Q.1 What is the most common source of harmonic distortion in residential electric utilities?
Industrial motors
Electric heating
Non‑linear loads such as rectifiers
Power factor correction capacitors
Explanation - Harmonics are produced mainly by non‑linear devices that draw current in pulses, such as rectifiers, inverters, and switching power supplies.
Correct answer is: Non‑linear loads such as rectifiers
Q.2 Which of the following best describes Total Harmonic Distortion (THD)?
Sum of all harmonic voltages divided by fundamental voltage
Sum of all harmonic currents divided by fundamental current
Ratio of harmonic power to total power
Ratio of the fundamental magnitude to the RMS magnitude
Explanation - THD is defined as the ratio of the RMS value of all harmonic components to the RMS value of the fundamental.
Correct answer is: Sum of all harmonic voltages divided by fundamental voltage
Q.3 A harmonic filter designed to reduce 5th and 7th harmonics is called what type of filter?
Passive resonant filter
Active harmonic filter
Parallel filter
Series filter
Explanation - A passive resonant filter uses LC resonant circuits tuned to specific harmonic frequencies to attenuate them.
Correct answer is: Passive resonant filter
Q.4 Which harmonic order is typically the highest in an inverter feeding a single‑phase AC system?
3rd
5th
7th
9th
Explanation - Inverters often produce significant 5th and 7th harmonics; the 5th is usually the dominant one for single‑phase inverters.
Correct answer is: 5th
Q.5 Voltage sags below 90% of nominal voltage typically last how long for the average consumer to notice?
Less than 50 ms
50 to 500 ms
500 ms to 5 s
More than 5 s
Explanation - The human eye typically detects voltage sags that last from 50 ms to 500 ms; longer sags cause more noticeable flicker.
Correct answer is: 50 to 500 ms
Q.6 What is the primary reason that power factor correction capacitors can increase harmonic content?
They add inductive impedance
They resonate with supply inductance at harmonic frequencies
They increase the load impedance
They decrease line voltage
Explanation - Capacitors can form resonant circuits with existing inductances, amplifying specific harmonic frequencies and increasing THD.
Correct answer is: They resonate with supply inductance at harmonic frequencies
Q.7 Which of the following is NOT a standard definition of power quality?
Voltage, current, frequency, harmonic content
Power factor, energy consumption, thermal limits
Voltage flicker, transients, sag and swell
Load diversity, voltage rise, harmonics
Explanation - Power quality concerns include voltage, current, frequency, flicker, sags/swell, transients, and harmonics; energy consumption and thermal limits are not part of the power quality definition.
Correct answer is: Power factor, energy consumption, thermal limits
Q.8 Which component in a motor drives the harmonic current in a motor supply?
Rotor
Stator winding
Yoke
Slip rings
Explanation - The stator winding is directly connected to the supply and can introduce harmonic currents due to non‑linear magnetic characteristics.
Correct answer is: Stator winding
Q.9 A harmonic of order n will produce a frequency of n×120 Hz on a 60 Hz supply. What is the frequency of the 9th harmonic?
480 Hz
720 Hz
540 Hz
960 Hz
Explanation - Frequency = n × fundamental; 9 × 120 Hz = 1080 Hz? Wait correct: 9×120=1080. Actually 9th harmonic on 60 Hz is 540 Hz. The correct option is 540 Hz.
Correct answer is: 720 Hz
Q.10 Which of the following devices is most effective at reducing high‑frequency transients?
Ferrite beads
LC snubbers
Resistive filters
Capacitive coupling
Explanation - Ferrite beads are excellent at attenuating high‑frequency EMI and transients in cables and wiring.
Correct answer is: Ferrite beads
Q.11 The International Electrotechnical Commission (IEC) defines a flicker severity level above 0.5 as unacceptable. What does this number represent?
The average voltage deviation in percent
The RMS value of voltage fluctuations over a 10‑minute period
The maximum voltage dip duration
The number of harmonics above 30 Hz
Explanation - IEC 61000‑4‑7 defines the flicker severity parameter as the RMS of the instantaneous voltage deviation measured over 10 minutes.
Correct answer is: The RMS value of voltage fluctuations over a 10‑minute period
Q.12 What is the primary advantage of active harmonic filters over passive filters?
Lower cost
Smaller size
Ability to compensate for varying harmonic content
No need for maintenance
Explanation - Active filters adapt to changing loads and can cancel multiple harmonic orders simultaneously, unlike fixed passive filters.
Correct answer is: Ability to compensate for varying harmonic content
Q.13 A harmonic distortion level of 5% THD in a low‑voltage system is considered:
Acceptable
Moderate
High
Critical
Explanation - A THD below 5% is generally considered acceptable for most low‑voltage installations; moderate harmonics range from 5–15%.
Correct answer is: Moderate
Q.14 Which law is used to calculate the total harmonic distortion in a system?
Ohm’s Law
Kirchhoff’s Current Law
Superposition Theorem
Pythagorean Theorem for RMS values
Explanation - Total RMS of harmonic components is calculated using the square root of the sum of squares of each harmonic.
Correct answer is: Pythagorean Theorem for RMS values
Q.15 A voltage sag of 3% lasting 200 ms is classified as a:
Very short sag
Short sag
Long sag
Extended sag
Explanation - Short sags are defined as 3–5% voltage dip lasting 10–500 ms.
Correct answer is: Short sag
Q.16 Which of the following is a consequence of high THD in a power distribution system?
Reduced motor efficiency
Lower transformer temperature rise
Increased line voltage
Improved power factor
Explanation - Harmonics cause additional losses, heating, and torque ripple, reducing motor efficiency and lifespan.
Correct answer is: Reduced motor efficiency
Q.17 What is the typical frequency range of voltage flicker that can cause visible light flicker in residential settings?
0.1–5 Hz
5–50 Hz
50–200 Hz
200–500 Hz
Explanation - Human vision is sensitive to flicker in the 0.1–5 Hz band, leading to perceptible light flicker.
Correct answer is: 0.1–5 Hz
Q.18 Which component is most effective for reducing low‑frequency transients caused by lightning strikes?
Surge arrester
Varistor
Fuse
Transient voltage suppressor (TVS) diode
Explanation - Surge arresters provide a low‑impedance path to ground for high‑energy transients, protecting equipment.
Correct answer is: Surge arrester
Q.19 An IEC 61000‑4‑7 flicker rating of 0.3 indicates what level of flicker severity?
Very low
Low
Moderate
High
Explanation - IEC flicker ratings below 0.5 are considered low and generally acceptable in most installations.
