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 31 of 158
601. The forced oil and air circulation method is usual one for transformers of capacities____________?
- A. upto 5 MVA
- B. upto 10 MVA
- C. upto 20 MVA
- D. 30 MVA upwards
Explanation: Forced oil and air circulation is used when natural cooling is insufficient for very large transformers, typically those rated 30 MVA and…
Correct answer: 30 MVA upwards- A. Corrugations
- B. Fins
- C. Tubes
- D. Radiator tanks
- E. All of the above
Explanation: Corrugations, fins, tubes and radiator tanks all increase the external surface area available for heat transfer from transformer oil to…
Correct answer: All of the above- A. 2 MVA
- B. 5 MVA
- C. 7.5 MVA
- D. 10 MVA
Explanation: Natural cooling with radiator systems is commonly used for transformers up to about 10 MVA; larger units generally require forced oil or…
Correct answer: 10 MVA- A. Electrical considerations
- B. Mechanical considerations
- C. Thermal considerations
- D. All of the above
Explanation: Transformer insulation must withstand electrical stress, retain mechanical strength against short-circuit forces, and tolerate thermal…
Correct answer: All of the above- A. 1.5 to 2.5 A/mm2
- B. 3.5 to 4.5 A/mm2
- C. 4.0 to 5.0 A/mm2
- D. 5.4 to 6.2 A/mm2
Explanation: Forced oil circulation or water-cooled coils remove heat more effectively, allowing a higher winding current density than ordinary natural…
Correct answer: 5.4 to 6.2 A/mm2- A. 1.0 Wb/m2
- B. 1.1 Wb/m2
- C. 1.3 Wb/m2
- D. 1.6 Wb/m2
- E. None of the above
Explanation: Cold-rolled grain-oriented steel has low core loss and can operate at a comparatively high flux density.
Correct answer: 1.6 Wb/m2- A. sometimes 2-layer type
- B. never 2-layer type
- C. always 2-layer type
- D. none of the above
Explanation: D.C. windings in transformer terminology are formed as two-layer windings, with the conductors arranged in two radial layers.
Correct answer: always 2-layer type- A. Cylindrical winding with circular conductors
- B. Cross-over winding with either circular or small rectangular conductors
- C. Continuous disc type winding with rectangular conductors
- D. All of the above types
Explanation: High-voltage transformer windings may be cylindrical with circular conductors, crossover type with circular or small rectangular…
Correct answer: All of the above types- A. 0.5 to 0.8 Wb/m2
- B. 0.8 to 1.0 Wb/m2
- C. 1.1 to 1.35 Wb/m2
- D. 1.4 to 1.8 Wb/m2
Explanation: Hot-rolled silicon steel is generally operated at a maximum flux density of about 1.1 to 1.35 Wb/m² in distribution transformers.
Correct answer: 1.1 to 1.35 Wb/m2- A. 1.0 to 1.2 A/mm2
- B. 1.5 to 2.0 A/mm2
- C. 2.2 to 3.2 A/mm2
- D. 3.2 to 4.2 A/mm2
Explanation: Large transformers with oil cooling or air-blast cooling commonly use a conductor current density of about 2.2 to 3.2 A/mm².
Correct answer: 2.2 to 3.2 A/mm2- A. 1 + 0.2 kVmm
- B. 2 + 0.5 kVmm
- C. 4 + 0.7 kV mm
- D. 5 + 0.9 kV mm
Explanation: The commonly used empirical expression for insulation thickness between LV and HV windings is approximately 5 + 0.9kV mm, with voltage…
Correct answer: 5 + 0.9 kV mm- A. low voltage transformers
- B. medium voltage transformers
- C. high voltage transformers
- D. any of the above
Explanation: Voltage surges become especially dangerous in high-voltage transformers because insulation stress rises sharply with transient…
Correct answer: high voltage transformers- A. minor insulation
- B. major insulation
- C. either of the above
- D. none of the above
Explanation: Major insulation separates the windings from the grounded core or tank and also separates windings of different voltage levels.
Correct answer: major insulation- A. 0.1 to 0.2 mm
- B. 0.2 to 0.3 mm
- C. 0.3 to 0.4 mm
- D. 0.4 to 0.5 mm
Explanation: Armature laminations in ordinary DC machines are commonly about 0.4 to 0.5 mm thick.
Correct answer: 0.4 to 0.5 mm- A. purely D.C. control systems
- B. purely AC. control systems
- C. both D.C. and AC. control systems
- D. none of the above
Explanation: A DC servomotor is designed for systems in which the actuating and control signals are DC, whereas AC servomotors are used for AC control…
Correct answer: purely D.C. control systems- A. upto 20 A
- B. upto 40 A
- C. upto 60 A
- D. upto 80 A
Explanation: Cylindrical windings made with circular conductors are suitable for relatively high currents, commonly rated up to about 80 A.
Correct answer: upto 80 A- A. Traction
- B. Drives for process industry
- C. Battery driven vehicles
- D. Automatic control
- E. All of the above
Explanation: D.C. motors are used in traction, industrial process drives, battery-powered vehicles and automatic-control systems because they provide…
Correct answer: All of the above- A. main poles
- B. interpoles
- C. frame
- D. all of the above
Explanation: The stator of a D.C. machine includes the frame, main poles and interpoles.
Correct answer: all of the above- A. Mild steel
- B. Copper
- C. Aluminium
- D. Cast-iron
Explanation: Brush rockers are commonly made of cast iron because it provides adequate mechanical strength and rigidity while supporting the brush…
Correct answer: Cast-iron- A. Metal graphite brushes
- B. Hard carbon brushes
- C. Electro-graphitic brushes
- D. Natural graphite brushes
Explanation: Metal-graphite brushes can carry high current density because the metallic content gives them low electrical resistance, while graphite…
Correct answer: Metal graphite brushes