Q.1 Which power apparatus is primarily used to isolate a portion of a power system for maintenance?
Circuit breaker
Disconnect switch
Fuse
Surge arrester
Explanation - A disconnect switch (or isolator) is designed to open or close a circuit for maintenance purposes. Unlike circuit breakers, disconnect switches are not intended for fault interruption.
Correct answer is: Disconnect switch
Q.2 A transformer’s purpose in a distribution system is to:
Reduce the voltage for residential use
Store electrical energy
Provide protection against surges
Isolate circuits from each other
Explanation - Distribution transformers step down the high transmission voltages to lower levels suitable for residential and commercial consumption.
Correct answer is: Reduce the voltage for residential use
Q.3 Which device is most effective at protecting equipment from transient overvoltages?
Circuit breaker
Fuse
Surge arrester
Disconnect switch
Explanation - Surge arresters are designed to clamp high voltage transients to safe levels, thereby protecting downstream equipment.
Correct answer is: Surge arrester
Q.4 A high-voltage circuit breaker can interrupt:
Only short-circuit currents
Both normal and fault currents
Only fault currents
Only normal currents
Explanation - High-voltage circuit breakers must be capable of interrupting normal load currents as well as fault currents that can be much higher.
Correct answer is: Both normal and fault currents
Q.5 Which of the following best describes a load tap changer?
A device that changes the voltage rating of a transformer
A device that adjusts the tap connections to control secondary voltage
A type of circuit breaker used for fault interruption
A protective relay for overcurrent detection
Explanation - A load tap changer changes tap positions on the transformer winding to adjust the output voltage under load conditions.
Correct answer is: A device that adjusts the tap connections to control secondary voltage
Q.6 What is the primary function of a Ground Fault Circuit Interrupter (GFCI)?
Detect and interrupt overcurrent conditions
Detect imbalance between live conductors and ground
Step down voltage for safety
Isolate the system during maintenance
Explanation - A GFCI monitors the current difference between the hot and neutral conductors; if a fault to ground occurs, it quickly disconnects the circuit.
Correct answer is: Detect imbalance between live conductors and ground
Q.7 Which apparatus provides a means for disconnecting a circuit after it has been isolated by a breaker?
Disconnect switch
Fuse
Surge arrester
Tap changer
Explanation - After a breaker opens, a disconnect switch can be manually closed to isolate the circuit for maintenance.
Correct answer is: Disconnect switch
Q.8 In a high-voltage transmission line, a 'shunt reactor' is used to:
Compensate reactive power and stabilize voltage
Increase line current
Protect against surges
Isolate sections of the line
Explanation - Shunt reactors absorb reactive power, helping to maintain system voltage levels in long transmission lines.
Correct answer is: Compensate reactive power and stabilize voltage
Q.9 Which of the following is NOT typically a characteristic of a circuit breaker?
Can interrupt high fault currents
Can be operated automatically or manually
Provides continuous monitoring of voltage
Has a rated breaking capacity
Explanation - Circuit breakers are primarily protective devices; they do not continuously monitor voltage—relays and sensors perform that function.
Correct answer is: Provides continuous monitoring of voltage
Q.10 An 'open circuit breaker' is most suitable for which of the following applications?
Short-circuit testing of transformers
Load switching in substations
Isolation during maintenance
Ground fault detection
Explanation - An open circuit breaker can be used to isolate a system for maintenance, but it is not designed for high fault currents.
Correct answer is: Isolation during maintenance
Q.11 What type of protection is provided by a 'current transformer' in a power system?
Overvoltage protection
Overcurrent protection
Earth fault protection
Frequency regulation
Explanation - Current transformers provide scaled-down current signals for relays, enabling overcurrent protection and monitoring.
Correct answer is: Overcurrent protection
Q.12 Which device is used to quickly isolate a faulted section of a power grid while maintaining power to the rest of the network?
Circuit breaker
Fuse
Disconnect switch
Voltage regulator
Explanation - Circuit breakers can disconnect a faulted section without shutting down the entire grid, preserving supply to unaffected parts.
Correct answer is: Circuit breaker
Q.13 In a transformer, the term 'turn ratio' refers to:
Ratio of primary to secondary windings
Ratio of voltage to current
Ratio of core area to winding area
Ratio of resistance to reactance
Explanation - The turn ratio determines the voltage transformation between primary and secondary windings of a transformer.
Correct answer is: Ratio of primary to secondary windings
Q.14 Which apparatus is used to absorb overcurrent conditions by melting a metal alloy?
Fuse
Circuit breaker
Disconnect switch
Surge arrester
Explanation - Fuses have a fusible element that melts when current exceeds its rating, opening the circuit.
Correct answer is: Fuse
Q.15 A 'step-up transformer' is used in which part of the power system?
Transmission
Distribution
Generation
All of the above
Explanation - Step-up transformers increase voltage to reduce line losses during transmission, then step down for distribution.
Correct answer is: Transmission
Q.16 What is the main purpose of a 'shunt capacitor' in an AC power system?
Provide reactive power compensation
Increase system impedance
Reduce system losses due to resistance
Detect fault currents
Explanation - Shunt capacitors inject reactive power into the system, improving voltage regulation and reducing losses.
Correct answer is: Provide reactive power compensation
Q.17 A 'thyratron' used as a high-power switch is mainly found in:
Power transformers
Motor starters
Fuse holders
Surge arresters
Explanation - Thyratrons are gas-filled tubes used for starting induction motors by providing high starting currents.
Correct answer is: Motor starters
Q.18 Which device provides a temporary isolation of a circuit to allow maintenance after a fault has been cleared?
Load tap changer
Circuit breaker
Disconnect switch
Fuse
Explanation - After a breaker clears a fault, a disconnect switch can be used to isolate the circuit for safe maintenance.
Correct answer is: Disconnect switch
Q.19 A 'universal circuit breaker' can handle:
Both AC and DC fault currents
Only AC fault currents
Only DC fault currents
Only low voltage systems
Explanation - Universal breakers are designed to interrupt both AC and DC faults, making them versatile for various applications.
Correct answer is: Both AC and DC fault currents
Q.20 Which apparatus is primarily used for power factor correction?
