(a) must be exactly equal to pole pitch.
(b) can never be equal to pole pitch.
(c) may or may not be exactly equal to pole pitch.
(d) none of the above.
Answer: (c) may or may not be exactly equal to pole pitch.
Explanation:
CONCEPT: Coil Span (Coil Pitch)
- Coil
span (or coil pitch) is defined as the angular distance
between the two sides of a coil.
- It
is usually expressed in:
- Electrical
degrees, or
- Number
of slots
- Pole
pitch is the angular distance between the centers of two adjacent
magnetic poles.
- One
pole pitch corresponds to:
Types of Coil Span
Full-Pitch Coil
- When
the coil span is exactly equal to the pole pitch:
- Such
a coil is called a full-pitch coil.
- Advantages:
- Maximum
induced EMF
- Disadvantages:
- Higher
harmonic content in the waveform
Short-Pitch (Fractional-Pitch) Coil
- When
the coil span is less than the pole pitch:
- Such
a coil is called a short-pitch or fractional-pitch coil.
- The
angle by which the coil is short-pitched is called the chording
angle (ξ).
- Advantages:
- Reduction
of harmonic components
- Improved
voltage waveform
- Reduced
copper length and losses
- Disadvantage:
- Slight
reduction in induced EMF
EXPLANATION
- Depending
on the design requirements:
- Full-pitch
coils are used when maximum EMF is required.
- Short-pitch
coils are used to reduce harmonics and improve performance.
- Hence,
the coil span does not have to be exactly equal to the
pole pitch.
FINAL CONCLUSION
- The
coil span:
- May
be equal to the pole pitch (full-pitch), or
- May
be less than the pole pitch (short-pitch)
- Therefore,
the correct statement is:
Correct Answer
✅ Option (c): May or may
not be exactly equal to pole pitch
✔️ Key One-Line Exam Statement
Coil span may be equal to pole pitch (full-pitch) or less
than pole pitch (short-pitch), depending on machine design requirements.