DISTURBANCES IN POLISH 15 KV NETWORK BY GROUND SHORT-CIRCUITS

Reliable supply of electric power depends to a great extent on efficient performance of medium voltage (MV) distribution networks. In Poland, these are largely 6 kV to 30 kV networks with 15 kV being the most common voltage. Frequently these networks operate with neutral point grounded through Petersen coil which makes the work conditions for the network’s earth fault protection systems particularly difficult. During recent years in Poland the protection systems with admittance criteria [1] have been widely implemented and since the earth faults are detected with better efficiency. In this paper 15 kV networks in Poland are briefly characterised, a relation between the magnitude of the earth fault disturbances in Poland’s MV networks and the quality of PE insulation are discussed. The features of admittance earth fault protection systems and their earth fault detection efficiency are presented.