Question

A 4-pole wave wound armature has 720 conductors and is rotated at 1000 rpm. If the useful flux is 20 mWb, calculate the generated voltage.

1. 480 V
2.  960 V
3. 360 V
4. 240 V

Answer 1

Correct Answer - Option 1 : 480 V

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

2. 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

ϕ = 20 mWb per pole

N = 1000 rpm

∴ No. of conductors (Z) = 720

A = 2

We know:

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

\({E_g} = \frac{{0.02 \times 720 \times 1000 \times 4}}{{60 \times 2}}\)

Eg = 480 V