METHOD OF CURRENT PROTECTION OF MOTOR WITH DEPENDENT CHARACTERISTIC OF OPERATION Russian patent published in 1994 - IPC

FIELD: electrical engineering. SUBSTANCE: temperature of cooling air is measured or set. Heat condition of motor is simulated mathematically using ratio of root-mean-square value of current to long-duration permissible current of stator in second power as value reflecting amount of heat recovered per time unit. In this case constants of times of heating and cooling are set separately for winding and magnetic core with account of operational condition of motor. Long-duration permissible multiplicity of current is determined with account of ambient air temperature and for multiplicities of current lesser than long-duration permissible one-temperature of heat balance of winding. Adiabatic character of heating process of winding is simulated in function of the square of multiplicity of stator current limiting it by temperature of heat balance with current multiplicities not exceeding permissible one for long duration. Process of heating of magnetic core is simulated by exponential law in function of difference of temperatures of winding and of winding heat balance or magnetic core temperature if it exceeds the latter. Motor is switched off with fall of voltage in system below threshold one if winding temperature exceeds maximum pre-start one. When simulating process of heating of winding upper level of limiting of multiplicity of stator current is specified. EFFECT: improved reliability of current protection. 3 cl, 1 dwg