN-US
Figure 64: Sequence of events during fault
where:
t=0
t=t
1
t=t
2
t=t
3
t=t
4
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 than the time t
values of protection operation time, breaker opening time and protection resetting time.
Therefore a safety margin has to be included. With normal values the needed time difference can
be calculated according to Equation 35.
D ³
t 40
EQUATION1266 V1 EN-US
where it is considered that:
the operate time of overcurrent protection B1 is 40 ms
the breaker open time
the resetting time of protection A1
the additional margin
Bay control REC670
Application manual
51
t=t t=t
1
Protection Breaker at
B1 trips B1 opens
is when the fault occurs
is when protection IED B1 and protection IED A1 start
is when the trip signal from the overcurrent protection at IED B1 is sent to the circuit breaker.
is when the circuit breaker at IED B1 opens. The circuit breaker opening time is t
is when the overcurrent protection at IED A1 resets. The protection resetting time is t
+ + +
ms 100 ms 40 ms
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B1
51
t=t
2 3
Protection
A1 resets
=
40 ms 220 ms
is 100 ms
is 40 ms and
is 40 ms
Current protection
Feeder
Time axis
en05000205_ansi.vsd
- t
3 2
- t .
4 3
. There are uncertainties in the
3
(Equation 35)
Section 8
143