System of Signal Injection and Extractioo for Protection and Insulation Monitoring in Medium Voltage Networks

Simple overcurrent criterion is most often used for detection and elimination of ground faults in radial industrial medium voltage networks. Since in Poland medium voltage networks work with noneffectively grounded neutral point, the ground fault currents can reach very low values, especially under high resistance faults. Such faults cannot be detected by any protection. Therefore, new methods to detect ground faults and to control the insulation in medium voltage network are of great importance. In the paper the idea for monitoring insulation parameters of the system, based on the simultaneous use of two different signals of non-industrial frequency, injected into the controlled network, is presented and discussed.