Current Differential Relay of Transmission Lines Based on Incremental Quantity

For improving the performance of current differential relay based on incremental quantity for transmission lines,a new protection scheme was proposed.It contains four parts: current differential relay,insensitive current differential relay,sensitive current differential relay and zero sequence current differential relay that are based on incremental quantity.Incremental quantity recursive algorithm was used to compute incremental quantity to accelerate the speed of protection.Sensitive coefficient was introduced to the restraint quantities in order to revise the operation characteristic in real time,and thus improve the reliability of the protection in the case of external short-circuit faults and the sensitivity of the protection in the case of internal short-circuit faults.For weak-feed transmission lines,an impedance differential relay based on incremental quantity was designed to open the current differential relay based on incremental quantity.The four incremental quantity based relays form a good inverse time characteristic in operation time.Results of dynamic simulation proved that the proposed scheme can operate quickly,and its performance is hardly influenced by voltage transformer(VT) breaking and fault resistances.