The GATE Grind

GATE 2026 EE – Question 21

Electrical Machines · Three-phase induction machines: principle of operation, types, performance, torque-speed characteristics, no-load and blocked-rotor tests, equivalent circuit, starting and speed control · 1 mark · Multiple choice

Which one of the following options is correct regarding the typical double-squirrel-cage structure used in induction motors?

  1. At starting, a larger portion of the rotor current flows in the outer cage
  2. At starting, a larger portion of the rotor current flows in the inner cage
  3. At rated speed, most of the rotor current flows in the outer cage
  4. The purpose of the double-squirrel-cage structure is to lower the effective rotor resistance at starting

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) At starting, a larger portion of the rotor current flows in the outer cage

Explanation

At starting, the rotor frequency is high, so the inner cage (embedded deep, with high leakage reactance) carries little current and most of the current flows in the outer cage, which has high resistance and low leakage reactance. This raises the effective rotor resistance at starting and improves starting torque (so D is wrong). At rated speed the frequency is low and most current flows in the low-resistance inner cage (so C is wrong).