Q.1 What is the primary purpose of a grid‑forming inverter in a renewable energy system?
To convert DC to AC with fixed frequency and voltage
To provide reactive power support only
To disconnect the renewable source during faults
To store excess energy in batteries
Explanation - Grid‑forming inverters can establish voltage and frequency on their own, allowing them to operate independently of the utility grid and supply stable AC power.
Correct answer is: To convert DC to AC with fixed frequency and voltage
Q.2 Which IEEE standard defines the interconnection requirements for distributed generation with the utility grid?
IEEE 1547
IEEE 802.3
IEEE 488
IEEE 1159
Explanation - IEEE 1547 specifies the technical requirements for interconnecting distributed resources, such as solar PV and wind, with the electric power system.
Correct answer is: IEEE 1547
Q.3 In a wind turbine, the power electronic converter that decouples the generator speed from grid frequency is called:
DC‑DC converter
DC‑AC inverter
Back‑to‑back converter
Phase‑locked loop
Explanation - A back‑to‑back converter consists of a rectifier and an inverter, allowing the variable‑speed generator to feed the fixed‑frequency grid.
Correct answer is: Back‑to‑back converter
Q.4 Which of the following is NOT a typical grid code requirement for solar PV plants?
Low‑voltage ride‑through capability
Active power curtailment on over‑frequency
Mandatory use of synchronous condensers
Reactive power control within a defined range
Explanation - Grid codes usually require voltage support and ride‑through, but they do not mandate synchronous condensers for PV; inverter‑based reactive support is common.
Correct answer is: Mandatory use of synchronous condensers
Q.5 What is the main advantage of using a DC‑coupled hybrid renewable system (PV + storage) over an AC‑coupled one?
Higher inverter efficiency
Simpler protection scheme
Reduced DC‑link voltage stress
Lower overall system cost
Explanation - DC‑coupled systems avoid multiple AC‑DC conversions, resulting in higher overall conversion efficiency compared to AC‑coupled configurations.
Correct answer is: Higher inverter efficiency
Q.6 Which parameter is primarily used to assess the impact of solar PV on grid voltage stability?
Short‑circuit current
Reactive power capability
Harmonic distortion level
Thermal rating of conductors
Explanation - PV inverters can inject or absorb reactive power, directly influencing voltage profiles and stability on the distribution network.
Correct answer is: Reactive power capability
Q.7 During a grid fault, which function allows a grid‑connected inverter to stay connected and support the system?
Maximum Power Point Tracking (MPPT)
Low‑Voltage Ride‑Through (LVRT)
Island Mode Operation
Power Factor Correction
Explanation - LVRT requires the inverter to remain connected and supply reactive power during short‑duration voltage dips, helping the grid recover.
Correct answer is: Low‑Voltage Ride‑Through (LVRT)
Q.8 What is the typical frequency range over which a modern grid‑forming inverter can operate while maintaining stability?
45–55 Hz
48–52 Hz
40–60 Hz
49.5–50.5 Hz
Explanation - Grid‑forming inverters are designed to tolerate frequency deviations of roughly ±5 Hz around nominal 50 Hz (or 60 Hz) to support system stability.
Correct answer is: 45–55 Hz
Q.9 Which technology is most commonly used for smoothing the output of a wind farm before feeding it to the grid?
Supercapacitor banks
Flywheel energy storage
Synchronous condensers
Hydrogen electrolyzers
Explanation - Flywheels can quickly absorb and release energy to reduce short‑term fluctuations in wind power output.
Correct answer is: Flywheel energy storage
Q.10 In power system studies, the term "hosting capacity" refers to:
Maximum renewable generation a grid can accommodate without violations
Total installed capacity of conventional power plants
Amount of energy stored in battery banks
Capacity of transmission lines for peak load
Explanation - Hosting capacity quantifies how much additional distributed generation can be added before voltage, thermal, or stability limits are exceeded.
