One of the current issues in a complex electrical network with isolated (compensated) neutral is the selective identification of the damaged element during a single-phase-to-ground fault (SPGF). In order to achieve selective and reliable operation of protections against SPGFs in complex networks with isolated (compensated) neutral, besides information about the zero-sequence current and connection, information about phase voltages, zero-sequence voltage of the electrical network, and the operation of protection devices against adjacent SPGFs is necessary.
In Ukraine, devices called "Altra" developed by the Institute of Microprocessor Systems for Object Control in Power Engineering are widely used for the protection of electrical networks with isolated and compensated neutral against SPGFs. These modern devices provide comprehensive insulation monitoring of each connection of the bus section at 6-35 kV, generate signals for disconnecting the faulty connection of the bus section after the occurrence of SPGF on it, and also record and store digitized analog and binary signals of power installations in normal and emergency conditions.
As operational experience has shown, it is not possible to coordinate the operation of SPGF protection devices in consecutive sections of the electrical network based solely on zero-sequence current and voltage. To ensure the selective operation of relay protection devices against SPGFs in such a network, their operation needs to be coordinated in terms of time and direction.
In some 20 kV voltage electrical networks recently introduced in the power systems of Ukraine, where the possibility of changing the power supply direction to individual distribution points (DPs) is provided, it is not always possible to ensure the selectivity of SPGF protection devices solely by selecting the operation time and direction. Selective operation of SPGF protection devices in such networks can be achieved by blocking their operation during SPGFs on power cables. Such blocking can be implemented using binary signals from protection devices of adjacent elements.
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