ABB REB670 Applications Manual page 179

1MRK 505 337-UUS -
Application manual
Example for time coordination
Assume two substations A and B directly connected to each other via one line, as shown
in the figure 81. 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 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
51
t=0 t=t
1
The fault Protection
occurs B1 trips
ANSI05000205 V1 EN
Figure 81: Sequence of events during fault
where:
t=0 is when the fault occurs
t=t is when the trip signal from the overcurrent protection at IED B1 is sent to the circuit breaker. The
1
operation time of this protection is t
t=t is when the circuit breaker at IED B1 opens. The circuit breaker opening time is t
2
t=t is when the overcurrent protection at IED A1 resets. The protection resetting time is 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
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 32.
B1
51
t=t t=t
2 3
Breaker at Protection
B1 opens A1 resets
1
Section 7
Current protection
Feeder
Time axis
en05000205_ansi.vsd
- t
2 1
- t .
3 2
. There
3
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