(a) Z / P
(b) 2Z / P
(c) Z / 2P
(d) Z / 4P
Answer: (a) Z / P
Explanation:
CONCEPT: EMF Equation of DC Generator
- The
generated EMF in a DC generator is given by:
Where:
= Flux per pole
= Total armature
conductors
= Speed (rpm)
= Number of poles
= Number of
parallel paths
Parallel Paths in DC Windings
Lap Winding
- For lap
winding:
- Used
for:
- Low
voltage
- High
current machines
Wave Winding
- For wave
winding:
- Used
for:
- High
voltage
- Low
current machines
Comparison of EMF in Lap and Wave Winding
- From
EMF equation:
For Lap Winding:
For Wave Winding:
- Since in wave winding
and in lap winding:
👉 EMF is higher
in wave winding than lap winding (for same machine parameters).
CONCEPT: Equalizer Rings
- Equalizer
rings are used only in lap-wound DC machines.
- Purpose:
- To
avoid circulating currents
- To
balance parallel paths
- To
reduce sparking
Why Equalizer Rings Are Required in Lap Winding
- In
lap winding:
- More
parallel paths → More chances of EMF imbalance
- This
causes circulating currents.
- Equalizer
rings connect points of equal potential.
Derivation: Maximum Number of Equalizer Rings
Step 1: Conductors Per Parallel Path
- Total
conductors =
- Parallel
paths =
So, conductors per path:
Step 2: Equal Potential Points
- In
lap winding:
- Each
parallel path has
conductors - These
points are theoretically at same potential
- Each
such point can be connected by an equalizer ring.
Step 3: Maximum Number
- Therefore,
maximum number of equalizer rings possible is:
EXPLANATION
- Each
parallel path has conductors.
- Equalizer
rings connect corresponding conductors of different paths.
- Hence,
at most, equalizer
connections are possible.
FINAL ANSWER
Important Points for Exam
- Equalizer
rings are:
- Used
only in lap winding
- Not
used in wave winding
- More
poles → More parallel paths → More need of equalizer rings
- Wave
winding does not need equalizer rings (A = 2)
ONE-LINE EXAM NOTE ⭐
The maximum number of equalizer rings in a lap-wound DC
generator is equal to Z/P.