Microprocssor thermal-safety relay for synchronous motors with a short-circuited rotor

摘要

Thermal safety systems for asynchronous motors with a short-circuited rotor are often based on electrothermal relays, in which the current flowing in the stator winding of the motor heats a bimetallic element. Electrothermal relays are relatively simple, small, and cheap. However, the time-current characteristics of thermal Rlays do not accurately correspond to the overload characteristics of motors, which reduces their effectiveness as Safety units for motors operating with small overloads and in frequent short-term mode.