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 32 of 158
621. Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?
- A. Increased I R losses
- B. Increased core losses
- C. Poor commutation
- D. Change in motor parameters
- E. All of the above
Explanation: Thyristor bridge supplies produce ripple and harmonics in the motor current, causing higher copper and core losses and often poorer…
Correct answer: All of the above- A. less than
- B. equal to
- C. greater than
- D. none of the above
Explanation: In the usual simplex lap-wound D.C. machine, one brush arm is provided for each pole, so the number of brush arms equals the number of…
Correct answer: equal to- A. worst, ventilation
- B. poor ventilation
- C. better ventilation
- D. none of the above
Explanation: A large air gap leaves more space around the armature, allowing air to circulate more freely and improving ventilation.
Correct answer: better ventilation- A. between 5 to 10 mm
- B. between 10 to 15 mm
- C. between 15 to 20 mm
- D. between 25 to 35 mm
Explanation: The usual D.C. armature slot pitch is kept around 25 to 35 mm. A very small pitch makes slots and teeth difficult to construct, while an…
Correct answer: between 25 to 35 mm- A. quiet
- B. noisy
- C. either of the above
- D. none of the above
Explanation: A larger air gap reduces the magnetic pull between the stator and armature, which lowers vibration and magnetic noise. Thus, D.C.
Correct answer: quiet- A. equal to that of armature mmf
- B. less in comparison with the armature mmf
- C. large in comparison with the armature mmf
- D. none of the above
Explanation: A strong field mmf dominates the armature mmf, so the armature reaction produces less relative distortion of the main field.
Correct answer: large in comparison with the armature mmf- A. 10 m/s
- B. 20 m/s
- C. 30 m/s
- D. 40 m/s
Explanation: The peripheral speed of a conventional DC machine is normally limited to about 30 m/s to control centrifugal stress, vibration, and…
Correct answer: 30 m/s- A. increase
- B. decrease
- C. either of the above
- D. none of the above
Explanation: For a given machine output, increasing the number of poles shortens the armature coil span and reduces the length of field coils, so less…
Correct answer: increase- A. 100 A
- B. 200 A
- C. 300 A
- D. 400 A
Explanation: The current carried by one brush arm is normally limited to about 400 A to prevent excessive heating and current density at the brushes…
Correct answer: 400 A- A. 4 mm
- B. 6 mm
- C. 8 mm
- D. 10 mm
Explanation: Ventilation ducts in DC machines are commonly assigned a width of about 10 mm.
Correct answer: 10 mm- A. increase
- B. decrease
- C. either of the above
- D. none of the above
Explanation: Increasing field mmf requires larger field coils and more magnetic material to produce the required flux, which increases the machine's…
Correct answer: increase- A. Increase in length of air gap at pole tips
- B. Increasing reluctance of pole tips
- C. Compensating windings
- D. Interpoles
- E. All of the above
Explanation: Armature-reaction effects can be reduced by increasing pole-tip reluctance, using compensating windings, and using interpoles; a longer…
Correct answer: All of the above- A. between 2 to 4
- B. between 6 to 8
- C. between 9 to 16
- D. between 20 to 30
Explanation: A practical DC armature commonly has about 9 to 16 slots per pole. This range provides enough conductors and commutator segments for…
Correct answer: between 9 to 16- A. 5 percent
- B. 10 percent
- C. 15 percent
- D. 30 percent
- E. none of the above
Explanation: With hot-rolled steel, the yoke is typically made about 15 percent larger in cross-sectional area than the core because its magnetic flux…
Correct answer: 15 percent- A. equal to 50 kVA
- B. equal to 100 kVA
- C. above 200 kVA
- D. none of the above
Explanation: In the conventional classification used in such design questions, transformers above 200 kVA are called power transformers, while smaller…
Correct answer: above 200 kVA- A. Closed windings
- B. Open windings
- C. Either of the above
- D. None of the above
Explanation: A closed armature winding forms a continuous electrical path through all coils, and its practical construction uses two coil sides per…
Correct answer: Closed windings- A. duplex winding
- B. triplex winding
- C. forced winding
- D. none of the above
Explanation: A dummy coil is inserted in a wave winding when the slot or coil number does not satisfy the normal wave-winding condition; this…
Correct answer: forced winding- A. short pitch
- B. full pitch
- C. either of the above
- D. none of the above
Explanation: A pole pitch is the distance between corresponding points of adjacent poles.
Correct answer: full pitch- A. front pitch
- B. winding pitch
- C. commutator pitch
- D. back pitch
Explanation: Winding pitch is the distance, measured in coil sides, between the starts of successive coils.
Correct answer: winding pitch- A. small machines
- B. large machines
- C. either A. or B.
- D. none of the above
Explanation: A dummy coil contributes no useful generated emf, so it wastes space and copper and is avoided in large machines where this loss becomes…
Correct answer: large machines