An experimental investigation of third harmonic current distortion in single-phase induction motors

Tests were performed to examine the relationship between third harmonic voltage distortion and third harmonic current distortion in single-phase capacitor-run induction motors. An arbitrary waveform generator was used to supply fundamental power along with a controllable third harmonic to three different types of capacitor motors. The motors were supplied with voltages containing fundamental-only, 2.5%, 5%, and 7.5% third harmonic content, and the phase angles of these harmonic voltages were varied relative to the fundamental. The distortion of the motor’s current was found to be quite sensitive to the magnitude of the voltage distortion, and also was dependent upon the value of the run capacitor. The phase angle of the third harmonic voltage had a minor impact on the current distortion. This paper provides experimental results and summaries of the response of these three small capacitor motors to voltage distortion, and provides insight into a significant source of triplen harmonic distortion in single-phase residential AC power systems.