I> I>A1 B1 FeederTime axist=0 t=t1 t=t2 t=t3The faultoccursProtectionB1 tripsBreaker atB1 opensProtectionA1 resetsen05000205.vsdIEC05000205 V1 EN-USFigure 76: Sequence of events during faultwhere:t=0 is when the fault occurst=t1 is when the trip signal from the overcurrent protection at IED B1 is sent to the circuit breaker. Theoperation time of this protection is t1t=t2 is when the circuit breaker at IED B1 opens. The circuit breaker opening time is t2 - t1t=t3 is when the overcurrent protection at IED A1 resets. The protection resetting time is t3 - t2.To ensure that the overcurrent protection at IED A1, is selective to the overcurrent protectionat IED B1, the minimum time difference must be larger than the time t3. There are uncertaintiesin the values of protection operation time, breaker opening time and protection resettingtime. Therefore a safety margin has to be included. With normal values the needed timedifference can be calculated according to equation 90.40 100 40 40 220t ms ms ms ms msD ³ + + + =EQUATION1266 V1 EN-US (Equation 90)where it is considered that:the operate time of overcurrent protection B1 is 40 msthe breaker open time is 100 msthe resetting time of protection A1 is 40 ms andthe additional margin is 40 ms8.3 Instantaneous residual overcurrent protection EFPIOCIP14508-1 v3Section 8 1MRK 505 363-UEN ACurrent protection140Application manual
