Reed-Switch Short-Circuit Protection with Zero-Sequence Current Filter, Self-Diagnostics and Duplication

A need in replacing metal-consuming current transformers with magnetically sensitive elements is noted. It is suggested to design relay protections which receive information about current in the electrical installation busbar from reed switches. It is pointed out that a number of reed switch protections have already been designed, but the issues of ensuring their reliability have not been considered. For current protections of network components with grounded neutrals and coplanar phases, a new measurement unit is suggested on the basis of reed switches. Its reliability is ensured by simple design, functional diagnostics, and duplication of its components. It simultaneously functions as a current relay which responds to the total phase currents and a zero-sequence current filter. The technique for selecting filter parameters is presented; it consists of twenty-three formulas. The operation of the measurement unit and the protection on its basis in different modes is described. The features of self-diagnostics are noted. Examples of constructions for mounting protection reed switches in the magnetic field of the phase currents of an electrical installation are given.