Earthing system evaluation and influence on protection performance in resonantly earthed MV networks

In Zagreb distribution area, Petersen coils are installed in five 110/10(20) kV substations. The advantages of resonantly earthed MV networks (continuous operation, arc self-extinction etc.) and some disadvantages (lower protection sensitivity) are well known. An overview of the procedure implemented before putting Peterson coils in operation is given, with emphasis on the earthing system evaluation, which has proved to be rather important. Protection testing should be performed for different types of faults. All data are given for two distribution areas in which Peterson coils have been recently installed.