Question

A 4-pole dc machine has an armature of radius 14 cm and an effective length of 18 cm. The poles cover 75% of the armature periphery. The armature winding consists of 30 coil, each coil having 6 turns. The coils are accommodated in 36 slots. The average flux density under each pole is 0.6 T. Armature is lap wound. The induced armature voltage (in volts) when the armature rotates at 1000 rpm is

• A. 166.2

Answer 1

The correct option is A 166.2
$\text{Area of Pole}\left(A_p\right)=\frac{\text{Circumference of armature}\times \text{Percentage area covered by poles}}{\text{Number of poles}}$

$=\frac{2\pi \times 0.14\times 0.28\times 0.75}{4}=46.18\times {10}^{-5}{m}^2$

$\text{Flux density}\left(B\right)=0.6T$

$\text{Flux per pole,}$ $\left(\varphi \right)=A_p\times B=46.18\times {10}^{-3}\times 0.6=0.0277Wb$

$\therefore$ $\text{Generated emf,}$ $E_a=K_a\times \varphi \times N$

$=\frac{ZP\varphi N}{60A}=\frac{2\times 30\times 6\times 4}{4\times 60}\times 0.0277\times 1000$

$=166.2V$