Induction motors with YY/D connection change for efficiency and power factor increasing at partial loads

Abstract

It is established that there exists a significant possibility for energy savings, on the basis of application of induction motors with YY/D connection change proposed in this paper, especially for power to 30 kW. In connection D (0.866Un), total losses and reactive loads are reduced to loads up to 75-85%. Benefits of such motors would be significant because more than 80% induction motors are light loaded (mean value ? 70%). In such manner one motor with two characteristics is attained, but that is better than to offer to the market two different motors, because only in exploitation it is possible to accurately select the one which is working with greater efficiency values in given conditions. However, at the motor with YY/D winding it is always possible, by selection of corresponding connection for (mean value) load measured in operation. Even, with connection change it is possible to adjust to load changes in future. Moreover, at loads ? 30%, energy saving by induction motors with YY/D connection is greater than the one using induction motors with thyristor controllers. Induction motors YY/D connection application may be economical in cases where it is not recommended to use higher costs of energy efficiency of motors.

Analysis of induction motor efficiency class change at partial load

“…p γP n = P γP n /P n The difference in efficiency between the motors varies with values of at ratio of no-load losses (P 0 ) to load losses in rated regime (P γP n ), the Fig.1 Total losses (a) and Efficiency (b) dependencies, from output power in p.u., i.e. from (P/P n ) values, varies for three (same) motors but with different number of turns per stator phase (W s ), - fig.2 [8]. Fig.…”