Novel thermal model aided motor derating under waveform distortion

Static power converters and nonlinear loads used by industries change the sinusoidal nature of power system voltages, resulting in the injection of harmonic voltages in the power system. Due to the presence of harmonics, the total losses of the motor will increase, resulting in a higher temperature rise of motor which may not be allowed due to the faster deterioration of the motor insulating materials, thereby reducing the life-expectancy of the motor. This paper reports on the development of a novel hybrid thermal model, based on which the temperature distributions along the motor cross-section under different operating conditions can be obtained. Utilising this thermal model, the derating of the motor can be carried out more effectively.