60 solved GATE EE questions on Electrical Machines, drawn from 9 exam years and grouped by year. Every question shows the official answer and a step-by-step solution.
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Revision companion
Separate magnetic models, electrical equivalent circuits, and mechanical power balances. These selected notes use original idealized examples to distinguish transformer ratios from induction-machine slip and converted power from shaft output.
Our study notes and original examples support the PYQs below; they are not official exam questions or a replacement for the current syllabus.
Define a = N₁/N₂ before using a ratio. Voltage magnitudes satisfy V₁/V₂ = a, while load-current magnitudes satisfy I₁/I₂ = 1/a. With no losses or magnetizing current, input and output power agree. Terminal polarities still matter for phasor signs.
Check yourself: Does a lower secondary voltage correspond to a higher secondary current?
A secondary impedance referred to the primary is a²Z₂, preserving the primary voltage-current relationship. Keep resistance, leakage reactance, and excitation branches on one named side before combining them.
Check yourself: Which winding side owns each impedance in your calculation?
For supply frequency f and p poles, synchronous speed is nₛ = 120f/p rpm. Induction-machine slip is s = (nₛ − nᵣ)/nₛ. In ordinary motoring, rotor speed is below synchronous speed and rotor electrical frequency is sf.
Check yourself: Have you used poles rather than pole pairs in this speed formula?
In the basic motoring equivalent circuit, rotor copper loss is sPgap and converted mechanical power is (1 − s)Pgap. Shaft output is lower after mechanical losses. Torque uses mechanical angular speed with converted power, or synchronous angular speed with air-gap power.
Check yourself: Are you dividing the selected power by the corresponding angular speed?
In steady synchronism, a synchronous rotor runs at synchronous speed; loading changes torque angle, not slip. DC-machine generated voltage depends on flux and speed; electromagnetic torque depends on flux and armature current.
Check yourself: Does your chosen relation belong to the machine named in the problem?
Original teaching example · not a PYQ
Original practice example: an ideal single-phase transformer has 600 primary turns and 150 secondary turns. A 240 V RMS sinusoidal primary supply feeds a 12 Ω resistive secondary load. Neglect magnetizing current, leakage, winding resistance, and core loss. Find secondary voltage, both current magnitudes, and input power.
V₂ = 60 V RMS; I₂ = 5 A RMS; I₁ = 1.25 A RMS; input power = 300 W.
A separate balanced three-phase induction motor has six poles, a 60 Hz supply, and steady rotor speed 1140 rpm in the rotating field's direction. Find slip and rotor electrical frequency.
Slip = 0.05, or 5%; rotor electrical frequency = 3 Hz.
Synchronous speed is 120 × 60/6 = 1200 rpm. The field overtakes the rotor by 60 rpm, so s = 60/1200 = 0.05 and sf = 0.05 × 60 = 3 Hz.
Supplemental reading, not an official GATE reading list or an endorsement of these notes.
Free supplemental chapter explaining ideal transformer ratios and impedance transformation.
Free supplemental induction-machine notes tracing the transformer model and slip-dependent power balance.
This page shows 60 recent questions from the released archive, newest first. For older questions and complete papers, browse all GATE EE papers. Questions can carry more than one subject tag; counts are not marks weightage.
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