Example for time coordination
Assume two substations A and B directly connected to each other via one line, as shown
in the Figure 259. Consider a fault located at another line from the station B. The fault
current to the overcurrent protection of IED B1 has a magnitude so that the overcurrent
protection will start and subsequently trip, and the overcurrent protection of IED A1 must
have a delayed operation in order to avoid maloperation. The sequence of events during
the fault can be described using a time axis shown in Figure
259.
A1 B1
Feeder
Time axis
t=0 t=t
1
t=t
2
t=t
3
The fault
occurs
Protection
B1 trips
Breaker at
B1 opens
Protection
A1 resets
en05000205_ansi.vsd
51
51
ANSI05000205 V1 EN
Figure 259: Sequence of events during fault
where:
t=0 is when the fault occurs
t=t
1
is when protection IED B1 and protection IED A1 start
t=t
2
is when the trip signal from the overcurrent protection at IED B1 is sent to the circuit breaker.
t=t
3
is when the circuit breaker at IED B1 opens. The circuit breaker opening time is t
3
- t
2
t=t
4
is when the overcurrent protection at IED A1 resets. The protection resetting time is t
4
- 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
3
. There
are uncertainties in the 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
454.
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 503
Application manual
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