Correct answer is: Maximum renewable generation a grid can accommodate without violations
Q.11 Which of the following control strategies is used to mitigate harmonic distortion introduced by inverter‑based generators?
Droop control
Selective Harmonic Elimination (SHE) PWM
Maximum Power Point Tracking
Frequency‑locked loop
Explanation - SHE PWM is a modulation technique designed to suppress specific harmonic orders in the inverter output.
Correct answer is: Selective Harmonic Elimination (SHE) PWM
Q.12 A "smart inverter" typically includes which of the following capabilities?
Only active power injection
Automatic islanding detection and disconnection
Voltage and frequency support, reactive power control, and communication
Physical isolation from the grid at all times
Explanation - Smart inverters can provide ancillary services such as voltage regulation, frequency response, and can communicate with grid operators for coordinated control.
Correct answer is: Voltage and frequency support, reactive power control, and communication
Q.13 The "Maximum Power Point Tracking" (MPPT) algorithm in a PV inverter primarily optimizes:
Grid frequency
Inverter temperature
Solar panel output power
Battery state of charge
Explanation - MPPT continuously adjusts the operating point of PV modules to extract the highest possible power under varying irradiance and temperature.
Correct answer is: Solar panel output power
Q.14 In a grid‑connected PV system, the term "anti‑islanding" refers to:
A method to increase power factor
A protective function that disconnects the inverter during loss of utility supply
A technique to store excess energy in batteries
A way to synchronize phase angles with the grid
Explanation - Anti‑islanding detection ensures that the inverter stops feeding power when the grid is absent, protecting utility workers and equipment.
Correct answer is: A protective function that disconnects the inverter during loss of utility supply
Q.15 Which of the following is a major challenge when integrating large amounts of solar PV into the transmission grid?
Excessive short‑circuit currents
Voltage rise during low load periods
High inertia of the system
Limited harmonic generation
Explanation - High PV output when load is low can cause voltage to exceed limits, especially on weak distribution feeders.
Correct answer is: Voltage rise during low load periods
Q.16 What does the term "dispatchable" mean in the context of renewable energy sources?
The source can be turned on/off at any time without restrictions
The source provides a constant power output regardless of conditions
The source can be scheduled to deliver a specified amount of power when needed
The source only operates during daylight hours
Explanation - Dispatchable renewables, such as hydro or storage‑coupled wind, can be controlled to meet a predetermined power schedule.
Correct answer is: The source can be scheduled to deliver a specified amount of power when needed
Q.17 Which component in a wind turbine converter system limits the fault current contribution to the grid?
DC‑link capacitor
Transformer
Crowbar circuit
Gearbox
Explanation - A crowbar protects the converter by shorting the DC link during severe over‑voltage, thereby limiting fault currents injected into the grid.
Correct answer is: Crowbar circuit
Q.18 The "droop control" method in inverter‑based generators is used to:
Maintain constant voltage regardless of load
Share active and reactive power among multiple inverters without communication
Increase the inverter switching frequency
Detect islanding conditions
Explanation - Droop characteristics allow parallel inverters to autonomously divide load based on frequency (P‑droop) and voltage (Q‑droop) deviations.
Correct answer is: Share active and reactive power among multiple inverters without communication
Q.19 Which storage technology provides the fastest response time for frequency regulation in a grid‑integrated renewable system?
Pumped hydro storage
Lithium‑ion batteries
Compressed air energy storage
Flow batteries
Explanation - Lithium‑ion batteries can discharge or charge within milliseconds, making them ideal for fast frequency response services.
Correct answer is: Lithium‑ion batteries
Q.20 What is the purpose of a "synchronverter" in renewable energy integration?
To convert AC to DC
To emulate the behavior of a synchronous generator using power electronics
To increase the line impedance
To provide DC‑DC voltage boost
Explanation - A synchronverter mimics the inertia and droop characteristics of a synchronous machine, helping to stabilize the grid.
