In a lap wound dc generator, the equalizer rings are provided to

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(a) neutralize the armature reaction effect.
(b) avoid short circuiting.
(c) avoid unequal distribution of currents at brushes.
(d) avoid harmonics generated in the emf.
(e) provide mechanical balancing.

Answer: (c) avoid unequal distribution of currents at brushes.

Explanation:

CONCEPT: Equalizer Rings

  1. Equalizer rings are low-resistance copper conductors used in lap-wound DC machines.
  2. They connect points in the armature winding which should theoretically be at the same potential.
  3. They are provided between commutator segments at equal potential points.
  4. Their main purpose is to control circulating currents and ensure uniform current distribution.

Where Are Equalizer Rings Used?

  1. Equalizer rings are used only in:

✅ Lap windings

  1. They are not required in wave windings because:
    • Wave winding has only two parallel paths
    • Circulating current problem is negligible

Why Equalizer Rings Are Needed

Ideal Condition (Theoretical Case)

  1. In a lap winding:



(Number of parallel paths = Number of poles)

  1. Ideally:
    • All poles have equal flux
    • Air gap is uniform
    • Magnetic material is identical
  2. Therefore:
    • EMF induced in each parallel path is equal
    • Current is equally shared by all brushes

Practical Condition (Actual Machine)

  1. In real machines:
  • Air gap is not perfectly uniform
  • Pole materials differ slightly
  • Flux distribution is uneven
  • Mechanical misalignment occurs
  1. Hence:
  • EMF induced in different paths becomes unequal
  • Some paths produce higher voltage
  • Some paths produce lower voltage

Problem: Circulating Current

  1. Due to unequal EMF:
  • Current flows from high-voltage path to low-voltage path
  • This is called circulating current
  1. Circulating current flows through:
  • Brushes
  • Commutator
  • Armature conductors
  1. This causes:

❌ Overloading of some brushes
❌ Underloading of other brushes
❌ Heating of armature
❌ Excessive sparking
❌ Poor commutation
❌ Uneven wear of commutator

WORKING of Equalizer Rings

  1. Equalizer rings connect:
  • Points of equal potential in the winding
  1. These connections provide:
  • A low-resistance path for circulating current
  1. Therefore:
  • Circulating current flows through equalizer rings
  • Instead of flowing through brushes
  1. Result:
  • Brushes are relieved from excess current
  • Current gets balanced automatically

FUNCTIONS of Equalizer Rings

1. Prevent Unequal Current Distribution

  1. They ensure:
  • All parallel paths carry nearly equal current
  • No brush is overloaded

2. Reduce Sparking

  1. Balanced current improves commutation.
  2. This reduces:
  • Arcing
  • Sparking at commutator surface

3. Improve Commutator Life

  1. Reduced sparking leads to:
  • Less pitting
  • Less burning
  • Uniform wear
  1. Hence, commutator life increases.

4. Improve Machine Efficiency

  1. By reducing losses due to circulating current:
  • Heating is reduced
  • Energy wastage is minimized

Why Other Options Are Incorrect

(a) Neutralize Armature Reaction ❌

  1. Armature reaction is neutralized by:
  • Interpoles
  • Compensating windings
  1. Equalizer rings do not oppose armature flux.

(b) Avoid Short Circuit ❌

  1. Equalizer rings do not prevent:
  • Turn-to-turn faults
  • Ground faults
  • Insulation failure
  1. They only manage circulating current.

(d) Avoid Harmonics ❌

  1. Harmonics are reduced by:
  • Short-pitch winding
  • Distributed winding
  1. Equalizer rings are not designed for harmonic suppression.

(e) Provide Mechanical Balancing ❌

  1. Mechanical balance is achieved by:
  • Proper rotor design
  • Uniform mass distribution
  1. Equalizer rings are electrical devices, not mechanical.

Important Relation with Lap Winding

  1. In lap winding:



  1. More parallel paths → More chance of imbalance
  2. Hence, equalizer rings are essential.
  3. In wave winding:



  1. Fewer paths → Less imbalance → No equalizer rings needed

FINAL CONCLUSION

  1. Equalizer rings are used in lap-wound DC machines to:

✅ Provide low-resistance path for circulating currents
✅ Balance current in parallel paths
✅ Prevent brush overloading
✅ Reduce sparking
✅ Improve commutation
✅ Increase machine life

Correct Answer (General MCQ Form)

👉 Function of equalizer rings:

✔️ To avoid unequal current distribution at brushes
✔️ To reduce sparking at commutator

ONE-LINE EXAM NOTE ⭐

Equalizer rings are low-resistance copper conductors used in lap-wound DC machines to bypass circulating currents and ensure uniform current distribution at brushes.

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