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 143 of 158
- A. Generators
- B. Motors
- C. Transmission line
- D. Transformers
Explanation: Negative-sequence current produces a reverse-rotating magnetic field that causes severe heating in generator rotors, so generators…
Correct answer: Generators- A. single bus
- B. double bus, double breaker
- C. main and transfer bus
- D. all of the above
Explanation: In a main-and-transfer-bus scheme, the bus coupler connects the main and transfer buses so a circuit can be shifted during breaker…
Correct answer: main and transfer bus2843. For cost and safety, the outdoor substations are installed for voltages above_________________?
- A. 11 kV
- B. 33 kV
- C. 60kV
- D. 110kV
Explanation: Outdoor substations become more economical and safer than indoor installations at higher voltages because large clearances and equipment…
Correct answer: 33 kV- A. single phase to ground faults
- B. phase to phase faults
- C. two phase to ground faults
- D. three phase faults
- E. any of these
Explanation: A short-circuit can occur from any listed fault, including phase-to-ground, phase-to-phase, two-phase-to-ground, or three-phase faults.
Correct answer: any of these- A. load flow
- B. load flow and short-circuit
- C. load flow and stability
- D. load flow, short-circuit and stability
- E. none of the above
Explanation: An A.C. network analyser models power-system operating conditions, including load-flow calculations, short-circuit studies and stability…
Correct answer: load flow, short-circuit and stability- A. reactors
- B. resistors
- C. capacitors
- D. none of the above
Explanation: Reactors add inductive reactance in series with the circuit, limiting the magnitude of short-circuit current.
Correct answer: reactors- A. current
- B. voltage
- C. impedance
- D. all of the above
Explanation: An induction-cup relay develops torque from the interaction of alternating magnetic fluxes, and its operation may be arranged to respond…
Correct answer: all of the above- A. zero
- B. infinity
- C. unity
- D. none of the above
Explanation: At an open circuit, the load impedance is infinite, so the voltage reflection coefficient is (ZL − Z0)/(ZL + Z0) = +1.
Correct answer: unity- A. lubricate the contacts
- B. insulate the contacts from switch body
- C. extinguish the arc
- D. all of the above
- E. none of the above
Explanation: When high-voltage switch contacts separate, an arc forms between them; the oil cools and deionises the arc path, helping extinguish it.
Correct answer: extinguish the arc- A. thermocouple
- B. electronic and bimetallic
- C. both (A) and (B)
- D. none of the above
Explanation: Low-power electrical equipment commonly uses electronic, bimetallic and thermocouple-based protective relays.
Correct answer: both (A) and (B)- A. 1 mega ohms
- B. 10 mega ohms
- C. 100 mega ohms
- D. 500 mega ohms
Explanation: High-voltage circuit breakers require very high insulation resistance to prevent leakage and flashover across open contacts; the…
Correct answer: 100 mega ohms- A. interception
- B. interception and conduction
- C. interception, conduction and dissipation
- D. interception, conduction, dissipation and reflection
- E. none of the above
Explanation: Lightning protection must first intercept the stroke, conduct its current safely to earth, and dissipate the energy into the grounding…
Correct answer: interception, conduction and dissipation- A. power frequencies
- B. higher frequencies entering generator or transformer units
- C. either of the above
- D. none of the above
Explanation: A wave trap, or line trap, presents high impedance to high-frequency carrier and surge signals while allowing normal power-frequency…
Correct answer: higher frequencies entering generator or transformer units- A. 33kVto66kV
- B. HkVto33kV
- C. 3.3kVandllkV
- D. none of the above
Explanation: Resistance grounding is commonly applied to medium-voltage systems, particularly around 3.3 kV to 11 kV, to limit earth-fault current and…
Correct answer: 3.3kVandllkV- A. arc suppressing blow out coils
- B. wide separation of the opened contacts
- C. high speed opening of contacts
- D. all of the above
Explanation: Large-current interruption requires rapid contact separation, sufficient contact gap, and arc-control devices such as blowout coils.
Correct answer: all of the above- A. in phase with the arc current
- B. lagging the arc current by 90″
- C. leading the arc current by 90°
- D. none of the above
Explanation: The arc behaves approximately like a resistive element, so its voltage is substantially in phase with the arc current.
Correct answer: in phase with the arc current- A. slow making and breaking of load circuit contacts
- B. foreign matter on the contact surface
- C. too low contact pressure
- D. all of the above
Explanation: Slow contact operation prolongs arcing, foreign material raises contact resistance, and insufficient pressure reduces the effective…
Correct answer: all of the above- A. short transmission line
- B. medium transmission line
- C. long transmission line
- D. medium and long transmission lines
Explanation: For a short transmission line, shunt capacitance is small enough to neglect, leaving only the series impedance in the basic model.
Correct answer: short transmission line- A. high temperature
- B. increase of mean free path
- C. increasing field strength
- D. all of the above
Explanation: Ionization is promoted by high temperature, which increases particle energy, a longer mean free path, which allows more ionizing…
Correct answer: all of the above- A. inrush protection
- B. distance protection
- C. time graded and current graded over current protection
- D. both (B) and (C)
- E. none of the above
Explanation: Transmission lines commonly use distance protection as the main protection, with time-graded or current-graded overcurrent protection as…
Correct answer: both (B) and (C)