Question

A lap wound DC machine having 4-poles has 720 armature conductors. Its field winding is excited from a DC source to create an air-gap flux of 32 mWb/pole. The generator is run from a prime mover at 1500 rpm and supplies a current of 100 A to an electric load. Calculate the electromagnetic power developed in the machine?
1. 50 kW
2. 65.7 kW
3. 76.5 kW
4. 57.6 kW

Answer 1

Correct Answer - Option 4 : 57.6 kW

Given that, the machine is lap wounded and has 4-poles

No. of conductors, Z = 720

Air gap flux = 32 × 10^-3 wb/pole

Generator run from a prime mover

Speed N = 1500 rpm

Supplies a current (I) = 100 A

Now, generated emf at DC generator-

\(Eg = \frac{{\phi ZNP}}{{60A}}\) 

As the machine is lap wound, number of parallel paths, A = P = 4

\(\Rightarrow Eg = \frac{{32\; \times \;{{10}^{ - 3}}\; \times \;720\; \times \;1500\; \times \;4}}{{60\; \times\; 4}}\) 

Eg = 576 V

Now, electromagnetic power developed-

P = E_g.I_a

= 576 × 100

⇒ P = 57.6 kW