Real And Reactive Power Saving In Three Phase Induction Machine Using Star-Delta Switching Schemes

ABSTRACT: Induction machines are the most commonly used industrial drives for variety of applications. It has been estimated that induction motors consumes approximately 50 % of all the electric energy generated. Further, in the area of renewable energy sources, such as wind or bio-mass energy, induction machines have been found suitable for functioning as generators. In this context, it may be mentioned that a star-delta switching is common for the starting of three-phase induction motor. Now, it is proposed to use this star-delta switching for energy conservation of induction machines, i.e., at times of reduced loads, the machine switched back to star connection. Using a three-phase, 400 V, 50 Hz, 4-pole induction machine, it has been demonstrated that the star-delta switching of stator winding of three-phase induction machine (motor / generator operations) reconnected in star at suitable reduced loads with a switching arrangement, can result in improved efficiency and power factor, as compared to a fixed delta or star connection. The predetermined values along with the experimental results have also been presented in this report. A simulation program has been developed for the predetermination of performance of the three-phase induction machine using exact equivalent circuit. A case study on a 250 kW, 400 V, 4-pole, threephase induction machine, operated with different load cycles, reveals the significant real and reactive power savings that could be obtained in the present proposal