Question

A 220 V, 200 A, 800 rpm dc separately excited motor has an armature resistance of 0.05 $\Omega$. The motor armature is fed from a variable voltage source with an internal resistance of 0.04 $\Omega$. The internal voltage of the variable voltage source when motor is operating in regenerative braking at 80% of rated motor torque and 600 rpm is ____ Volts.

• A. 140

Answer 1

The correct option is A 140
Since, Torque is proportional to armature current, motor armature current when motor operating in regenerative braking mode is

$I_{a2}=0.8\times 200=160A$

$E_1=220-200\times 0.06=208V$

$E_2=\frac{N_2}{N_1}{E}_1=\frac{600}{900}\times 208=156V$

Internal voltage of the variable voltage source

$=156-160(0.06+0.04)$

$=140V$