Shunt reactor
Shunt capacitor
Load tap changer
Surge arrester
Explanation - Shunt capacitors add leading reactive power, correcting lagging power factor in power systems.
Correct answer is: Shunt capacitor
Q.21 The 'trip' function of a circuit breaker is triggered by:
Manual operation
Automatic detection of fault currents
Low voltage detection
High temperature sensing
Explanation - Trip mechanisms are designed to detect fault conditions automatically and interrupt the circuit.
Correct answer is: Automatic detection of fault currents
Q.22 Which device is used to protect against 'overvoltages' caused by lightning?
Surge arrester
Fuse
Circuit breaker
Disconnect switch
Explanation - Surge arresters clamp excessive voltage spikes, such as those from lightning strikes, preventing damage to equipment.
Correct answer is: Surge arrester
Q.23 A 'pressure switch' in a power system is used to:
Sense hydraulic pressure in a transformer coolant system
Detect overvoltage in power lines
Measure current flow
Control tap changer positions
Explanation - Pressure switches monitor coolant pressure, triggering alarms or shutdowns if pressure deviates from normal ranges.
Correct answer is: Sense hydraulic pressure in a transformer coolant system
Q.24 The main safety function of a 'ground fault relay' is to:
Trip the circuit breaker when a fault to ground is detected
Limit overcurrent in the system
Step down voltage for residential use
Capacitively couple the system to ground
Explanation - Ground fault relays detect current imbalance between phase conductors and ground, tripping breakers to protect personnel.
Correct answer is: Trip the circuit breaker when a fault to ground is detected
Q.25 Which apparatus can provide a 'slow trip' operation to allow for load fluctuations before opening?
Mechanical fuse
Thermal overload relay
Circuit breaker
Disconnect switch
Explanation - Thermal overload relays detect sustained overcurrent and trip after a delay, protecting motors from overheating.
Correct answer is: Thermal overload relay
Q.26 A 'phase failure relay' is designed to detect:
Loss of one phase in a three-phase system
Overvoltage conditions
Ground faults
Short-circuit currents
Explanation - Phase failure relays monitor the presence of all three phases; if one disappears, they trigger a protective action.
Correct answer is: Loss of one phase in a three-phase system
Q.27 What is the purpose of a 'neutral grounding resistor' in a power system?
To limit fault currents to earth ground
To increase system voltage
To detect overcurrent conditions
To provide isolation for maintenance
Explanation - Neutral grounding resistors restrict the magnitude of fault currents that can flow to earth, improving system reliability.
Correct answer is: To limit fault currents to earth ground
Q.28 Which of the following devices can be used to control the voltage in a high-voltage transmission line?
Shunt reactor
Load tap changer
Fuse
Disconnect switch
Explanation - Load tap changers on transformers adjust voltage levels by changing the turns ratio under load conditions.
Correct answer is: Load tap changer
Q.29 What type of switch is typically used for 'low voltage' applications in household circuits?
Circuit breaker
Fuse holder
Disconnect switch
Switchgear
Explanation - Fuse holders allow easy replacement of fuses in low-voltage domestic circuits, providing overcurrent protection.
Correct answer is: Fuse holder
Q.30 Which apparatus is essential for 'fault isolation' during an emergency in a power grid?
Shunt capacitor
Circuit breaker
Neutral grounding resistor
Fuse
Explanation - Circuit breakers can quickly disconnect faulted sections, isolating them from the rest of the system during emergencies.
Correct answer is: Circuit breaker
Q.31 A 'polyphase transformer' is used to step up or step down voltage in:
Single-phase circuits only
Three-phase circuits only
Both single-phase and three-phase circuits
Only DC circuits
Explanation - Polyphase transformers can handle both single-phase and multi-phase (e.g., three-phase) power systems.
Correct answer is: Both single-phase and three-phase circuits
Q.32 The 'tripping time' of a circuit breaker depends on:
The magnitude of fault current
The voltage of the system
The age of the breaker
The type of insulation
Explanation - Higher fault currents result in faster trip times; breakers are designed to open within specified times based on fault level.
Correct answer is: The magnitude of fault current
Q.33 Which apparatus is primarily used for 'high voltage isolation' of an energized circuit?
Circuit breaker
Disconnect switch
Fuse
Switchgear
Explanation - Disconnect switches can be safely operated on energized circuits to provide isolation for maintenance purposes.
Correct answer is: Disconnect switch
Q.34 A 'vacuum circuit breaker' uses a vacuum as the interrupter medium to:
Reduce arcing and improve cleanliness
Increase the breaking capacity
Lower the cost of operation
Provide isolation for DC systems
Explanation - Vacuum interrupters quickly extinguish arcs and leave no residue, making them ideal for high-voltage applications.
Correct answer is: Reduce arcing and improve cleanliness
Q.35 Which protective device is designed to trip when the voltage exceeds a predetermined level?
Voltage relay
Fuse
Ground fault relay
Circuit breaker
Explanation - Voltage relays detect overvoltage or undervoltage conditions and initiate protective actions.
Correct answer is: Voltage relay
Q.36 What is the main advantage of using 'line reactors' in HVDC systems?
Reduce reactive power losses
Improve voltage stability
Prevent DC fault currents from affecting AC system
Step down voltage for distribution
Explanation - Line reactors in HVDC systems block high-frequency currents and isolate DC faults from the AC network.
Correct answer is: Prevent DC fault currents from affecting AC system
Q.37 Which device can be used to measure the 'resistance' of a transformer secondary winding?
Ohmmeter
Thermocouple
Clamp meter
Volt meter
Explanation - An ohmmeter applies a small DC current and measures voltage drop to calculate resistance in winding circuits.
Correct answer is: Ohmmeter
Q.38 The 'inverse time characteristic' of a relay is important for:
Determining the time it takes for a relay to trip based on current magnitude
Measuring voltage levels
Counting cycles of power
Regulating frequency
Explanation - Inverse time characteristics mean the higher the current, the shorter the delay before tripping.
Correct answer is: Determining the time it takes for a relay to trip based on current magnitude
Q.39 In a distribution system, a 'microgrid' typically includes:
Multiple transformers and a small number of loads
A single large transformer serving the entire grid
Only power lines with no substations
A set of high-voltage circuit breakers only
Explanation - Microgrids are small-scale power networks with local generation, storage, and distribution equipment.
