Question

In double-field revolving theory, slip with respect to forward flux and backward flux are:
1. s_f = 1 – s, and s_b = s
2. s_f = 2 – s, and s_b = 1 - s
3. s_f = s, and s_b = 2 - s
4. s_f = 1 – s, and s_b = 2 - s

Answer 1

Correct Answer - Option 3 : s_f = s, and s_b = 2 - s

Explanation:

Double field revolving theory:

• According to the double field revolving theory, we can resolve any alternating quantity into two components.
• Each component has a magnitude equal to half of the maximum magnitude of the alternating quantity, and both these components rotate in the opposite direction to each other.

 

For example,

• A flux, φ can be resolved into two components \(\frac{{{\phi _m}}}{2}\;and - \frac{{{\phi _m}}}{2}\)
• Each of these components rotates in the opposite direction i.e. if one \(\frac{{{\phi _m}}}{2}\) is rotating in a clockwise direction then the other \(\frac{{{\phi _m}}}{2}\) rotates in an anticlockwise direction.
• In a single-phase induction motor, let us call these two components of flux as forwarding component of flux \({\phi _f}\) and the backward component of flux \({\phi _b}\).
• The resultant of these two components of flux at any instant of time gives the value of instantaneous stator flux at that particular instant.
  \({\phi _r} = {\phi _f} + {\phi _b}\)

 

The forward flux has a slip of s and the backward flux has a slip of 2-s.