A 220 V,three-phase,four-pole,50 Hz wound-rotor induction motor has negligible stator resistance, magnetizing reactance and core loss. Maximum torque is 225% of full-load torque at slip 0.15. Actual rotor resistance is 0.03 Ω/phase. Find added rotor resistance for maximum torque at starting.
With negligible stator resistance, maximum-torque slip is proportional to total rotor resistance: sm=R2/Xeq on a consistent rotor basis.
Initially 0.15=0.03/Xeq, giving Xeq=0.2 Ω. To make sm=1, total resistance must become 0.2 Ω.
The external addition is 0.2−0.03=**0.17 Ω per rotor phase**, within 0.16–0.18. The maximum-torque magnitude ratio is not needed for this shift.
More Three-phase induction machines: principle of operation, types, performance, torque-speed characteristics, no-load and blocked-rotor tests, equivalent circuit, starting and speed control questions
GATE 2026 EE Q21– Which one of the following options is correct regarding the typical double-squirrel-cage…
GATE 2026 EE Q59– A balanced three-phase supply is given to a 30 kW, 4-pole, 400 V, 50 Hz, wound rotor…
GATE 2025 EE Q45– A 3-phase, 400 V, 4 pole, 50 Hz star connected induction motor has the following…
GATE 2024 EE Q17– A three phase, 50 Hz, 6 pole induction motor runs at 960 rpm. The stator copper loss, core…
GATE 2024 EE Q54– A 3-phase star connected slip ring induction motor has the following parameters referred…
GATE 2023 EE Q15– The following columns present various modes of induction machine operation and the ranges…