Q.1 What is the primary purpose of an insulation resistance test on a power transformer?
To measure the transformer's output voltage
To verify the winding resistance
To determine the insulation condition between windings and case
To assess the transformer's cooling fan speed
Explanation - An insulation resistance test (megger test) checks the integrity of the insulation between windings, case, and earth, ensuring the transformer can safely operate at rated voltage.
Correct answer is: To determine the insulation condition between windings and case
Q.2 Which device is primarily used for detecting overcurrent in a circuit breaker test?
Clamp meter
Voltage transformer
Ground fault detector
Current transformer (CT)
Explanation - During a circuit breaker test, a CT provides a scaled-down current that can be safely measured to determine if overcurrent protection functions correctly.
Correct answer is: Current transformer (CT)
Q.3 In a dielectric withstand test, what voltage is typically applied to a switchgear component?
10 kV
50 kV
100 kV
200 kV
Explanation - A dielectric withstand test, also called a high potential test, usually applies 100 kV to verify the insulating capability of switchgear components.
Correct answer is: 100 kV
Q.4 Which type of maintenance focuses on the inspection and servicing of components before failure occurs?
Corrective maintenance
Predictive maintenance
Preventive maintenance
Reliability-centered maintenance
Explanation - Preventive maintenance involves scheduled checks and servicing to prevent failures, distinguishing it from reactive approaches.
Correct answer is: Preventive maintenance
Q.5 What is the standard IEC test for assessing the insulation resistance of high voltage transformers?
IEC 60086
IEC 60068
IEC 60068-2-6
IEC 60068-2-1
Explanation - IEC 60068-2-6 specifies the method for measuring insulation resistance in high-voltage transformers using a megger.
Correct answer is: IEC 60068-2-6
Q.6 Which of the following is NOT a typical parameter measured during a power factor correction test?
Capacitance
Inductance
Resistance
Impedance
Explanation - Power factor correction mainly concerns reactive components (capacitance and inductance) and overall impedance; pure resistance is generally not a focus.
Correct answer is: Resistance
Q.7 What does a short-circuit current test on a transformer verify?
The transformer's winding resistance
The transformer's core saturation point
The transformer's ability to withstand fault currents
The transformer's voltage regulation
Explanation - The short-circuit test measures the transformer's voltage drop and current under fault conditions, ensuring it can handle the expected fault currents without damage.
Correct answer is: The transformer's ability to withstand fault currents
Q.8 Which testing method is used to determine the earth leakage current of a circuit breaker?
Ground fault test
Overload test
Short-circuit test
Thermal imaging test
Explanation - A ground fault test applies a known current to the earth terminal and measures leakage, verifying the circuit breaker’s protection against earth faults.
Correct answer is: Ground fault test
Q.9 When performing a motor windings resistance test, a very low resistance reading indicates:
Shorted windings
Open windings
Proper insulation
High resistance insulation
Explanation - Low resistance suggests that windings may be shorted or that a fault path has developed, potentially leading to overheating and failure.
Correct answer is: Shorted windings
Q.10 Which of the following is a key benefit of predictive maintenance using vibration analysis?
Reduces manual inspections entirely
Detects failures before they happen
Prevents all types of equipment failure
Increases equipment lifespan by 100%
Explanation - Vibration analysis can identify abnormal mechanical conditions indicating impending faults, allowing timely intervention.
Correct answer is: Detects failures before they happen
Q.11 What is the primary purpose of a relay testing device called a relay test set?
To generate high voltage for dielectric tests
To simulate fault conditions for relay operation
To measure temperature rise in motors
To calibrate CTs and VTs
Explanation - Relay test sets generate controlled electrical conditions to verify that protective relays operate correctly under simulated fault scenarios.
Correct answer is: To simulate fault conditions for relay operation
Q.12 Which component is primarily inspected during a visual inspection of a gas-insulated switchgear?
The cooling fan
The internal gas purity level
The physical condition of the gas seals
The transformer oil level
Explanation - Visual inspection focuses on the integrity of gas seals, ensuring there are no leaks or damage that could compromise insulation.
Correct answer is: The physical condition of the gas seals
Q.13 In the context of power apparatus maintenance, what does the term 'root cause analysis' refer to?
Identifying the primary source of a failure
Determining the most expensive component
Calculating the total downtime cost
Evaluating the quality of repair work
Explanation - Root cause analysis systematically investigates the underlying cause of a failure to prevent recurrence.
Correct answer is: Identifying the primary source of a failure
Q.14 Which of the following is a typical symptom of a failing power transformer core?
Increased oil temperature
High insulation resistance
Low neutral-to-ground voltage
Large noise and vibration
Explanation - Core problems often manifest as excess noise, vibration, and sometimes overheating, indicating magnetic flux issues.
Correct answer is: Large noise and vibration
Q.15 What type of test is performed to evaluate the mechanical strength of a circuit breaker’s contacts?
Electrical stress test
Mechanical pull test
Dielectric breakdown test
Thermal endurance test
Explanation - A mechanical pull test applies a force to the contacts to ensure they can withstand separation forces without deforming.
Correct answer is: Mechanical pull test
Q.16 Which parameter is NOT typically measured during a thermal imaging inspection of power apparatus?
Hot spot temperature
Ambient temperature
Oil viscosity
Voltage level
Explanation - Thermal imaging detects surface temperatures but does not measure oil viscosity directly.
Correct answer is: Oil viscosity
Q.17 In a high voltage circuit breaker, the 'trip time' is the duration between:
The breaker opening and the fault clearance
The fault occurrence and the relay trip signal
The relay activation and the breaker arc extinguishment
The breaker closing and the load reaching full current
Explanation - Trip time is the interval from relay activation to successful arc extinction and circuit interruption.
Correct answer is: The relay activation and the breaker arc extinguishment
Q.18 Which standard specifies the method for testing the electrical isolation of electrical installations up to 1000 V?
IEC 60065
IEC 60204-1
IEC 60870-5-101
IEC 60060-4
Explanation - IEC 60870-5-101 covers safety testing, including insulation resistance checks for installations up to 1000 V.
Correct answer is: IEC 60870-5-101
Q.19 What is the main advantage of using a digital insulation resistance tester over a traditional analog tester?
Higher maximum voltage
Simplified operation and data logging
Lower cost
Larger test range
Explanation - Digital testers provide automated readings, record-keeping, and easier interface, improving reliability of test data.
Correct answer is: Simplified operation and data logging
Q.20 When conducting a winding resistance test, which factor can significantly affect the measured resistance value?
Ambient temperature
Number of turns
Core material
Cooling fan speed
Explanation - Resistance increases with temperature; therefore, temperature correction factors are applied to obtain accurate values.
Correct answer is: Ambient temperature
Q.21 In a motor, an increase in no-load current typically indicates:
Reduced load
Improved insulation
Higher core losses
Lower speed
Explanation - Higher no-load current usually reflects increased core losses due to magnetic flux issues or aging insulation.
Correct answer is: Higher core losses
Q.22 Which maintenance activity is essential after a power transformer oil leak has been repaired?
Replace the transformer immediately
Test the transformer for phase balance
Replace the transformer core
Perform an insulation resistance test
Explanation - Oil leaks can compromise insulation; thus, an insulation test verifies the integrity of the transformer before operation.
Correct answer is: Perform an insulation resistance test
Q.23 What does the 'dielectric strength' of a material refer to?
Its ability to conduct electricity
The maximum voltage it can withstand without breakdown
The mechanical strength of the insulation
Its thermal conductivity
Explanation - Dielectric strength measures the insulating capability of a material under high voltage stress.
Correct answer is: The maximum voltage it can withstand without breakdown
Q.24 Which test is used to assess the arc resistance of a circuit breaker?
Arc flash test
Arc impedance test
Arc voltage test
Arc current test
Explanation - An arc impedance test measures the resistance presented by the breaker during an arc to evaluate its arc extinguishing performance.
Correct answer is: Arc impedance test
Q.25 What does a high voltage breakdown test of a gas insulated switchgear (GIS) confirm?
The cooling efficiency of the GIS
The integrity of the gas pressure
The insulation capability against high voltage stress
The mechanical strength of the busbar
Explanation - Breakdown tests apply a high voltage to verify that the GIS can withstand stress without initiating an arc or leakage.
Correct answer is: The insulation capability against high voltage stress
Q.26 During a preventive maintenance schedule, what is the purpose of cleaning the cooling fan of a transformer?
To reduce electrical noise
To improve air flow and cooling efficiency
To increase the transformer's voltage rating
To remove oil contamination
Explanation - Cleaning the fan removes dust and debris, ensuring proper cooling and preventing overheating.
Correct answer is: To improve air flow and cooling efficiency
Q.27 Which parameter is not directly measured in a thermal overload test of a circuit breaker?
Time to trip
Overcurrent value
Temperature rise in contacts
Load factor
Explanation - The thermal overload test focuses on current, time, and temperature; load factor is a separate performance metric.
Correct answer is: Load factor
Q.28 What is the main function of a fuse in a power distribution system?
To store electrical energy
To provide a backup power source
To protect against overcurrent by melting
To regulate voltage level
Explanation - Fuses interrupt the circuit by melting the fuse element when the current exceeds the rated value.
Correct answer is: To protect against overcurrent by melting
Q.29 Which type of test is used to evaluate the effectiveness of a grounding system?
Ground resistance test
Load test
Dielectric test
Vibration test
Explanation - A ground resistance test measures how easily current can flow into the earth, indicating grounding system efficacy.
Correct answer is: Ground resistance test
Q.30 During an oil sampling test for a transformer, what does a high dissolved gas analysis (DGA) level indicate?
Excellent insulation condition
Potential internal fault or overheating
Proper oil filtration
Low moisture content
Explanation - Elevated dissolved gases often result from transformer faults such as winding short circuits or overheating.
Correct answer is: Potential internal fault or overheating
Q.31 Which of the following best describes the concept of 'overcurrent protection coordination'?
Ensuring all breakers trip simultaneously
Setting up protection devices so that the nearest device operates first
Calibrating devices to trip at the highest current possible
Removing all interlocks between breakers
Explanation - Coordination ensures that only the device closest to the fault trips, protecting upstream equipment.
Correct answer is: Setting up protection devices so that the nearest device operates first
Q.32 What is the key purpose of a moisture analyzer in transformer oil testing?
To determine the oil's viscosity
To measure the water content in the oil
To check the oil's color
To evaluate the oil's temperature rise
Explanation - Moisture analyzer quantifies water concentration, which can affect insulation resistance and dielectric strength.
Correct answer is: To measure the water content in the oil
Q.33 Which component is most likely to be inspected during a 'coil winding inspection' of a transformer?
Core laminations
Terminal box
Winding insulation
Cooling fan
Explanation - Coil winding inspection focuses on the integrity and condition of the insulation layers around the windings.
Correct answer is: Winding insulation
Q.34 Which type of fault is a 'phase to ground' fault?
A fault between two phases
A fault between a phase and neutral
A fault between a phase and ground
A fault between two grounds
Explanation - Phase-to-ground faults involve a direct connection between a phase conductor and the earth or ground conductor.
Correct answer is: A fault between a phase and ground
Q.35 In a relay testing procedure, what is the function of the 'trip' test?
To ensure the relay opens the circuit under fault conditions
To verify the relay's temperature rise
To measure the relay's mechanical strength
To test the relay's voltage rating
Explanation - Trip tests simulate fault conditions to confirm that the relay can trigger breaker tripping in time.
Correct answer is: To ensure the relay opens the circuit under fault conditions
Q.36 Which of the following is a common symptom of a failing circuit breaker contact?
Low voltage output
High insulation resistance
Arc flash
Reduced oil level
Explanation - Failing contacts often generate arcs, which can cause flashovers, overheating, and potential safety hazards.
Correct answer is: Arc flash
Q.37 What is the typical test voltage applied during the insulation resistance test of a 10 kVA transformer?
200 V
500 V
1 kV
10 kV
Explanation - The test voltage is often a multiple of the transformer rating; for 10 kVA, a standard 1 kV is applied.
Correct answer is: 1 kV
Q.38 Which type of fault detection test is most effective for detecting high-impedance faults?
Ground fault test
Impedance test
Thermal test
Short-circuit test
Explanation - Impedance tests can identify faults with high impedance by measuring the voltage drop across the fault path.
Correct answer is: Impedance test
Q.39 During the preventive maintenance of a distribution board, why is it important to check the tightening torque of all terminal screws?
To ensure proper insulation
To prevent overheating due to loose connections
To maintain aesthetic appearance
To reduce electromagnetic interference
Explanation - Loose terminals increase resistance, causing heating and potential fire hazards.
Correct answer is: To prevent overheating due to loose connections
Q.40 Which parameter is most indicative of a transformer’s oil condition during a moisture test?
Water content
Temperature
Viscosity
Color
Explanation - Higher water content typically indicates oil contamination or degradation affecting dielectric properties.
Correct answer is: Water content
Q.41 The purpose of a 'current interruption' test on a circuit breaker is to:
Check the breaker's ability to start up
Verify the breaker can interrupt high current fault safely
Measure the breaker's voltage rating
Test the breaker’s mechanical wear
Explanation - Current interruption tests simulate fault currents to ensure the breaker can break the circuit without damage.
Correct answer is: Verify the breaker can interrupt high current fault safely
Q.42 In a typical maintenance procedure, when should a transformer’s insulation resistance be measured?
Only during commissioning
Every time the transformer is turned on
Annually and after any major event
Only when the transformer fails
Explanation - Regular yearly checks and post-incident tests help detect insulation degradation early.
Correct answer is: Annually and after any major event
Q.43 Which of these tests is used to evaluate the magnetic flux leakage in a transformer core?
Fluxmeter test
Oil viscosity test
Dielectric test
Temperature rise test
Explanation - A fluxmeter measures flux leakage, indicating core defects or misalignments.
Correct answer is: Fluxmeter test
Q.44 During an oil analysis, a sudden increase in hydrogen concentration typically indicates:
High moisture content
Presence of metal oxides
Partial discharge activity
Proper oil age
Explanation - Hydrogen is a gas produced by partial discharges inside the insulation.
Correct answer is: Partial discharge activity
Q.45 Which component is used in a high voltage circuit breaker to isolate the live circuit from the ground during operation?
Arc chute
Contact bar
Breaker latch
Ground rod
Explanation - Contact bars physically disconnect the live conductors from the grounded frame when the breaker opens.
Correct answer is: Contact bar
Q.46 What is the main advantage of using a 'rotating ring' test on a high voltage switchgear?
Simplifies the test setup
Provides a more realistic fault current path
Reduces testing time
Increases the maximum test voltage
Explanation - A rotating ring simulates a fault path around the switchgear, offering accurate fault current testing.
Correct answer is: Provides a more realistic fault current path
Q.47 Which test would you perform to detect 'differential current' faults in a transformer?
Dielectric test
Differential protection test
Oil viscosity test
Thermal imaging test
Explanation - Differential protection compares currents entering and leaving a transformer to detect imbalances.
Correct answer is: Differential protection test
Q.48 In the maintenance of an HVAC unit, why is it important to inspect the 'coolant level'?
To ensure proper mechanical pressure
To prevent overheating of compressors
To improve sound insulation
To maintain electrical grounding
Explanation - Low coolant reduces heat transfer, leading to compressor overheating and potential failure.
Correct answer is: To prevent overheating of compressors
Q.49 Which of the following best describes a 'partial discharge' in an electrical insulator?
A full-scale electrical fault
A localized ionization event within the insulation
A complete breakdown of the insulation
A high current surge across the entire insulator
Explanation - Partial discharge is a small, localized ionization that occurs without complete breakdown.
Correct answer is: A localized ionization event within the insulation
Q.50 During an arc flash hazard assessment, what factor is most important to calculate the incident energy level?
Ambient temperature
Fault current magnitude
Transformer oil viscosity
Number of conductors
Explanation - Incident energy is directly related to the available fault current and the duration of the arc.
Correct answer is: Fault current magnitude
Q.51 Which type of test is used to evaluate a circuit breaker’s ability to maintain contacts under high thermal stress?
Thermal overload test
Arc resistance test
Insulation test
Short-circuit test
Explanation - This test exposes the contacts to high temperatures to ensure they can handle thermal stress without degradation.
Correct answer is: Thermal overload test
Q.52 What is the role of a 'neutral grounding resistor' in a power distribution system?
To limit fault current during ground faults
To increase voltage regulation
To reduce system frequency
To improve transformer lifespan
Explanation - A grounding resistor limits the amount of current that can flow to earth during a fault, reducing arc flash risk.
Correct answer is: To limit fault current during ground faults
Q.53 In a high voltage transformer, what does an 'oil temperature rise' exceeding 5 °C during a short-circuit test indicate?
Excellent cooling
Possible internal fault or inadequate cooling
No issues
Low oil viscosity
Explanation - Excessive temperature rise during fault tests signals possible winding short or cooling problems.
Correct answer is: Possible internal fault or inadequate cooling
Q.54 Which of the following is NOT a standard for testing the insulation of electrical cables up to 10 kV?
IEC 60204-1
IEC 60287
IEC 60870-5-101
IEC 60755
Explanation - IEC 60287 relates to cable ampacity, not insulation testing.
Correct answer is: IEC 60287
Q.55 What is the main advantage of using an 'optical fiber' for fault detection in power lines?
High electrical conductivity
Real-time fault localization
Low installation cost
Easy manual inspection
Explanation - Optical fibers can detect fault-induced light changes, enabling accurate, immediate fault location.
Correct answer is: Real-time fault localization
Q.56 When performing a 'voltage ratio test' on a potential transformer, the test ensures that:
The transformer is correctly grounded
The output voltage matches the rated value
The voltage drop across the transformer is zero
The core saturation is avoided
Explanation - Voltage ratio test confirms the transformer's accuracy by comparing its output to its expected voltage.
Correct answer is: The output voltage matches the rated value
Q.57 Which of the following is a key indicator of insulation deterioration in a high voltage switchgear?
Low oil level
High insulation resistance readings
Visible cracks in the gas seal
Stable temperature profile
Explanation - Cracks indicate gas leaks, compromising the insulating environment inside the switchgear.
Correct answer is: Visible cracks in the gas seal
Q.58 In preventive maintenance, what is the primary purpose of checking the 'seal integrity' of a transformer tank?
To ensure mechanical strength
To maintain pressure and oil level
To prevent oil leaks and moisture ingress
To calibrate the transformer’s tap changer
Explanation - Seal integrity ensures no oil leaks or moisture contamination, preserving insulation performance.
Correct answer is: To prevent oil leaks and moisture ingress
Q.59 Which test is typically performed to determine the 'phase-to-phase' voltage tolerance of a circuit breaker?
Arc flash test
Dielectric withstand test
Voltage surge test
Short-circuit test
Explanation - Dielectric tests apply high voltage across phases to ensure the breaker can withstand phase-to-phase surges.
Correct answer is: Dielectric withstand test
Q.60 What is the typical response of a protective relay during a 'reverse-polarity' test?
No response, as reverse polarity is harmless
Immediate trip to open the circuit
Gradual current reduction
Activation of a warning flag
Explanation - Reverse-polarity conditions can cause damage; the relay trips to protect equipment.
Correct answer is: Immediate trip to open the circuit
Q.61 Which component is critical for controlling the arc extinction in a high voltage circuit breaker?
Contact busbar
Arc chute
Ground rod
Cooling fan
Explanation - The arc chute directs and quenches the arc, preventing it from damaging contacts.
Correct answer is: Arc chute
Q.62 When performing a 'hot spot temperature' measurement on a transformer using infrared thermography, what does a high temperature area indicate?
Good thermal performance
Cooling fan failure
Core saturation
Proper oil circulation
Explanation - Hot spots often correlate with core or winding overloading, indicating saturation or overheating.
Correct answer is: Core saturation
Q.63 Which of the following tests is most relevant for assessing the 'mechanical integrity' of a circuit breaker’s interlocking system?
Arc flash test
Mechanical pull test
Dielectric test
Temperature rise test
Explanation - A pull test verifies that the interlocking mechanism can physically hold the breaker in position under load.
Correct answer is: Mechanical pull test
Q.64 In a gas-insulated switchgear, what is the typical maximum gas pressure maintained during normal operation?
0.5 bar
1.0 bar
1.5 bar
2.0 bar
Explanation - GIS is usually operated at 1.0 bar above atmospheric pressure to maintain insulation quality.
Correct answer is: 1.0 bar
Q.65 Which of these is an essential safety precaution during high voltage dielectric testing?
Wear a grounding strap
Ensure all personnel are in the room
Close the breaker immediately
Use a high-voltage transformer
Explanation - Grounding straps protect testers against accidental shocks during high voltage tests.
Correct answer is: Wear a grounding strap
Q.66 During an oil analysis, a sudden increase in 'acetylene' levels suggests:
High moisture content
Mechanical wear
Partial discharge activity
Proper oil aging
Explanation - Acetylene is a gas formed during partial discharges, indicating insulation problems.
Correct answer is: Partial discharge activity
Q.67 Which of the following is a standard method to assess the 'temperature rise' in a transformer during operation?
Oil sampling
Temperature sensor measurement
Dielectric test
Insulation resistance test
Explanation - Temperature sensors or infrared cameras measure the actual temperature rise under load.
Correct answer is: Temperature sensor measurement
Q.68 In the maintenance of a motor, what is the primary reason for checking the 'bearing lubrication'?
To reduce electrical losses
To ensure low noise levels
To prevent mechanical wear and overheating
To increase motor speed
Explanation - Proper lubrication reduces friction, wear, and heat generation, extending bearing life.
Correct answer is: To prevent mechanical wear and overheating
Q.69 Which of the following parameters is most indicative of a transformer’s core loss?
Voltage regulation
Magnetic flux density
Core temperature
No-load current
Explanation - No-load current largely represents core losses (hysteresis and eddy currents).
Correct answer is: No-load current
Q.70 What is the purpose of a 'ground fault relay' in a power distribution panel?
To detect and interrupt faults between a phase and earth
To measure voltage levels
To regulate power factor
To increase system voltage
Explanation - A ground fault relay senses low-level currents to the earth and trips protective devices.
Correct answer is: To detect and interrupt faults between a phase and earth
Q.71 Which test ensures that a circuit breaker’s 'mechanical travel' meets design specifications?
Arc flash test
Mechanical pull test
Voltage ratio test
Thermal overload test
Explanation - This test checks the travel distance and mechanical strength of the breaker’s contacts.
Correct answer is: Mechanical pull test
Q.72 During a preventive maintenance inspection, what is the significance of checking the 'oil level' in a transformer?
To ensure proper mechanical strength of the tank
To verify the transformer’s cooling capability
To check the voltage rating
To adjust the core saturation
Explanation - Oil level affects heat dissipation; low oil can lead to overheating.
Correct answer is: To verify the transformer’s cooling capability
Q.73 Which of the following is the main goal of 'reliability-centered maintenance' for power equipment?
To replace all components annually
To focus on critical equipment based on failure probability
To eliminate all preventive maintenance
To reduce maintenance costs by ignoring faults
Explanation - Reliability-centered maintenance prioritizes equipment that poses the greatest risk and cost of failure.
Correct answer is: To focus on critical equipment based on failure probability
Q.74 Which of the following is NOT a typical outcome of a high voltage dielectric test on a power line?
Detection of insulation breakdown
Measurement of conductor temperature
Assessment of dielectric strength
Verification of insulation resistance
Explanation - Dielectric tests evaluate insulation, not temperature, which is measured separately.
Correct answer is: Measurement of conductor temperature
Q.75 What does a 'negative sequence current' in an electrical system indicate?
Balanced load conditions
Unbalanced load or fault conditions
No fault present
Perfect grounding
Explanation - Negative sequence currents arise when phases are unequal, often due to faults.
Correct answer is: Unbalanced load or fault conditions
Q.76 Which of the following tests is used to evaluate the 'short-circuit rating' of a circuit breaker?
Insulation resistance test
Short-circuit test
Voltage ratio test
Temperature rise test
Explanation - Short-circuit testing measures how much current the breaker can interrupt during a fault.
Correct answer is: Short-circuit test
Q.77 Which component in a transformer is responsible for reducing the voltage to a safer level for testing?
Primary winding
Secondary winding
Core
Tap changer
Explanation - The secondary winding typically provides a lower voltage that is safer for manual testing.
Correct answer is: Secondary winding
Q.78 In a 'phase-to-phase' short circuit test, what is the expected voltage drop across the transformer?
Zero volts
High voltage
Approximately the rated voltage
Negative voltage
Explanation - During a short-circuit, the voltage across the transformer will drop close to zero, showing the fault condition.
Correct answer is: Approximately the rated voltage
Q.79 Which of the following is a primary objective of a 'thermal imaging' inspection in power apparatus?
Detecting mechanical cracks
Measuring electrical resistance
Identifying hotspots and potential overheating
Assessing core saturation
Explanation - Thermal imaging reveals temperature anomalies that may indicate impending failures.
Correct answer is: Identifying hotspots and potential overheating
Q.80 What is the main difference between 'preventive' and 'corrective' maintenance?
Preventive maintenance is scheduled; corrective maintenance is reactive
Preventive maintenance is reactive; corrective is scheduled
Both are scheduled
Both are reactive
Explanation - Preventive maintenance anticipates failures, while corrective maintenance responds to actual failures.
Correct answer is: Preventive maintenance is scheduled; corrective maintenance is reactive
Q.81 During an oil sampling test, which parameter is most indicative of a transformer’s age?
Moisture content
Dissolved gas analysis (DGA) profile
Viscosity
Color
Explanation - The DGA profile changes predictably as oil ages and degrades.
Correct answer is: Dissolved gas analysis (DGA) profile
Q.82 Which of the following is a typical sign of a failing 'fuse element'?
Smooth metal surface
No visible changes
Burnt or melted core
Clear plastic housing
Explanation - When a fuse blows, the core melts, often leaving a darkened residue.
Correct answer is: Burnt or melted core
Q.83 What type of test would you perform to evaluate a circuit breaker’s 'arc extinction time'?
Voltage ratio test
Arc flash test
Short-circuit test
Insulation resistance test
Explanation - Arc flash tests measure how long the breaker takes to extinguish an arc during fault conditions.
Correct answer is: Arc flash test
Q.84 Which parameter is most directly affected by the 'core loss' in a transformer?
Voltage regulation
No-load current
Neutral-to-ground voltage
Temperature rise during operation
Explanation - Core loss manifests as no-load current that flows when the transformer is energized but unloaded.
Correct answer is: No-load current
Q.85 What is the primary reason for 'oil circulation' in a power transformer?
To maintain oil viscosity
To provide mechanical support for the core
To remove heat and maintain insulation temperature
To regulate voltage
Explanation - Oil circulates to carry heat away from the windings, keeping the transformer within safe temperature limits.
Correct answer is: To remove heat and maintain insulation temperature
Q.86 In a gas-insulated switchgear, what does a 'gas pressure test' verify?
Electrical connectivity between busbars
Integrity of the gas seal and insulation
The temperature of the gas
The oil level inside the switchgear
Explanation - The test confirms that the gas seal is intact and that the gas provides adequate insulation.
Correct answer is: Integrity of the gas seal and insulation
Q.87 Which of the following is a standard method for testing a transformer’s 'impedance voltage'?
Short-circuit test
No-load test
Oil sampling test
Dielectric test
Explanation - The short-circuit test determines the voltage required to produce rated current, revealing transformer impedance.
Correct answer is: Short-circuit test
Q.88 What is the purpose of performing a 'partial discharge' test on high voltage cables?
To confirm mechanical wear
To detect early insulation degradation
To measure current carrying capacity
To calibrate voltage regulators
Explanation - Partial discharge tests reveal insulation defects before they cause full-scale failure.
Correct answer is: To detect early insulation degradation
Q.89 Which of these is a common symptom of a 'ground fault' in a power distribution system?
Uniform voltage across all phases
Sudden voltage drop
Increased current on the ground path
Zero temperature rise
Explanation - A ground fault increases the current that flows to earth, triggering protective devices.
Correct answer is: Increased current on the ground path
Q.90 Which component is typically checked for 'wear' during the inspection of a circuit breaker?
Cooling fan
Contact bars
Transformer oil
Ground rod
Explanation - Contact bars are subject to wear from repeated opening and closing cycles.
Correct answer is: Contact bars
Q.91 During the preventive maintenance of a motor, why is it important to check the 'phase sequence'?
To ensure the motor rotates in the correct direction
To maintain transformer core balance
To reduce motor temperature rise
To avoid oil contamination
Explanation - Incorrect phase sequence can cause the motor to run in reverse or not start.
Correct answer is: To ensure the motor rotates in the correct direction
Q.92 Which of these parameters is most relevant for assessing the 'temperature stability' of a transformer’s insulation?
Oil viscosity
Ambient temperature
Core saturation level
Voltage regulation
Explanation - Oil viscosity influences heat transfer and thus insulation temperature stability.
Correct answer is: Oil viscosity
Q.93 What is the main function of a 'current transformer' in a protective relay setup?
To provide voltage to the relay
To reduce current to a manageable level for measurement
To increase current for fault detection
To convert AC to DC
Explanation - A CT scales down high currents so relays can safely measure them.
Correct answer is: To reduce current to a manageable level for measurement
Q.94 Which test would you use to evaluate the 'voltage withstand capability' of a high voltage switchgear component?
Short-circuit test
Arc flash test
Dielectric withstand test
Temperature rise test
Explanation - Dielectric tests subject the component to high voltage to assess its ability to withstand breakdown.
Correct answer is: Dielectric withstand test
Q.95 During a 'no-load test' of a transformer, a high voltage is applied to the primary winding. What is measured?
Core loss and magnetizing current
Short-circuit current
Voltage regulation
Temperature rise
Explanation - A no-load test assesses core loss by measuring magnetizing current while the transformer is unloaded.
Correct answer is: Core loss and magnetizing current
Q.96 What does an increased 'dissolved gas' concentration in transformer oil typically indicate?
Good insulation condition
Oil contamination with water
Possible partial discharge or overheating
Proper cooling
Explanation - Dissolved gases such as CO₂ and H₂S are produced during insulation breakdown or overheating.
Correct answer is: Possible partial discharge or overheating
Q.97 Which of the following tests is performed to determine the 'short-circuit voltage' of a transformer?
Insulation resistance test
Short-circuit test
Voltage ratio test
Temperature rise test
Explanation - The short-circuit test applies a reduced voltage until rated current flows, revealing the short-circuit voltage.
Correct answer is: Short-circuit test
Q.98 When inspecting a power transformer, which component’s 'crack' is most indicative of a possible mechanical failure?
Cooling fan blade
Oil filter
Core laminations
Vent cover
Explanation - Cracks in core laminations can lead to increased eddy currents and core loss, potentially causing failure.
Correct answer is: Core laminations
Q.99 Which of these tests is used to evaluate a relay’s 'inverse-time characteristic'?
Short-circuit test
Inverse-time test
Insulation resistance test
Temperature rise test
Explanation - An inverse-time test measures the delay of a relay in response to different current levels.
Correct answer is: Inverse-time test
Q.100 During preventive maintenance, which tool is essential for measuring the 'torque' of terminal screws?
Multimeter
Torque wrench
Clamp meter
Thermal camera
Explanation - A torque wrench ensures terminal screws are tightened to the specified torque for reliable connections.
Correct answer is: Torque wrench
Q.101 Which of the following is the main safety precaution when performing a 'short-circuit' test?
Use a high-voltage transformer
Ensure all personnel are at a safe distance
Close the breaker immediately
Use a grounding strap for the tester only
Explanation - Short-circuit tests involve high currents that can cause severe hazards; keeping personnel safe is paramount.
Correct answer is: Ensure all personnel are at a safe distance
Q.102 What is the typical purpose of a 'cooling fan' in a high voltage transformer?
To increase core saturation
To reduce oil viscosity
To dissipate heat from the transformer core and windings
To regulate voltage
Explanation - The cooling fan helps maintain safe operating temperatures by moving air around the transformer's external parts.
Correct answer is: To dissipate heat from the transformer core and windings
Q.103 Which of the following is a typical indication that a circuit breaker’s 'arc chute' is compromised?
No change in contact resistance
Visible scorch marks or discoloration
Higher voltage rating
Improved cooling
Explanation - Arcing can burn or discolor the arc chute, indicating it can no longer effectively extinguish arcs.
Correct answer is: Visible scorch marks or discoloration
Q.104 Which test is performed to evaluate the 'electrical isolation' between the transformer’s primary and secondary windings?
Insulation resistance test
Short-circuit test
No-load test
Voltage ratio test
Explanation - The insulation resistance test measures the resistance between windings to confirm electrical isolation.
Correct answer is: Insulation resistance test
Q.105 What does a 'phase-to-phase' fault typically result in?
A surge in neutral voltage
An increase in ground current
A loss of one phase
An increase in all phase voltages
Explanation - A phase-to-phase fault removes one phase from the circuit, causing a loss of supply to that phase.
Correct answer is: A loss of one phase
Q.106 Which of the following is a typical symptom of a 'high voltage' partial discharge in a cable?
No audible noise
Visible arc glow near the insulation
Increased resistance
Temperature drop
Explanation - Partial discharges produce faint glow or sparking near the insulation, indicating impending breakdown.
Correct answer is: Visible arc glow near the insulation
Q.107 Which parameter is most closely related to a transformer’s 'voltage regulation'?
No-load current
Short-circuit impedance
Core loss
Cooling fan speed
Explanation - Voltage regulation depends on how much voltage drops under load, which is directly linked to short-circuit impedance.
Correct answer is: Short-circuit impedance
Q.108 During the maintenance of a power switchgear, what is the main function of checking 'gas purity'?
Ensuring adequate electrical conduction
Preventing gas leakage
Maintaining the insulating properties of the gas
Increasing the pressure inside the switchgear
Explanation - Gas purity must be maintained to keep the gas’s dielectric strength, preventing breakdown.
Correct answer is: Maintaining the insulating properties of the gas
Q.109 Which of the following is a standard method to detect 'oil contamination' in a transformer?
Insulation resistance test
Oil color test
Short-circuit test
Voltage ratio test
Explanation - Oil color can indicate contamination or degradation, as oil becomes darker when contaminated.
Correct answer is: Oil color test
Q.110 What is the purpose of a 'safety interlock' on a circuit breaker?
To increase breaker speed
To prevent accidental opening of a closed circuit breaker
To measure voltage
To reduce core loss
Explanation - Safety interlocks ensure that breakers cannot be opened while live, protecting personnel and equipment.
Correct answer is: To prevent accidental opening of a closed circuit breaker
Q.111 Which of the following tests determines a transformer's 'no-load loss'?
Short-circuit test
No-load test
Voltage ratio test
Thermal imaging test
Explanation - A no-load test measures power consumed by the transformer when unloaded, revealing core loss.
Correct answer is: No-load test
Q.112 What is the main reason for performing a 'partial discharge' test on an electrical switchgear?
To evaluate mechanical wear
To detect early signs of insulation breakdown
To measure the voltage rating
To calibrate the breaker
Explanation - Partial discharge testing identifies small discharges that indicate insulation degradation before catastrophic failure.
Correct answer is: To detect early signs of insulation breakdown
Q.113 During preventive maintenance, why is it necessary to check the 'oil level' after a transformer has been in operation for a month?
Oil level affects transformer cooling
Oil level determines voltage rating
Oil level indicates mechanical wear
Oil level is irrelevant after a month
Explanation - Oil loss or evaporation reduces cooling efficiency, which can lead to overheating.
Correct answer is: Oil level affects transformer cooling
Q.114 Which component of a transformer is most likely to cause a 'short-circuit' if it becomes damaged?
Core laminations
Windings
Tap changer
Cooling fan
Explanation - Damaged windings can create a direct electrical short between conductors.
Correct answer is: Windings
Q.115 During the testing of a circuit breaker, a 'trip delay' is observed. This delay is most influenced by:
The breaker’s mechanical travel
The relay’s inverse-time characteristic
The voltage rating of the breaker
The core saturation level
Explanation - The relay’s inverse-time characteristic determines how long before it trips in response to a fault current.
Correct answer is: The relay’s inverse-time characteristic
Q.116 Which of the following is a sign that a transformer’s 'oil condition' is deteriorating?
Low viscosity
Clear color
High dissolved gas levels
Low temperature rise
Explanation - Elevated dissolved gases indicate degradation of oil and potential insulation failure.
Correct answer is: High dissolved gas levels
Q.117 What is the purpose of a 'neutral-to-ground resistor' in a power system?
To increase fault current
To limit fault current and reduce arc flash energy
To raise system voltage
To regulate power factor
Explanation - The resistor limits the current that can flow during a ground fault, reducing hazard.
Correct answer is: To limit fault current and reduce arc flash energy
Q.118 During the testing of a gas-insulated switchgear, a 'breakdown' test is performed by applying voltage across which element?
The gas chamber
The cooling fan
The transformer core
The terminal box
Explanation - Breakdown tests apply voltage across the gas chamber to assess dielectric strength of the gas.
Correct answer is: The gas chamber
Q.119 Which of the following tests is used to verify the 'voltage rating' of a relay?
Insulation resistance test
Voltage rating test
Short-circuit test
Temperature rise test
Explanation - A voltage rating test ensures the relay can handle the maximum voltage expected in its application.
Correct answer is: Voltage rating test
Q.120 In the maintenance of a motor, a sudden 'increase in motor noise' most likely indicates:
Improved lubrication
Bearing wear or imbalance
Reduced oil temperature
Lower load condition
Explanation - Excessive noise is often caused by bearing wear or imbalance in rotating machinery.
Correct answer is: Bearing wear or imbalance
Q.121 Which of the following is a common test to verify the 'short-circuit impedance' of a transformer?
Short-circuit test
No-load test
Voltage ratio test
Thermal imaging test
Explanation - The short-circuit test applies reduced voltage until rated current is achieved to determine impedance.
Correct answer is: Short-circuit test
Q.122 What is the primary function of a 'circuit breaker' in a power system?
To increase current flow
To disconnect the circuit during fault conditions
To regulate voltage
To reduce transformer core loss
Explanation - Circuit breakers interrupt the circuit when abnormal currents occur, protecting equipment.
Correct answer is: To disconnect the circuit during fault conditions
Q.123 Which of the following is a typical method for detecting 'oil contamination' in a transformer?
Insulation resistance test
Oil viscosity test
Short-circuit test
Voltage ratio test
Explanation - Viscosity changes can indicate contamination or aging of transformer oil.
Correct answer is: Oil viscosity test
Q.124 During a 'no-load' test of a transformer, the measured 'no-load current' primarily represents:
Copper loss
Core loss
Short-circuit current
Temperature rise
Explanation - No-load current is largely due to the magnetic core losses in the transformer.
Correct answer is: Core loss
Q.125 Which of the following is the most common type of fault in a power distribution line?
Ground fault
Phase-to-phase fault
Phase-to-neutral fault
All of the above
Explanation - Ground, phase-to-phase, and phase-to-neutral faults all occur frequently in distribution networks.
Correct answer is: All of the above
Q.126 In a gas-insulated switchgear, what is the primary role of 'gas purging'?
To fill the chamber with nitrogen
To remove moisture and improve dielectric strength
To cool the gas chamber
To increase gas pressure
Explanation - Purging removes water vapor and other contaminants to enhance the gas’s insulating properties.
Correct answer is: To remove moisture and improve dielectric strength
Q.127 Which of the following tests is commonly performed to assess the 'arc flash hazard' of a circuit breaker?
Arc flash test
Dielectric withstand test
Short-circuit test
Temperature rise test
Explanation - Arc flash tests simulate fault conditions to quantify incident energy and hazard levels.
Correct answer is: Arc flash test
Q.128 Which of these is NOT a typical step in the 'maintenance of a transformer'?
Oil sampling
Core inspection
Winding temperature measurement
Battery replacement
Explanation - Transformers do not contain batteries; maintenance involves oil, core, and winding checks.
Correct answer is: Battery replacement
Q.129 Which parameter is most affected by 'core loss' in a transformer?
Voltage regulation
No-load current
Neutral-to-ground voltage
Oil viscosity
Explanation - Core loss manifests as a current drawn by the transformer when it is energized but not loaded.
Correct answer is: No-load current
Q.130 What is the main purpose of an 'overcurrent protection device' in a power system?
To increase the system voltage
To monitor temperature
To disconnect the circuit when current exceeds a set threshold
To regulate power factor
Explanation - Overcurrent devices protect equipment by interrupting the circuit during overcurrent events.
Correct answer is: To disconnect the circuit when current exceeds a set threshold
Q.131 Which of the following is the most common cause of a transformer’s 'oil level' dropping during operation?
Mechanical leakage
Thermal expansion of the oil
Oil absorption by the core
Use of high-viscosity oil
Explanation - Leakage from seals or fittings reduces oil level, compromising cooling and insulation.
Correct answer is: Mechanical leakage
Q.132 During a 'dielectric test' on a power cable, what is the main safety concern?
Cable temperature rise
Cable length measurement
Cable insulation breakdown
Cable color change
Explanation - Dielectric testing can inadvertently cause insulation failure if the applied voltage is too high.
Correct answer is: Cable insulation breakdown
Q.133 Which component is tested with a 'high potential (HP) test' to ensure insulation integrity in high voltage equipment?
Cooling fan
Circuit breaker contacts
Insulation between conductors and chassis
Ground rod
Explanation - High potential testing subjects the insulation to high voltage to verify dielectric performance.
Correct answer is: Insulation between conductors and chassis
Q.134 During preventive maintenance of a transformer, why is it important to check 'core gap'?
To ensure accurate voltage regulation
To reduce core loss
To maintain oil temperature
To improve mechanical strength
Explanation - A core gap increases core loss; checking prevents inefficiencies and overheating.
Correct answer is: To reduce core loss
Q.135 Which of the following tests is used to verify a protective relay’s 'time-current characteristic'?
Short-circuit test
Time-current characteristic test
Insulation resistance test
Temperature rise test
Explanation - This test determines how the relay’s trip time varies with different fault currents.
Correct answer is: Time-current characteristic test
Q.136 What does a 'high oil temperature' in a transformer typically indicate?
Good cooling efficiency
Overloading or inadequate cooling
Low core loss
Proper insulation condition
Explanation - Elevated oil temperature is a sign of excessive heat generation due to overload or cooling issues.
Correct answer is: Overloading or inadequate cooling
Q.137 Which of the following is a typical indicator of 'partial discharge' activity in a power apparatus?
Increase in oil viscosity
Visible arc glow near insulation
Decreased temperature rise
Reduced voltage regulation
Explanation - Partial discharges often produce a faint glow or sparking at points of insulation weakness.
Correct answer is: Visible arc glow near insulation
Q.138 What is the purpose of a 'current transformer' in a protective relay system?
To step down high current for safe relay measurement
To step up voltage for relay operation
To measure temperature rise in the circuit
To increase current to trip the breaker
Explanation - The CT provides a reduced, proportional current that the relay can measure safely.
Correct answer is: To step down high current for safe relay measurement
Q.139 Which of the following is NOT a standard test for a circuit breaker’s 'arc resistance'?
Arc resistance test
Dielectric withstand test
Insulation resistance test
Thermal imaging test
Explanation - Arc resistance tests specifically measure resistance during an arc; thermal imaging does not.
Correct answer is: Thermal imaging test
Q.140 During the inspection of a power transformer, a 'crack' is found in the core laminations. What is the most likely consequence?
Increased core loss and overheating
Improved insulation
Reduced oil viscosity
Higher voltage regulation
Explanation - Cracks in core laminations lead to eddy currents, raising loss and temperature.
Correct answer is: Increased core loss and overheating
Q.141 Which of the following is a typical measure taken during preventive maintenance of a transformer to reduce the risk of oil contamination?
Replace the cooling fan regularly
Use a higher voltage rating
Seal the tank tightly and perform regular oil sampling
Increase the oil temperature
Explanation - Proper sealing and sampling detect leaks or contamination early, maintaining oil quality.
Correct answer is: Seal the tank tightly and perform regular oil sampling
Q.142 During a 'short-circuit' test, why is it important to apply a reduced voltage until rated current is achieved?
To avoid overheating the transformer
To ensure accurate measurement of short-circuit impedance
To increase core loss
To reduce the test duration
Explanation - Applying reduced voltage limits damage while still generating the required fault current for impedance calculation.
Correct answer is: To ensure accurate measurement of short-circuit impedance
Q.143 Which of the following is a typical symptom of a transformer’s 'oil aging'?
Decreased core loss
Higher oil viscosity
Lower temperature rise
Clear color of oil
Explanation - Aging oil tends to become thicker, increasing viscosity and reducing cooling efficiency.
Correct answer is: Higher oil viscosity
Q.144 What is the primary function of the 'neutral conductor' in a power distribution system?
To carry the majority of load current
To provide a return path for current
To increase voltage
To act as a ground for the entire system
Explanation - The neutral conductor connects the unbalanced load currents back to the source.
Correct answer is: To provide a return path for current
Q.145 Which of the following is a common method to reduce the risk of 'arc flash' incidents during maintenance?
Use a lower-rated transformer
Wear a full-body arc-rated protective suit
Avoid grounding the equipment
Use higher current test levels
Explanation - Arc-rated clothing protects personnel from high-energy arcs during maintenance work.
Correct answer is: Wear a full-body arc-rated protective suit
Q.146 During the testing of a high voltage cable, what is the purpose of measuring the 'partial discharge inception voltage' (PDIV)?
To determine the maximum current the cable can handle
To assess the cable’s insulation breakdown point
To measure the cable’s mechanical strength
To evaluate the cable’s voltage rating
Explanation - PDIV is the voltage at which partial discharges begin; it indicates insulation health.
Correct answer is: To assess the cable’s insulation breakdown point
Q.147 What does a 'voltage ratio test' primarily determine about a transformer?
Its core loss
Its voltage regulation
Its voltage transformation ratio
Its temperature rise
Explanation - The test measures how the input voltage is transformed to the output voltage, confirming the ratio.
Correct answer is: Its voltage transformation ratio
Q.148 In the context of protective relays, what is the definition of an 'inverse-time' characteristic?
A relay that trips faster at lower currents
A relay that trips slower at higher currents
A relay that trips faster at higher currents
A relay that is not time-dependent
Explanation - Inverse-time relays have a shorter delay as the fault current increases.
Correct answer is: A relay that trips faster at higher currents
Q.149 What is the main advantage of using a 'high voltage' transformer with a 'core gap' in certain applications?
Increased core loss
Higher voltage rating without saturating the core
Lower voltage regulation
Reduced cooling requirements
Explanation - A core gap reduces saturation, enabling higher voltage operation.
Correct answer is: Higher voltage rating without saturating the core
Q.150 Which of the following is an essential step during a 'dielectric strength' test of a power circuit breaker?
Applying a low voltage to the contacts
Applying a high voltage across the contacts until breakdown occurs
Measuring the temperature rise in the contacts
Inspecting the mechanical strength of the latch
Explanation - Dielectric strength tests subject the contacts to high voltage to confirm their insulating properties.
Correct answer is: Applying a high voltage across the contacts until breakdown occurs