Flicker attenuation - Part I: Response of three-phase induction motors to regular voltage fluctuations

Voltage fluctuations leading to lamp flicker that originate in one place in a power system tend to propagate to other parts of the network with some level of attenuation depending on the network impedances and the loads connected. Numerous sub synchronous type frequency components exist in these voltage fluctuations that are responsible for lamp flicker. The rudimentary theory and the experimental measurements support the idea that industrial load bases which contain a large percentage of mains connected induction motors tend to attenuate flicker better compared to residential load bases having mainly passive loads. This paper reports on the response of three phase induction motors of several sizes when subjected to low frequency voltage fluctuations, firstly the case where a balanced single frequency component is superimposed on the mains voltage and secondly the case where the mains voltage is sinusoidally amplitude modulated, a scheme that is frequently used in flicker related work. Small signal models are presented that will enable systematic understanding of the behaviour which is verified using large signal models.