NEW METHODS FOR CONTROL AND PROTECTION RELAY IN A COMPENSATED MEDIUM VOLTAGE DISTRIBUTION NETWORK BASED ON INJECTING VARIOUS FREQUENCY CURRENT

Traditional methods for protection relay and control in compensated network are difficult to meet the requirement of distribution system automation. New methods based on injecting current are presented in this paper. Petersen coil automation tuning system is implemented, which is based on measuring the system resonance frequency. High impedance fault detection is implemented by measuring the zero sequence voltage caused by injecting current. And the fault feeder is detected by measuring the zero sequence power factor caused by injecting current. This principle is not affected by system operation. It has high precision and high reliability. The prototypes for protection relay and control is developed, which have passed the simulation test. While Petersen coil automation tuning system has been tested on the network for many years.