ABB REB670 Applications Manual page 188

Section 7
Current protection
182
protection operation time: 15-60 ms
protection resetting time: 15-60 ms
Breaker opening time: 20-120 ms
Example
Assume two substations A and B directly connected to each other via one line, as shown
in the figure below. We study 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 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 84.
A1
I>
t=0 t=t
1
The fault Protection
occurs B1 trips
IEC05000205 V1 EN
Figure 84: Sequence of events during fault
where:
t=0 is the fault occurs,
t=t is the trip signal from the overcurrent protection at IED B1 is sent. Operation time of this protection
1
is t1,
t=t is the circuit breaker at IED B1 opens. The circuit breaker opening time is t2 - t1 and
2
t=t is the overcurrent protection at IED A1 resets. The protection resetting time is t3 - t2.
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
B1
I>
t=t t=t
2 3
Breaker at Protection
B1 opens A1 resets
1MRK 505 337-UUS -
Feeder
Time axis
en05000205.vsd
Application manual