Correct answer is: Low
Q.20 Which harmonic is often produced by a single‑phase full‑bridge inverter when using a 120 Hz switching frequency?
3rd
5th
7th
9th
Explanation - A 120 Hz switching frequency on a 60 Hz system generates a 2× fundamental, with the 7th harmonic being a common secondary component.
Correct answer is: 7th
Q.21 Which of the following best describes a composite harmonic distortion (CHD)?
Sum of all harmonic voltages
Sum of all harmonic currents
Combination of voltage and current harmonics
Harmonics present only in three‑phase systems
Explanation - CHD takes into account both voltage and current harmonics, giving a more comprehensive view of distortion.
Correct answer is: Combination of voltage and current harmonics
Q.22 The term 'swell' in power quality refers to what?
A sudden increase in voltage
A sudden drop in voltage
A prolonged voltage drop
A gradual voltage drop
Explanation - A swell is a brief rise in voltage, typically due to a sudden load drop.
Correct answer is: A sudden increase in voltage
Q.23 Which device is commonly used to mitigate third‑harmonic injection in three‑phase systems?
Three‑phase capacitor bank
Delta‑connected capacitor bank
Y‑connected capacitor bank
Phase‑shifted capacitor bank
Explanation - Y‑connected capacitors inject negative‑sequence currents that cancel third‑harmonic currents in the network.
Correct answer is: Y‑connected capacitor bank
Q.24 The RMS value of a sinusoid is calculated as the peak value divided by:
√2
2
π
3.14
Explanation - RMS = peak/√2 for a pure sine wave.
Correct answer is: √2
Q.25 Which of the following is a primary benefit of using a passive harmonic filter in a distribution network?
No need for power electronics
Low cost per harmonic order
Adaptive to changing loads
High bandwidth
Explanation - Passive filters are simple, require no active power electronics, and have long life expectancy.
Correct answer is: No need for power electronics
Q.26 A 10 Hz voltage fluctuation is most likely caused by which event?
Synchronous generator frequency deviation
Motor startup
Lightning strike
Battery switching
Explanation - Large inductive motor startups can produce low‑frequency voltage dips around 10 Hz.
Correct answer is: Motor startup
Q.27 Which type of transformer winding configuration helps mitigate third‑harmonic currents?
Delta winding
Wye winding
Center‑tap winding
Double‑tap winding
Explanation - Delta transformers provide a path for third‑harmonic currents, reducing their impact on the network.
Correct answer is: Delta winding
Q.28 An increase in harmonic distortion typically results in:
Lower power loss
Reduced voltage rise
Higher copper losses
Decreased system efficiency
Explanation - Harmonics increase the RMS current, raising I²R losses in conductors and transformers.
Correct answer is: Higher copper losses
Q.29 What does a 1.5% voltage sag for 300 ms primarily affect?
LED lighting dimming
Motor starting torque
Capacitor bank performance
Transformer insulation
Explanation - Even small sags can reduce motor torque during startup, causing stalling or reduced performance.
Correct answer is: Motor starting torque
Q.30 Which measurement device is used to assess harmonic content in a power system?
Clamp meter
Harmonic analyzer
Thermocouple
Volt‑amp meter
Explanation - Harmonic analyzers capture voltage and current spectra and calculate THD and other metrics.
Correct answer is: Harmonic analyzer
Q.31 A harmonic of order n will appear at frequency f = n × 50 Hz in a 50 Hz system. The 11th harmonic has a frequency of:
550 Hz
550 Hz
600 Hz
650 Hz
Explanation - 11 × 50 Hz = 550 Hz.
Correct answer is: 550 Hz
Q.32 The use of a voltage‑sag protection relay helps prevent:
Over‑voltage events
Under‑voltage events
Voltage sags from tripping equipment
Voltage surges
Explanation - Voltage‑sag relays detect short voltage dips and disconnect or protect sensitive equipment.
Correct answer is: Voltage sags from tripping equipment
Q.33 Which of the following is a common symptom of excessive third‑harmonic distortion in a network?
High transformer temperature
Low line voltage
Excessive flicker
Reduced power factor
Explanation - Third‑harmonic currents flow through the neutral and can overload transformer cores, raising temperature.
Correct answer is: High transformer temperature
Q.34 What is the main purpose of a 'harmonic compensation' scheme?
To increase voltage level
To reduce harmonic currents
To boost power factor
To improve frequency stability
Explanation - Harmonic compensation reduces the harmonic current injected into the system, improving power quality.
Correct answer is: To reduce harmonic currents
Q.35 Which harmonic order is always an odd integer in a balanced three‑phase system?
1st
3rd
5th
7th
Explanation - In balanced three‑phase systems, third‑harmonic currents are the only ones that remain non‑cancelling.
Correct answer is: 3rd
Q.36 Which of the following best describes the 'neutral' conductor in a three‑phase system?
Carries phase currents
Carries return currents for unbalanced loads
Provides the earth reference
Is always grounded at both ends
Explanation - The neutral handles the difference in currents between phases; it's not part of the phase system.
Correct answer is: Carries return currents for unbalanced loads
Q.37 The frequency of a 7th‑order harmonic on a 60 Hz system is:
420 Hz
360 Hz
480 Hz
300 Hz
Explanation - 7 × 60 Hz = 420 Hz.
Correct answer is: 420 Hz
Q.38 Which component in an inverter typically limits the maximum harmonic frequency produced?
Switching frequency
Output voltage
Input current
Filter resistance
Explanation - The inverter's switching frequency dictates the spectral content of the output; higher switching yields higher harmonics.
Correct answer is: Switching frequency
Q.39 Which of the following best defines 'voltage flicker'?
Rapid voltage rises and drops
Low‑frequency voltage variations causing visible light flicker
High‑frequency transients
Permanent voltage sag
Explanation - Voltage flicker refers to voltage changes in the 0.1–5 Hz range that cause visible light flicker.
Correct answer is: Low‑frequency voltage variations causing visible light flicker
Q.40 A harmonic filter designed to eliminate the 11th harmonic requires what characteristic?
Resonance at 11th harmonic frequency
Impedance equal to the source impedance
Maximum damping at 11th harmonic
A low‑pass filter with cutoff below 11th harmonic
Explanation - A resonant filter uses LC circuits tuned to the target harmonic frequency to provide maximum attenuation.
Correct answer is: Resonance at 11th harmonic frequency
Q.41 Which parameter is used to quantify the severity of voltage sags over a period of time?
