1. The main function of a substation is to
A. Generate electricity
B. Transmit electricity
C. Convert voltage levels
D. Consume power
✅ Answer: C
Explanation: A substation mainly changes voltage levels (step-up or step-down) for efficient transmission and distribution.
2. Which substation is used to reduce transmission voltage for consumers?
A. Primary substation
B. Generating substation
C. Distribution substation
D. Switching substation
✅ Answer: C
Explanation: Distribution substations step down voltage to levels suitable for consumers.
3. Bus bars in a substation are used to
A. Measure voltage
B. Store energy
C. Collect and distribute power
D. Protect equipment
✅ Answer: C
Explanation: Bus bars are conductors that collect power from incoming feeders and distribute it to outgoing feeders.
4. Which circuit breaker uses SF₆ gas as insulating medium?
A. Oil circuit breaker
B. Air circuit breaker
C. Vacuum circuit breaker
D. SF₆ circuit breaker
✅ Answer: D
Explanation: SF₆ gas has excellent dielectric and arc-quenching properties.
5. Lightning arresters are installed in substations to
A. Improve power factor
B. Reduce losses
C. Protect equipment from overvoltage
D. Control frequency
✅ Answer: C
Explanation: Lightning arresters protect equipment from lightning and switching surges.
Grounding (Earthing) MCQs
6. The main purpose of grounding is to
A. Reduce voltage
B. Increase current
C. Protect equipment and human life
D. Improve efficiency
✅ Answer: C
Explanation: Grounding provides a low-resistance path for fault current, preventing electric shock.
7. Which material is commonly used for earthing electrodes?
A. Aluminum
B. Copper
C. Iron wire
D. Lead
✅ Answer: B
Explanation: Copper has low resistivity and high corrosion resistance, making it ideal for earthing.
8. The resistance of an earthing system should be
A. Very high
B. Moderate
C. Zero
D. As low as possible
✅ Answer: D
Explanation: Low earthing resistance ensures quick dissipation of fault current.
9. Which type of earthing is commonly used in substations?
A. Plate earthing
B. Pipe earthing
C. Rod earthing
D. Mat (grid) earthing
✅ Answer: D
Explanation: Substations use mat earthing to reduce step and touch potentials.
10. Step potential is defined as
A. Voltage between equipment and earth
B. Voltage between two hands
C. Voltage between two feet of a person
D. Voltage across earthing electrode
✅ Answer: C
Explanation: Step potential is the voltage difference between two points on the ground one meter apart.
Combined Concept MCQs
11. Neutral grounding in substations helps in
A. Increasing voltage
B. Limiting fault current
C. Improving insulation
D. Reducing power loss
✅ Answer: B
Explanation: Neutral grounding limits earth fault current and improves system protection.
12. Which grounding method reduces over-voltages during earth faults?
A. Solid grounding
B. Resistance grounding
C. Reactance grounding
D. Ungrounded system
✅ Answer: B
Explanation: Resistance grounding limits fault current and reduces over-voltage.
13. Touch potential refers to
A. Voltage between phase and neutral
B. Voltage between two points on earth
C. Voltage between equipment body and earth
D. Voltage across transformer
✅ Answer: C
Explanation: Touch potential occurs when a person touches equipment during a fault.
14. Earthing mat in substations is placed
A. On roof
B. Below ground surface
C. On control panel
D. Around transformer only
✅ Answer: B
Explanation: Earthing mat is buried underground to ensure uniform potential distribution.
15. Which device is used to isolate faulty equipment in substations?
A. Transformer
B. Isolator
C. Bus bar
D. Earthing switch
✅ Answer: B
Explanation: Isolators disconnect faulty equipment during maintenance (no load condition).
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