Impact of over/under and voltage unbalanced supplies on Energy-Efficient motors

There are several significant power quality and performance issues relating to energy efficient (EE) motors. This paper addresses some of these issues through detailed testing, analysis and comparison of standard (STD) and EE motors. The power quality issues addressed in this paper are over/under voltage and unbalanced supplies. The investigation was conducted on four (STD) and four EE motors, each group with ratings of 3kW, 7.5kW, 11kW and 15kW. It was found that the voltage unbalance results in a larger % current unbalance in EE motors. This is primarily due to the lower negative sequence impedance associated with EE motors. Experimental results verify the theoretical results. Furthermore, the experimental results show that the peak of the efficiency curves shift to lower loads during under-voltage conditions and towards higher loads during over-voltage.