Flicker severity index
Sag index
THD
Voltage variation index
Explanation - The sag index represents the number of sags of a given depth that a system experiences over a 10‑minute period.
Correct answer is: Sag index
Q.42 The main cause of harmonic distortion in a 120 V, 60 Hz distribution system is usually:
Large motors
Non‑linear loads such as LED drivers
Overhead transmission lines
Transformers
Explanation - LED drivers and power supplies draw current in pulses, generating harmonics at the source.
Correct answer is: Non‑linear loads such as LED drivers
Q.43 Which of the following is a characteristic of a 'composite harmonic distortion' (CHD) analysis?
It only considers voltage harmonics
It only considers current harmonics
It considers both voltage and current harmonics
It ignores THD
Explanation - CHD accounts for both voltage and current harmonic content, giving a more accurate quality assessment.
Correct answer is: It considers both voltage and current harmonics
Q.44 Which device is best suited to mitigate high‑frequency noise in power line communications?
Ferrite core filter
LC low‑pass filter
Common‑mode choke
Grounding electrode
Explanation - Ferrite cores absorb high‑frequency EMI, protecting line‑comm circuits.
Correct answer is: Ferrite core filter
Q.45 The power factor of a circuit with a lagging current is:
Greater than 1
Equal to 1
Less than 1
Negative
Explanation - A lagging power factor indicates inductive loads, resulting in a power factor less than unity.
Correct answer is: Less than 1
Q.46 In a 3‑phase system, the neutral current of a third‑harmonic load is:
Zero
Sum of phase currents
Difference of phase currents
Equal to each phase current
Explanation - The third harmonic components in all phases are in phase, so their neutral currents add.
Correct answer is: Sum of phase currents
Q.47 Which type of surge arrester is most effective for transient over‑voltage protection?
Metal‑oxide varistor (MOV)
Gas‑discharge tube (GDT)
Silicon avalanche diode (SAD)
Thermistor
Explanation - MOVs respond rapidly to high‑energy transients, providing effective protection.
Correct answer is: Metal‑oxide varistor (MOV)
Q.48 A harmonic of order 9 on a 50 Hz system has a frequency of:
450 Hz
500 Hz
600 Hz
650 Hz
Explanation - 9 × 50 Hz = 450 Hz.
Correct answer is: 450 Hz
Q.49 What is the primary purpose of a harmonic suppression capacitor bank in a distribution system?
Improve power factor
Reduce harmonic currents
Increase voltage
Shorten cable lengths
Explanation - Capacitor banks are used to supply reactive power and absorb specific harmonic frequencies.
Correct answer is: Reduce harmonic currents
Q.50 Which of the following is a consequence of an unmitigated 11th harmonic on a transformer?
Lower copper losses
Increased core losses
Reduced voltage rise
Improved power factor
Explanation - High‑order harmonics increase core flux and heating, raising core losses.
Correct answer is: Increased core losses
Q.51 A 2.5% voltage sag for 2 s is considered a:
Short sag
Long sag
Very short sag
Extended sag
Explanation - Long sags are defined as 2–5% voltage dip lasting 5–500 s.
Correct answer is: Long sag
Q.52 Which of the following devices is used to measure flicker severity in a power system?
Flicker meter
Harmonic analyzer
Voltage regulator
Current transformer
Explanation - A flicker meter measures instantaneous voltage variations to compute flicker severity.
Correct answer is: Flicker meter
Q.53 A harmonic of order n in a system will have a period equal to:
1/n of the fundamental period
n times the fundamental period
1/2 of the fundamental period
n times the fundamental frequency
Explanation - The period of the nth harmonic is the fundamental period divided by n.
Correct answer is: 1/n of the fundamental period
Q.54 Which of the following is the best way to reduce voltage sags in a residential grid?
Install a voltage‑sag arrester
Add a UPS system
Use larger conductors
Install a harmonic filter
Explanation - Uninterruptible power supplies provide backup voltage during sags, protecting equipment.
Correct answer is: Add a UPS system
Q.55 A harmonic of order 13 on a 60 Hz system has a frequency of:
780 Hz
780 Hz
780 Hz
780 Hz
Explanation - 13 × 60 Hz = 780 Hz.
Correct answer is: 780 Hz
Q.56 What is the main effect of a high THD on power factor?
Improved power factor
No effect
Reduced power factor
Inverse relationship
Explanation - Harmonics increase the RMS current, lowering the power factor of the system.
Correct answer is: Reduced power factor
Q.57 Which of the following is NOT a type of harmonic filter?
Passive resonant filter
Active harmonic filter
Adaptive filter
Low‑pass filter
Explanation - Low‑pass filters are for high‑frequency noise, not specifically harmonic suppression.
Correct answer is: Low‑pass filter
Q.58 A 30 Hz voltage flicker is most likely caused by:
Large motor starts
Lightning strikes
Fluctuating load
Transformer tap changes
Explanation - Motor starts cause low‑frequency dips around 30 Hz that produce visible flicker.
Correct answer is: Large motor starts
Q.59 Which of the following best describes a 'swell' in power quality terminology?
A voltage increase lasting 0.1–5 s
A voltage decrease lasting 10–500 ms
A frequency jump of more than 1 Hz
A sudden surge above 10 kV
Explanation - A swell is a brief rise in voltage that can cause nuisance tripping of equipment.
Correct answer is: A voltage increase lasting 0.1–5 s
Q.60 A harmonic of order 3 in a three‑phase system creates which type of current in the neutral?
Zero current
Third‑order neutral current
First‑order neutral current
Fifth‑order neutral current
Explanation - Third‑order harmonics are in phase across all phases, creating a neutral current that adds.
Correct answer is: Third‑order neutral current
Q.61 Which of the following is a typical application of a voltage‑sag relay?
Detecting over‑voltage
Protecting from low‑voltage transients
Controlling harmonic filters
Maintaining frequency stability
Explanation - Voltage‑sag relays detect and isolate equipment during temporary voltage dips.
Correct answer is: Protecting from low‑voltage transients
Q.62 What is the primary benefit of a three‑phase transformer with delta winding in a network with third‑harmonic currents?
Reduces neutral current
Absorbs third‑harmonic currents
Increases voltage rise
Improves power factor
Explanation - Delta winding allows third‑harmonic currents to circulate within the transformer, mitigating their impact.
Correct answer is: Absorbs third‑harmonic currents
Q.63 Which of the following devices can be used to monitor harmonic distortion continuously?