Correct answer is: To emulate the behavior of a synchronous generator using power electronics
Q.21 Which of the following grid‑support services can a battery energy storage system (BESS) NOT provide?
Peak shaving
Black‑start capability
Voltage regulation
Permanent load shedding
Explanation - BESS can perform temporary load shedding (curtailment) but cannot permanently disconnect loads; permanent shedding is a system planning action.
Correct answer is: Permanent load shedding
Q.22 In a high‑penetration solar scenario, which device is most effective at mitigating flicker caused by cloud transients?
Static VAR compensator (SVC)
Dynamic voltage restorer (DVR)
Synchronous condenser
Large‑scale battery inverter
Explanation - Battery inverters can rapidly absorb or inject active power, smoothing out fast power fluctuations due to passing clouds.
Correct answer is: Large‑scale battery inverter
Q.23 The term "inertia constant (H)" for a rotating machine is expressed in:
Seconds
Hertz
Volts
Amperes
Explanation - The inertia constant H denotes the stored kinetic energy at rated speed per unit of rated apparent power, measured in seconds.
Correct answer is: Seconds
Q.24 Which of the following is a key advantage of using a multilevel inverter for grid‑connected PV systems?
Reduced number of power devices
Higher output voltage with lower switching frequency
Simplified control algorithm
Elimination of MPPT requirement
Explanation - Multilevel inverters generate a staircase voltage waveform, achieving higher voltage levels and lower harmonic content without high‑frequency switching.
Correct answer is: Higher output voltage with lower switching frequency
Q.25 When a photovoltaic inverter operates in "grid‑support mode", it primarily provides:
Maximum active power only
Voltage support through reactive power injection
Frequency control by varying DC link voltage
Isolation from the grid
Explanation - Grid‑support mode enables the inverter to regulate local voltage by supplying or absorbing reactive power as needed.
Correct answer is: Voltage support through reactive power injection
Q.26 Which phenomenon describes the increase in grid voltage due to high PV generation on a lightly loaded feeder?
Voltage dip
Voltage rise
Voltage sag
Voltage flicker
Explanation - When generation exceeds local consumption, the voltage can rise above nominal limits, especially on long, low‑impedance lines.
Correct answer is: Voltage rise
Q.27 The main function of a "Static Synchronous Compensator (STATCOM)" in renewable integration is to:
Provide fast reactive power support
Convert DC to AC
Store energy during off‑peak hours
Regulate frequency through active power
Explanation - STATCOMs can inject or absorb reactive power quickly, helping to maintain voltage stability in grids with high renewable penetration.
Correct answer is: Provide fast reactive power support
Q.28 In a power system, the term "short‑term frequency deviation" is typically measured in:
Milliseconds
Seconds
Minutes
Hours
Explanation - Short‑term frequency deviations occur over a few seconds following a sudden imbalance of generation and load.
Correct answer is: Seconds
Q.29 Which control method is used by wind turbines to limit the mechanical torque during high wind speeds?
Pitch control
MPPT control
Voltage droop control
Current limiting
Explanation - Pitch control adjusts blade angles to reduce aerodynamic torque, protecting the turbine from overspeed.
Correct answer is: Pitch control
Q.30 A "grid‑code compliant" inverter must be able to perform:
Only active power injection at unity power factor
Active power curtailment, voltage regulation, and fault ride‑through
Frequency modulation above 100 Hz
Self‑isolation from the grid at all times
Explanation - Compliance requires the inverter to support voltage, frequency, ride‑through, and curtailment as defined by the grid operator.
Correct answer is: Active power curtailment, voltage regulation, and fault ride‑through
Q.31 Which type of renewable energy source inherently provides inertia to the power system?
Solar PV
Wind turbine with full‑scale converter
Hydropower with synchronous generators
Battery storage
Explanation - Conventional hydropower plants use rotating generators that naturally contribute mechanical inertia to the grid.
