Topic: Electrical Machines
Neglecting saturation, if the current taken by DC series motor is increased from 10A to 12A, percentage increase in the torque will be
- A. 44%
- B. 40%
- C. 20%
- D. 16%
Answer: A. 44%
Explanation: In a DC series motor, before magnetic saturation, the flux $\phi$ is directly proportional to the armature current $I_a$. Since Torque $T \propto \phi I_a$, we get $T \propto I_a^2$.
Let initial torque $T_1 \propto 10^2 = 100$.
Let final torque $T_2 \propto 12^2 = 144$.
The percentage increase in torque is $\frac{T_2 - T_1}{T_1} \times 100\% = \frac{144 - 100}{100} \times 100\% = 44\%$.