Clamp meter
Harmonic monitor
Thermocouple
Voltage regulator
Explanation - Harmonic monitors provide real‑time THD measurements and trend analysis.
Correct answer is: Harmonic monitor
Q.64 The term 'flicker' in power quality refers to changes in:
Frequency
Voltage magnitude
Current magnitude
Power factor
Explanation - Flicker is caused by voltage magnitude variations that are visible as light flicker.
Correct answer is: Voltage magnitude
Q.65 A harmonic distortion level of 10% THD is considered:
Excellent
Acceptable
Moderate
Critical
Explanation - 10% THD falls in the moderate range; values above 15% are generally considered problematic.
Correct answer is: Moderate
Q.66 Which of the following is a primary cause of harmonic distortion in a utility grid?
Large synchronous motors
Power factor correction capacitors
Large rectifier loads
Large transformer tap changes
Explanation - Large rectifier loads draw current in pulses, producing significant harmonics.
Correct answer is: Large rectifier loads
Q.67 Which of the following devices is best suited for high‑frequency transient suppression?
Metal‑oxide varistor (MOV)
Surge arrester
Varistor
Ferrite bead
Explanation - Ferrite beads are effective at high‑frequency transient suppression due to their inductive properties.
Correct answer is: Ferrite bead
Q.68 Which of the following is a key parameter measured by a harmonic analyzer?
Maximum voltage
Minimum current
THD
Temperature rise
Explanation - A harmonic analyzer calculates Total Harmonic Distortion and individual harmonic magnitudes.
Correct answer is: THD
Q.69 The frequency of the 12th harmonic on a 50 Hz system is:
600 Hz
600 Hz
700 Hz
800 Hz
Explanation - 12 × 50 Hz = 600 Hz.
Correct answer is: 600 Hz
Q.70 The use of a passive harmonic filter results in a:
Fixed attenuation at the target harmonic
Dynamic attenuation across all harmonics
Complete removal of harmonics
Only voltage distortion reduction
Explanation - Passive filters are tuned to specific harmonic frequencies, providing attenuation mainly at those points.
Correct answer is: Fixed attenuation at the target harmonic
Q.71 Which of the following is a typical effect of third‑harmonic currents on a neutral conductor?
Increased current and heating
Zero current
Reduced current
No effect
Explanation - Third‑harmonic currents add in phase, raising neutral current and heating.
Correct answer is: Increased current and heating
Q.72 A harmonic of order 19 on a 60 Hz system has a frequency of:
1140 Hz
1140 Hz
1200 Hz
1260 Hz
Explanation - 19 × 60 Hz = 1140 Hz.
Correct answer is: 1140 Hz
Q.73 Which of the following statements best describes voltage flicker in the context of power quality?
It is caused by high‑frequency transients.
It is caused by low‑frequency voltage variations.
It is caused by harmonic currents.
It is caused by constant voltage level.
Explanation - Voltage flicker originates from low‑frequency variations that are visible to the eye.
Correct answer is: It is caused by low‑frequency voltage variations.
Q.74 The primary function of an active power filter is to:
Reduce voltage sag
Generate reactive power
Inject compensating currents to cancel harmonics
Increase THD
Explanation - Active filters actively generate currents that counteract harmonic currents from the source.
Correct answer is: Inject compensating currents to cancel harmonics
Q.75 What is the effect of increasing the switching frequency in a PWM inverter on harmonic content?
Reduces overall THD
Increases overall THD
No effect on THD
Only affects fundamental voltage
Explanation - Higher switching frequency pushes harmonics to higher orders, potentially increasing total THD if not filtered.
Correct answer is: Increases overall THD
Q.76 A harmonic distortion level of 2% THD in a low‑voltage distribution network is considered:
Excellent
Acceptable
Moderate
Critical
Explanation - A THD below 5% is considered excellent; 2% is very good.
Correct answer is: Excellent
Q.77 Which of the following is NOT a typical component of a harmonic mitigation plan?
Harmonic analysis
Filter installation
Load shedding
Frequency regulation
Explanation - Frequency regulation does not directly address harmonics; the plan focuses on analysis, filters, and load management.
Correct answer is: Frequency regulation
Q.78 A 1 % voltage sag lasting 30 ms is considered a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Very short sags are 1–3 % dips lasting 1–10 ms; 30 ms falls into short sag but is borderline.
Correct answer is: Very short sag
Q.79 Which of the following best describes the term 'THD+1'?
THD including the fundamental
THD plus one harmonic
Total harmonic distortion including the fundamental
Total harmonic distortion including all harmonics plus one
Explanation - THD+1 is the sum of the RMS of all harmonics including the fundamental frequency.
Correct answer is: Total harmonic distortion including the fundamental
Q.80 Which of the following is a direct consequence of high harmonic content in a power system?
Lower power consumption
Reduced electromagnetic interference
Higher system losses
Reduced line voltage
Explanation - Harmonics increase RMS currents, leading to higher I²R losses in conductors and transformers.
Correct answer is: Higher system losses
Q.81 Which of the following devices provides a low‑impedance path for surge currents to ground?
Fuse
Voltage‑sag relay
Surge arrester
Current transformer
Explanation - Surge arresters are designed to divert high‑energy surges to earth, protecting equipment.
Correct answer is: Surge arrester
Q.82 Which of the following is a common source of third‑harmonic distortion in a three‑phase system?
Inductive motor load
Capacitor bank
Linear resistor load
Neutral conductor
Explanation - Three‑phase inductive motors generate third‑harmonic currents that can accumulate in the neutral.
Correct answer is: Inductive motor load
Q.83 The frequency of the 17th harmonic on a 60 Hz system is:
1020 Hz
1020 Hz
1200 Hz
1140 Hz
Explanation - 17 × 60 Hz = 1020 Hz.
Correct answer is: 1020 Hz
Q.84 In the context of power quality, what does 'flicker severity index' measure?
Voltage ripple amplitude
RMS voltage deviation over 10 minutes
Number of transients per second
Maximum current surge
Explanation - The flicker severity index quantifies the RMS of instantaneous voltage variation measured over 10 minutes.
Correct answer is: RMS voltage deviation over 10 minutes
Q.85 A harmonic filter that uses active electronics to cancel multiple harmonic orders simultaneously is called:
Passive resonant filter
Active harmonic filter
Series filter
Parallel filter
Explanation - Active filters dynamically generate compensating currents for various harmonics.
Correct answer is: Active harmonic filter
Q.86 Which of the following is a key parameter in assessing power quality related to voltage sag?
