Motors-when running in tune with harmonics

Where motors are connected in parallel with power factor correction capacitors, the effective capacitance as seen from the power supply circuit will vary depending on the connected and running motor load. As a result, `lumped´ capacitor banks connected to LV and MV power distribution centres and motor control centres may form a series resonance circuit with the connected area distribution transformer. This paper identifies, and illustrates with practical examples, how resonant conditions and associated voltage distortion may be created. Also the importance of developing an accurate model for the transformer damping resistance for use in harmonic analysis is demonstrated