ABB RELION 670 Series Applications Manual page 160

Section 7
Current protection
overcurrent protection of IED B1 has a magnitude so that the protection will have instantaneous
function. The overcurrent protection of IED A1 must have a delayed function. The sequence of
events during the fault can be described using a time axis, see figure 81.
A1
t=0
The fault
occurs
ANSI05000205 V1 EN-US
Figure 81: 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 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 32.
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
154
51
t=t
1
Protection Breaker at
B1 trips B1 opens
is when the fault occurs
is when the trip signal from the overcurrent protection at IED B1 is sent to the circuit breaker. The
operation time of this protection is t
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
B1
51
t=t t=t
2 3
Protection
A1 resets
1
=
40 ms 220 ms
is 100 ms
is 40 ms and
is 40 ms
1MRK 505 337-UUS A
Feeder
Time axis
en05000205_ansi.vsd
- t
2 1
- t .
3 2
. There are uncertainties in the
3
(Equation 32)
Application manual