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 wound-rotor induction motor, adding external resistance to the rotor circuit:
Answer: A
External rotor resistance shifts the point of maximum torque to higher slip values
Q.122Medium
The commutation in a DC machine is said to be 'overcommutated' when:
Answer: B
Over-commutation occurs when induced EMF > required EMF, causing sparking at trailing edge of brushes
Q.123Medium
In an induction motor, the torque under running conditions is proportional to:
Answer: C
T ∝ Ir × cos(φr) × r/s, where torque depends on rotor current magnitude and its power factor
Q.124Medium
Which of the following represents the condition for maximum power transfer in a DC generator connected to external load?
Answer: A
Maximum power transfer theorem: Load resistance equals source resistance for maximum power output
Q.125Medium
In a 3-phase transformer with Y-Δ connection, the secondary voltage lags the primary by:
Answer: B
Y-Δ connection introduces 30° phase shift with secondary lagging primary voltage phasor
Q.126Medium
For a DC shunt motor operating at rated conditions, if the load is suddenly increased, the motor will:
Answer: B
Increased load increases Ia, causing larger voltage drop (IaRa), reducing back EMF and speed until new equilibrium
Q.127Medium
A DC series motor is used in electric trains. If the load torque decreases suddenly, what happens to the motor speed?
Answer: A
In a DC series motor, as load decreases, back EMF increases relative to applied voltage, causing field current to reduce. This results in a significant increase in motor speed.
Q.128Medium
In a 3-phase squirrel cage induction motor, which parameter can be increased to improve the starting torque?
Answer: C
Starting torque in an induction motor is proportional to rotor current and rotor resistance. Increasing rotor resistance improves starting torque at the cost of full-load efficiency.
Q.129Medium
The slot leakage reactance in an induction motor depends on:
Answer: B
Slot leakage reactance is determined by the magnetic flux confined within the stator and rotor slots, hence depends on dimensions of both stator and rotor slots.
Q.130Medium
In a DC generator, armature reaction causes:
Answer: C
Armature reaction in DC generators creates a demagnetizing effect and shifts the neutral plane forward (in direction of rotation), both effects occurring simultaneously.
Q.131Medium
The power factor of a transformer at no-load is low because:
Answer: B
At no-load, the transformer draws mainly magnetizing current which lags the applied voltage by approximately 90°, resulting in low power factor (typically 0.1-0.2).
Q.132Medium
Which of the following losses in an induction motor is proportional to slip?
Answer: C
Rotor copper loss = sP_gap, where s is slip and P_gap is the air gap power. It is directly proportional to slip.
Q.133Medium
In a separately excited DC motor, if flux is reduced to half while keeping the supply voltage constant, the armature current will:
Answer: C
Back EMF = KΦω. When Φ is halved, back EMF reduces, so armature current (Ia = (V - Eb)/Ra) increases approximately to double for the same load.
Q.134Medium
The regulation of a DC shunt generator is poor because:
Answer: B
In a DC shunt generator, as load increases, armature current increases, causing armature reaction that demagnetizes the field, reducing terminal voltage significantly.
Q.135Medium
In a 3-phase synchronous generator, the pitch factor (or coil span factor) accounts for:
Answer: B
Pitch factor (Kp) accounts for the reduction in EMF when the coil span is less than the pole pitch (full pitch), representing incomplete flux linkage.
Q.136Medium
In a transformer connected to a load with lagging power factor, the secondary current will:
Answer: B
If the load has lagging power factor, the secondary current lags the secondary voltage. The phase relationship between primary and secondary depends on the load power factor.
Q.137Medium
A 3-phase squirrel cage induction motor is running at 960 rpm when connected to a 50 Hz supply. If the supply frequency is suddenly changed to 60 Hz, what will be the approximate new speed of the motor, assuming the slip remains constant?
Answer: A
Synchronous speed Ns = 120f/P. When frequency changes from 50 Hz to 60 Hz with constant slip, new speed will be proportional to frequency. New speed = 960 × (5060) = 1152 rpm. This is because slip s = (Ns - N)/Ns remains approximately constant for the same load.
Q.138Medium
The stability of a power system depends on which of the following factors?
Answer: B
Power system stability is determined by the rotor dynamics characterized by inertia (M), damping (D), and synchronizing coefficient (Ks).
Q.139Medium
The per-unit (p.u.) system in power systems is used primarily to:
Answer: A
Per-unit system normalizes all quantities relative to chosen base values, simplifying analysis and comparison across different voltage levels and equipment ratings.
Q.140Medium
Which protective relay is used for phase-to-phase fault detection in transmission lines?
Answer: B
Differential relays compare currents at both ends of a line and trip if there is a mismatch indicating an internal fault.