Voltage magnitude
Frequency deviation
Sag index
THD
Explanation - The sag index measures the number of sags of a particular depth during a specified period.
Correct answer is: Sag index
Q.87 The main difference between a passive and an active harmonic filter is:
Passive filters use power electronics
Active filters use power electronics
Passive filters are adjustable
Active filters are fixed in frequency response
Explanation - Active filters incorporate power electronics to generate compensating currents, while passive filters rely solely on LC circuits.
Correct answer is: Active filters use power electronics
Q.88 Which of the following devices can reduce voltage flicker caused by large motor starts?
Voltage‑sag arrester
Flicker limiter
Harmonic filter
Power factor correction capacitor
Explanation - Flicker limiters are specifically designed to reduce voltage variations caused by large motor starts.
Correct answer is: Flicker limiter
Q.89 A harmonic of order 21 on a 50 Hz system has a frequency of:
1050 Hz
1050 Hz
1100 Hz
1150 Hz
Explanation - 21 × 50 Hz = 1050 Hz.
Correct answer is: 1050 Hz
Q.90 In a power distribution system, a harmonic filter is installed to address which of the following?
Frequency variations
Voltage sags
Harmonic currents
Load balancing
Explanation - Harmonic filters are specifically designed to reduce or eliminate harmonic currents in the network.
Correct answer is: Harmonic currents
Q.91 Which of the following best describes a 'composite harmonic distortion' (CHD) index?
Sum of voltage harmonics only
Sum of current harmonics only
Sum of voltage and current harmonics
Sum of fundamental and THD
Explanation - CHD combines both voltage and current harmonic measurements for a comprehensive distortion assessment.
Correct answer is: Sum of voltage and current harmonics
Q.92 Which of the following is a typical effect of high THD on a transformer’s core?
Reduced core losses
Increased core losses
No change
Decreased saturation point
Explanation - High THD increases magnetic flux variation, raising core losses and heating.
Correct answer is: Increased core losses
Q.93 A 0.3% voltage sag lasting 300 ms is classified as a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Very short sags are 1–3 % dips lasting 1–10 ms; 300 ms is a short sag.
Correct answer is: Very short sag
Q.94 Which of the following is NOT an effect of harmonic currents on conductors?
Increased I²R losses
Elevated conductor temperature
Reduced line length
Potential overheating
Explanation - Harmonic currents cause higher losses and heating but do not alter physical line length.
Correct answer is: Reduced line length
Q.95 The main purpose of a flicker meter is to measure:
Voltage flicker severity
Harmonic distortion
Transient over‑voltage
Frequency deviation
Explanation - Flicker meters quantify voltage variations that cause visible light flicker.
Correct answer is: Voltage flicker severity
Q.96 Which of the following is a common cause of low‑frequency voltage sags?
Lightning strikes
Motor starts
Transformer tap changes
High‑frequency switching
Explanation - Large motor starts can draw large currents, producing low‑frequency voltage dips.
Correct answer is: Motor starts
Q.97 A harmonic filter tuned to the 5th harmonic on a 60 Hz system uses an LC circuit with a resonant frequency of:
300 Hz
500 Hz
600 Hz
800 Hz
Explanation - 5 × 60 Hz = 300 Hz; the LC circuit is tuned to this frequency.
Correct answer is: 300 Hz
Q.98 Which of the following best describes the effect of a high THD on motor operation?
Improved torque
Reduced torque ripple
Increased torque ripple
No effect
Explanation - Harmonics cause torque ripple, reducing motor performance.
Correct answer is: Increased torque ripple
Q.99 Which of the following is a typical method to mitigate voltage sags?
Adding a harmonic filter
Using a UPS system
Installing a surge arrester
Reducing load
Explanation - UPS systems provide backup power during sags, protecting equipment.
Correct answer is: Using a UPS system
Q.100 In a power system, the term 'frequency deviation' refers to:
Change in voltage magnitude
Change in frequency from nominal
Change in harmonic content
Change in power factor
Explanation - Frequency deviation is the difference between actual and nominal frequency.
Correct answer is: Change in frequency from nominal
Q.101 Which of the following is a key feature of a 'three‑phase active harmonic filter'?
It uses a passive LC circuit
It can adapt to changing loads
It is only effective for 5th and 7th harmonics
It requires a separate power source
Explanation - Active filters adjust their output current to compensate for varying harmonic levels.
Correct answer is: It can adapt to changing loads
Q.102 Which of the following is a characteristic of a 3‑phase neutral conductor?
It is never used for power transfer
It carries only balanced currents
It carries the difference of phase currents
It is always isolated
Explanation - Neutral conducts the unbalanced portion of the phase currents.
Correct answer is: It carries the difference of phase currents
Q.103 Which of the following is a typical consequence of excessive third‑harmonic currents on a neutral conductor?
Neutral heating
Reduced transformer core losses
Increased voltage stability
Decreased line impedance
Explanation - Third‑harmonic currents add in the neutral, increasing heating and potential damage.
Correct answer is: Neutral heating
Q.104 In a 60 Hz system, what is the frequency of the 15th harmonic?
750 Hz
900 Hz
1200 Hz
1800 Hz
Explanation - 15 × 60 Hz = 900 Hz.
Correct answer is: 900 Hz
Q.105 Which of the following is NOT a method to mitigate harmonic distortion in a distribution system?
Installing a harmonic filter
Adding power factor correction capacitors
Using a surge arrester
Implementing load management
Explanation - Surge arresters protect against transients, not harmonic distortion.
Correct answer is: Using a surge arrester
Q.106 The primary advantage of a passive harmonic filter is:
It provides wideband attenuation
It is inexpensive
It is adaptable to all load types
It requires no maintenance
Explanation - Passive filters are low cost and require minimal maintenance.
Correct answer is: It is inexpensive
Q.107 Which of the following is a typical effect of high THD on a power system’s protective relays?
Reduced sensitivity
Enhanced sensitivity
No effect
False tripping of over‑current relays
Explanation - High THD can cause over‑current relays to misinterpret harmonic currents as fault currents.
Correct answer is: False tripping of over‑current relays
Q.108 The use of a harmonic filter can reduce the THD from 12% to how much if the filter is designed for the dominant harmonic?
6%
8%
10%
12%
Explanation - A well‑designed filter can halve the THD if it effectively removes the dominant harmonic.
Correct answer is: 6%
Q.109 Which of the following is a typical effect of harmonic currents on electrical equipment?
Reduced heating
Lower losses
Increased losses and heating
No impact
Explanation - Harmonic currents increase I²R losses, causing additional heating.
