Controller module 3BSE009514R1

Controller module 3BSE009514R1

Controller module 3BSE009514R1

It is possible to expect faster IED operation and breaker opening at the bus closer to fault, which will reverse the current direction in healthy circuit. Distance IED RBB will suddenly detect fault in forward direction and, if CRBB signal is still present due to long reset time of IED RAB and especially telecommunication equipment, trip its related circuit breaker, since all conditions for POTT have been fulfilled.

Zero sequence mutual impedance will additionally influence this process, since it increases the magnitude of fault current in healthy circuit after the opening of first circuit breaker. The so called current reversal phenomenon may cause unwanted operation of protection on healthy circuit and this way endangers even more the complete system stability.

To avoid the unwanted tripping, some manufacturers provide a feature in their distance protection which detects that the fault current has changed in direction and temporarily blocks distance protection. Another method employed is to temporarily block the signals received at the healthy line as soon as the parallel faulty line protection initiates tripping. The second mentioned method has an advantage in that not the whole protection is blocked for the short period. The disadvantage is that a local communication is needed between two protection devices in the neighboring bays of the same substation. Distance protection used on series compensated lines must have a high overreach to cover the whole transmission line also when the capacitors are bypassed or out of service.

When the capacitors are in service, the overreach will increase tremendously and the whole system will be very sensitive for false teleprotection signals. Current reversal difficulties will be accentuated because the ratio of mutual impedance against self-impedance will be much higher than for a non-compensated line. If non-unit protection is to be used in a directional comparison mode, schemes based on negative sequence quantities offer the advantage that they are ins