Free Electrical Machines MCQs with Answers
1,061 Electrical Machines MCQs from Electrical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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- 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- 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