Correct answer is: Hydropower with synchronous generators
Q.32 The "N‑1 contingency" concept in grid planning ensures that:
The system can survive the loss of any single component without violating limits
All generators operate at maximum capacity
Renewable generation is limited to 10% of total capacity
Frequency is always fixed at 50 Hz
Explanation - N‑1 means the grid remains secure after the outage of any one element (line, transformer, generator).
Correct answer is: The system can survive the loss of any single component without violating limits
Q.33 In a distributed generation system, the "power factor" is defined as:
Ratio of active power to apparent power
Ratio of reactive power to active power
Ratio of voltage to current
Ratio of frequency to voltage
Explanation - Power factor = P (kW) / S (kVA) and indicates the phase relationship between voltage and current.
Correct answer is: Ratio of active power to apparent power
Q.34 Which of the following is a primary reason for using a transformer with an on‑load tap changer (OLTC) in renewable‑rich grids?
To adjust voltage levels in real time as generation varies
To increase the short‑circuit current
To provide frequency control
To convert DC to AC
Explanation - OLTCs allow voltage regulation without interrupting service, compensating for fluctuations from variable renewable sources.
Correct answer is: To adjust voltage levels in real time as generation varies
Q.35 What is the typical control bandwidth (in Hz) of a grid‑forming inverter’s voltage regulation loop?
0.1–0.5 Hz
1–5 Hz
10–20 Hz
50–60 Hz
Explanation - Voltage regulation loops are usually designed with a bandwidth of a few hertz to respond adequately to grid disturbances.
Correct answer is: 1–5 Hz
Q.36 Which of the following describes "synthetic inertia" provided by power electronic converters?
Physical mass attached to the inverter
Fast active power injection proportional to frequency deviation
Increasing the DC‑link capacitance
Using large capacitors to store kinetic energy
Explanation - Synthetic inertia mimics the inertial response of rotating machines by adjusting power output based on measured frequency changes.
Correct answer is: Fast active power injection proportional to frequency deviation
Q.37 During a grid fault, the "current limiting mode" of a wind turbine converter aims to:
Increase active power output
Prevent damage by restricting fault current contribution
Switch to island mode
Activate MPPT
Explanation - Current limiting reduces the inverter output during severe over‑currents, protecting both the turbine and the grid.
Correct answer is: Prevent damage by restricting fault current contribution
Q.38 A "Phase‑locked loop" (PLL) in a grid‑connected inverter is used to:
Measure grid voltage frequency and phase
Control battery charging
Limit harmonic distortion
Switch between grid and island mode
Explanation - PLL synchronizes the inverter’s internal reference frame with the grid’s voltage waveform.
Correct answer is: Measure grid voltage frequency and phase
Q.39 Which parameter is most directly affected by the "X/R ratio" of a transmission line during a fault?
Fault current magnitude
Voltage rise after fault clearance
Frequency deviation
Power factor
Explanation - A higher X/R ratio results in a more inductive line, influencing the decay of fault currents.
Correct answer is: Fault current magnitude
Q.40 In a hybrid renewable system, the term "energy arbitrage" refers to:
Buying electricity at low price and selling at high price using storage
Balancing active and reactive power
Maintaining constant voltage
Controlling turbine blade pitch
Explanation - Energy arbitrage uses storage to shift energy from periods of low price (or high generation) to periods of high demand or price.
Correct answer is: Buying electricity at low price and selling at high price using storage
Q.41 Which grid code requirement ensures that a PV inverter can ride through a voltage dip of 0.7 pu for 0.5 seconds?
Low‑Voltage Ride‑Through (LVRT) curve
Frequency droop characteristic
Reactive power set‑point
Maximum Power Point Tracking
Explanation - LVRT curves define the permissible voltage‑time combinations that an inverter must withstand without disconnecting.
Correct answer is: Low‑Voltage Ride‑Through (LVRT) curve
Q.42 Which technology can provide "grid inertia" without rotating masses?