Correct answer is: Multiple transformers and a small number of loads
Q.40 Which of the following is a key function of a 'fuse holder' in a power system?
Allow quick replacement of fuses
Provide overcurrent protection
Detect short circuits
Capacitively couple loads
Explanation - Fuse holders are designed to hold fuses securely while enabling rapid replacement after blowing.
Correct answer is: Allow quick replacement of fuses
Q.41 A 'short-circuit test' on a transformer primarily determines:
Core losses
Equivalent impedance and percent impedance
Open-circuit voltage
Thermal capacity
Explanation - During a short-circuit test, the transformer’s impedance and voltage drop under fault conditions are measured.
Correct answer is: Equivalent impedance and percent impedance
Q.42 Which device can be used to 'limit the inrush current' when energizing a transformer?
Inrush current limiter (ICL)
Fuse
Shunt capacitor
Circuit breaker
Explanation - ICLs are designed to allow normal startup current while preventing excessive inrush that can trip protective devices.
Correct answer is: Inrush current limiter (ICL)
Q.43 In a three-phase system, if one phase fails, the system voltage:
Drops to zero
Remains unchanged
Increases
Becomes unpredictable
Explanation - If a single phase is lost, the system can no longer deliver power, and the voltage effectively goes to zero for that phase.
Correct answer is: Drops to zero
Q.44 Which protective device is used to isolate a faulted section of a network during normal operation?
Relay
Breaker
Switchgear
Fuse
Explanation - Circuit breakers can isolate faulted sections without shutting down the entire network during normal operations.
Correct answer is: Breaker
Q.45 A 'remote controlled circuit breaker' can be operated from:
Only manually
From a central control room
By a fuse holder
From a disconnect switch
Explanation - Remote controlled breakers allow operators to open/close from a central location, improving safety and control.
Correct answer is: From a central control room
Q.46 The primary purpose of a 'thermal overload relay' in motor circuits is to:
Protect against overcurrent
Detect overvoltage
Detect phase imbalance
Control motor speed
Explanation - Thermal overload relays protect motors from overheating by monitoring current and time delay characteristics.
Correct answer is: Protect against overcurrent
Q.47 Which apparatus is typically used to 'measure the frequency' of an AC power system?
Frequency meter
Clamp meter
Voltmeter
Ampermeter
Explanation - Frequency meters measure the number of cycles per second, providing critical data for system monitoring.
Correct answer is: Frequency meter
Q.48 A 'reverse power relay' is used to detect:
Reverse phase angle indicating reverse power flow
Overcurrent conditions
Phase failure
Low voltage conditions
Explanation - Reverse power relays detect when power is flowing in the opposite direction, protecting generators from reverse operation.
Correct answer is: Reverse phase angle indicating reverse power flow
Q.49 In a power system, a 'ballast' is used with:
High voltage lamps to limit current
Transformers to increase impedance
Circuit breakers to reduce arc size
Disconnect switches to isolate sections
Explanation - Ballasts provide a stable current for fluorescent or high-voltage discharge lamps, preventing overload.
Correct answer is: High voltage lamps to limit current
Q.50 The 'short-circuit impedance' of a transformer is important for:
Calculating the transformer's voltage rating
Determining fault current levels
Measuring temperature rise
Assessing insulation levels
Explanation - Transformer impedance determines how much fault current will flow under a short-circuit condition.
Correct answer is: Determining fault current levels
Q.51 Which device is used for 'current measurement' in high-power circuits without direct contact?
Clamp meter
Volt meter
Thermocouple
Ammeter
Explanation - Clamp meters use magnetic induction to measure current without physically connecting to the conductor.
Correct answer is: Clamp meter
Q.52 A 'busbar' in power systems serves as a:
Physical conduit for cables only
Common point of connection for multiple conductors
Device for measuring voltage
Switch to isolate sections
Explanation - Busbars provide a shared point for connecting many conductors, enabling efficient distribution of power.
Correct answer is: Common point of connection for multiple conductors
Q.53 In a distribution network, which device is used to 'control the flow of power from a generator to the load during normal operation'?
Circuit breaker
Disconnect switch
Fuse
Thermal relay
Explanation - Circuit breakers are used for switching power flow while providing protection against faults.
Correct answer is: Circuit breaker
Q.54 The function of a 'load break switch' is to:
Break the circuit without interrupting load currents
Detect overcurrent conditions
Measure voltage
Control frequency
Explanation - Load break switches are designed to open or close while carrying normal load currents, allowing maintenance under load.
Correct answer is: Break the circuit without interrupting load currents
Q.55 Which device can provide a 'soft start' for motors to reduce inrush current?
Soft starter
Circuit breaker
Fuse
Disconnect switch
Explanation - Soft starters gradually ramp up voltage to the motor, limiting the initial surge of current.
Correct answer is: Soft starter
Q.56 What is the main purpose of an 'overvoltage relay' in a power distribution system?
Detect overvoltage and initiate breaker tripping
Detect overcurrent and open fuses
Detect short circuits
Regulate power factor
Explanation - Overvoltage relays monitor voltage levels and trigger protective actions when thresholds are exceeded.
Correct answer is: Detect overvoltage and initiate breaker tripping
Q.57 A 'breaker' with a 'manual operation' feature allows:
Only remote control operation
Manual opening and closing by a technician
Automatic operation only
Only the use of fuses
Explanation - Manual operation is essential for maintenance and testing, providing direct control to the operator.
Correct answer is: Manual opening and closing by a technician
Q.58 Which apparatus is primarily used for 'short-circuit testing' of a transformer?
Open-circuit test
Short-circuit test
Load test
Thermal test
Explanation - The short-circuit test applies a low voltage to the transformer while shorting the secondary to determine impedance.
Correct answer is: Short-circuit test
Q.59 A 'power factor relay' is used to:
Trip when power factor falls below a threshold
Trip when voltage exceeds a threshold
Detect phase imbalances
Measure load current
Explanation - Power factor relays protect generators and power stations from poor power factor conditions, which can cause overheating.
