Impact of mains connected three-phase induction motor loading levels on network voltage unbalance attenuation

Voltage unbalance (VU) in power systems should be managed in a systematic manner in order to minimise its adverse effects on both customer equipment and supply utilities. It is a well known fact that three-phase induction motor performance can be significantly affected in the presence of supply voltage unbalance. It is also known that three-phase induction motors can help to reduce pre-existing network voltage unbalance levels. Recently undertaken research aligned with IEC/TR 61000-3-13:2008 Technical Report on voltage unbalance management (emission allocation and emission assessment) have quantified the contribution made by induction motors to the net voltage unbalance at a point of connection. It is perceived that loading level of three-phase induction motors will have an influence on this contribution. Hence, this study focuses on a sensitivity analysis of induction motor loading level on the voltage unbalance emission contribution to the point of connection. Simulation work undertaken indicates that increased loading levels on induction motors tend to exacerbate negative sequence voltage unbalance factor (VUF) at the point of connection in comparison to lightly loaded induction motors.