Distribution line automation system based on non-communication protection in the case of symmetrical fault

Distribution line non-communication protection (DNCP) can quickly and selectively isolate unsymmetrical fault, but the performance of this distribution line automation system is not satisfying in the case of symmetrical fault. This paper proposes a scheme which can quickly isolate symmetrical fault and block the operation of BPS: DNCP which is closed to the source can operate instantaneously, that can avoid overheating damage of electrical equipment; when the magnitude of voltage falls, BPS will detect the magnitude of negtive voltage two cycles ago to make a decision, that can avoid the process of connecting to permanent fault and tripping again for the ring main unit. EMTP simulation results show the effectiveness of the scheme.