Test method for permissible heating of asynchronous electric motors operating in intermittent modes as part of variable frequency drives with pulse-width modulation

Abstract

Currently, energy saving problems, especially in the agro-industrial sector, is of significant importance and relevance, in this regard, studies of energy modes of frequency-controlled asynchronous AC electric drives with pulse-width modulation (PWM) are of particular practical importance. To a large extent, this concerns the most important for energy saving modes indices of power losses in a frequency-controlled asynchronous machine and its overheating during operation in stationary and cyclic modes widely used in water supply installations in rural areas, conveyors in grain storage facilities, agro-industrial complexes for raising livestock and poultry. The research goal is to eliminate the possibility of overheating of asynchronous electric motors operating in intermittent modes as part of frequency-controlled electric drives with PWM. The essence of checking an asynchronous electric motor for heating is to compare the permissible temperature for the insulation class of its windings with the one it has when performing technological processes. This check is performed by direct or indirect methods of research and calculations. The studies discussed were conducted using mathematical calculations and modeling of electromechanical processes. A necessary condition for the normal operation of a frequency-controlled asynchronous machine without thermal overheating in continuous modes is not exceeding the actually created total electromagnetic power of losses and thus, by the power losses, equivalent current, torque, one can indirectly judge the overheating of the motor. The formulas of dependencies derived in the study may be used for engineering calculations to check the permissible thermal heating and control the energy consumption of self-ventilated asynchronous electric motors fed from static converters with PWM and operating in variable repetitive modes including at livestock and poultry enterprises.