Flywheel energy storage
Synthetic inertia from inverter control
Hydropower turbines
Synchronous condensers
Explanation - Synthetic inertia is generated by power electronic controllers that emulate the inertial response of rotating generators.
Correct answer is: Synthetic inertia from inverter control
Q.43 What is the main advantage of using a "soft‑starter" for a wind turbine generator?
Reduces mechanical stress during start‑up
Eliminates the need for a converter
Provides reactive power support
Increases turbine blade speed
Explanation - Soft‑starters gradually ramp up voltage and frequency, limiting torque spikes on the turbine shaft.
Correct answer is: Reduces mechanical stress during start‑up
Q.44 In a power system with high renewable penetration, the "frequency response" service is primarily provided by:
Synchronous generators
Battery energy storage systems
Transmission line inductance
Load tap changers
Explanation - BESS can quickly inject or absorb active power to counteract frequency deviations, offering fast frequency response.
Correct answer is: Battery energy storage systems
Q.45 The term "harmonic distortion" in a grid‑connected inverter is usually quantified by:
Total Harmonic Distortion (THD)
Power Factor
Frequency Deviation
Voltage Sag
Explanation - THD measures the ratio of the sum of harmonic component magnitudes to the fundamental component.
Correct answer is: Total Harmonic Distortion (THD)
Q.46 Which of the following best describes a "distributed generation" (DG) system?
A large central power plant
Small‑scale generation located close to the load
A transmission line upgrade
A high‑voltage substation
Explanation - DG includes rooftop solar, small wind turbines, and other generators sited near consumption points.
Correct answer is: Small‑scale generation located close to the load
Q.47 During a grid fault, the "symmetrical components" method is used to:
Separate the fault current into positive, negative, and zero sequence components
Calculate the power factor
Determine the PV array orientation
Control the battery state of charge
Explanation - Symmetrical components simplify analysis of unbalanced faults by breaking currents and voltages into sequence networks.
Correct answer is: Separate the fault current into positive, negative, and zero sequence components
Q.48 What is the typical rating (in kVA) of a distribution transformer used for a 1 MW solar farm?
500 kVA
1 MVA
2 MVA
5 MVA
Explanation - A 1 MW PV plant usually requires a transformer rated about twice the inverter capacity to handle overloads and reactive power.
Correct answer is: 2 MVA
Q.49 Which of the following is a key benefit of using a "Virtual Power Plant" (VPP) concept for renewable integration?
Physical aggregation of generators into a single plant
Coordinated control of dispersed resources to act as a single market participant
Elimination of all grid codes
Increase of line resistance
Explanation - VPP aggregates multiple small generators and storage devices, providing dispatchable power and ancillary services.
Correct answer is: Coordinated control of dispersed resources to act as a single market participant
Q.50 In a renewable‑integrated grid, which device can provide "black‑start" capability without external power?
Synchronous generator
Battery energy storage system
Solar PV inverter
Wind turbine with full‑scale converter
Explanation - BESS can supply the necessary power to start other generators and restore the grid after a blackout.
Correct answer is: Battery energy storage system
Q.51 The "Maximum Voltage Ride‑Through" (MVRT) requirement for an inverter is intended to:
Allow the inverter to stay connected during over‑voltage events
Force the inverter to disconnect immediately
Limit active power output to zero
Increase the inverter switching frequency
Explanation - MVRT ensures that inverters can tolerate short‑duration over‑voltages without tripping, supporting grid stability.
Correct answer is: Allow the inverter to stay connected during over‑voltage events
Q.52 Which renewable energy technology typically requires a "DC‑cable" of higher current rating compared to PV?
Onshore wind turbines
Concentrated solar power (CSP)
Geothermal plants
Hydroelectric turbines
Explanation - CSP plants often use high‑temperature thermal storage and generate high DC currents for large‑scale inverters.
Correct answer is: Concentrated solar power (CSP)
Q.53 What does the "capacity factor" of a renewable plant indicate?
