ABB Relion 670 Series Applications Manual page 145

1MRK 511 401-UEN Rev. K
significantly between different protective equipment. The following time delays can be
estimated:
Protection operation
time:
Protection resetting
time:
Breaker opening time:
Example for time coordination
Assume two substations A and B directly connected to each other via one line, as shown in the
Figure 64. 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 64.
t=0
The fault
occurs
IEC05000205 V2 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
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 35.
Bay control REC670
Application manual
15-60 ms
15-60 ms
20-120 ms
A1
I>
t=t t=t
1 2
B1 and A1 B1 trips and
start A1 starts
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
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B1
I>
t=t
3
Breaker at
B1 opens
=IEC05000205=2=en=Original.vsd
Current protection
Feeder
Fault
Time axis
t=t
4
Protection
A1 resets
- t
3 2
- t .
4 3
. There are uncertainties
3
Section 8
139