Q. The term `cogging` is associated with
Answer: Induction Motors
This action is due to the fact that, flux wave produced by a stator winding is not a pure sine wave. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. The fundamental wave revolves synchronously at synchronous speed Ns whereas 3rd, 5th, 7th harmonics may rotate in forward or backward direction at Ns/3, Ns/5, Ns/7 speeds respectively. Hence, harmonic torques are also developed in addition to fundamental torque.
A. Three phase transformers
B. Compound generators
C. D.C. series motors
D. Induction motors
B. Compound generators
C. D.C. series motors
D. Induction motors
Answer: Induction Motors
Crawling & Cogging is associated with Induction Motor
What is cogging and crawling in Induction Machines?
Cogging
The phenomenon of Magnetic Locking between the stator and the rotor teeth is called Cogging or Teeth Locking. Even after applying full voltage to the stator winding, the rotor of a 3 phase induction motor fails to start. This condition arises when the number of stator and rotor slots are either equal or have an integral ratio.Crawling
Sometimes, squirrel cage induction motors exhibit a tendency to run at very slow speeds (as low as one-seventh of their synchronous speed). This phenomenon is called as crawling of an induction motor.This action is due to the fact that, flux wave produced by a stator winding is not a pure sine wave. Instead, it is a complex wave consisting a fundamental wave and odd harmonics like 3rd, 5th, 7th etc. The fundamental wave revolves synchronously at synchronous speed Ns whereas 3rd, 5th, 7th harmonics may rotate in forward or backward direction at Ns/3, Ns/5, Ns/7 speeds respectively. Hence, harmonic torques are also developed in addition to fundamental torque.
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