Revisiting the Effects of Supply Voltage Unbalance on the Losses of Three Phase Induction Motors

Abstract

The impact of supply voltage unbalance (VU) on three-phase induction motors (IMs) is well known in terms of extra losses and associated derating to ensure that the motors do not prematurely fail. Theoretical studies, experimental results and standards exist in this regard. However, the approaches taken in the past are not seen be exhaustive now considering the modern tools such as Finite Element Modelling (FEM) software. Also, the relevant documentation available to-date on the subject does not cover the level of variability in the outcomes such as extra losses that can arise when an IM is subjected to the same level of VU that can be produced in a range of different ways. This paper emphasises the importance of Positive Sequence Voltage and the Complex Voltage Unbalance Factor (CVUF) in analysing the losses of a motor under different VU scenarios. Statistical analysis of the losses of three-phase IMs operating under different supply voltage unbalance scenarios is presented in this paper giving special focus to the behaviour of the core loss and copper loss. Two dimensional (2D) FEM is used to model the electromagnetics of the motor and Bertotti core loss model is used to evaluate the core losses. The outcomes of this analysis will be useful in the process of developing improved and cost effective mechanism of derating for mains connected three-phase IMs as well as in their design optimisation.