Electrical Engineering questions for GATE, PSU recruitment and SSC JE draw from network theory, electrical machines, power systems, control systems, measurements and instrumentation, analog and digital electronics, and electromagnetic fields. Numerical answers include the formula used and the unit at each stage, which is where marks are commonly lost even when the approach is correct.
In a synchronous motor, the pull-out torque depends on:
Answer: C
Pull-out torque τmax = 1.5(PΦIf)/(ωs), depends on pole flux and field current (excitation) and supply voltage.
Q.208Hard
A transformer is operating at 110% of rated voltage. The core loss will be approximately:
Answer: C
Core loss Pc ∝ B² ∝ V². At 1.1V, loss = (1.1)² × rated loss = 1.21 × rated ≈ 21% increase
Q.209Medium
Which starting method is suitable for a 3-phase induction motor with locked rotor current limit?
Answer: D
Both star-delta and autotransformer starting reduce starting current. Star-delta reduces current by 31 of DOL current.
Q.210Hard
The efficiency of a DC generator is maximum when:
Answer: C
Maximum efficiency occurs when variable losses (copper) equal constant losses (friction, windage, and core losses).
Q.211Hard
A 100 kW, 3-phase induction motor has a full-load slip of 0.04. The rotor copper loss at full load is:
Answer: B
Rotor copper loss = s × Pg, where Pg is air gap power. At full load, assuming 96% efficiency, losses ≈ 4.17 kW ≈ 4 kW
Q.212Medium
In a DC motor, the starting resistance is required because:
Answer: B
At starting, back EMF is zero. Starting resistance limits initial armature current to safe values: Ia = V/(Ra + Rstart)
Q.213Medium
Which transformer connection is preferred for step-up operations in power generation?
Answer: C
Star-delta connection reduces neutral point problems on primary (generator side) and utilizes delta on secondary for better voltage utilization.
Q.214Hard
The reluctance torque in a synchronous motor is maximum when the load angle is:
Answer: B
Reluctance torque τrel ∝ sin(2δ), which is maximum when sin(2δ) = 1, i.e., when δ = 45°
Q.215Easy
In a DC motor, the back EMF is proportional to which of the following?
Answer: A
Back EMF in DC motor: Eb = PΦN/60, which depends on flux (Φ) and speed (N). It is independent of armature current and load torque.
Q.216Easy
What is the synchronous speed of a 6-pole, 3-phase induction motor operating at 50 Hz frequency?
Answer: B
Synchronous speed Ns = 120f/P = (120 × 50)/6 = 1000 RPM, where f = frequency and P = number of poles.
Q.217Easy
The slip of an induction motor at rated load is typically in the range of:
Answer: A
For standard induction motors, slip at full load is typically 0.5% to 2%, ensuring minimal speed variation and high efficiency.
Q.218Medium
Which type of DC motor provides excellent speed control characteristics and is suitable for cranes and hoists?
Answer: C
Compound DC motors combine advantages of series (high starting torque) and shunt (stable speed) motors, making them ideal for cranes requiring both high starting torque and controlled speed.
Q.219Medium
In a 3-phase transformer with Delta-Star connection, the secondary voltage phase angle leads the primary by:
Answer: B
Delta-Star (Dy) connection introduces a 30° phase shift. Secondary voltage leads primary by 30°, which is standard for Dy11 configuration.
Q.220Easy
The copper loss in a transformer is minimum when:
Answer: A
Copper loss PCu = I²R is proportional to current squared. It is minimum when load current is zero (no-load condition).