Correct answer is: Trip when power factor falls below a threshold
Q.60 Which component is essential for 'isolating a transformer from the ground' during maintenance?
Ground fault relay
Disconnect switch
Shunt capacitor
Fuse
Explanation - Disconnect switches are used to isolate circuits from the ground, ensuring safety during maintenance.
Correct answer is: Disconnect switch
Q.61 Which apparatus is used to detect 'low voltage' conditions in a power system?
Under-voltage relay
Overvoltage relay
Power factor relay
Ground fault relay
Explanation - Under-voltage relays sense a voltage drop below a threshold and initiate protective actions.
Correct answer is: Under-voltage relay
Q.62 Which device provides 'continuous monitoring' of transformer temperature?
Thermocouple
Fuse holder
Voltage meter
Clamp meter
Explanation - Thermocouples measure temperature continuously and feed data to protective relays for overload protection.
Correct answer is: Thermocouple
Q.63 A 'phase-to-phase fault' in a three-phase system causes:
Higher fault current than a line-to-ground fault
Lower fault current than a line-to-ground fault
No effect on fault current
Only a voltage drop but no current
Explanation - Phase-to-phase faults bypass the neutral and typically involve higher fault current levels.
Correct answer is: Higher fault current than a line-to-ground fault
Q.64 The term 'breakover voltage' refers to:
Voltage at which a fuse melts
Voltage at which a circuit breaker opens
Voltage at which an insulator fails
Voltage at which a transformer steps up
Explanation - Breakover voltage is the threshold at which insulating material breaks down and conducts electricity.
Correct answer is: Voltage at which an insulator fails
Q.65 Which device is commonly used to 'protect the circuit from overcurrent during startup of motors'?
Inrush current limiter
Fuse
Ground fault relay
Disconnect switch
Explanation - Inrush current limiters allow normal startup current while limiting excess inrush that could trip fuses.
Correct answer is: Inrush current limiter
Q.66 A 'bifurcated' device in a power system is:
A device that splits a single conductor into two
A type of circuit breaker
An instrument for measuring frequency
A device for isolation of a single phase
Explanation - A bifurcated conductor splits the current path, often used in distribution networks.
Correct answer is: A device that splits a single conductor into two
Q.67 What is the primary function of a 'surge suppression device' in a power system?
Absorb overvoltage transients
Regulate frequency
Increase transformer core size
Reduce reactive power losses
Explanation - Surge suppression devices (e.g., surge arresters) clamp high voltage spikes to prevent damage.
Correct answer is: Absorb overvoltage transients
Q.68 Which device can be used to 'measure the resistance of a power line'?
Ohmmeter
Clamp meter
Voltage sensor
Thermocouple
Explanation - An ohmmeter measures resistance by applying a known voltage and measuring the resulting current.
Correct answer is: Ohmmeter
Q.69 In an HV transmission network, a 'quasi-DC fault' typically occurs during:
Short-circuit of a transformer winding
Failure of a DC link in a HVDC converter
Short-circuit of a line-to-ground fault
Short-circuit of a three-phase system
Explanation - Quasi-DC faults arise when a DC link fails, producing a slowly decaying DC component in the fault current.
Correct answer is: Failure of a DC link in a HVDC converter
Q.70 What is a key benefit of a 'high-impedance circuit breaker'?
Reduces arcing during fault interruption
Increases fault current levels
Provides faster tripping times
Reduces cost
Explanation - High-impedance breakers create a high-resistance path, limiting arc current and enhancing safety.
Correct answer is: Reduces arcing during fault interruption
Q.71 Which of the following devices is primarily used for 'providing temporary power' during outages?
Battery backup
Fuse
Circuit breaker
Shunt capacitor
Explanation - Battery backups store electrical energy and supply power during outages until the main supply resumes.
Correct answer is: Battery backup
Q.72 A 'transformer tap changer' is used to:
Control the voltage ratio under load
Measure voltage
Provide grounding
Interrupt fault currents
Explanation - Tap changers adjust the turns ratio, altering the secondary voltage while the transformer is loaded.
Correct answer is: Control the voltage ratio under load
Q.73 Which apparatus is essential for 'isolating a power line from the neutral during maintenance'?
Neutral grounding resistor
Disconnect switch
Fuse
Ground fault relay
Explanation - Disconnect switches are used to isolate energized conductors from neutral, ensuring safety during maintenance.
Correct answer is: Disconnect switch
Q.74 The term 'impedance matching' in power transmission is used to:
Maximize power transfer and reduce reflections
Increase core losses
Reduce transformer size
Improve frequency regulation
Explanation - Impedance matching ensures efficient transfer of power and minimizes voltage reflections in transmission lines.
Correct answer is: Maximize power transfer and reduce reflections
Q.75 Which device can be used to detect a 'phase-to-phase fault' in a three-phase system?
Phase-fault relay
Current transformer
Voltage sensor
Thermal relay
Explanation - Phase-fault relays monitor differential currents to detect faults between phases.
Correct answer is: Phase-fault relay
Q.76 Which of the following is NOT a function of a 'disconnect switch'?
Provide isolation for maintenance
Interrupt fault currents
Enable manual operation under load
Provide a reliable means of isolation when energized
Explanation - Disconnect switches are not designed for fault interruption; circuit breakers handle that function.
Correct answer is: Interrupt fault currents
Q.77 What is the purpose of a 'shunt reactor' in a distribution network?
Absorb reactive power and stabilize voltage
Inject reactive power to correct power factor
Measure voltage drop
Protect against overcurrent
Explanation - Shunt reactors absorb leading reactive power, reducing voltage rise and stabilizing system voltage.
Correct answer is: Absorb reactive power and stabilize voltage
Q.78 Which apparatus provides 'fast fault interruption' for high voltage lines?
Vacuum circuit breaker
Fuse
Disconnect switch
Shunt capacitor
Explanation - Vacuum breakers interrupt faults quickly without arcing, ideal for high-voltage applications.
Correct answer is: Vacuum circuit breaker
Q.79 In power systems, a 'load test' on a transformer measures:
Core losses
Load loss
Open-circuit voltage
Shunt impedance
Explanation - Load tests apply rated load to measure copper and core losses under normal operating conditions.
