Alternative Resource-Saving Current Protections for Electric Motors

In the article the author presents the principle of operation of alternative resource-saving maximum current and longitudinal differential protections, the purpose of which is to protect high-voltage electric motors from external and internal short circuits. The presented protections are performed without the use of widely used in the electric power industry measuring current transformers (CT) with metal cores, which have significant weight and dimensional parameters and high cost. The proposed protections are made using magnetically controlled elements such as reed switches and inductance coils. Protections with their application can be used as an alternative to traditional motor protections and at the same time are not inferior to them in terms of speed. The developed protections represent an innovative approach in realization of relay protection of various electrical installations. Resource-saving of these protections is in the use of inductive coils and reed switches, which are, both in terms of cost and weight and dimensional parameters, an order of magnitude cheaper and smaller in size and weight than the above-mentioned current transformers. Protections are recommended for use in high-voltage electric motors, presented in the form of maximum current protection (MCP) and differential protection against multiphase short circuits and internal faults. The proposed protections are performed in the form of devices, with their installation inside the cell of complete switchgear (complete switchgear), voltage 6–10 kV and electric motor. The use of the presented protections increases the reliability relay protection, as protected electric motors, and the cell of the complete switchgear.