Harmonics in variable speed fan systems

The characteristics of harmonics generated by variable speed fan systems used for ventilation of agricultural buildings are reported. The fan system is controlled with a variable speed, triac-based fan controller and is fitted with a three-bladed, 30° pitch polypropylene propeller. A test is conducted to evaluate voltage and current harmonics produced as a result of the triac´s presence in the fan system circuit. The triac introduced harmonics into the current waveform which reduced the motor efficiency. The fan system is not a significant source of voltage harmonics for the utility. Current harmonics are at significant levels with the third current harmonic being the highest at 100% of the fundamental