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1MRK 505 370-UEN D
t=0
The fault
occurs
IEC05000205 V2 EN-US
Figure 93: 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 35.
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
7.3
Directional residual overcurrent protection, four steps
EF4PTOC
Busbar protection REB670
Application manual
A1
I>
t=t
t=t
1
2
B1 and A1
B1 trips and
start
A1 starts
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
3
Breaker at
B1 opens
=
40
ms
220
ms
is 100 ms
is 40 ms and
is 40 ms
Current protection
Feeder
Fault
Time axis
t=t
4
Protection
A1 resets
=IEC05000205=2=en=Original.vsd
Section 7
(Equation 35)
IP14509-1 v8
159
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