SOLUTION

Rotating machines also act as the source of harmonics in the power systems. Causes of harmonics generation in rotating electrical machines are classified into the following categories:

Harmonics in Rotating Machine

Magnetic nonlinearities of the core material: Nonlinear magnetization characteristics of the core material cause harmonic generation.

Non-uniform flux distribution in air gap: often it is assumed that the air-gap flux distribution is uniform and the operating principles of rotating machines are discussed based on this assumption. But in most of the rotating machines, flux distribution in air-gap is not uniform which leads to harmonics production.

Slot harmonics: Slots are inevitable in rotating machines. The alternate presence of slots and teeth changes the reluctance of the magnetic flux varies in a similar type of alternating fashion. This variation acts as a reason for a harmonic generation. Harmonics are produced due to pitch factor and distribution factor.

Rotors saliency: Rotor saliency brings the variation of reluctance in the magnetic path and reactance in the electric path which contribute to the harmonic generation.

Crawling: It is a common problem faced by induction motors. During this fault, odd harmonics like 5th and 7th orders appear. Fifth harmonics rotate in the same direction as the fundamental but 7th order harmonics rotate in opposite to this direction. It changes the operating characteristics of the motor. During crawling, 7th harmonics is dominating over the 5th harmonics and lowers the stable operating zone to the one-seventh speed of the rated value.