All Free Electrical Engineering MCQs with Answers
Every Electrical Engineering question in the bank, across all chapters, each with the correct answer and a written explanation. Free and unlimited, with no account needed.
3,143 questions · page 33 of 158
- A. at one-fourth load
- B. at one-half load
- C. at or near full load
- D. any of the above
Explanation: Power transformers operate continuously near their rated load, so they are designed for maximum efficiency at or near full load.
Correct answer: at or near full load- A. small capacity transformers
- B. medium capacity transformers
- C. large capacity transformers
- D. any of the above
Explanation: A rectangular yoke section is economical for small transformers because the magnetic flux is relatively low and simple construction is…
Correct answer: small capacity transformers- A. a.c. supply
- B. d.c. supply
- C. either a.c. or d.c. supply
- D. none of the above
Explanation: Tractive magnets produce linear pulling or holding force and may be designed for either AC or DC operation.
Correct answer: either a.c. or d.c. supply- A. Flat-faced armature type
- B. Horse shoe type
- C. Flat-faced plunger type
- D. All of the above
Explanation: Flat-faced armature, horseshoe, and flat-faced plunger designs are all commonly used electromagnet structures, so the inclusive option is…
Correct answer: All of the above- A. Tractive
- B. Portative
- C. Either of the above
- D. None of the above
Explanation: Portative electromagnets are designed to hold or lift ferromagnetic objects, whereas tractive electromagnets primarily produce pulling…
Correct answer: Portative- A. Method of average losses
- B. Equivalent current method
- C. Equivalent torque method
- D. Equivalent power method
- E. All of the above
Explanation: Variable-load motor rating can be estimated by average losses or by equivalent current, torque, or power methods, each relating the…
Correct answer: All of the above- A. Total m.m.f. required
- B. The number of turns in the exciting winding
- C. The way in which the winding is distributed
- D. All of the above
Explanation: Magnetizing current follows approximately from I = MMF/N, so it depends on the required total MMF and the number and distribution of…
Correct answer: All of the above- A. One sided axial ventilation
- B. Two sided axial ventilation
- C. Multiple inlet system
- D. All of the above
Explanation: Air-cooled turbo-alternators may use one-sided axial ventilation, two-sided axial ventilation, or multiple-inlet ventilation depending on…
Correct answer: All of the above- A. The current in the slot conductors is uniformly distributed over their cross-section
- B. The leakage path is straight across the slot and around the iron at the bottom
- C. The permanence of air paths is only considered. The reluctance of iron paths is assumed as zero
- D. All of the above
Explanation: Slot-leakage calculations assume uniformly distributed slot current, a simplified straight leakage path, and negligible iron reluctance so…
Correct answer: All of the above- A. Equivalent power method
- B. Equivalent current method
- C. Method of average losses
- D. Equivalent torque method
Explanation: The method of average losses uses the mean loss over the duty cycle and does not directly account for the peak temperature rise…
Correct answer: Method of average losses- A. heating time constant
- B. cooling time constant
- C. either A. or B.
- D. none of the above
Explanation: For exponential heating, the temperature reaches 1 − e⁻¹ = 0.632 of its final value after one heating time constant.
Correct answer: heating time constant- A. 200 MW
- B. 300 MW
- C. 400 MW
- D. 600 MW
Explanation: Direct water cooling removes heat very effectively from the conductors, allowing large turbo-generators to reach ratings of roughly 600…
Correct answer: 600 MW- A. 2 to 3 times greater
- B. 3 to 4 times greater
- C. 4 to 5 times greater
- D. none of the above
Explanation: In a self-cooled motor, the fan or rotating parts provide much less airflow when the motor is stopped, so cooling is slower at standstill.
Correct answer: 2 to 3 times greater- A. no mechanical difficulties
- B. lesser mechanical difficulties
- C. greater mechanical difficulties
- D. none of the above
Explanation: Water passing through a rotating rotor winding requires reliable insulation, seals, joints and rotating connections, creating greater…
Correct answer: greater mechanical difficulties- A. solid
- B. hollow
- C. perforated
- D. any ofthe above
Explanation: In direct hydrogen cooling, hydrogen must flow through the conductors to remove heat from the winding interior, so both stator and rotor…
Correct answer: hollow- A. "supercharged"
- B. "inner cooled"
- C. "conductor cooled"
- D. any of the above
Explanation: Direct cooling carries the coolant directly through or along the conductors, so such machines are described as supercharged, inner-cooled…
Correct answer: any of the above- A. 0.07
- B. 1.5
- C. 2.5
- D. 3.5
Explanation: Hydrogen has a relative density of approximately 0.07 compared with air, making it much lighter.
Correct answer: 0.07- A. Increase in efficiency
- B. Increase in ratings
- C. Increase in life
- D. Smaller size of coolers
- E. All of the above
Explanation: Hydrogen cooling reduces windage loss, improves heat transfer and permits a more compact cooler, thereby increasing efficiency and rating…
Correct answer: All of the above- A. Conduction
- B. Convection
- C. Radiation
- D. All of the above
Explanation: Heat can leave an electrical machine by conduction through solid parts, convection to the surrounding fluid and radiation from exposed…
Correct answer: All of the above- A. air
- B. hydrogen
- C. either A. or B.
- D. none of the above
Explanation: Hydrogen is much less dense than air, so a rotor experiences less windage and produces less aerodynamic noise while rotating in it.
Correct answer: hydrogen