Schemes, Neutral Grounding Treatment and Organization of Ground Fault Relay Protection in 20 kV Networks of Megalopolises

The paper presents modern schemes of 20 kV networks used in Moscow, which development is reasonable under the high density of electrical loads in the megalopolis. Features of neutral grounding through a low-value resistor in 20 kV networks of different countries are considered. Schemes of resistor connection into a neutral point are analyzed using recommendations of IEEE Std 142-2007. The possibility for active current changing during a ground fault depending on a temperature coefficient of resistance of resistor material is studied. The general principles of relay protection and automation in the 20 kV network of the Moscow power system are presented. Main features of calculation of ground fault relay protection are given with determination of the required resistor current with various types of zero-sequence current sensors.