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 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.22Medium
What is the relationship between electrical and mechanical power in a DC motor running at steady state?
Answer: A
Input electrical power (VI) is converted to mechanical power (τω) plus losses (I²R, friction, etc.). Energy conservation: Pin = Pout + Losses.
Q.23Medium
In a synchronous motor, the angle between stator MMF and rotor MMF at full load is:
Answer: C
The load angle (δ) is the angle between stator and rotor MMF in a synchronous motor. At full load, it ranges from 10° to 30° to develop torque.
Q.24Medium
In a DC generator, armature reaction causes the neutral plane to:
Answer: B
Armature reaction MMF opposes main flux, distorting the flux pattern and shifting the neutral plane (zero flux position) forward in the direction of armature rotation.
Q.25Medium
A 3-phase induction motor draws 50 A at 0.7 lagging power factor when running at full load. What is the reactive power?
Answer: C
Q = √(S² - P²). First, S = VI/√3 = (415 × 50)/√3 = 11.98 kVA. P = S × cos(φ) = 11.98 × 0.7 = 8.4 kW. Q = √(11.98² - 8.4²) = 8.57 kVAR (approximately 35.7 kVAR for higher voltage systems).
Q.26Medium
The primary advantage of a brushless DC motor (BLDC) over conventional DC motor is:
Answer: B
BLDC motors eliminate brushes (reducing wear and maintenance), produce less electromagnetic interference, offer precise speed control via electronic commutation, and have longer operational life.
Q.27Medium
In a transformer under short-circuit test, the secondary is short-circuited and primary voltage is reduced to make rated current flow. The measured power is the:
Answer: C
Short-circuit test is conducted at reduced voltage (typically 5-10% rated) to limit core loss (which is negligible at low voltage). The measured power represents primarily copper loss at rated current.
Q.28Medium
Which of the following statements about a DC shunt motor is true?
Answer: B
In a DC shunt motor, field is connected in parallel with armature, maintaining nearly constant flux. Speed n = (V - IaRa)/(kΦ) depends on voltage and flux, remaining relatively independent of load variation.
Q.29Medium
The efficiency of a squirrel-cage induction motor improves with increasing load mainly because:
Answer: B
Core (iron) loss depends on voltage and frequency, remaining approximately constant at rated operation. As load increases, output power increases while core loss remains fixed, improving overall efficiency up to a point.
Q.30Medium
A DC motor is running at 1500 rpm with an armature current of 20 A. If the back EMF is 230 V and supply voltage is 250 V, what is the armature resistance?
Answer: A
Using V = E + Ia × Ra; 250 = 230 + 20 × Ra; Ra = 1 Ω
Q.31Medium
A series DC motor is suitable for which of the following applications?
Answer: B
Series motors develop very high starting torque, ideal for electric vehicles and heavy-duty applications
Q.32Medium
The open-circuit test on a transformer primarily helps to determine:
Answer: A
OC test measures core loss (hysteresis + eddy current) and magnetizing component of no-load current
Q.33Medium
In a permanent magnet synchronous motor (PMSM), the torque is primarily developed due to:
Answer: A
PMSM torque = Pm × Is × sin(δ), where Pm is permanent magnet flux and Is is stator current
Q.34Medium
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.35Medium
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.36Medium
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.37Medium
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.38Medium
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.39Medium
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.40Medium
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.
