Question

A 4-pole DC generator has 800 armature conductors and a flux per pole of 10 mWb running at 600 rpm. Calculate the EMF generated when the armature is connected as a simplex lap winding.
1. 75 V
2. 85 V
3. 80 V
4. 70 V

Answer 1

Correct Answer - Option 3 : 80 V

Concept:

EMF equation of a DC Generator:

As the armature rotates, a voltage is generated in its 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

Also,

A = P ⋅ m

Where,

m = Multiplexity (simplex/duplex)

In wave winding, multiplexity is always 2 (two)

Therefore, A = 2

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

Application:

P = 4

Z = 800

ϕ = 10 mWb = 10 × 10^-3 Wb

N = 600 rpm

A = P = 4

\({E_g} = \frac{{\phi ZNP}}{{60A}} = \frac{{10 \times 10^{-3}\;\times \;800\; \times\;600\; \times \;4}}{{60\;\times\;4}}=80\;V\)

∴  The EMF generated is 80 V.