Substation Technician Certification
Exam – Practice Test (100 Questions
with Answers & Rationales)
1. What is the main function of a substation in a power system?
a) Generate power
b) Step up or step down voltage levels
c) Store electrical energy
d) Convert AC to DC
Rationale: Substations are designed to transform voltage levels
between transmission and distribution systems for efficient
power transfer.
2. Which device is used to protect a substation from lightning
strikes?
a) Transformer
b) Circuit breaker
c) Lightning arrester
d) Load tap changer
Rationale: Lightning arresters divert high-voltage surges caused
by lightning safely to the ground.
3. What is the typical voltage level for a distribution substation?
a) 1–5 kV
b) 5–15 kV
c) 11–33 kV
d) 66–132 kV
Rationale: Distribution substations typically operate between
11–33 kV for local power distribution.
,4. Which type of transformer is used to measure current in
substations?
a) Voltage transformer
b) Current transformer
c) Power transformer
d) Autotransformer
Rationale: Current transformers step down current to
measurable levels for meters and protective relays.
5. What is the purpose of a circuit breaker in a substation?
a) Voltage transformation
b) Interrupting fault current
c) Power factor correction
d) Grounding protection
Rationale: Circuit breakers interrupt fault currents to protect
equipment and maintain system stability.
6. What medium is commonly used for insulation in high-voltage
circuit breakers?
a) Water
b) Air only
c) SF6 gas
d) Oil-free vacuum
Rationale: SF6 gas provides excellent arc quenching and
insulation properties for high-voltage breakers.
7. Which of the following devices is used for overcurrent protection?
a) Relay
b) Isolator
c) Transformer
d) Reactor
, Rationale: Protective relays detect overcurrent conditions and
trigger breakers to isolate faults.
8. What is the function of a busbar in a substation?
a) Step up voltage
b) Step down current
c) Distribute electrical power to outgoing feeders
d) Measure electrical parameters
Rationale: Busbars act as conductors that distribute power
among multiple circuits or transformers.
9. Which substation component isolates a circuit for maintenance?
a) Isolator (disconnect switch)
b) Circuit breaker
c) Transformer
d) Relay
Rationale: Isolators disconnect sections of the substation for safe
maintenance when de-energized.
10. What is the main advantage of a gas-insulated substation
(GIS)?
a) Lower cost
b) Simpler design
c) Compact size and reduced maintenance
d) Easier to repair
Rationale: GIS systems are more compact and require less
maintenance due to enclosed, gas-insulated equipment.
11. Which of the following is a grounding component?
a) Transformer
b) Bus coupler
Exam – Practice Test (100 Questions
with Answers & Rationales)
1. What is the main function of a substation in a power system?
a) Generate power
b) Step up or step down voltage levels
c) Store electrical energy
d) Convert AC to DC
Rationale: Substations are designed to transform voltage levels
between transmission and distribution systems for efficient
power transfer.
2. Which device is used to protect a substation from lightning
strikes?
a) Transformer
b) Circuit breaker
c) Lightning arrester
d) Load tap changer
Rationale: Lightning arresters divert high-voltage surges caused
by lightning safely to the ground.
3. What is the typical voltage level for a distribution substation?
a) 1–5 kV
b) 5–15 kV
c) 11–33 kV
d) 66–132 kV
Rationale: Distribution substations typically operate between
11–33 kV for local power distribution.
,4. Which type of transformer is used to measure current in
substations?
a) Voltage transformer
b) Current transformer
c) Power transformer
d) Autotransformer
Rationale: Current transformers step down current to
measurable levels for meters and protective relays.
5. What is the purpose of a circuit breaker in a substation?
a) Voltage transformation
b) Interrupting fault current
c) Power factor correction
d) Grounding protection
Rationale: Circuit breakers interrupt fault currents to protect
equipment and maintain system stability.
6. What medium is commonly used for insulation in high-voltage
circuit breakers?
a) Water
b) Air only
c) SF6 gas
d) Oil-free vacuum
Rationale: SF6 gas provides excellent arc quenching and
insulation properties for high-voltage breakers.
7. Which of the following devices is used for overcurrent protection?
a) Relay
b) Isolator
c) Transformer
d) Reactor
, Rationale: Protective relays detect overcurrent conditions and
trigger breakers to isolate faults.
8. What is the function of a busbar in a substation?
a) Step up voltage
b) Step down current
c) Distribute electrical power to outgoing feeders
d) Measure electrical parameters
Rationale: Busbars act as conductors that distribute power
among multiple circuits or transformers.
9. Which substation component isolates a circuit for maintenance?
a) Isolator (disconnect switch)
b) Circuit breaker
c) Transformer
d) Relay
Rationale: Isolators disconnect sections of the substation for safe
maintenance when de-energized.
10. What is the main advantage of a gas-insulated substation
(GIS)?
a) Lower cost
b) Simpler design
c) Compact size and reduced maintenance
d) Easier to repair
Rationale: GIS systems are more compact and require less
maintenance due to enclosed, gas-insulated equipment.
11. Which of the following is a grounding component?
a) Transformer
b) Bus coupler
