Accelerated insulation aging in phase angle controlled single phase induction motors

Thyristor based, phase angle controlled, speed regulators are widely used for energy efficient control of single-phase induction motors. This leads to power saving but adversely affects the life of insulation in the motors due to non-sinusoidal voltage and current waveforms. The accelerated insulation ageing is due to increased voltage peaks, voltage transients, sharp dV/dt and increased thermal stress. Voltage harmonics increase dielectric and core losses. Current peaks increase the overall heating of the winding hence cause thermal stress in the insulation. This paper presents the effect of non-sinusoidal voltage and current waveforms impressed on single-phase induction motors due to power electronic speed regulator. Experimental and simulated results with power electronic phase angle-controlled regulator are presented along with the experimental results of conventional resistive regulator. The results compare quantitatively the insulation stress parameters due to non-sinusoidal & sinusoidal voltage and current on motor. The results can be used to estimate the accelerated insulation ageing due to phase angle controlled speed regulators in single-phase induction motors.