Engineering Tutorial

Harmonics effect on Induction Motor

Harmonics in the power system are generated due to the usage of non linear load. Some of the effects of harmonics on the performance of induction machine are:

Core losses in the Induction machine increases
Torque of the Induction motor reduces
Increase in the Skin effect
Damage of the induction motor insulation
Electromagnetic Interference
Deviation in the induction motor Torque-Speed curves

Increase in Core Loss:

Core loss in any machine machine constitutes both hysteresis loss and eddy current loss. Hysteresis loss of the induction machine is proportional to the applied frequency and eddy current loss is proportional to the frequency squared. Frequency of the harmonics will be in the order of the multiples of the fundamental frequency. Therefore core loss is major concern at higher frequencies due to harmonics. Also harmonic currents and voltages reduces the overall efficiency of the machine

Increase in Skin effect:

Increase in the harmonics frequency results in increase in skin effect tending the current to flow on the surface of the conductor. Skin effect contributes the loss in the form of resistance to the flow of current

Electromagnetic Interference:

Harmonics increase the Electromagnetic Interference(EMI). This EMI does not affect the motor, however it affects the operation of nearby electronics, control and communication circuits

Reduced Motor Torque:

Fundamental frequency of the induction motor produces forward operating torque. However it is observed that harmonics frequency will generate torque in both forward and in reverse direction. For example 5^th 7^th and 11^th harmonics produce torques in reverse direction and on the other hand 7^th, 13^th and 19^th harmonics components produces torque in forward direction.5^th harmonic components will have higher magnitude compared to 7^th harmonics. Hence harmonics torque will reduce the operating torque of the machine

Deviation from Torque-Speed Characteristics:

Losses which occur due to Harmonics will cause the deviation in the torque speed characteristics of the motor from original and affects the performance of the motor