1 Impact of Steady-State Voltage Supply Anomalies on Three-Phase Squirrel-Cage Induction Motors Fernando J. T. E. Ferreira 1,2 , Aníbal T. de Almeida 2 , Wim Deprez 3 , Ronnie Belmans 3 and Ge Baoming 4 1 Dep. Electrical Engineering, Engineering Institute of Coimbra, Coimbra, Portugal 2 Institute of Systems and Robotics, University of Coimbra, Coimbra, Portugal 3 Dep. Electrical Engineering, Katholieke Universiteit Leuven, Heverlee, Belgium 4 School of Electrical Engineering, Beijing Jiaotong University, Beijing, China E-mail: fernando@mail.isec.pt , jeepisr@isr.uc.pt Abstract - In this paper, the consequences of steady-state voltage supply anomalies on the behavior, losses and operating limits of low-power, low-voltage, three-phase, squirrel-cage induction motors is presented. The study is mainly based on simulations and previously published works, but experimental results are also presented. The well-known motor derating curves proposed by NEMA are questioned. It is demonstrated that they are too general, and do not consider combined effects of voltage unbalance, magnitude deviation, and distortion. Additionally, the effects of ambient temperature and motor characteristics (e.g. rated power, frame type, rotor type and efficiency class) should also be considered. Another important issue discussed in this paper is the fact that voltage unbalance and voltage distortion definitions should be properly revised in order to eliminate ambiguities. A clear methodology to evaluate the impact of the referred power anomalies on motors is proposed. An artificial neural network-based approach for mathematical description of motor derating curves as a function of multiple variables is also proposed and validated. Several relevant considerations on motor simulation within power quality scope are presented. I. INTRODUCTION Three-phase squirrel-cage induction motors (IMs) [1, 2] are the most important electric motors. They are applied in more than 90% of the electric motor driven systems. Since the beginning of the second half of 20 th century, the effects of poor power quality (PQ) on IMs have been widely discussed [3-23], including voltage unbalance and magnitude deviation, and, more recently, voltage distortion. However, the combined effects of these supply voltage anomalies on IMs require further discussion. The main standards on IMs or PQ define limits for voltage magnitude deviation, unbalance and distortion, and, some of them establish derating curves for IMs, as a function of those parameters. Motor derating curves define output power limits under non-ideal power supply conditions to prevent motor early failure due to overheating. Derating curves or equations proposed in standards are based on average data, computed from theoretical analysis, simulations and/or experimental tests. Moreover, combined effects are not covered by those derating curves or equations in most standards. This paper presents a study on the impact of steady- state voltage supply anomalies on the performance (e.g. efficiency and slip) and operating limits (e.g. derating curves) of low-voltage IMs. The influence of ambient temperature and motor characteristics on required motor derating is also analyzed. The study is intended as an overview, based on simulations, experiments and previously published works. Therefore and also due to paper size limitations, many presented conclusions are not supported by presented data. II. MOTOR DERATING ANALYSIS In the context of this paper, data obtained from experiments, simulations and related reports, papers or documents is assessed, interpreted and summarized. Most of the consulted material is listed in the references. The motor simulations were carried out using per-phase equivalent circuit based models (ECMs). Three large and two small, low-voltage, TEFC, IMs (400 kW, 4 poles; 200 kW, 2 poles & 4 poles; 7.5 kW, 4 poles; 3 kW, 4 poles) were simulated. For the large IMs the typical IEC 1 -defined ECM is used, whose parameters were provided by one of the largest motor manufacturers. For the 7.5-kW IM, the IEC-defined ECM is used, whose parameters were experimentally estimated by the authors. For the 3-kW IM, a hybrid model is used, described in [6], which includes a set of ECMs and a thermal model (TM). The skin effect impact on rotor effective leakage inductance and effective resistance [3, 6], as well as the frequency dependent core loss resistance variation, are included in all models, using convenient adaptation. Magnetizing inductance variation as a function of magnetizing current (saturation effect) and stray load losses (SLLs) are included only in the 3-kW IM model. Moreover, to simulate different types of rotor bars, six different (frequency dependent) rotor resistance cases are considered in the 3-kW IM model, shown in Fig. 1 and Table I. A. Voltage Distortion Voltage distortion (VD) means that voltage, and, consequently, the current waveforms have a non-sinusoidal shape. The distorted periodic waveform corresponds to the sum of different sine waves with different magnitude and phase, having frequencies that are multiples of power system frequency, commonly known as harmonics. This PQ problem, its causes and consequences are well known and described in several publications [4, 17-21] and standards (e.g. IEEE Std. 519). One of the main consequences of VD, and in the context of this paper the most important one, is its detrimental effect on efficiency of electric machines (particularly motors). Among 1 IEC – International Electrotechnical Commission.