Practice over 1000+ GATE-level questions from this topic!
Designed to match the latest GATE pattern with topic-wise precision, difficulty tagging, and detailed solutions.
A 3-phase, 
pole, 50 Hz star connected induction motor has the following parameters referred to the stator:
Stator resistance, magnetizing reactance and core loss of the motor are neglected. The motor is run with constant 
control from a drive. For maximum starting torque, the voltage and frequency output, respectively, from the drive, is closest to,
400 V and 50 Hz
200 V and 25 Hz
100 V and 12.5 Hz
300 V and 37.5 Hz
Given:
- Rotor resistance referred to stator:
- Stator + rotor leakage reactance at
- Constant V/f control:
Key Insight:
For maximum torque at start, the starting slip (s=1) must equal the slip for maximum torque:
Where 
is the total reactance at the new frequency 
.
Step 1: Set 
for Maximum Starting Torque
Step 2: Find New Frequency
Since reactance scales with frequency:
Set 
:
Step 3: Compute New Voltage 
Using constant :
Line-to-line voltage:
