Q.1 Which device is commonly used to limit voltage sags caused by sudden load changes?
Surge arrester
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Uninterruptible Power Supply (UPS)
Explanation - A DVR injects a compensating voltage in series with the supply to restore the load voltage during sags, making it the preferred device for sag mitigation.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.2 What is the primary purpose of a Static Synchronous Compensator (STATCOM) in power quality improvement?
To provide harmonic filtering
To regulate voltage magnitude and reactive power
To protect against over‑current faults
To convert AC to DC power
Explanation - STATCOMs are shunt-connected FACTS devices that can quickly inject or absorb reactive power, thereby stabilising voltage levels and improving power quality.
Correct answer is: To regulate voltage magnitude and reactive power
Q.3 Which mitigation technique is most effective against voltage flicker caused by large motor start‑ups?
Installation of a capacitor bank
Using a soft‑starter with a ramp‑up control
Adding series reactors
Employing line‑side voltage regulators
Explanation - Soft‑starters gradually increase motor voltage, reducing the sudden inrush current that produces flicker, making them ideal for flicker mitigation.
Correct answer is: Using a soft‑starter with a ramp‑up control
Q.4 Harmonic distortion in a power system is most effectively reduced by:
Series reactors
Passive harmonic filters
Voltage regulators
Ground fault relays
Explanation - Passive filters, tuned to specific harmonic frequencies, provide low‑impedance paths for harmonics, thereby attenuating them.
Correct answer is: Passive harmonic filters
Q.5 A UPS provides power quality improvement mainly by:
Limiting short‑circuit currents
Eliminating voltage sags and supplying backup power
Reducing line-to-ground faults
Balancing three‑phase loads
Explanation - UPS units can ride‑through sags and supply uninterrupted power during outages, improving voltage stability and continuity of service.
Correct answer is: Eliminating voltage sags and supplying backup power
Q.6 Which of the following is a characteristic of a series‑connected Dynamic Voltage Restorer (DVR)?
It supplies reactive power only
It injects voltage in series with the supply line
It operates only during voltage swells
It provides frequency regulation
Explanation - A series‑connected DVR adds a compensating voltage directly in series with the feeder, enabling fast correction of sags, swells, and interruptions.
Correct answer is: It injects voltage in series with the supply line
Q.7 What is the main advantage of using a shunt Active Power Filter (APF) over a passive filter?
Lower cost
Simpler installation
Dynamic compensation of varying harmonic spectra
No need for a control system
Explanation - Active filters can adapt in real time to changes in harmonic content, whereas passive filters are fixed‑tuned and only effective at specific frequencies.
Correct answer is: Dynamic compensation of varying harmonic spectra
Q.8 Which power quality issue does a line‑side voltage regulator (LVR) primarily address?
Harmonic distortion
Voltage sags and swells
Frequency deviations
Neutral shift
Explanation - LVRs adjust the tap position of a transformer under load to maintain a constant output voltage, thus mitigating sags and swells.
Correct answer is: Voltage sags and swells
Q.9 A common method to mitigate voltage unbalance in a three‑phase system is:
Installing a delta‑connected transformer
Using a phase‑balancing transformer
Adding series capacitors
Deploying a static VAR compensator
Explanation - Phase‑balancing transformers (also known as zig‑zag transformers) redistribute the unbalanced currents, reducing voltage unbalance.
Correct answer is: Using a phase‑balancing transformer
Q.10 Which of the following devices can simultaneously provide harmonic filtering and reactive power support?
Series capacitor bank
Hybrid (active‑passive) filter
Voltage sag ride‑through controller
Lightning arrester
Explanation - Hybrid filters combine passive filter elements for low‑order harmonics and active components for dynamic compensation, also providing reactive power support.
Correct answer is: Hybrid (active‑passive) filter
Q.11 The term "Transient Voltage Suppressor (TVS) diode" is most closely associated with protection against:
Voltage sags
Voltage spikes from lightning
Harmonic distortion
Frequency variations
Explanation - TVS diodes clamp high‑energy voltage spikes, protecting sensitive equipment from transient over‑voltages such as those caused by lightning.
Correct answer is: Voltage spikes from lightning
Q.12 Which mitigation technique is employed to reduce the impact of voltage fluctuations caused by large non‑linear loads?
Installing a static VAR compensator
Using a dynamic voltage restorer
Applying a harmonic filter with a low‑pass characteristic
Implementing a ride‑through controller
Explanation - Low‑pass harmonic filters attenuate high‑frequency components generated by non‑linear loads, smoothing voltage fluctuations.
Correct answer is: Applying a harmonic filter with a low‑pass characteristic
Q.13 In power quality terminology, the "K factor" is used to rate:
The ability of a UPS to handle overloads
The harmonic content a transformer can tolerate
The voltage rating of surge arresters
The switching speed of a DVR
Explanation - The K factor indicates the level of harmonic currents a transformer can safely carry without overheating.
Correct answer is: The harmonic content a transformer can tolerate
Q.14 Which of the following best describes the function of a shunt‑connected STATCOM during a voltage dip?
It absorbs reactive power from the system
It injects reactive power to raise the voltage
It disconnects the load temporarily
It converts DC to AC power
Explanation - During a dip, a STATCOM rapidly supplies reactive power, boosting the local voltage and improving stability.
Correct answer is: It injects reactive power to raise the voltage
Q.15 What is the main disadvantage of using series capacitors for voltage sag mitigation?
They introduce resonance with system inductance
They cannot improve power factor
They require frequent maintenance
They increase harmonic distortion
Explanation - Series capacitors can create parallel resonance with system inductance, potentially amplifying certain harmonic frequencies.
Correct answer is: They introduce resonance with system inductance
Q.16 A common method to mitigate voltage swells caused by sudden load drop is:
Installing a dynamic voltage restorer (DVR)
Using a static VAR compensator (SVC)
Connecting a line‑side voltage regulator (LVR)
Deploying a harmonic filter
Explanation - A DVR can subtract voltage from the line during a swell, keeping the load voltage within limits.
Correct answer is: Installing a dynamic voltage restorer (DVR)
Q.17 Which device is specifically designed to protect equipment from transient over‑voltages caused by switching operations?
Surge protective device (SPD)
Static VAR compensator (SVC)
Dynamic voltage restorer (DVR)
Uninterruptible power supply (UPS)
Explanation - SPDs clamp high‑frequency transients generated by switching events, safeguarding downstream equipment.
Correct answer is: Surge protective device (SPD)
Q.18 What is the typical response time of a DVR to a voltage sag?
Less than 1 ms
10–20 ms
100–200 ms
1–2 seconds
Explanation - DVRs employ power electronic converters that can respond within microseconds, effectively eliminating the sag for most loads.
Correct answer is: Less than 1 ms
Q.19 Which mitigation technique is most suitable for addressing harmonic currents generated by a large number of variable‑frequency drives (VFDs)?
Passive harmonic filters tuned to 5th and 7th harmonics
Series reactors
Active Power Filters (APFs)
Voltage regulators
Explanation - APFs can adapt to the varying harmonic spectrum of VFDs, providing dynamic compensation that passive filters cannot achieve efficiently.
Correct answer is: Active Power Filters (APFs)
Q.20 In the context of power quality, the term "ride‑through" refers to:
The ability of a device to survive a short‑circuit fault
The capability of equipment to continue operating during voltage sags or frequency deviations
The process of filtering harmonics
The method of balancing three‑phase loads
Explanation - Ride‑through (or low‑voltage ride‑through) allows generators and loads to remain connected during brief disturbances, improving system stability.
Correct answer is: The capability of equipment to continue operating during voltage sags or frequency deviations
Q.21 A "soft‑starter" primarily helps mitigate which power quality problem?
Voltage unbalance
Voltage flicker caused by motor inrush
Harmonic distortion
Frequency drift
Explanation - Soft‑starters gradually ramp up voltage to motors, reducing the high inrush current that can cause flicker.
Correct answer is: Voltage flicker caused by motor inrush
Q.22 Which of the following is a drawback of using a passive harmonic filter in a weak grid?
It cannot filter low‑order harmonics
It may cause resonance with the grid impedance
It requires complex control algorithms
It increases voltage sag depth
Explanation - In weak grids, the interaction between filter reactance and grid impedance can create resonance, amplifying certain harmonic frequencies.
Correct answer is: It may cause resonance with the grid impedance
Q.23 Which power quality mitigation device is typically used in data‑center environments to guarantee uninterrupted operation?
Dynamic Voltage Restorer (DVR)
Uninterruptible Power Supply (UPS)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Explanation - UPS systems provide battery backup and voltage conditioning, ensuring continuous operation of critical data‑center equipment.
Correct answer is: Uninterruptible Power Supply (UPS)
Q.24 What is the main purpose of a neutral‑grounding transformer (NGT) in power quality improvement?
To limit fault currents during ground faults
To provide harmonic filtering
To regulate voltage magnitude
To balance three‑phase loads
Explanation - NGTs provide a path for zero‑sequence currents, controlling ground fault current magnitude and protecting equipment.
Correct answer is: To limit fault currents during ground faults
Q.25 A "phase‑shifting transformer" is primarily used to mitigate:
Voltage sags
Harmonic resonance
Voltage unbalance
Frequency deviation
Explanation - Phase‑shifting transformers change the phase angle between parallel paths, reducing the likelihood of resonant harmonic amplification.
Correct answer is: Harmonic resonance
Q.26 Which of the following is an advantage of using an active power filter (APF) over a DVR for harmonic mitigation?
Lower initial cost
Ability to compensate both harmonics and reactive power
Simpler hardware
No need for a control system
Explanation - APFs can simultaneously filter harmonics and supply/absorb reactive power, whereas DVRs mainly address voltage sags/swells.
Correct answer is: Ability to compensate both harmonics and reactive power
Q.27 Which power quality issue is most effectively addressed by installing a line‑side voltage regulator (LVR) with tap‑changing capability?
Voltage sag
Voltage swell
Voltage fluctuation (slow variations)
Harmonic distortion
Explanation - LVRs adjust taps to correct slow‑changing voltage variations, keeping the load voltage within acceptable limits.
Correct answer is: Voltage fluctuation (slow variations)
Q.28 A "crowbar circuit" is used in power quality protection to:
Suppress voltage sags
Clamp over‑voltage transients
Filter harmonics
Balance three‑phase voltages
Explanation - Crowbar circuits provide a low‑impedance path that short‑circuits the supply during over‑voltage, protecting sensitive equipment.
Correct answer is: Clamp over‑voltage transients
Q.29 When selecting a harmonic filter, the term "tuned filter" refers to:
A filter that adjusts its resonance automatically
A filter designed for a specific harmonic frequency
A filter that operates over a wide frequency range
A filter that only works during voltage sags
Explanation - Tuned (or band‑pass) filters are resonant circuits set to attenuate a particular harmonic (e.g., 5th, 7th).
Correct answer is: A filter designed for a specific harmonic frequency
Q.30 Which mitigation technique can simultaneously improve voltage stability and reduce flicker caused by large inductive loads?
Installing a STATCOM
Using a series reactor
Deploying a surge arrester
Applying a passive harmonic filter
Explanation - STATCOMs can inject reactive power quickly, stabilising voltage and reducing flicker caused by inductive load variations.
Correct answer is: Installing a STATCOM
Q.31 A "rotating machine" equipped with a power‑electronic converter can be used for power quality mitigation. This configuration is known as:
Static VAR Compensator (SVC)
Rotating Converter
Dynamic Voltage Restorer (DVR)
Active Power Filter (APF)
Explanation - Rotating converters (e.g., motor‑generator sets) provide inertial energy storage and can supply reactive power, aiding in voltage support.
Correct answer is: Rotating Converter
Q.32 In power quality studies, the term "THD" stands for:
Total Harmonic Distortion
Transient Harmonic Deviation
Time‑varying Harmonic Distribution
Thermal Harmonic Derating
Explanation - THD quantifies the ratio of harmonic content to the fundamental component, indicating the severity of distortion.
Correct answer is: Total Harmonic Distortion
Q.33 Which device is specifically designed to limit the depth of voltage dips caused by utility faults?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Uninterruptible Power Supply (UPS)
Explanation - DVRs inject compensating voltage in series to raise the load voltage during dips, limiting dip depth.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.34 The primary function of a "series reactor" in a distribution network is to:
Increase short‑circuit current
Limit fault current and reduce inrush current
Provide harmonic filtering
Regulate voltage magnitude
Explanation - Series reactors add impedance, thereby limiting the magnitude of fault and inrush currents, improving system protection.
Correct answer is: Limit fault current and reduce inrush current
Q.35 Which power quality mitigation technique is most appropriate for a facility that experiences frequent voltage sags due to nearby heavy industry?
Installation of a STATCOM
Deployment of a Dynamic Voltage Restorer (DVR)
Use of a passive harmonic filter
Adding a surge protective device (SPD)
Explanation - A DVR can quickly compensate for sags, making it suitable for environments with recurrent sags caused by external loads.
Correct answer is: Deployment of a Dynamic Voltage Restorer (DVR)
Q.36 Which mitigation method can reduce the effect of voltage unbalance caused by single‑phase loads?
Phase‑balancing transformer
Series capacitor bank
Dynamic Voltage Restorer (DVR)
Active Power Filter (APF)
Explanation - Phase‑balancing transformers re‑distribute load currents among phases, reducing unbalance caused by uneven single‑phase loads.
Correct answer is: Phase‑balancing transformer
Q.37 A "Zig‑Zag transformer" is primarily used for:
Voltage regulation
Harmonic filtering
Neutral grounding and unbalance correction
Frequency conversion
Explanation - Zig‑zag connections provide a grounded neutral and help mitigate unbalance by circulating zero‑sequence currents.
Correct answer is: Neutral grounding and unbalance correction
Q.38 Which of the following devices can provide both voltage sag mitigation and power factor correction simultaneously?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Hybrid active‑passive filter
Uninterruptible Power Supply (UPS)
Explanation - Hybrid filters incorporate active circuitry for sag mitigation and passive components for power factor correction.
Correct answer is: Hybrid active‑passive filter
Q.39 When a power system experiences a voltage swell, the appropriate response by a DVR is to:
Inject additional voltage
Subtract voltage from the line
Increase reactive power output
Disconnect the load
Explanation - During a swell, the DVR generates a voltage opposite in phase to the excess, effectively reducing the net voltage at the load.
Correct answer is: Subtract voltage from the line
Q.40 Which mitigation technique is best suited for eliminating flicker caused by the operation of large arc furnaces?
Dynamic Voltage Restorer (DVR)
Soft‑starter with controlled ramp‑up
Active Power Filter (APF)
Voltage regulator with tap‑changing
Explanation - DVRs can instantly compensate for the rapid voltage changes caused by arc furnaces, thus eliminating flicker.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.41 The main advantage of a shunt‑connected STATCOM over a traditional capacitor bank is:
Lower cost
Higher harmonic filtering capability
Fast, continuous reactive power control without discrete steps
Ability to provide fault current
Explanation - STATCOMs can vary reactive power output continuously and rapidly, unlike capacitor banks that switch in discrete steps.
Correct answer is: Fast, continuous reactive power control without discrete steps
Q.42 Which device is typically installed at the service entrance to protect against both lightning and switching transients?
Surge Protective Device (SPD)
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Uninterruptible Power Supply (UPS)
Explanation - SPDs at the service entrance clamp over‑voltages from external sources such as lightning and switching events.
Correct answer is: Surge Protective Device (SPD)
Q.43 In a weak grid, which mitigation approach helps avoid resonance when using passive harmonic filters?
Increasing filter capacitance
Adding a damping resistor (detuned filter)
Using a series reactor only
Employing a larger transformer
Explanation - Detuned filters incorporate resistors to damp resonant peaks, preventing amplification of harmonics in weak grids.
Correct answer is: Adding a damping resistor (detuned filter)
Q.44 Which power quality issue is most directly addressed by installing a line‑reactor (inductor) in series with a feeder?
Voltage unbalance
Voltage sag
Inrush current limiting
Harmonic distortion
Explanation - Series reactors limit the rate of current rise during energisation, reducing inrush currents.
Correct answer is: Inrush current limiting
Q.45 A "dynamic voltage restorer" (DVR) is classified as which type of power electronic converter?
Voltage‑source converter (VSC)
Current‑source converter (CSC)
Hybrid converter
Matrix converter
Explanation - DVRs are built using voltage‑source converters that synthesize the required compensating voltage.
Correct answer is: Voltage‑source converter (VSC)
Q.46 What is the main benefit of using a multi‑level converter in a DVR for power quality applications?
Reduced total harmonic distortion in the output voltage
Lower cost compared to two‑level converters
Simpler control algorithms
Higher fault current capability
Explanation - Multi‑level converters produce output voltages with lower THD, improving the quality of voltage compensation.
Correct answer is: Reduced total harmonic distortion in the output voltage
Q.47 Which mitigation device is most suitable for correcting a low‑order (5th, 7th) harmonic problem in a medium‑voltage network?
Passive tuned filter
Series reactor
Dynamic Voltage Restorer (DVR)
Voltage regulator
Explanation - Passive tuned filters are designed to target specific low‑order harmonics efficiently in medium‑voltage systems.
Correct answer is: Passive tuned filter
Q.48 A "ride‑through capability" is a requirement for which type of generation equipment in many modern grids?
Wind turbines
Diesel generators
Steam turbines
Hydroelectric generators
Explanation - Grid codes often require wind turbines to stay connected during short voltage sags, ensuring system stability.
Correct answer is: Wind turbines
Q.49 Which of the following is a common symptom of excessive voltage unbalance in three‑phase motors?
Increased bearing temperature
Reduced harmonic distortion
Higher power factor
Lower line current
Explanation - Unbalance causes uneven magnetic forces, leading to higher mechanical stress and temperature rise in motor bearings.
Correct answer is: Increased bearing temperature
Q.50 In power quality mitigation, the term "detuned filter" refers to:
A filter that automatically adjusts its resonant frequency
A filter with added resistance to broaden the bandwidth and suppress resonance
A filter designed for high‑frequency transients only
A filter that works only during voltage sags
Explanation - Detuned filters include resistors to damp resonance peaks, preventing amplification of harmonics.
Correct answer is: A filter with added resistance to broaden the bandwidth and suppress resonance
Q.51 Which mitigation technique is most appropriate for limiting the effects of voltage fluctuations caused by rapid load changes in a micro‑grid?
Static VAR Compensator (SVC)
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Series capacitor bank
Explanation - SVCs can quickly adjust reactive power, stabilising voltage against rapid load variations in micro‑grids.
Correct answer is: Static VAR Compensator (SVC)
Q.52 The purpose of a "ground fault detector" in a power quality system is to:
Prevent voltage sags
Detect and isolate ground faults quickly
Filter harmonic currents
Regulate voltage magnitude
Explanation - Ground fault detectors sense zero‑sequence currents and trigger protective actions to isolate faults, preserving power quality.
Correct answer is: Detect and isolate ground faults quickly
Q.53 Which of the following devices can provide instantaneous voltage correction without storing energy?
Dynamic Voltage Restorer (DVR)
Battery Energy Storage System (BESS)
Flywheel energy storage
Rotating converter
Explanation - DVRs use power electronic converters to synthesize voltage instantly, without reliance on stored energy.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.54 Which mitigation device is specifically designed to protect against over‑voltages caused by capacitor bank switching?
Surge Protective Device (SPD)
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Active Power Filter (APF)
Explanation - SPDs clamp the transient over‑voltage generated when capacitor banks are switched on or off.
Correct answer is: Surge Protective Device (SPD)
Q.55 What is the typical operating principle of a "shunt active power filter" (APF)?
Injects compensating current into the line to cancel harmonics
Blocks harmonic currents using resonance
Stores energy in inductors to smooth voltage
Regulates frequency by varying speed of a motor
Explanation - Shunt APFs generate currents equal in magnitude but opposite in phase to the harmonic components, canceling them at the point of common coupling.
Correct answer is: Injects compensating current into the line to cancel harmonics
Q.56 In a distribution system, the use of "voltage ride‑through (VRT)" capability is primarily aimed at:
Preventing equipment shutdown during short voltage sags
Reducing harmonic distortion
Balancing phase currents
Increasing system frequency
Explanation - VRT allows generators and loads to remain connected through brief voltage sags, maintaining system stability.
Correct answer is: Preventing equipment shutdown during short voltage sags
Q.57 A "low‑order harmonic" typically refers to:
Harmonics with order ≤ 3
Harmonics with order 5, 7, 11, 13
All harmonics above the 15th order
Harmonics caused by DC offset
Explanation - Low‑order harmonics are the first few non‑fundamental frequencies that most significantly affect power quality.
Correct answer is: Harmonics with order 5, 7, 11, 13
Q.58 Which mitigation technique is most suitable for reducing voltage unbalance caused by asymmetrical line impedances?
Phase‑shifting transformer
Series capacitor bank
Dynamic Voltage Restorer (DVR)
Neutral grounding transformer
Explanation - Phase‑shifting transformers alter the phase angle between parallel paths, helping balance voltages despite impedance asymmetry.
Correct answer is: Phase‑shifting transformer
Q.59 When a power system suffers from a high level of third‑harmonic distortion, the most effective mitigation device is:
Passive tuned filter for 3rd harmonic
Series reactor
Active Power Filter (APF)
Voltage regulator
Explanation - APFs can dynamically cancel the 3rd harmonic regardless of load changes, whereas passive filters for the 3rd harmonic are rarely used due to resonance issues.
Correct answer is: Active Power Filter (APF)
Q.60 Which of the following statements about "frequency deviation" mitigation is true?
DVRs are used to correct frequency deviations
STATCOMs can provide some frequency support through active power control
Surge arresters limit frequency variations
Passive harmonic filters stabilize frequency
Explanation - While primarily reactive, STATCOMs can be configured to inject or absorb active power, aiding frequency regulation.
Correct answer is: STATCOMs can provide some frequency support through active power control
Q.61 A "crowbar protection" is typically employed in which type of equipment?
Transformers
Inverters and converters
Rotating machines
Surge protective devices
Explanation - Crowbar circuits protect power electronic devices from over‑voltage conditions by short‑circuiting the output momentarily.
Correct answer is: Inverters and converters
Q.62 Which power quality mitigation method can be used to improve the voltage profile in long radial distribution feeders?
Installation of series reactors
Deployment of voltage regulators (on‑load tap changers)
Use of passive harmonic filters
Adding shunt capacitors
Explanation - On‑load tap changers adjust transformer taps under load, compensating for voltage drop along long feeders.
Correct answer is: Deployment of voltage regulators (on‑load tap changers)
Q.63 Which device is most effective at mitigating voltage sags caused by short‑circuit faults on the utility side?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Series capacitor bank
Explanation - DVRs can quickly inject voltage to counteract sag caused by utility faults, preserving load voltage.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.64 Which mitigation technique can be used to reduce the impact of neutral shift in a three‑phase four‑wire system?
Installation of a neutral grounding resistor (NGR)
Use of a series reactor
Deployment of a DVR
Adding a passive harmonic filter
Explanation - NGR limits neutral current during unbalanced conditions, reducing neutral shift and associated voltage problems.
Correct answer is: Installation of a neutral grounding resistor (NGR)
Q.65 Which of the following is an advantage of a "multi‑pulse converter" in reducing harmonic generation?
It eliminates the need for any filters
Higher pulse numbers lower the harmonic spectrum amplitude
It reduces the cost of converters
It provides better voltage regulation
Explanation - Multi‑pulse converters (e.g., 12‑pulse) produce lower harmonic amplitudes due to phase‑shifted transformer arrangements.
Correct answer is: Higher pulse numbers lower the harmonic spectrum amplitude
Q.66 Which mitigation device is specifically designed to protect sensitive electronic loads from voltage spikes generated by lightning?
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Static VAR Compensator (SVC)
Active Power Filter (APF)
Explanation - SPDs clamp high‑energy transients, providing essential protection for sensitive electronics against lightning‑induced spikes.
Correct answer is: Surge Protective Device (SPD)
Q.67 In a power quality improvement scheme, the term "load‑side compensation" refers to:
Installing devices at the utility side of the meter
Placing mitigation equipment downstream of the main breaker, close to the load
Connecting filters in series with the supply line
Using only passive devices
Explanation - Load‑side compensation addresses power quality at the point of use, ensuring protection for downstream equipment.
Correct answer is: Placing mitigation equipment downstream of the main breaker, close to the load
Q.68 Which mitigation technique can help reduce the effect of voltage flicker caused by rapidly cycling electric heating elements?
Dynamic Voltage Restorer (DVR)
Soft‑starter
Phase‑balancing transformer
Series capacitor bank
Explanation - DVRs can instantly correct voltage dips and rises caused by fast‑cycling loads, mitigating flicker.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.69 A "static synchronous compensator" (STATCOM) is most similar in function to which traditional device?
Shunt capacitor bank
Series reactor
Voltage regulator
Transformer
Explanation - Both STATCOMs and shunt capacitors provide reactive power support, but STATCOMs offer fast, controllable compensation.
Correct answer is: Shunt capacitor bank
Q.70 Which power quality mitigation method is commonly used to address the problem of "over‑voltage" caused by capacitor bank switching in a substation?
Installation of a surge protective device (SPD)
Deployment of a Dynamic Voltage Restorer (DVR)
Use of a detuned passive filter
Adding a neutral grounding transformer
Explanation - SPDs limit the over‑voltage transients generated when capacitor banks are switched on or off.
Correct answer is: Installation of a surge protective device (SPD)
Q.71 When a system exhibits high total harmonic distortion (THD), the most immediate remedial action is:
Install a series reactor
Add an active power filter (APF)
Replace all loads with linear loads
Increase the system voltage
Explanation - APFs can quickly mitigate THD by injecting compensating currents, providing an immediate solution.
Correct answer is: Add an active power filter (APF)
Q.72 Which of the following devices can provide both voltage sag mitigation and power factor correction?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Hybrid active‑passive filter
Uninterruptible Power Supply (UPS)
Explanation - Hybrid filters combine active components for sag mitigation and passive elements for power factor correction.
Correct answer is: Hybrid active‑passive filter
Q.73 What is the main reason for installing a neutral grounding resistor (NGR) in a high‑voltage substation?
To limit fault current during ground faults
To improve power factor
To reduce voltage sags
To filter harmonics
Explanation - NGRs provide a controlled path for zero‑sequence currents, limiting ground fault currents and protecting equipment.
Correct answer is: To limit fault current during ground faults
Q.74 In the context of power quality, the term "flicker" is most closely associated with:
Rapid voltage variations that cause visible changes in lighting intensity
High‑frequency harmonic distortion
Frequency fluctuations in the supply
Neutral voltage shift
Explanation - Flicker is caused by short‑term voltage fluctuations that affect lighting, leading to perceptible changes.
Correct answer is: Rapid voltage variations that cause visible changes in lighting intensity
Q.75 Which mitigation technique can help prevent voltage dip propagation from a large motor starting event?
Soft‑starter with controlled ramp
Dynamic Voltage Restorer (DVR)
Series capacitor bank
Static VAR Compensator (SVC)
Explanation - Soft‑starters limit the inrush current of motors, reducing voltage dips that could propagate through the network.
Correct answer is: Soft‑starter with controlled ramp
Q.76 A "detuned filter" is often used in conjunction with which other device to improve overall power quality?
Active Power Filter (APF)
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Voltage regulator
Explanation - Detuned passive filters complement APFs by providing additional harmonic attenuation while avoiding resonance.
Correct answer is: Active Power Filter (APF)
Q.77 Which mitigation device is commonly employed to protect against over‑voltages caused by switching of large capacitor banks?
Surge Protective Device (SPD)
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Active Power Filter (APF)
Explanation - SPDs clamp the transient over‑voltage generated when capacitor banks are switched, protecting downstream equipment.
Correct answer is: Surge Protective Device (SPD)
Q.78 Which power quality mitigation approach can be used to limit voltage unbalance caused by asymmetrical loads in a three‑phase system?
Phase‑shifting transformer
Series reactor
Dynamic Voltage Restorer (DVR)
Passive harmonic filter
Explanation - Phase‑shifting transformers alter the phase relationship between parallel paths, balancing voltages despite load asymmetry.
Correct answer is: Phase‑shifting transformer
Q.79 In a power quality improvement plan, a "ride‑through" capability is primarily required for:
Wind turbines and solar inverters
Transformers
Capacitor banks
Voltage regulators
Explanation - Grid codes often mandate that renewable generators stay connected during short voltage sags, providing ride‑through capability.
Correct answer is: Wind turbines and solar inverters
Q.80 Which mitigation technique is most appropriate for correcting a low power factor caused by a large inductive load?
Installation of shunt capacitors
Deployment of a DVR
Use of a series reactor
Installation of a surge arrester
Explanation - Shunt capacitors provide leading reactive power, compensating the lagging reactive power of inductive loads and improving power factor.
Correct answer is: Installation of shunt capacitors
Q.81 Which device can be used to mitigate voltage sags as well as provide reactive power support in a distribution network?
Static VAR Compensator (SVC)
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Passive harmonic filter
Explanation - SVCs can rapidly inject reactive power to support voltage during sags and also improve overall voltage regulation.
Correct answer is: Static VAR Compensator (SVC)
Q.82 Which of the following is a key limitation of using series capacitors for voltage sag mitigation?
They cannot be used in three‑phase systems
They increase the risk of resonance with system inductance
They provide no reactive power support
They are ineffective against voltage swells
Explanation - Series capacitors can create parallel resonance with system inductance, potentially amplifying certain harmonic frequencies.
Correct answer is: They increase the risk of resonance with system inductance
Q.83 A "Dynamic Voltage Restorer" (DVR) primarily uses which type of power electronic converter topology?
Voltage‑source converter (VSC)
Current‑source converter (CSC)
Hybrid converter
Matrix converter
Explanation - DVRs employ VSCs to synthesize the compensating voltage needed for sag/swells correction.
Correct answer is: Voltage‑source converter (VSC)
Q.84 Which mitigation method is most effective for reducing the impact of high‑frequency transients caused by lightning strikes?
Surge Protective Device (SPD)
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Passive harmonic filter
Explanation - SPDs are designed to clamp high‑frequency transient over‑voltages generated by lightning.
Correct answer is: Surge Protective Device (SPD)
Q.85 Which of the following devices can be used to improve voltage quality by providing both real and reactive power support during short disturbances?
Battery Energy Storage System (BESS)
Static VAR Compensator (SVC)
Series capacitor bank
Passive harmonic filter
Explanation - BESS can inject real power and, when combined with power electronics, can also supply reactive power to support voltage during disturbances.
Correct answer is: Battery Energy Storage System (BESS)
Q.86 Which mitigation device is specifically designed to limit the depth of voltage dips caused by short‑circuit faults on the utility side?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Series reactor
Explanation - DVRs can quickly inject a compensating voltage to maintain load voltage during utility‑side faults.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.87 Which mitigation technique can be applied to reduce the harmonic distortion caused by a large number of variable‑frequency drives (VFDs) in an industrial plant?
Active Power Filter (APF)
Series reactor
Dynamic Voltage Restorer (DVR)
Voltage regulator
Explanation - APFs dynamically cancel harmonics generated by VFDs, offering a flexible solution for varying harmonic spectra.
Correct answer is: Active Power Filter (APF)
Q.88 When designing a power quality mitigation scheme, the term "K factor" is used to describe:
The ability of a transformer to handle harmonic currents
The voltage rating of a surge arrester
The response time of a DVR
The power factor correction capacity of a capacitor bank
Explanation - A transformer's K factor indicates its capability to carry non‑sinusoidal (harmonic) currents without overheating.
Correct answer is: The ability of a transformer to handle harmonic currents
Q.89 Which device is most suitable for mitigating voltage unbalance in a three‑phase four‑wire system with a high neutral current?
Zig‑zag transformer
Series capacitor bank
Dynamic Voltage Restorer (DVR)
Active Power Filter (APF)
Explanation - Zig‑zag transformers provide a grounded neutral path and help balance phase voltages, reducing neutral currents.
Correct answer is: Zig‑zag transformer
Q.90 Which mitigation technique helps prevent voltage sags caused by the energisation of large transformer windings?
Soft‑starter
Inrush current limiter (ICL)
Dynamic Voltage Restorer (DVR)
Series reactor
Explanation - ICLs limit the initial magnetising current of transformers, reducing voltage sags during energisation.
Correct answer is: Inrush current limiter (ICL)
Q.91 What is the typical function of a "detuned passive filter" in a power quality system?
To broaden the filtering bandwidth and avoid resonance
To automatically adjust its resonant frequency
To store energy for voltage sag compensation
To regulate system frequency
Explanation - Detuned filters add resistance to the resonant circuit, damping resonances and extending the range of harmonic attenuation.
Correct answer is: To broaden the filtering bandwidth and avoid resonance
Q.92 Which mitigation approach can simultaneously address voltage sags, voltage swells, and harmonic distortion in a distribution network?
Hybrid active‑passive filter
Series capacitor bank
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Explanation - Hybrid filters combine active components for fast voltage compensation and passive components for harmonic filtering, covering all three issues.
Correct answer is: Hybrid active‑passive filter
Q.93 A "crowbar" circuit is most often employed to protect which part of a power electronic system?
The output stage of an inverter
The input transformer
The line voltage regulator
The harmonic filter
Explanation - Crowbar circuits provide a low‑impedance path across the inverter output during over‑voltage events, protecting semiconductor devices.
Correct answer is: The output stage of an inverter
Q.94 Which mitigation technique can be used to limit the effect of voltage fluctuations caused by large, intermittent industrial loads?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Series capacitor bank
Explanation - SVCs can quickly adjust reactive power, smoothing voltage variations caused by intermittent large loads.
Correct answer is: Static VAR Compensator (SVC)
Q.95 Which device is typically employed to mitigate the impact of neutral shift in a 4‑wire distribution system?
Neutral grounding resistor (NGR)
Series capacitor bank
Dynamic Voltage Restorer (DVR)
Active Power Filter (APF)
Explanation - NGR limits the neutral current during unbalanced conditions, reducing neutral voltage shift.
Correct answer is: Neutral grounding resistor (NGR)
Q.96 In power quality improvement, the term "ride‑through capability" primarily refers to:
The ability of a device to remain connected during short voltage sags
The capacity to filter high‑order harmonics
The speed of voltage regulation
The level of surge protection offered
Explanation - Ride‑through ensures generators or loads do not disconnect during transient voltage dips, helping maintain system stability.
Correct answer is: The ability of a device to remain connected during short voltage sags
Q.97 Which mitigation technique is most suitable for reducing the voltage unbalance caused by an unbalanced single‑phase load distribution?
Phase‑balancing transformer
Series reactor
Dynamic Voltage Restorer (DVR)
Passive harmonic filter
Explanation - Phase‑balancing transformers redistribute currents among phases, mitigating unbalance caused by uneven single‑phase loads.
Correct answer is: Phase‑balancing transformer
Q.98 Which of the following devices can provide instantaneous voltage correction without storing energy?
Dynamic Voltage Restorer (DVR)
Battery Energy Storage System (BESS)
Flywheel Energy Storage
Rotating Converter
Explanation - DVRs use power electronic converters to synthesize the required voltage instantly, without relying on stored energy.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.99 Which mitigation device is typically used to limit the depth of voltage sags caused by short‑circuit faults in the utility network?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Series capacitor bank
Explanation - A DVR can quickly inject compensating voltage during a fault, reducing the magnitude of the sag seen by the load.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.100 Which power quality mitigation method can simultaneously improve voltage profile and reduce flicker caused by large, fluctuating industrial loads?
Static VAR Compensator (SVC)
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Passive harmonic filter
Explanation - SVCs provide fast reactive power support, stabilising voltage and reducing flicker from fluctuating loads.
Correct answer is: Static VAR Compensator (SVC)
Q.101 Which mitigation technique is most effective against voltage spikes caused by sudden capacitor bank switching?
Surge Protective Device (SPD)
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Active Power Filter (APF)
Explanation - SPDs clamp the transient over‑voltage generated when capacitor banks are switched, protecting downstream equipment.
Correct answer is: Surge Protective Device (SPD)
Q.102 A "Dynamic Voltage Restorer" (DVR) can correct voltage sags by:
Injecting a series voltage in phase with the sag
Absorbing reactive power from the line
Switching off loads
Providing ground fault protection
Explanation - DVRs synthesize and inject a compensating voltage in series with the supply, restoring load voltage during a sag.
Correct answer is: Injecting a series voltage in phase with the sag
Q.103 Which mitigation technique can be used to reduce the effect of voltage unbalance caused by an unbalanced distribution feeder?
Phase‑shifting transformer
Series capacitor bank
Dynamic Voltage Restorer (DVR)
Passive harmonic filter
Explanation - Phase‑shifting transformers modify the phase angle between parallel feeder sections, helping balance voltages.
Correct answer is: Phase‑shifting transformer
Q.104 Which device provides fast reactive power compensation and is often used to mitigate voltage sags in industrial plants?
Static VAR Compensator (SVC)
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Passive harmonic filter
Explanation - SVCs can quickly inject reactive power, supporting voltage during sags and improving overall power quality.
Correct answer is: Static VAR Compensator (SVC)
Q.105 Which mitigation method is most suitable for reducing harmonic distortion caused by a large number of nonlinear loads in a factory?
Active Power Filter (APF)
Series reactor
Dynamic Voltage Restorer (DVR)
Voltage regulator
Explanation - APFs dynamically inject compensating currents, effectively cancelling harmonics from varying nonlinear loads.
Correct answer is: Active Power Filter (APF)
Q.106 Which device is commonly used to limit the impact of voltage sags caused by short‑circuit faults on the utility side?
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Series capacitor bank
Explanation - DVRs can instantly inject the necessary voltage to keep the load voltage within acceptable limits during utility faults.
Correct answer is: Dynamic Voltage Restorer (DVR)
Q.107 Which mitigation technique can be used to address voltage flicker caused by frequent start‑stop of large compressors?
Soft‑starter with controlled ramp
Dynamic Voltage Restorer (DVR)
Passive harmonic filter
Series reactor
Explanation - Soft‑starters limit the inrush current of compressors, reducing the voltage fluctuations that cause flicker.
Correct answer is: Soft‑starter with controlled ramp
Q.108 Which mitigation technique helps improve voltage stability in a weak grid with high impedance?
Static VAR Compensator (SVC)
Dynamic Voltage Restorer (DVR)
Surge Protective Device (SPD)
Series capacitor bank
Explanation - SVCs provide fast reactive power support, compensating for voltage drops typical in weak grids.
Correct answer is: Static VAR Compensator (SVC)
Q.109 The purpose of a "detuned filter" in conjunction with a passive harmonic filter is to:
Broaden the filter bandwidth and avoid resonance
Automatically adjust filter tuning
Store energy for voltage sag compensation
Regulate system frequency
Explanation - Detuned filters add damping resistance to prevent resonance with system impedances, extending the effective harmonic attenuation range.
Correct answer is: Broaden the filter bandwidth and avoid resonance
Q.110 Which mitigation device is most appropriate for protecting against voltage transients caused by lightning strikes?
Surge Protective Device (SPD)
Dynamic Voltage Restorer (DVR)
Static VAR Compensator (SVC)
Passive harmonic filter
Explanation - SPDs are specifically designed to clamp high‑energy, high‑frequency transients generated by lightning.
Correct answer is: Surge Protective Device (SPD)
Q.111 Which mitigation technique is best suited for correcting a low power factor caused by large inductive motors?
Shunt capacitor bank
Dynamic Voltage Restorer (DVR)
Series reactor
Surge arrester
Explanation - Capacitors supply leading reactive power, compensating the lagging reactive power of inductive motors and improving power factor.
Correct answer is: Shunt capacitor bank
Q.112 Which device can simultaneously mitigate voltage sags, swells, and provide harmonic filtering?
Hybrid active‑passive filter
Series capacitor bank
Static VAR Compensator (SVC)
Surge Protective Device (SPD)
Explanation - Hybrid filters combine active converters for fast voltage correction with passive components for harmonic attenuation.
Correct answer is: Hybrid active‑passive filter
Q.113 Which mitigation approach is most effective for limiting the depth of voltage dips caused by large motor starting currents?
Soft‑starter
Dynamic Voltage Restorer (DVR)
Series reactor
Passive harmonic filter
Explanation - Soft‑starters control the voltage applied to motors during start‑up, limiting inrush current and reducing voltage dips.
Correct answer is: Soft‑starter
Q.114 In a power quality improvement plan, a "crowbar circuit" is used to protect which component?
Power electronic converters (e.g., inverters)
Transformers
Surge arresters
Passive filters
Explanation - Crowbar circuits create a low‑impedance path across the converter output during over‑voltage events, safeguarding semiconductor devices.
Correct answer is: Power electronic converters (e.g., inverters)
Q.115 Which mitigation technique is most appropriate for reducing voltage unbalance caused by an asymmetrical distribution feeder?
Phase‑shifting transformer
Series reactor
Dynamic Voltage Restorer (DVR)
Passive harmonic filter
Explanation - Phase‑shifting transformers change the phase angle between parallel feeder sections, helping to balance voltages.
Correct answer is: Phase‑shifting transformer
Q.116 Which device provides instantaneous voltage support during short‑duration sags without storing energy?
Dynamic Voltage Restorer (DVR)
Battery Energy Storage System (BESS)
Flywheel energy storage
Rotating converter
Explanation - DVRs synthesize compensating voltage via power electronics, offering immediate voltage support without reliance on stored energy.
Correct answer is: Dynamic Voltage Restorer (DVR)