(a) +1 or −1
(b) twice average pitch.
(c) average pitch.
(d) half average pitch.
Answer: (c) average pitch.
Explanation:
CONCEPT: Commutator Pitch in Simplex Wave Winding
- Commutator
pitch (
) is
defined as:
The distance between the two commutator segments to which
the two ends of a single armature coil are connected.
- It
is measured in terms of commutator segments.
Armature Windings in DC Machines
- Modern
DC machines generally use two types of armature windings:
- Lap
winding
- Wave
winding
- The
most commonly used windings are simplex lap and simplex
wave windings.
Simplex Wave Winding
- In
a simplex wave winding:
- The
end of one coil is connected to the start of another coil having
the same polarity.
- The
coil sides progress forward around the armature, successively passing
under N and S poles, and finally return to a conductor under
the starting pole.
- Due
to this progression, the winding forms a wave-like pattern,
hence the name wave winding.
Pitch Definitions (Important)
Back Pitch ( 
)
- Back
pitch is:
- The
distance between the top and bottom coil sides of a coil,
measured around the back of the armature.
Front Pitch ( 
)
- Front
pitch is:
- The
distance between the two coil sides connected to the same
commutator segment, measured at the front of the armature.
Resultant (Winding) Pitch ( 
)
- Resultant
pitch is:
- The
distance between the starts of two consecutive coils, measured in terms of
coil sides.
- It
is given by:
Commutator Pitch ( 
)
- Commutator
pitch is:
- The
distance between the two commutator segments connected to the ends of one
coil.
- For
a simplex wave winding:
where 
is the average
pitch.
Average Pitch in Wave Winding
- The average
pitch is given by:
- Alternatively,
for wave winding:
Where:
= total number of
armature conductors
= number of poles
sign → Progressive
winding
sign → Retrogressive
winding
Properties of Simplex Wave Winding
- In
simplex wave winding:
- Back
pitch
and front
pitch 
are both
odd. - They
are of the same sign.
- They
are nearly equal to the pole pitch and may differ
by ±2.
- Hence:
Comparison with Lap Winding
- For simplex
lap winding:
- Thus,
unlike lap winding, the commutator pitch in wave winding is not 1,
but equal to the average pitch.
FINAL CONCLUSION
- In
a simplex wave winding:
- The commutator
pitch equals the average pitch.
- This
is a key identifying feature of wave windings in DC
machines.
✔️ Key One-Line Exam Statement
For a simplex wave winding, the commutator pitch is equal
to the average pitch and is given by 
.