Free Power Systems MCQs with Answers

• 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.

• 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…

• 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…

• 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…

• 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…

• 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.

• 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.

• 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…

• 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.

• 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…

• 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…

• A. current wave only
• B. voltage wave only
• C. Both (A) and (B)
• D. power factor wave only

Explanation: Energizing a transmission line creates a traveling electromagnetic wave, consisting of related voltage and current waves that propagate…

• A. required to operate the circuit breaker
• B. absorbed by the circuit of relay
• C. developed by the relay circuit
• D. none of the above

Explanation: Relay burden is the power absorbed by the relay circuit, usually expressed in volt-amperes at the rated current or voltage.

• A. lengthening of the gap
• B. cooling and blast effect
• C. both (A) and (B)
• D. deionizing the oil with forced air
• E. none of the above

Explanation: After the arc current reaches its natural zero, circuit breakers prevent restriking by increasing the gap and removing heat and ionization…

• A. the spring tension
• B. the rate of flux built up
• C. armature core air gap
• D. all of the above

Explanation: Relay speed is influenced by spring tension, the rate at which operating flux builds up, and the armature core air gap.

• A. resistance, reactance or impedance
• B. voltage and current
• C. light intensity
• D. temperature
• E. all above

Explanation: Protective relays can be made responsive to electrical quantities such as current, voltage, resistance, reactance, or impedance, and to…

• A. good selectivity and reliability
• B. economy and simplicity
• C. high speed and selectivity
• D. all of the above

Explanation: Good protective relaying must combine selectivity, reliability, speed, simplicity, and economy.

• A. two currents
• B. two voltages
• C. two or more similar electrical quantities
• D. none of the above

Explanation: A differential relay compares corresponding currents or other similar electrical quantities entering and leaving a protected zone, using…

• A. current during abnormal condition
• B. voltage during abnormal condition
• C. constantly the electrical quantities which differ during normal and abnormal conditions
• D. none of the above

Explanation: A protective relay continuously monitors electrical quantities such as current and voltage and responds when their values or relationships…

• A. recovery
• B. surge
• C. operating
• D. arc
• E. none of the above

Explanation: The recovery voltage is the voltage that appears across the circuit-breaker contacts after the arc has been extinguished.