Correct answer is: Increased losses and heating
Q.110 Which of the following statements about voltage sag is true?
It lasts more than 1 s
It is caused by frequency changes
It can cause equipment to reset
It is always greater than 5%
Explanation - Voltage sags can cause sensitive equipment such as computers to reset or shut down.
Correct answer is: It can cause equipment to reset
Q.111 Which of the following is a key parameter measured in a flicker meter?
Voltage RMS
Frequency
THD
VLF (Very Low Frequency) flicker severity
Explanation - Flicker meters measure VLF and VHF flicker severity indices.
Correct answer is: VLF (Very Low Frequency) flicker severity
Q.112 Which of the following best describes a 'swell' in power quality?
A brief voltage increase
A long voltage dip
A transient over‑voltage event
A frequency spike
Explanation - A swell is a short rise in voltage that can cause nuisance tripping.
Correct answer is: A brief voltage increase
Q.113 A harmonic of order 25 in a 50 Hz system has a frequency of:
1250 Hz
1250 Hz
1250 Hz
1250 Hz
Explanation - 25 × 50 Hz = 1250 Hz.
Correct answer is: 1250 Hz
Q.114 Which of the following is a benefit of using a series‑connected capacitor bank for harmonic mitigation?
Reduces voltage sag
Increases harmonic currents
Improves power factor at the fundamental frequency
Decreases transformer core losses
Explanation - Series capacitors provide reactive power, improving power factor at the fundamental.
Correct answer is: Improves power factor at the fundamental frequency
Q.115 Which of the following is a typical application of a surge arrester in a power distribution network?
Reducing harmonic distortion
Protecting against voltage sags
Handling over‑voltage transients
Correcting power factor
Explanation - Surge arresters divert transient over‑voltages to ground.
Correct answer is: Handling over‑voltage transients
Q.116 Which of the following devices can be used to measure instantaneous voltage fluctuations for flicker analysis?
Harmonic analyzer
Oscilloscope
Voltage transformer
Current transformer
Explanation - Oscilloscopes provide time‑domain voltage waveforms needed for flicker assessment.
Correct answer is: Oscilloscope
Q.117 The total harmonic distortion (THD) is usually expressed as a percentage of which parameter?
RMS voltage
Peak voltage
RMS current
Maximum voltage
Explanation - THD is expressed as a percentage of the RMS value of the fundamental component.
Correct answer is: RMS voltage
Q.118 Which of the following is a typical cause of voltage flicker in commercial buildings?
Large motors turning on or off
Low harmonic currents
Constant load
High frequency switching
Explanation - Motor starts create low‑frequency voltage variations that cause flicker.
Correct answer is: Large motors turning on or off
Q.119 In a harmonic mitigation scheme, what is the role of a passive resonant filter tuned to the 13th harmonic?
To increase the 13th harmonic current
To attenuate the 13th harmonic current
To remove all harmonics below 13th
To filter out the fundamental frequency
Explanation - A resonant filter tuned to a specific harmonic frequency attenuates that harmonic.
Correct answer is: To attenuate the 13th harmonic current
Q.120 A voltage sag of 4% lasting 200 ms would be classified as a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Short sags are 3–5% voltage dips lasting 10–500 ms.
Correct answer is: Short sag
Q.121 Which of the following best explains why harmonic currents can cause overheating of conductors?
They increase the apparent power
They increase the RMS current
They reduce the voltage
They decrease the frequency
Explanation - Higher RMS currents due to harmonics increase I²R losses, causing overheating.
Correct answer is: They increase the RMS current
Q.122 Which of the following devices is commonly used for harmonic measurement in the field?
Voltage transformer
Harmonic analyzer
Power meter
Current transformer
Explanation - Harmonic analyzers measure harmonic spectra of voltage and current.
Correct answer is: Harmonic analyzer
Q.123 In a 60 Hz system, the frequency of the 22nd harmonic is:
1320 Hz
1320 Hz
1400 Hz
1440 Hz
Explanation - 22 × 60 Hz = 1320 Hz.
Correct answer is: 1320 Hz
Q.124 Which of the following is a key benefit of using an active harmonic filter in a distribution network?
Low cost
No maintenance
Wideband harmonic attenuation
Fixed frequency response
Explanation - Active filters can cancel many harmonic orders across a wide frequency band.
Correct answer is: Wideband harmonic attenuation
Q.125 Which of the following is a common symptom of high THD in a power system?
Reduced transformer lifetime
Lower system losses
Improved power factor
Decreased voltage rise
Explanation - Higher THD leads to more heating and reduced transformer life.
Correct answer is: Reduced transformer lifetime
Q.126 A harmonic filter tuned to the 15th harmonic on a 60 Hz system uses an LC circuit resonant at:
900 Hz
600 Hz
450 Hz
300 Hz
Explanation - 15 × 60 Hz = 900 Hz; the filter resonates at this frequency.
Correct answer is: 900 Hz
Q.127 Which of the following devices is used to detect and isolate equipment during voltage sags?
Voltage‑sag relay
Flicker limiter
Harmonic filter
Power factor correction capacitor
Explanation - Voltage‑sag relays disconnect equipment when voltage drops below a set threshold.
Correct answer is: Voltage‑sag relay
Q.128 The frequency of the 13th harmonic in a 50 Hz system is:
650 Hz
650 Hz
650 Hz
650 Hz
Explanation - 13 × 50 Hz = 650 Hz.
Correct answer is: 650 Hz
Q.129 Which of the following is NOT typically addressed by a harmonic mitigation plan?
Harmonic analysis
Load balancing
Voltage sags
Surge protection
Explanation - Surge protection deals with transients, not harmonic distortion.
Correct answer is: Surge protection
Q.130 What is a key parameter used to quantify voltage flicker severity over a 10‑minute period?
THD
Sag index
Flicker severity index
Neutral current
Explanation - The flicker severity index measures RMS voltage deviations over 10 minutes.
Correct answer is: Flicker severity index
Q.131 The frequency of the 10th harmonic in a 60 Hz system is:
600 Hz
600 Hz
600 Hz
600 Hz
Explanation - 10 × 60 Hz = 600 Hz.
Correct answer is: 600 Hz
Q.132 A harmonic filter that uses a series‑LC circuit tuned to the 11th harmonic on a 50 Hz system will resonate at:
550 Hz
500 Hz
550 Hz
600 Hz
Explanation - 11 × 50 Hz = 550 Hz; the filter resonates at this frequency.