Correct answer is: Load loss
Q.80 What is the primary role of a 'ground fault relay' in a power system?
Detect a fault to ground and trip a circuit breaker
Detect overcurrent conditions
Regulate frequency
Measure voltage levels
Explanation - Ground fault relays sense imbalance between phase currents and ground, initiating protective actions.
Correct answer is: Detect a fault to ground and trip a circuit breaker
Q.81 Which device is used to 'prevent the opening of a circuit breaker during a fault'?
Time delay relay
Inverse time relay
Voltage relay
Current transformer
Explanation - Time delay relays add a delay to the trip operation, preventing nuisance tripping during transient faults.
Correct answer is: Time delay relay
Q.82 The 'rated breaking capacity' of a breaker indicates:
Maximum fault current the breaker can safely interrupt
Maximum voltage it can withstand
Maximum temperature it can handle
Maximum mechanical stress it can sustain
Explanation - Rated breaking capacity defines the highest fault current a breaker can safely interrupt without damage.
Correct answer is: Maximum fault current the breaker can safely interrupt
Q.83 Which device is essential for 'controlling the flow of DC power in HVDC transmission'?
Converter station
Shunt reactor
Transformer
Surge arrester
Explanation - Converter stations convert AC to DC and vice versa, controlling the flow in HVDC systems.
Correct answer is: Converter station
Q.84 A 'fuse' is considered a 'passive protective device' because:
It requires no external power or control to operate
It can be reactivated after blowing
It uses a relay to detect faults
It is self-resetting
Explanation - Fuses react chemically to high current and do not require external control or power to function.
Correct answer is: It requires no external power or control to operate
Q.85 Which apparatus is used to provide a 'temporary isolation' during a fault before the circuit breaker clears the fault?
Disconnect switch
Load tap changer
Shunt capacitor
Fuse
Explanation - Disconnect switches can be used to isolate faulted sections before the breaker fully opens.
Correct answer is: Disconnect switch
Q.86 Which device is essential for measuring the 'voltage drop' across a power line?
Voltmeter
Clamp meter
Thermocouple
Frequency meter
Explanation - A voltmeter directly measures potential difference across conductors.
Correct answer is: Voltmeter
Q.87 A 'reverse power relay' is used in a generator to protect it from:
Reverse power flow due to load changes
Overcurrent
Under-voltage conditions
Short circuits
Explanation - It protects generators from operating in reverse due to sudden load changes or faults.
Correct answer is: Reverse power flow due to load changes
Q.88 The main difference between a 'fuse' and a 'circuit breaker' is that a fuse:
Is a resettable device
Requires no external power to operate
Can interrupt high fault currents
Is used for short-circuit testing
Explanation - Fuses operate based on thermal or electrical properties without external power or control mechanisms.
Correct answer is: Requires no external power to operate
Q.89 Which power apparatus is typically used to 'prevent overcurrent due to short circuits'?
Fuse
Ground fault relay
Shunt capacitor
Voltage regulator
Explanation - Fuses are designed to interrupt circuits when current exceeds their rating, preventing damage.
Correct answer is: Fuse
Q.90 Which device can be used to 'measure the current flowing through a conductor' without contacting it?
Clamp meter
Fuse holder
Voltage meter
Thermocouple
Explanation - A clamp meter uses magnetic induction to measure current without breaking the circuit.
Correct answer is: Clamp meter
Q.91 Which protective device uses a 'mechanical switch' to open or close a circuit?
Circuit breaker
Fuse
Ground fault relay
Disconnect switch
Explanation - Circuit breakers have a mechanical switching element that opens or closes under fault conditions.
Correct answer is: Circuit breaker
Q.92 A 'shunt capacitor bank' is used for:
Reactive power compensation
Ground fault protection
Overcurrent protection
Voltage regulation
Explanation - Shunt capacitors provide leading reactive power, improving the power factor of the system.
Correct answer is: Reactive power compensation
Q.93 What is the main function of a 'high voltage disconnect switch'?
Isolate circuits for maintenance when energized
Interrupt fault currents
Provide overvoltage protection
Detect phase imbalance
Explanation - High voltage disconnect switches are used to isolate circuits while they remain live for safety.
Correct answer is: Isolate circuits for maintenance when energized
Q.94 The term 'slip' in a transformer refers to:
The difference between synchronous and actual speed
The amount of voltage loss
The core loss at no load
The ratio of primary to secondary voltage
Explanation - Slip is defined as (Ns - Nr)/Ns for synchronous machines, indicating load conditions.
Correct answer is: The difference between synchronous and actual speed
Q.95 In a power system, a 'phase-to-ground fault' typically results in:
Reduced fault current
High fault current
No fault current
Moderate fault current
Explanation - Phase-to-ground faults cause large currents due to low impedance path to ground.
Correct answer is: High fault current
Q.96 Which device is used to detect an 'overvoltage condition' and trip a breaker?
Overvoltage relay
Ground fault relay
Overcurrent relay
Thermal relay
Explanation - Overvoltage relays monitor the voltage level and activate protective actions when thresholds are exceeded.
Correct answer is: Overvoltage relay
Q.97 What does a 'phase-fault relay' detect in a power system?
A fault between phases
A fault to ground
An overcurrent condition
A voltage drop
Explanation - Phase-fault relays sense differential currents between phases to detect phase-to-phase faults.
Correct answer is: A fault between phases
Q.98 A 'swing breaker' is used to:
Connect a load during a fault
Provide a temporary fault interruption
Control the voltage level
Prevent overcurrent
Explanation - Swing breakers temporarily disconnect and reconnect the circuit to isolate a faulted section.
Correct answer is: Provide a temporary fault interruption
Q.99 Which apparatus is used for 'providing a low impedance path to ground' during fault conditions?
Neutral grounding resistor
Shunt capacitor
Fuse holder
Circuit breaker
Explanation - Neutral grounding resistors limit fault currents by providing a controlled low-resistance path to earth.
Correct answer is: Neutral grounding resistor
Q.100 What is the primary function of a 'current transformer' in a power system?
Step down current for measurement and protection
Step down voltage for distribution
Detect overvoltage conditions
Isolate circuits for maintenance
Explanation - Current transformers reduce high currents to manageable levels for relays and meters.
