Dependancy of Three Phase Induction Motor Derating Aspects on Complex Voltage Unbalance Factor: A Calorimetric and Finite Element Simulation Study

Abstract

It is well known that three-phase induction motors have to be derated in the presence of supply voltage unbalance (negative sequence) exceeding a stipulated limit of 1% based on several widely used standards. Generally, voltage unbalance limits are decided based on the magnitude of negative sequence voltage unbalance factor which is quantified as the ratio of negative sequence voltage to positive sequence voltage. However, a specified voltage unbalance magnitude can arise as a result of numerous possibilities of the three phase supply voltages. Therefore, it is hypothesised that the current derating curve, which defines a derating factor that is dependent on the magnitude of the voltage unbalance, is not optimal and may not be economical and/or safe for some voltage unbalance conditions. To examine the validity of this hypothesis, modelling and experimental validation need to be carried out considering motor losses and temperature rise which are the main factors that help determine the derating factor of an induction motor. Realising these requirements, the emphasis of this study is to examine the dependency of losses, temperature rise and torque oscillations of a three-phase induction motor on the complex nature of voltage unbalance through calorimetric and finite element simulation-based studies. The outcomes are expected to assist in the development of suitable derating factors.

An Alternative Methodology for Quantifying Voltage Unbalance Based on the Effects of the Temperatures and Efficiency of Induction Motors

“…Some authors [4]- [8] have investigated the limitations of the indexes employed to quantify the VU. They mentioned, among several other aspects, that many unbalance conditions, which produce different effects on electric equipment, are associated with the same index used to quantify VU.…”

“…Given it is an index based on the analysis of current, the results of its application are restricted to the loads responsible for generating the positive and negative sequence currents used in its calculation. In [8], the dependency of the TIM derating aspects on CVUF was investigated. In this study, tests were carried out under various VU conditions to examine the effect of the VUF, the V1, and the CCUF angle.…”