Question

A dc generator generates 300 V on open circuit, running at speed of 600 rpm with diameter of pole shoe circle 0.4 m and ratio of pole arc to pole pitch 0.8. Being a 6 pole dc machine with pole shoe length 0.2 m it carries 1000 armature conductors, connected in wave winding arrangement, then the average flux density will be_________ Tesla.

• A. 0.298

Answer 1

The correct option is A 0.298
$\text{We know,}$
$\text{Pole pitch}=\frac{\text{Periphery of armature}}{\text{No. of poles}}=\frac{2\pi r}{P}=\frac{\pi \times 0.4}{6}$

$\frac{\text{Pole arc}}{\text{pole pitch}}=0.8$

$\therefore \text{Pole arc}=\frac{0.8\times \pi \times 0.4}{6}=0.168m$

$\text{Area of pole face}=0.168\times 0.2=0.0336m^2$

$\text{Emf,}{E}_b=\frac{P\varphi ZN}{60A}$

$\Rightarrow 300=\frac{600\times 6\times \varphi \times 1000}{60\times 2}=0.01Wb$

$\text{Flux density}=\frac{\varphi }{A}=\frac{0.01}{0.0336}=0.2976\text{Tesla}$