Certain approaches in the design of induction machines for energy conservation

Abstract

Induction motors are widely used as main drives in Textile industries, Machine Tools and Agriculture. More than 60% of electrical energy generated being utilized by induction motors. Any improvement in power factor and efficiency will be cost effective for the nation. The research work is focused to suggest design modifications and efficient operation of three phase induction motor for energy conservation. Efficiency and power factor of an induction motor depends on load current. With regard to the factors of safety and available standard specifications, normally, over rated motors are employed, that lead to poor efficiency and power factor. Double Winding Induction Motor (DWIM) with constructional modification and efficient operation is considered for power factor improvement in this research work. A 3 kW, 415 V, 3-phase DWIM has been designed, fabricated and tested. This motor consists of two sets of identical windings in same stator core. While one set of winding is connected to a three phase supply to work as a conventional induction motor to meet mechanical load, a three phase EMF is induced in the other set of winding, which works as an Induction Alternator (IA). A small three phase load or single phase load may be connected to second set of winding. Since both windings were loaded, in addition to improvement in power factor and efficiency, energy conservation is made possible in this machine. A Microcontroller based control circuit has been designed to operate DWIM in power balancing mode in which the machine is operated at its rated capacity and in energy efficiency mode, it is operated at a load current that corresponds to maximum efficiency. Depending upon the mechanical load on the first set of winding, electrical load is switched to second set of winding such that the machine is operated, based on the mode of selection. An equivalent circuit has been developed for a DWIM from no load test, blocked rotor test and various combinations of electrical and mechanical load on both windings.