ABB REG670 Applications Manual page 340

Section 9
Current protection
334
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 176.
A1
I>
t=0 t=t
1
The fault B1 and A1 B1 trips and
occurs start
IEC05000205 V2 EN
Figure 176: Sequence of events during fault
where:
t=0 is when the fault occurs
t=t is when protection IED B1 and protection IED A1 start
1
t=t is when the trip signal from the overcurrent protection at IED B1 is sent to the circuit breaker.
2
t=t is when the circuit breaker at IED B1 opens. The circuit breaker opening time is t
3
t=t is when the overcurrent protection at IED A1 resets. The protection resetting time is 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
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 186.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
t=t t=t
2 3
Breaker at
A1 starts B1 opens
1MRK 502 071-UEN -
B1
Fault
I>
t=t
4
Protection
A1 resets
=IEC05000205=2=en=Original.vsd
3
Application manual
Feeder
Time axis
- t
2
- t .
4 3
.
3