Impact of steady-state voltage supply anomalies on three-phase squirrel-cage induction motors

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.

Subharmonic measurement using DFT and Wavelet-Packet Transform in an IEC extended framework

“…The most important effect of subharmonics is the impact on light flicker [1]. Other effects are asymmetry of the hysteresis loop in transformers, reduction of the useful life due to the thermal effect, disturbances in turbogenerators, incorrect operation of remote control systems, and reduction of the useful life of induction motors [2][3][4][5][6][7]. Based on these effects a strict limit of 0.1% has been proposed in [2] for subharmonic voltages in order to prevent the additional temperature rise in the stator winding of induction motors.…”

Experiments to observe the impact of power quality and voltage-source inverters on the temperature of three-phase cage induction motors using an infra-red camera

“…Power quality is related with the mains supply reliability and quality of the respective voltage waveforms, in terms of shape and amplitude. The most common long-duration voltage anomalies in the power network, such as voltage magnitude deviation, unbalance, and/or harmonic distortion, have a significant impact in the performance and lifetime of three-phase, squirrel-cage, induction motors (IMs) [1,2], which are, by far, the most used electric motor type in industry. Therefore, it is important to evidence that impact in the electric machines and power electronics courses, as well as the importance of derating motors operating in such conditions in order to avoid internal overtemperature in steady-state operation, since it can lead to a significant reduction in their lifetime.…”

“…The voltage harmonic distortion is provoked by nonlinear loads (such as VSIs, which typically incorporate diode rectifiers at the input stage). The 5 th -order harmonic is particularly baneful, since it produces a negative-sequence stray rotating magnetic field, dragging the motor and heating the rotor [2]. In general, all negative-and positive-sequence current harmonics, resulting from voltage harmonics at the motor terminals, lead to extra losses in the motor stator core and windings.…”

“…2b, in which the intermediate temperature rise, between points 2 and 3 is given by (2), similarly to a voltage divider.…”

“…2 After the motor starting transient period, at rated load, the motor equivalent lumped thermal capacity and resistance can be both approximately determined by simply recording over time the frame temperature rise (e.g., using an infrared thermometer with USB communication to the PC, with proper data visualization software), motor efficiency, and input power (allowing for the losses calculation), and then fitting to the temperature rise vs. time data a curve with the form ͳ െ ݁ ି௧ ఛ Τ in which οߠ ൌ ܴ ௧ ȉ ܲ ௦௦௦ and ‫ܥ‬ ൌ ߬ ௧ ܴ ௧ Τ .…”