Answer: A. Switch, control, protect circuits. Switchgear combines devices used to switch, control, measure, and protect electrical circuits.
Which apparatus clears fault current?
A Busbar
B Isolator
C Circuit breaker
D Voltage transformer
Answer: C. Circuit breaker. A circuit breaker opens its contacts and interrupts fault current after a trip command.
Which device provides off-load isolation?
A Isolator
B Fuse link
C Protective relay
D Circuit breaker
Answer: A. Isolator. An isolator gives a visible separation point and is operated after current has been interrupted.
What is the purpose of an earthing switch?
A Interrupt load current
B Measure line voltage
C Charge breaker springs
D Ground isolated equipment
Answer: D. Ground isolated equipment. An earthing switch grounds de-energized equipment after it has been safely isolated.
A common LV MCB combines which mechanisms?
A Optical and hydraulic
B Thermal and magnetic
C Chemical and acoustic
D Capacitive and inductive
Answer: B. Thermal and magnetic. Many miniature circuit breakers use a thermal element for overloads and a magnetic element for short circuits.
What does MCCB stand for?
A Main control cable box
B Motor current control board
C Metal-clad circuit bus
D Moulded case circuit breaker
Answer: D. Moulded case circuit breaker. An MCCB is a moulded-case circuit breaker used for low-voltage circuit protection.
What is a busbar in a switchboard?
A Protective earth only
B Breaker operating spring
C Common electrical connection
D Voltage-measuring instrument
Answer: C. Common electrical connection. A busbar is a common conductor connecting incoming and outgoing switchgear circuits.
What does a CT provide to a protection relay?
A Scaled relay voltage
B Mechanical closing force
C Arc-quenching gas
D Scaled relay current
Answer: D. Scaled relay current. A current transformer supplies a proportional secondary current for measurement and protection.
What does a VT provide to a protection relay?
A Scaled relay current
B Scaled relay voltage
C Trip-coil motion
D Breaker contact pressure
Answer: B. Scaled relay voltage. A voltage transformer supplies a proportional secondary voltage for measurement and protection.
What normally initiates a breaker trip?
A Busbar temperature only
B Operator nameplate check
C Protection trip signal
D Motor speed increase
Answer: C. Protection trip signal. A relay or control circuit energizes the trip coil to command the breaker open.
What does a breaker closing coil do?
A Opens the earthing switch
B Measures fault current
C Extinguishes the arc
D Closes breaker mechanism
Answer: D. Closes breaker mechanism. The closing coil releases or drives the mechanism that closes the breaker contacts.
What recharges a spring-operated breaker mechanism?
A Current transformer
B Charging motor
C Bus coupler
D Arc chute
Answer: B. Charging motor. A small motor charges the stored-energy spring so the breaker can perform its next operation.
A breaker rated current indicates what?
A Continuous current capability
B Maximum line frequency
C Fault-current peak only
D Trip-coil voltage only
Answer: A. Continuous current capability. Rated current is the current the equipment can carry continuously under specified conditions.
A breaker rated voltage indicates what?
A Maximum system voltage
B Current-transformer ratio
C Contact opening speed
D Busbar short-time current
Answer: A. Maximum system voltage. Rated voltage identifies the highest system voltage for which the switchgear is designed.
Breaking capacity indicates what?
A Continuous load power
B Fault current interruption limit
C Relay pickup level
D Busbar insulation color
Answer: B. Fault current interruption limit. Breaking capacity states the fault-current level a circuit breaker can interrupt under specified conditions.
Making capacity relates to which breaker duty?
A Opening an isolator under load
B Measuring voltage at rest
C Charging a spring motor
D Closing onto a fault
Answer: D. Closing onto a fault. Making capacity describes the ability to close onto a short-circuit current and withstand its peak.
Short-time withstand rating covers what?
A Fault current for a duration
B Normal voltage for one cycle
C Relay output signal strength
D Contact resistance at zero load
Answer: A. Fault current for a duration. The rating states the short-circuit current the equipment can withstand for a specified short time.
A fuse operates mainly by what action?
A Contact lubrication
B Spring charging
C Element melting
D Voltage transformation
Answer: C. Element melting. Excess current heats and melts the fuse element, opening the circuit.
What does a protection relay mainly do?
A Detects and signals faults
B Interrupts current directly
C Provides visible isolation
D Connects bus sections
Answer: A. Detects and signals faults. A relay evaluates electrical quantities and sends a trip command when its criteria are met.
Which device connects two busbar sections?
A Earthing switch
B Voltage transformer
C Bus coupler
D Trip coil
Answer: C. Bus coupler. A bus coupler breaker can connect or separate busbar sections in a switchboard.
A load-break switch is designed to switch what?
A Maximum short-circuit current
B Transformer differential current
C Any fault current alone
D Normal load current
Answer: D. Normal load current. A load-break switch can make and interrupt specified normal load current but may need a fuse or breaker for faults.
What does a switchgear enclosure help provide?
A Higher power frequency
B Protection from contact and environment
C Automatic fault calculation
D Lower transformer ratio
Answer: B. Protection from contact and environment. An enclosure protects people from live parts and helps shield equipment from environmental conditions.
Why use electrical or mechanical interlocking?
A Prevent unsafe operation
B Increase rated current
C Raise busbar voltage
D Reduce CT ratio error
Answer: A. Prevent unsafe operation. Interlocks prevent an operation when the equipment is in an unsafe or incompatible state.
Which device gives a visible circuit break?
A Current transformer
B Protective relay
C Isolator
D Closing coil
Answer: C. Isolator. An open isolator provides a visible separation gap for safe maintenance procedures.
Where are switchgear controls and indications commonly grouped?
A Cable trench only
B Control panel
C Busbar support insulator
D Transformer conservator
Answer: B. Control panel. A control panel groups local controls, meters, indicators, and protection interfaces for the switchgear.