What is cogging in induction motor

The harmonic fluxes in the motor will create an extra torque field. In an induction motor, crawling is less because of its high starting torque. Thus, this is all about an overview of crawling and cogging of the induction motor. The crawling of this motor can occur at the portion of rated speed whereas the cogging of this motor can occur if the no.

If the mechanical load on the shaft involves constant load torque, the torque developed by the motor may fall below this load torque. This phenomenon is called as crawling in induction motors. Cogging Magnetic locking or teeth locking Sometimes, the rotor of a squirrel cage induction motor refuses to start at all, particularly if the supply voltage is low.

This happens especially when number of rotor teeth is equal to number of stator teeth, because of magnetic locking between the stator teeth and the rotor teeth. When the rotor teeth and stator teeth face each other, the reluctance of the magnetic path is minimum, that is why the rotor tends to remain fixed. The flux in the air-gap of an induction motor set up by the 3-phase stator windings carrying sinusoidal currents is of non-sinusoidal wave shape. According to the Fourier series analysis, any non-sinusoidal flux is equivalent to the combination of a number of sinusoidal fluxes of fundamental and higher order harmonics.

Since the wave shapes of the air-gap flux have half-wave symmetry, hence all the even harmonics i. Thus, a non-sinusoidal flux wave can be resolved into fluxes of fundamental and higher-order odd harmonics i. The 3 rd harmonic flux wave produced by each of the three phases neutralise one another.

Hence, the resultant air gap flux is free from the third and its multiples i. The space harmonics are produced by windings, slotting, magnetic saturation and inequalities in the air gap length etc. These harmonic flux waves induce EMFs and circulate harmonic currents in rotor windings.

These harmonic currents in the rotor windings interact with the harmonic fluxes to produce harmonic torques, vibrations and noise. This generates a small amount of reverse braking torque on the rotor which can be neglected. Facebook Twitter. Previous Post Next Post.