Centralized Protections of Busbars and Electric Motors Connected to Them

Centralized protections have several advantages over autonomous protections; however, incorrect actions of the former can result in more serious consequences. The reliability of their operation can be ensured with the help of majorization principle, but the number of devices with different principles of operation is insufficient so far. Three centralized protections are suggested; one of them allows duplication of current transformers. They all are based on the fact that the electric motors of feeders feed a short-circuit point; as a result, the current in a feeder damaged becomes higher than the current at the power input, and the currents in undamaged feeders change the direction to opposite. The conditions for protection actuation are presented. Operation of the protections in different modes is described in detail.