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 A 4-pole d.c. generator runs at 750 rpm. and generates an emf. of 240 V. The armature is wave-wound and has 792 conductors. If the total flux from each pole is 0.0145 Wb, what is the leakage coefficient?


1. 1.6
2. 1.8
3. 1.5
4. 1.2

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Correct Answer - Option 4 : 1.2

Concept:

EMF equation of a DC Generator:

As the armature rotates, a voltage is generated in it’s coils, which is called Generated EMF or Armature EMF and is denoted by Eg.

\({E_g} = \frac{{\phi ZNP}}{{60A}}\)

Where,

Eg = Generated Emf

P = Number of poles of the machine

ϕ = flux per pole in weber

Z = total number of armature conductors

N = speed of armature in revolution per minute (r.p.m)

A = number of parallel paths in the armature winding

The number of parallel Paths:

A = P ⋅ m

Where,

m = multiplexity (simplex/duplex)

In wave winding, multiplexity is always 2 (two)

Therefore A = 2P

While in lap winding, there are two types:

  1. Simplex Lap winding : m = 1
  • A = P
  1. Duplex Lap winding : m = 2
    • A = 2P

NOTE:

If multiplexity is not mentioned, then always take simplex lap winding i.e. m = 1

Calculation:

Given:

P = 4

N = 750 rpm

∴ No. of conductors (Z) = 792

A = 2

Eg = 240 V

\({E_g} = \frac{{\phi ZNP}}{{60A}}\)

\(240 = \frac{{\phi \times 792 \times 750 \times 4}}{{60 \times 2}}\)

⇒ ϕ = 12.12 mWb

total flux from each pole = 0.0145 Wb = 14.5 mWb

Leakage coefficient = 14.5/12.12 = 1.2

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