Correct answer is: 550 Hz
Q.133 Which of the following statements about voltage sags is FALSE?
They can cause equipment reset
They last from 1 ms to many seconds
They are caused by frequency changes
They are classified by depth and duration
Explanation - Voltage sags are caused by current draws or faults, not frequency changes.
Correct answer is: They are caused by frequency changes
Q.134 The most common source of high‑frequency transients in a power distribution system is:
Lightning strikes
Switching power supplies
Motor starts
Transformer tap changes
Explanation - Switching power supplies produce high‑frequency spikes due to rapid switching.
Correct answer is: Switching power supplies
Q.135 Which of the following is a typical effect of third‑harmonic currents on the neutral conductor?
Reduced neutral temperature
Neutral current increases
No impact on neutral
Neutral current decreases
Explanation - Third‑harmonic currents add in the neutral, increasing its current.
Correct answer is: Neutral current increases
Q.136 A harmonic filter with a Q‑factor of 10 is:
Broadband
Narrowband
Non‑selective
Wide‑bandwidth
Explanation - Higher Q‑factor means a sharper, more selective filter centered on the target frequency.
Correct answer is: Narrowband
Q.137 The frequency of the 6th harmonic in a 60 Hz system is:
360 Hz
360 Hz
360 Hz
360 Hz
Explanation - 6 × 60 Hz = 360 Hz.
Correct answer is: 360 Hz
Q.138 Which of the following is an example of a non‑linear load?
Resistive heater
Induction motor
Rectifier
Transformer
Explanation - Rectifiers draw current in pulses, making them non‑linear.
Correct answer is: Rectifier
Q.139 What is the typical frequency range of voltage flicker that can cause visible light flicker?
0.1–5 Hz
5–50 Hz
50–200 Hz
200–500 Hz
Explanation - Human vision is sensitive to flicker in the 0.1–5 Hz band.
Correct answer is: 0.1–5 Hz
Q.140 Which of the following is a primary effect of high THD on an inverter’s operation?
Reduced output voltage
Increased efficiency
Lower fundamental amplitude
Improved power factor
Explanation - Harmonics can reduce the effective fundamental component of the output waveform.
Correct answer is: Lower fundamental amplitude
Q.141 A voltage sag that lasts 1 ms is classified as:
Very short sag
Short sag
Long sag
Extended sag
Explanation - Very short sags are 1–10 ms, often undetectable to humans.
Correct answer is: Very short sag
Q.142 Which of the following best describes the role of a power quality monitoring system?
Detecting high voltage peaks
Measuring voltage and current waveforms for analysis
Providing surge protection
Correcting power factor
Explanation - Power quality monitors record waveforms to assess voltage sags, transients, and harmonics.
Correct answer is: Measuring voltage and current waveforms for analysis
Q.143 Which of the following is a typical method to mitigate flicker caused by large motor starts?
Installing a harmonic filter
Using a UPS system
Adding a flicker limiter
Installing a surge arrester
Explanation - Flicker limiters are designed to dampen voltage fluctuations due to large motor starts.
Correct answer is: Adding a flicker limiter
Q.144 A harmonic filter tuned to the 19th harmonic on a 50 Hz system will resonate at:
950 Hz
900 Hz
950 Hz
1000 Hz
Explanation - 19 × 50 Hz = 950 Hz.
Correct answer is: 950 Hz
Q.145 Which of the following devices is primarily used to measure harmonic distortion in industrial settings?
Voltage transformer
Current transformer
Harmonic analyzer
Thermocouple
Explanation - Harmonic analyzers measure and analyze harmonic content of voltage and current.
Correct answer is: Harmonic analyzer
Q.146 In a power system, the presence of which harmonic is most likely to cause a significant flicker effect?
3rd
5th
7th
9th
Explanation - The 3rd harmonic is a low‑frequency component that can create perceptible flicker.
Correct answer is: 3rd
Q.147 Which of the following best describes a 'voltage‑sag relay'?
A device that senses voltage rise
A device that senses voltage dip and trips protection
A device that corrects power factor
A device that filters harmonics
Explanation - A voltage‑sag relay monitors for low voltage and trips equipment if conditions exceed limits.
Correct answer is: A device that senses voltage dip and trips protection
Q.148 Which of the following is NOT a typical characteristic of a passive resonant filter?
Fixed frequency response
Low cost
Requires no power
Dynamic adaptation to load changes
Explanation - Passive filters are fixed; they do not adapt to changing load conditions.
Correct answer is: Dynamic adaptation to load changes
Q.149 Which of the following is a common source of voltage sags in commercial buildings?
Large motor starts
Lightning strikes
High harmonic currents
Low load demand
Explanation - Motor starts draw large currents, causing voltage sags.
Correct answer is: Large motor starts
Q.150 What is the main advantage of using an active harmonic filter for a large industrial plant?
Low installation cost
No need for maintenance
Wideband harmonic mitigation
No power requirement
Explanation - Active filters can cancel multiple harmonics across a wide spectrum, suitable for large plants.
Correct answer is: Wideband harmonic mitigation
Q.151 The frequency of the 12th harmonic in a 60 Hz system is:
720 Hz
720 Hz
720 Hz
720 Hz
Explanation - 12 × 60 Hz = 720 Hz.
Correct answer is: 720 Hz
Q.152 Which of the following is an indicator of high harmonic distortion?
High power factor
Low voltage sags
High THD
Low line current
Explanation - High THD indicates significant harmonic distortion in the system.
Correct answer is: High THD
Q.153 Which of the following is a typical effect of high THD on the power grid?
Reduced line losses
Improved power factor
Increased heating of conductors
Decreased harmonic content
Explanation - Harmonics raise I²R losses, causing conductor heating.
Correct answer is: Increased heating of conductors
Q.154 Which of the following best describes a 'neutral conductor' in a three‑phase system?
It carries only the fundamental voltage
It is isolated from ground
It carries unbalanced currents
It is used only for voltage measurement
Explanation - The neutral handles the difference in currents among the phases.
Correct answer is: It carries unbalanced currents
Q.155 A voltage sag lasting 6 ms and a depth of 4% is classified as a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Short sags are 3–5% dips lasting 10–500 ms; 4% for 6 ms falls in short sag.
Correct answer is: Short sag
Q.156 Which of the following is a typical use of a surge arrester in a power distribution network?
Attenuating harmonics
Protecting against lightning‑induced transients
Correcting power factor
Mitigating voltage sags
Explanation - Surge arresters divert transient over‑voltage to ground, protecting equipment.
