The power factor and dispersion coefficient of an induction motor have relationship.The smaller the dispersion coefficient the better the power factor. Power factor is an important factor in designing of induction motor. Power factor depends upon two factors:
i) Magnetizing current :
A large value of the magnetizing current indicates poor power factor. Magnetizing current is indirectly proportional to the power factor. As the magnetizing current is large, the power factor is poor.
ii) Ideal short circuit current (Isc):
It is defined as the current drawn by the motor at standstill neglecting its resistance. A large value of ideal short circuit current will be drawn for small value of leakage reactance giving good power factor.
Dispersion coefficient defined as the ratio of magnetizing current to ideal short circuit current.
Thus dispersion coefficient,
i) Magnetizing current :
A large value of the magnetizing current indicates poor power factor. Magnetizing current is indirectly proportional to the power factor. As the magnetizing current is large, the power factor is poor.
ii) Ideal short circuit current (Isc):
It is defined as the current drawn by the motor at standstill neglecting its resistance. A large value of ideal short circuit current will be drawn for small value of leakage reactance giving good power factor.
Dispersion coefficient defined as the ratio of magnetizing current to ideal short circuit current.
Thus dispersion coefficient,
σ = Im/Isci
= Im/(Es /Xs ) Isci = Es /Xs
=Im.Xs /Es
For small values of Im and Xs dispersion coefficient is small and power factor is good. Thus for a small value of dispersion coefficient power factor is good, whereas for large value of dispersion coefficient power factor is poor.
The dispersion coefficient gets increased with increase in the number of poles. The induction motor of large number of poles has higher dispersion coefficient and thus, the power factor of the induction motor is poor.
The dispersion coefficient gets increased with increase in the number of poles. The induction motor of large number of poles has higher dispersion coefficient and thus, the power factor of the induction motor is poor.

Related Posts on Induction Motor
 Three Phase Induction Motor Interview Questions & Answers
 60 Top Induction Motor Interview Questions and Answers Part1
 Why do 3 phase induction motors not need a neutral?
 Different Ways to Improve Starting Torque of A.C. Induction Motors
 Why Three Phase Induction Motor SelfStarting?
 What is the slip value of a 3phase induction motor at synchronous speed and starting speed?
 Why an Induction Motor is almost constant Speed Motor?
 Why the rotor winding of three phase wound rotor induction motor is star connected?
 Advantages and Disadvantages of Induction Motor
 Why Induction Motor is called Rotating Transformer?
 Why Induction Motor is called Asynchronous Motor?
 What is no load Current of Induction Motor?
Please follow and like us: