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:
- Simplex Lap winding : m = 1
- Duplex Lap winding : m = 2
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