A novel sufficient differential protection for distribution network with DGs based on fault synchronous information

The differential protection scheme is the most effective way to solve the protection problem of distribution network with DGs. Limited to the level of distribution network communication automation, traditional differential protection scheme can´t be applied in distribution network with DGs. To solve the problem above, this paper proposes a fault synchronous identification technology. As the moment of fault is the same time for both ends of line, the technology uses the moment of fault as a time reference. The measurement about the interval between the first zero point of fundamental frequency current wave rising edge (or falling edge) after fault and the moment of fault will be carried out, and then intervals will be used to calculate phase change, which can effectively overcome the difficulty of high precision synchronous sampling. Based on fault synchronous identification technology, this paper proposes sufficient differential protection compound criterion. Only amplitude of fundamental current wave and time information after the failure are used to structure braking equation. Besides the sufficient current amplitude comparison criterion is lead up. New criterion overcomes contradiction between improving phase shift restraint capacity and sensitivity at the same time. Simulation verified the accuracy of the synchronous identification technology, the new criterion based on which has good action features too.