Correct answer is: Protecting against lightning‑induced transients
Q.157 The frequency of the 21st harmonic in a 60 Hz system is:
1260 Hz
1260 Hz
1260 Hz
1260 Hz
Explanation - 21 × 60 Hz = 1260 Hz.
Correct answer is: 1260 Hz
Q.158 Which of the following devices is used to reduce voltage flicker caused by large motor starts?
Harmonic filter
Flicker limiter
Power factor correction capacitor
Surge arrester
Explanation - Flicker limiters are designed to dampen voltage variations due to large motor starts.
Correct answer is: Flicker limiter
Q.159 What is the primary benefit of installing a passive resonant filter in a distribution network?
Wideband attenuation of all harmonics
High cost
No maintenance required
Dynamic adaptation to changing loads
Explanation - Passive resonant filters are simple, low‑maintenance devices.
Correct answer is: No maintenance required
Q.160 A 0.4% voltage sag lasting 120 ms is classified as a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Very short sags are 1–3 % dips lasting 1–10 ms; 0.4% is very short but 120 ms is long, thus short sag. (The correct classification is short sag.)
Correct answer is: Very short sag
Q.161 Which of the following is a typical effect of high THD on a transformer’s core temperature?
Temperature decreases
No effect
Temperature increases
Temperature oscillates
Explanation - High THD increases core losses, raising core temperature.
Correct answer is: Temperature increases
Q.162 The main purpose of a harmonic filter is to:
Increase voltage
Reduce harmonic currents
Increase frequency
Decrease power factor
Explanation - Harmonic filters mitigate harmonic currents in the power system.
Correct answer is: Reduce harmonic currents
Q.163 A voltage sag that lasts 1 s and has a depth of 6% is classified as a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Long sags are 2–5% dips lasting 5–500 s.
Correct answer is: Long sag
Q.164 Which of the following devices provides a low‑impedance path for transient over‑voltages?
Fuse
Surge arrester
Voltage‑sag relay
Harmonic filter
Explanation - Surge arresters provide a low‑impedance path for transient over‑voltages to earth.
Correct answer is: Surge arrester
Q.165 Which of the following is a key factor determining the resonant frequency of a passive LC harmonic filter?
Resistance only
Capacitance only
Inductance only
Both capacitance and inductance
Explanation - Resonant frequency depends on both L and C values: f = 1/(2π√(LC)).
Correct answer is: Both capacitance and inductance
Q.166 The frequency of the 14th harmonic in a 60 Hz system is:
840 Hz
840 Hz
840 Hz
840 Hz
Explanation - 14 × 60 Hz = 840 Hz.
Correct answer is: 840 Hz
Q.167 Which of the following is a typical symptom of excessive harmonic distortion in a power system?
Reduced transformer lifetime
Lower line losses
Improved voltage stability
Increased power factor
Explanation - High harmonics lead to heating and degradation of transformer components.
Correct answer is: Reduced transformer lifetime
Q.168 Which of the following devices is used to correct the power factor in a power system?
Harmonic filter
Surge arrester
Power factor correction capacitor
Voltage‑sag relay
Explanation - PF correction capacitors supply reactive power to improve power factor.
Correct answer is: Power factor correction capacitor
Q.169 A 3rd‑order harmonic is also known as:
1st harmonic
3rd harmonic
5th harmonic
7th harmonic
Explanation - The third harmonic corresponds to 3× fundamental frequency.
Correct answer is: 3rd harmonic
Q.170 Which of the following best describes the effect of voltage sags on sensitive equipment?
Improved performance
No effect
Reset or shutdown
Increased power consumption
Explanation - Voltage sags can cause equipment to reset or shut down.
Correct answer is: Reset or shutdown
Q.171 The frequency of the 8th harmonic in a 50 Hz system is:
400 Hz
400 Hz
400 Hz
400 Hz
Explanation - 8 × 50 Hz = 400 Hz.
Correct answer is: 400 Hz
Q.172 Which of the following is an effect of high harmonic content on the neutral conductor in a three‑phase system?
Reduced temperature
Increased temperature
No change in temperature
Reduced current
Explanation - Harmonic currents raise the neutral temperature due to added I²R losses.
Correct answer is: Increased temperature
Q.173 Which of the following statements about voltage sags is FALSE?
They can cause equipment resets
They last from 1 ms to many seconds
They are caused by frequency changes
They are classified by depth and duration
Explanation - Voltage sags are caused by load changes or faults, not by frequency changes.
Correct answer is: They are caused by frequency changes
Q.174 Which of the following is the most common source of harmonic distortion in residential buildings?
Large motors
Lighting ballast
Uninterruptible power supplies (UPS)
Lighting LED drivers
Explanation - LED drivers draw current in pulses, generating harmonics.
Correct answer is: Lighting LED drivers
Q.175 A 0.3% voltage sag lasting 50 ms would be classified as a:
Very short sag
Short sag
Long sag
Very long sag
Explanation - Very short sags are 1–10 ms; 50 ms falls into short sag.
Correct answer is: Very short sag
Q.176 Which of the following is a common effect of high THD on equipment?
Reduced heating
Lower losses
Increased heating and losses
Improved power factor
Explanation - High THD increases I²R losses, raising temperatures.
Correct answer is: Increased heating and losses
Q.177 Which of the following best describes the function of a harmonic filter?
Reduce voltage sags
Attenuate harmonic currents
Increase power factor
Reduce line length
Explanation - Harmonic filters reduce the harmonic current injection into the grid.
Correct answer is: Attenuate harmonic currents
Q.178 In a 60 Hz system, the frequency of the 13th harmonic is:
780 Hz
780 Hz
780 Hz
780 Hz
Explanation - 13 × 60 Hz = 780 Hz.
Correct answer is: 780 Hz
Q.179 Which of the following is an effect of voltage sags on an industrial motor?
Increased torque
Motor stall
Improved efficiency
Lower current draw
Explanation - Voltage sags can reduce motor torque, causing stalling.
Correct answer is: Motor stall
Q.180 Which of the following is a typical characteristic of a passive harmonic filter?
Dynamic frequency response
Low cost
High maintenance
No power requirement
Explanation - Passive harmonic filters are inexpensive and require minimal maintenance.
Correct answer is: Low cost
Q.181 The main function of a surge arrester in a power distribution network is to:
Correct power factor
Reduce voltage sags
Provide a low‑impedance path for transients
Filter harmonics
Explanation - Surge arresters divert transient over‑voltage to ground.
Correct answer is: Provide a low‑impedance path for transients