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.
Highlights
V OLTAGE Unbalance (VU) is a common and unavoidable condition in power systems which arises for many reasons that are well documented [1]
This shows that the Loss Increase Rate (LIR) sharply increases with the magnitude of Complex Voltage Unbalance Factor (CVUF) (i.e. LIR sharply increases with the negative sequence voltage), and it can be different between the two cases even though the |CVUF| level is identical
This paper presents a comprehensive study on the factors influencing the derating of three-phase induction motors using both experimental and numerical modelling platforms
Summary
V OLTAGE Unbalance (VU) is a common and unavoidable condition in power systems which arises for many reasons that are well documented [1]. It is essential to study the impact of the magnitude of VU, angle of CCUF, and positive sequence voltage on the variation of losses, temperature rise, and vibration level of three-phase IM operating under supply VU. Experimental investigations were carried out using an improved version of an advanced air-cooled doublechamber calorimeter (DCC) developed with a higher measurement accuracy and reduced measuring time compared to the calorimeters detailed in the literature [9] This calorimeter platform was improved into an electrical machine testing platform which can be used to examine their losses, temperature variations, and torque and speed oscillations under different network conditions.
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