A New Intelligent Method for Parallel Transmission Lines Protection

In many countries, the parallel lines are widely used in transmission systems due to economic and technical benefits. Distance relays have poor performance on the protection of parallel transmission lines because of the mutual coupling effect. The distance relay may underreach when both lines are in-service. On the other hand the over reach problem may arise when only one line is in-service and another line is disconnected and grounded at both sides. Therefore, a new intelligent method is presented to protect parallel lines comprehensively in different operating modes. In the first stage, considering the status of circuit breakers as well as measured current signals at both sides of parallel lines, the fault types are identified by allocating a probabilistic neural network (PNN). Then, in the second stage, the fault location is estimated by assigning an artificial neural network (ANN) to each type of fault. The results obtained from the simulation of a part of the power system including 230-kV parallel lines, show that the proposed method can accurately detect all fault types and also it can precisely locate the fault points with an accuracy of 98.8%.