Correct answer is: Step down current for measurement and protection
Q.101 Which device is used to detect a 'phase imbalance' in a three-phase system?
Phase-fault relay
Overvoltage relay
Under-voltage relay
Power factor relay
Explanation - Phase-fault relays monitor differential currents to detect phase imbalance or faults.
Correct answer is: Phase-fault relay
Q.102 A 'breakout box' in a substation is primarily used for:
Routing cables and providing terminal connections
Housing protective relays
Discharging surge voltage
Controlling transformer taps
Explanation - Breakout boxes facilitate cable management and provide convenient terminal connections for equipment.
Correct answer is: Routing cables and providing terminal connections
Q.103 The 'inverse time characteristic' of a relay means:
Higher fault currents result in longer trip times
Higher fault currents result in shorter trip times
Trip time is independent of fault current
Trip time is inversely proportional to voltage
Explanation - Inverse time relays reduce the delay as the fault current increases, providing timely protection.
Correct answer is: Higher fault currents result in shorter trip times
Q.104 Which device is used to 'limit the size of an arc' during a fault interruption?
Arc quenching chamber
Fuse
Shunt capacitor
Disconnect switch
Explanation - Arc quenching chambers contain the arc and limit its growth, improving breaker performance.
Correct answer is: Arc quenching chamber
Q.105 What is the purpose of a 'short-circuit test' on a transformer?
Determine core losses
Determine impedance and percent impedance
Determine open-circuit voltage
Determine transformer temperature rise
Explanation - The short-circuit test measures the voltage drop and current under shorted conditions to calculate impedance.
Correct answer is: Determine impedance and percent impedance
Q.106 Which of the following devices is used to 'detect overcurrent in DC circuits'?
Thermal relay
DC breaker
Fuse holder
Voltage relay
Explanation - DC breakers are designed to interrupt high-current faults in direct current circuits.
Correct answer is: DC breaker
Q.107 A 'remote controlled circuit breaker' allows operators to:
Open and close the breaker from a central location
Measure current without contact
Detect overvoltage conditions
Set the breaker trip time
Explanation - Remote control enables safe operation of breakers without physical presence at the location.
Correct answer is: Open and close the breaker from a central location
Q.108 Which device is used to provide a 'slow fault clearing time' in motor circuits?
Thermal overload relay
Inverse time relay
Voltage relay
Ground fault relay
Explanation - Thermal overload relays are designed to trip after a sustained overcurrent, protecting motors.
Correct answer is: Thermal overload relay
Q.109 A 'surge arrester' is typically connected:
Across the transformer secondary
Across the transmission line
On the busbar
All of the above
Explanation - Surge arresters can be placed across various points to clamp voltage spikes.
Correct answer is: All of the above
Q.110 Which power apparatus is used to 'limit the current during a fault without interruption of the load'?
Synchronous condenser
Circuit breaker
Load tap changer
Fuse holder
Explanation - Synchronous condensers provide reactive power and can limit fault currents by controlling reactive power output.
Correct answer is: Synchronous condenser
Q.111 The 'neutral to ground resistor' is installed to:
Reduce fault currents to earth
Increase fault current
Protect against overvoltage
Control transformer voltage
Explanation - Installing a neutral grounding resistor limits the magnitude of fault currents flowing to earth.
Correct answer is: Reduce fault currents to earth
Q.112 A 'busbar' in a power system is primarily made of:
Aluminium
Copper
Steel
Plastic
Explanation - Busbars are typically copper for high conductivity and mechanical strength.
Correct answer is: Copper
Q.113 Which device can be used to 'measure the phase angle between voltage and current' in a power system?
Power quality analyzer
Voltage sensor
Current transformer
Fuse holder
Explanation - Power quality analyzers can measure voltage, current, and phase angles for power factor calculation.
Correct answer is: Power quality analyzer
Q.114 The primary function of a 'load tap changer' is to:
Adjust the transformer voltage under load
Measure load current
Isolate the load from the source
Protect against overvoltage
Explanation - Load tap changers change the transformer turns ratio to maintain voltage under varying load.
Correct answer is: Adjust the transformer voltage under load
Q.115 Which apparatus is used to 'prevent arc flash in a high-voltage circuit breaker'?
Arc suppression chamber
Fuse
Ground fault relay
Disconnect switch
Explanation - Arc suppression chambers are designed to contain and extinguish arcs safely during breaker operation.
Correct answer is: Arc suppression chamber
Q.116 A 'high-voltage disconnect switch' can be safely operated when:
The circuit is live
The circuit is dead
Both of the above
Neither of the above
Explanation - High-voltage disconnect switches can be operated on energized circuits for safety isolation.
Correct answer is: Both of the above
Q.117 Which device is used to 'prevent the opening of a circuit breaker during a short fault'?
Time delay relay
Inverse time relay
Voltage relay
Overcurrent relay
Explanation - Time delay relays delay the trip operation to avoid nuisance tripping during transient faults.
Correct answer is: Time delay relay
Q.118 Which apparatus is used for 'isolating a faulted section of a network from the rest of the system'?
Circuit breaker
Fuse
Disconnect switch
Shunt capacitor
Explanation - Circuit breakers can isolate faulted sections, allowing the rest of the system to continue operating.
Correct answer is: Circuit breaker
Q.119 Which device is used to 'measure the temperature rise of a transformer winding'?
Thermocouple
Fuse holder
Voltage meter
Frequency meter
Explanation - Thermocouples provide real-time temperature readings for protective relays.
Correct answer is: Thermocouple
Q.120 Which apparatus is used to 'interrupt fault currents in a high voltage circuit'?
Circuit breaker
Fuse
Disconnect switch
Surge arrester
Explanation - Circuit breakers are designed to interrupt fault currents safely in high voltage systems.
Correct answer is: Circuit breaker
Q.121 Which device is used to detect an 'overvoltage condition' in a power system?
Overvoltage relay
Under-voltage relay
Current transformer
Thermocouple
Explanation - Overvoltage relays monitor voltage and trigger protective actions when the voltage exceeds set limits.
