The Method of Monitoring of the State of Insulation for Operational DC Grids in Power Plants and Substations

Operational direct current grids (ODCG) are one of the most important components of many power plants and substations, for example, hydroelectric power plants. They are designed for power supply of relay protection devices, signalization and automation, and for the power supply of important equipment, emergency lighting, drives of highvoltage switches, etc. The importance of this type of equipment leads to high-reliability demands of the ODCG. Quality of cable insulation of the ODCG is crucial. The research conducted in this field shows that both gradual and sudden short-term insulation resistance fluctuations depend on many factors. Among them are the mode of operation, network load, state of cable channels, and state of switching equipment. The results of five-year observations on insulation resistance of open distribution unit ODU-110/330 kV Dniester HPP-1, an distribution unit of DU-35 kV HPP-2 and a complete distribution unit CDU-330 kV of a pumping station in 2012–2017 are analyzed.