The characteristics of electric power harmonics generated by four succ
essive designs of a 41 cm diameter, variable-speed fan system used for
ventilation of agricultural buildings were investigated Harmonic anal
yzers were programmed to calculate harmonic frequencies of the 2nd thr
ough the 63rd orders at several motor control voltages during tests of
each fan design. Alterations to the fan system included changes to th
e motor, the impeller, and the controller. Motors used in this study w
ere single-phase 0.25 kW and 0.20 kW. The 230 Vac fan motor produced g
reater total harmonic distortion with a triac-based controller in the
circuit to reduce motor voltage when compared with no controller. The
third harmonic was the greatest contributor to total harmonic distorti
on of current and voltage. The magnitudes of even order harmonics were
negligible, and odd harmonics decreased with increasing order. Fan st
atic pressure had relatively little effect (less than 10%) on harmonic
levels. Heavier motor loading and smaller motor capacitors tended to
lower the generation of harmonics from the fan system. Comparisons of
harmonic generation were made between triac and transformer-based cont
rollers. Also, voltage harmonics before and after a triac-based contro
ller were evaluated.