Performance of High Efficiency Induction Motors with Power Quality Problems

P.D. DONOLO; C.M. PEZZANI; A. F. BONELLI; A. R. AOKI; R. A. NEHLS; G.R. BOSSIO; G.O. GARCÍA

Paris

Congreso; CIGRE 45th Session 2014; 2014

CIGRE

Most of the electric energy generated is consumed by induction motors (IMs) in the industry. As a consequence, even small efficiency improvements in their performance yield large energy savings [1]-[4]. To promote the development of even more efficient IMs, the standard IEC 60034-30 from 2008 specified three efficiency classes [1] [2]. At full load and under ideal voltage supply conditions, IMs in higher efficiency class use less energy than IMs in lower efficiency classes. For example, IMs in the IE3 class waste at least 30% less energy than IMs in class IE1. However, the behavior of higher efficiency class IMs under distorted and unbalanced voltages is not fully documented [5]-[7]. Initial studies by Van Wyk et. al. suggest that higher efficiency IMs are more affected by voltage supply problems [5]. In this paper we study the effect of voltage unbalance, harmonic voltages and load level on the efficiency of the IM. We analyzed the efficiency of two 4.5 kW 60 Hz IMs, one in the standard efficiency class (IE1) and the other in the high efficiency class (IE2). We also analyzed two 5.5 kW 50 Hz IMs, one in the standard efficiency class (IE1) and the other in the premium efficiency class (IE3). We used a programmable power supply to feed the IMs. We adjusted the wave shape and the unbalance ratio to obtain different voltage harmonic distortions and voltage unbalance levels. The IM under test was coupled to another IM driven by a commercial torque-controlled variable-speed drive that acts as a variable load. We measured two phase currents and two line voltages to calculate the input power. We also measured the mechanical torque and speed to calculate the output power and to estimate the efficiency. In the unbalanced voltage tests, we noticed that the efficiency of the premium performance IM deteriorated the most as the voltage unbalance grew. This result is consistent with negative sequence impedance values estimated from the starting currents of the IMs. For the unbalanced voltage tests, we also found that the degradation of the IMs efficiency does not change with the loading of the IM. On the harmonic voltage distortion tests, we found that the efficiency of IMs in the high and premium efficiency classes deteriorated at the same rate as the IMs in the standard efficiency class.