Correct answer is: Overvoltage relay
Q.122 A 'neutral grounding resistor' is installed in a power system to:
Limit the fault current to earth
Increase the fault current to earth
Prevent overvoltage
Reduce reactive power losses
Explanation - Installing a neutral grounding resistor reduces fault currents by providing a higher impedance path to earth.
Correct answer is: Limit the fault current to earth
Q.123 Which device can be used to 'measure the voltage difference between two points'?
Voltmeter
Clamp meter
Thermocouple
Frequency meter
Explanation - A voltmeter measures the potential difference directly between two points in a circuit.
Correct answer is: Voltmeter
Q.124 Which apparatus is used to 'disconnect a circuit while it remains live for maintenance'?
Disconnect switch
Fuse holder
Voltage relay
Ground fault relay
Explanation - Disconnect switches allow isolation of live circuits for maintenance without breaking the circuit.
Correct answer is: Disconnect switch
Q.125 What is the main advantage of a 'vacuum circuit breaker'?
Fast fault interruption with no arc
Low cost
Ability to handle DC faults
Simple mechanical operation
Explanation - Vacuum circuit breakers extinguish arcs quickly in a vacuum, enhancing safety and reliability.
Correct answer is: Fast fault interruption with no arc
Q.126 A 'transformer tap changer' can be operated in a:
Manual mode
Automatic mode
Both manual and automatic modes
None of the above
Explanation - Tap changers can be manually switched or automatically controlled based on system conditions.
Correct answer is: Both manual and automatic modes
Q.127 Which device is used to 'interrupt the circuit when a fault to ground is detected'?
Ground fault relay
Overcurrent relay
Under-voltage relay
Voltage relay
Explanation - Ground fault relays detect imbalance to ground and trigger a circuit breaker to interrupt the fault.
Correct answer is: Ground fault relay
Q.128 Which apparatus is used to provide a 'low impedance path to ground' for fault currents?
Neutral grounding resistor
Shunt capacitor
Fuse holder
Voltage regulator
Explanation - Neutral grounding resistors provide a low impedance path to ground, limiting fault currents.
Correct answer is: Neutral grounding resistor
Q.129 A 'load tap changer' is typically found on:
Transformers
Circuit breakers
Fuses
Shunt capacitors
Explanation - Load tap changers are attached to transformers to adjust the secondary voltage under load.
Correct answer is: Transformers
Q.130 Which device is used to measure the 'temperature rise' of a transformer under load?
Thermocouple
Fuse holder
Voltage meter
Frequency meter
Explanation - Thermocouples provide continuous temperature measurements for transformer protection relays.
Correct answer is: Thermocouple
Q.131 Which device is used to 'prevent a transformer from overheating due to overcurrent'?
Thermal overload relay
Overcurrent relay
Ground fault relay
Voltage relay
Explanation - Thermal overload relays open the circuit if the temperature exceeds safe limits, protecting transformers.
Correct answer is: Thermal overload relay
Q.132 A 'shunt capacitor bank' is used to:
Improve the power factor
Reduce the voltage rise due to reactive power
Increase the fault current
Both a and b
Explanation - Shunt capacitors provide leading reactive power, improving power factor and reducing voltage rise.
Correct answer is: Both a and b
Q.133 Which device is used to measure the 'current flow' without breaking the circuit?
Clamp meter
Fuse holder
Voltage meter
Thermocouple
Explanation - Clamp meters use magnetic induction to measure current in a live conductor without contact.
Correct answer is: Clamp meter
Q.134 Which power apparatus is used to provide a 'low-resistance connection to ground' during fault conditions?
Neutral grounding resistor
Shunt capacitor
Fuse holder
Circuit breaker
Explanation - Neutral grounding resistors provide a low-resistance path, limiting fault current and improving fault detection.
Correct answer is: Neutral grounding resistor
Q.135 The term 'short-circuit current' refers to:
The maximum current a circuit can carry under normal conditions
The current that flows when the circuit is shorted
The current that flows during a fault to ground
The current that flows during overvoltage
Explanation - Short-circuit current is the high current that flows when a circuit is shorted, causing potential damage.
Correct answer is: The current that flows when the circuit is shorted
Q.136 A 'power factor relay' is used to:
Detect and trip on poor power factor
Detect overcurrent
Detect overvoltage
Detect under-voltage
Explanation - Power factor relays monitor the power factor and initiate protective actions if it falls below a set threshold.
Correct answer is: Detect and trip on poor power factor
Q.137 Which device is used to detect an 'overvoltage condition' and trip the breaker?
Overvoltage relay
Under-voltage relay
Overcurrent relay
Ground fault relay
Explanation - The overvoltage relay monitors the voltage level and opens the circuit when the voltage exceeds its set limits.
Correct answer is: Overvoltage relay
Q.138 Which apparatus is used to 'provide a temporary isolation for maintenance' in a power system?
Disconnect switch
Circuit breaker
Fuse holder
Shunt capacitor
Explanation - Disconnect switches isolate a circuit while it remains live, allowing safe maintenance procedures.
Correct answer is: Disconnect switch
Q.139 Which device is used to 'limit the fault current in a high voltage circuit'?
Circuit breaker
Fuse
Shunt capacitor
Ground fault relay
Explanation - Circuit breakers interrupt high fault currents and protect the system from damage.
Correct answer is: Circuit breaker
Q.140 What is the purpose of a 'neutral grounding resistor'?
To limit fault currents to the ground
To increase fault currents
To provide a low impedance path to ground
To provide high impedance to the ground
Explanation - The resistor limits the magnitude of fault currents flowing to earth during a fault.
Correct answer is: To limit fault currents to the ground
Q.141 Which apparatus is used to measure the 'voltage drop' across a power line?
Voltmeter
Clamp meter
Thermocouple
Frequency meter
Explanation - A voltmeter directly measures the potential difference between two points in a circuit.
Correct answer is: Voltmeter
Q.142 Which device can be used to 'detect the fault current' in a high voltage circuit?
Current transformer
Voltage sensor
Fuse holder
Shunt capacitor
Explanation - Current transformers provide a scaled-down current signal for protection relays to detect fault currents.
Correct answer is: Current transformer
Q.143 A 'safety relay' is used to:
Protect personnel from live circuits
Protect equipment from overload
Protect equipment from under-voltage
Protect equipment from over-voltage
Explanation - Safety relays ensure that circuits are isolated for maintenance and personnel safety.
