Presenting a new comparative protection scheme to improve the protection of compensated transmission lines

Transmission lines protected by distance relays have restrictions in presence of series compensation. When the error loop contains series capacitor, the observed impedance reduces by distance relays. Level of compensation in each level depends on the number of capacitors attached on that time; thus, it is necessary to have information about the present compensation level in transmission line in order for accurate function of distance relay. It is possible to match the settings in numerical relays by using gathered data through communication systems. PMU is an electrical equipment which measures in high speed the amplitude and phase of voltage and current and puts a timestamp with microsecond accuracy on them. In this article, the adaptive protection plan based on recognition of series compensation level has been investigated with very high accuracy in the shortest time. In this respect, an algorithm has been mentioned to recognize the compensated level and then, adjustment of distance protection according to this level of compensation. The proposed method has been implemented in order to verify in two systems of small and big samples. From the results obtained, it can be observed that the suggested method with an acceptable level of error will estimate the compensation percentage of transmission line. Therefore, modifying the settings of distance relay according to system’s condition, relay has correct function to different errors.

Keywords:

Protection , Transmission Line , Series Capacitor , Distance relay , Adaptive Protection , PMU