Integral Energy Power Quality

In radial power systems flicker transfer from a higher voltage level (upstream) to a lower voltage level (down-stream) is seen to be significantly affected by the down-stream load composition. Industrial load bases contain-ing mains connected induction motors are known to be effective in the flicker attenuation process compared to residential load bases containing passive loads. For better understanding of the flicker attenuation influenced by induction motors their dynamic behaviour has to be closely investigated under fluctuating supply conditions. This paper presents the methodology and results of investigations undertaken to examine the response of an induction motor to small perturbations in the supply voltage using a transfer function approach (small signal modelling). The motor response established employing this approach is used to evaluate the effective impedance of the motor which in turn is used to explain the flicker attenuation at the point of common coupling (PCC) in a qualitative manner. Furthermore, the dependency of the effective impedance on the frequency of voltage fluctuations is also examined. 1