chapter  18
32 Pages

Effects of Harmonics

WithJ.C. Das

Harmonics have deleterious effects on electrical equipment. The effect of the harmonics on motor losses should consider the subdivision of losses into windage and friction, stator copper loss, core loss, rotor copper loss, and stray loss in the core and conductors and the effect of harmonics on each of these components. The effective rotor and stator leakage inductance decreases and the resistance increases with frequency. Harmonics will produce elastic deformation, that is, shaft deflection, parasitic torques, vibrations noise, additional heating, and lower the efficiency of rotating machines. The harmonic fluxes superimposed upon the main flux may cause tooth saturation, and zigzag leakage can generate unbalanced magnetic pull, which moves around the rotor. If the inverter is a six-step type, then a sixth harmonic torque ripple is created, which would vary from 36 to 360 Hz when the motor is operated over the frequency range of 6–60 Hz.