All Free Electrical Engineering MCQs with Answers

• A. 0.555
• B. 0.578
• C. 0.5457
• D. 0.6

Explanation: For superheated steam, using an isentropic exponent of about 1.3 gives a critical pressure ratio near 0.546.

• A. 0.6
• B. 0.578
• C. 0.555
• D. 0.5457

Explanation: For initially dry-saturated steam, the critical pressure ratio is approximately 0.577 to 0.578. Therefore, option b is the closest value.

• A. pvls=C
• B. pv1126 = C
• C. pv1A = C
• D. pv = C

Explanation: Superheated steam behaves approximately like a gas during nozzle expansion, so its isentropic relation is commonly written as p v^1.3 = C.

• A. series wound generator
• B. shunt wound generator
• C. synchronous generator
• D. none of the above

Explanation: A booster is normally a series-wound generator connected in series with a feeder to compensate for voltage drop.

• A. reactors
• B. generators
• C. transformers
• D. all of the above

Explanation: Electromechanical voltage regulators, such as regulators used with alternators, adjust generator excitation to maintain terminal voltage.

• A. using reactors
• B. increasing the load
• C. adjusting the governor
• D. reducing the terminal voltage
• E. none of the above

Explanation: Generator frequency follows f = PN/120, so it increases when rotor speed is increased.

• A. Its secondary current is 5 A
• B. Its secondary voltage is 400 V
• C. Its rating is 2 kVA
• D. Its secondary current is 20 A
• E. It is a step-up transformer

Explanation: For an ideal transformer, V₂/V₁ = N₂/N₁ = 2, so V₂ = 400 V, while current changes inversely to 5 A.

• A. hysteresis and eddy current losses
• B. friction and windage losses
• C. copper losses
• D. none of the above

Explanation: At fixed applied voltage and frequency, hysteresis and eddy-current losses depend mainly on the core flux and remain nearly constant as…

• A. friction and windage losses
• B. magnetic losses
• C. hysteresis and eddy current losses
• D. copper losses

Explanation: Friction and windage losses require moving mechanical parts, so they occur in rotating machines but not in a stationary transformer.

• A. eddy current loss will decrease
• B. eddy current loss will increase
• C. eddy current loss will remain unchanged
• D. none of the above

Explanation: With applied voltage fixed, core flux is approximately proportional to 1/frequency.

• A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
• B. to absorb the line surge voltage and save the winding of transformer from damage
• C. to reflect the line surge and save the winding of a transformer from damage
• D. none of the above

Explanation: A line surge produces a nonuniform voltage distribution in the end turns because of the winding's shunt capacitance, placing excessive…

• A. core built-up of laminations of cold rolled grain oriented steel
• B. core built-up of laminations of hot rolled sheet
• C. either of the above
• D. none of the above

Explanation: Cold-rolled grain-oriented steel provides high permeability along the grain direction and lower hysteresis and eddy-current losses than…

• A. zoom
• B. hum
• C. ringing
• D. buzz

Explanation: The familiar low-frequency noise of a transformer is called hum, mainly caused by magnetostriction and the resulting vibration of the core…

• A. Bushings
• B. Core
• C. Primary winding
• D. Secondary winding

Explanation: Bushings pass the transformer conductors safely through the earthed tank and are mounted externally, so they can be seen from outside.

• A. Cellulose
• B. Asbestos
• C. Mica
• D. Glass fibre

Explanation: Mica has excellent dielectric strength and a very high temperature capability, commonly associated with Class C insulation.

• A. short-circuit test
• B. back-to-back test
• C. open circuit test
• D. any of the above

Explanation: The back-to-back, or Sumpner, test uses two identical transformers to reproduce full-load conditions while measuring losses, temperature…

• A. Horn gaps
• B. Thermal overload relays
• C. Breather
• D. Conservator

Explanation: Horn gaps provide a low-resistance path for lightning and switching surges, diverting them safely to earth.

• A. A good voltage regulation of a transformer means
• B. output voltage fluctuation from no load to full load is least
• C. output voltage fluctuation with power factor is least
• D. difference between primary and secondary voltage is least
• E. difference between primary and secondary voltage is maximum

Explanation: Good voltage regulation means the secondary-terminal voltage changes very little between no-load and full-load conditions.

• A. 0.8 leading power factor
• B. 0.8 lagging power factor
• C. zero power factor
• D. unity power factor

Explanation: With load current fixed, transformer losses are essentially fixed, while useful output is proportional to power factor.

• A. on full-load
• B. on overload
• C. on leading power factor
• D. on zero power factor

Explanation: At a leading power factor, the voltage drop caused by transformer leakage reactance can be offset by the resistive drop, bringing…