Correct answer is: Protect personnel from live circuits
Q.144 Which device is used to 'prevent the opening of a circuit breaker during a short fault'?
Time delay relay
Inverse time relay
Voltage relay
Ground fault relay
Explanation - Time delay relays provide a delay before tripping, preventing nuisance operations during transient faults.
Correct answer is: Time delay relay
Q.145 Which of the following devices is used to measure the 'temperature rise' of a transformer under load?
Thermocouple
Fuse holder
Voltage meter
Frequency meter
Explanation - Thermocouples provide temperature data for protective relays to monitor transformer health.
Correct answer is: Thermocouple
Q.146 Which apparatus is used to 'provide a low-resistance path for fault currents'?
Neutral grounding resistor
Shunt capacitor
Fuse holder
Voltage regulator
Explanation - The resistor offers a low-resistance route to earth during faults, limiting fault currents.
Correct answer is: Neutral grounding resistor
Q.147 A 'short-circuit test' is performed on a transformer to:
Measure core losses
Determine impedance and percent impedance
Measure open-circuit voltage
Measure temperature rise
Explanation - Short-circuit tests provide data on transformer impedance by applying a low voltage while shorting the secondary.
Correct answer is: Determine impedance and percent impedance
Q.148 Which device is used to measure the 'current flowing through a conductor' without contact?
Clamp meter
Fuse holder
Voltage meter
Thermocouple
Explanation - Clamp meters use magnetic induction to measure current in a live conductor without breaking the circuit.
Correct answer is: Clamp meter
Q.149 Which apparatus can be used to 'isolate a faulted section of a network' while it remains live?
Circuit breaker
Fuse
Disconnect switch
Shunt capacitor
Explanation - Disconnect switches are used to isolate circuits for maintenance even when the circuit is energized.
Correct answer is: Disconnect switch
Q.150 The main function of a 'ground fault relay' is to:
Detect fault to ground and trip a circuit breaker
Detect overcurrent
Detect overvoltage
Detect under-voltage
Explanation - Ground fault relays sense imbalance between phase currents and earth, triggering the breaker.
Correct answer is: Detect fault to ground and trip a circuit breaker
Q.151 Which apparatus can be used to 'provide a temporary isolation for maintenance' in a power system?
Disconnect switch
Circuit breaker
Fuse holder
Shunt capacitor
Explanation - Disconnect switches allow a circuit to be isolated while it remains live, enabling safe maintenance.
Correct answer is: Disconnect switch
Q.152 A 'high-voltage circuit breaker' is designed to interrupt:
Normal load currents only
Fault currents only
Both normal and fault currents
Only short-circuit currents
Explanation - High-voltage circuit breakers are designed to handle normal operating currents and fault-level currents.
Correct answer is: Both normal and fault currents
Q.153 Which device is used to measure the 'voltage difference' between two points in a circuit?
Voltmeter
Clamp meter
Thermocouple
Frequency meter
Explanation - A voltmeter directly measures the potential difference between two points.
Correct answer is: Voltmeter
Q.154 Which apparatus is used to 'interrupt high fault currents' in a high voltage circuit?
Circuit breaker
Fuse
Disconnect switch
Shunt capacitor
Explanation - Circuit breakers are specifically designed to interrupt high fault currents safely.
Correct answer is: Circuit breaker
Q.155 Which device is used to 'prevent overcurrent by melting a metal alloy'?
Fuse
Circuit breaker
Disconnect switch
Ground fault relay
Explanation - Fuses rely on a fusible element that melts under excessive current, interrupting the circuit.
Correct answer is: Fuse
Q.156 A 'load tap changer' is typically found on a:
Transformer
Circuit breaker
Fuse holder
Shunt capacitor
Explanation - Load tap changers are installed on transformers to adjust the secondary voltage under load conditions.
Correct answer is: Transformer
Q.157 Which device is used to measure the 'current flowing through a conductor' without breaking the circuit?
Clamp meter
Fuse holder
Voltage meter
Thermocouple
Explanation - Clamp meters use magnetic induction to measure current without contact.
Correct answer is: Clamp meter
Q.158 What does a 'safety relay' do in a power system?
Protect personnel by isolating live circuits
Protect equipment from overcurrent
Detect under-voltage
Measure power quality
Explanation - Safety relays ensure circuits are isolated for safe maintenance and personnel protection.
Correct answer is: Protect personnel by isolating live circuits
Q.159 Which device is used to 'detect an overvoltage condition' and trip the breaker?
Overvoltage relay
Under-voltage relay
Overcurrent relay
Ground fault relay
Explanation - The overvoltage relay monitors voltage and initiates a trip when it exceeds a predetermined limit.
Correct answer is: Overvoltage relay
Q.160 Which apparatus can be used to 'provide a low-resistance path to earth' during a fault?
Neutral grounding resistor
Shunt capacitor
Fuse holder
Voltage regulator
Explanation - A neutral grounding resistor offers a low-resistance path to limit fault currents flowing to earth.
Correct answer is: Neutral grounding resistor
Q.161 Which device is used to 'measure the temperature rise of a transformer under load'?
Thermocouple
Fuse holder
Voltage meter
Frequency meter
Explanation - Thermocouples provide real-time temperature readings for protective relays in transformers.
Correct answer is: Thermocouple
Q.162 Which apparatus is used to 'prevent the opening of a circuit breaker during a short fault'?
Time delay relay
Inverse time relay
Voltage relay
Ground fault relay
Explanation - Time delay relays delay tripping to avoid nuisance operations during transient faults.
Correct answer is: Time delay relay
Q.163 Which device is used to measure the 'voltage difference' between two points in a circuit?
Voltmeter
Clamp meter
Thermocouple
Frequency meter
Explanation - Voltmeter directly measures the potential difference between two points in a circuit.
Correct answer is: Voltmeter
Q.164 Which apparatus is used to 'interrupt high fault currents' in a power system?
Circuit breaker
Fuse
Disconnect switch
Shunt capacitor
Explanation - Circuit breakers interrupt fault currents to protect the system and equipment.
Correct answer is: Circuit breaker