Ratio of actual energy produced to its nameplate capacity over a period
Maximum power output at peak sun
Average voltage level of the plant
Number of turbines in the wind farm
Explanation - Capacity factor reflects how effectively a plant utilizes its rated capacity over time.
Correct answer is: Ratio of actual energy produced to its nameplate capacity over a period
Q.54 Which of the following control actions is most effective for mitigating a sudden drop in wind speed?
Increasing blade pitch angle
Reducing reactive power output
Switching to island mode
Increasing inverter switching frequency
Explanation - Pitch control quickly reduces aerodynamic torque, helping to smooth power output during wind gust changes.
Correct answer is: Increasing blade pitch angle
Q.55 In a grid‑connected inverter, the "grid current sensor" is primarily used to:
Measure the inverter’s output current
Detect islanding conditions
Synchronize with the grid voltage phase
Control MPPT algorithm
Explanation - The current sensor provides feedback for the PLL and ensures proper phase alignment with the grid.
Correct answer is: Synchronize with the grid voltage phase
Q.56 Which of the following is a common method to increase the effective inertia of a power system with high renewable penetration?
Deploying more synchronous generators
Using synthetic inertia from inverter controls
Installing larger transformers
Increasing line capacitance
Explanation - Synthetic inertia provides fast, inertia‑like response without physical rotating mass.
Correct answer is: Using synthetic inertia from inverter controls
Q.57 The "Curtailment" of renewable generation is typically performed when:
Voltage exceeds limits or there is insufficient demand
The sun is shining too brightly
The turbine blades are damaged
Battery SOC is at 100 %
Explanation - Curtailment reduces output to maintain grid stability or avoid over‑generation.
Correct answer is: Voltage exceeds limits or there is insufficient demand
Q.58 Which of the following statements about “net metering” is correct?
It allows consumers to sell excess generated electricity back to the grid at retail rates
It requires all renewable generators to operate at full capacity
It only applies to wind farms
It eliminates the need for inverters
Explanation - Net metering credits customers for excess energy exported to the utility, offsetting their electricity bills.
Correct answer is: It allows consumers to sell excess generated electricity back to the grid at retail rates
Q.59 In power electronics, the term "switching loss" refers to:
Losses due to resistance in conductors
Losses caused by the transition of semiconductor devices between ON and OFF states
Losses due to harmonic distortion
Losses in the magnetic core of transformers
Explanation - Switching loss occurs each time a MOSFET or IGBT changes state, affecting overall inverter efficiency.
Correct answer is: Losses caused by the transition of semiconductor devices between ON and OFF states
Q.60 Which of the following is a primary function of a "Dynamic Voltage Restorer" (DVR) in renewable integration?
Inject corrective voltage during sags to protect sensitive loads
Store energy for night‑time use
Control turbine speed
Convert DC to AC
Explanation - A DVR adds a series voltage to maintain load voltage during dips, improving power quality.
Correct answer is: Inject corrective voltage during sags to protect sensitive loads
Q.61 What does the "X/R ratio" of a short‑circuit influence in protection settings?
The required time‑delay for over‑current relays
The voltage magnitude at the load
The frequency of the system
The reactive power capability of inverters
Explanation - Higher X/R ratios result in slower decay of fault currents, affecting relay coordination.
Correct answer is: The required time‑delay for over‑current relays
Q.62 Which of the following is the most suitable metric to evaluate the impact of solar PV on a distribution feeder’s voltage profile?
Voltage deviation index (VDI)
Frequency deviation index
Total harmonic distortion (THD)
Short‑circuit ratio
Explanation - VDI quantifies how far bus voltages deviate from nominal values due to PV injection.
Correct answer is: Voltage deviation index (VDI)
Q.63 In a wind turbine’s full‑scale converter, the DC‑link voltage is typically regulated at:
400 V
600 V
1 kV to 1.5 kV
10 kV
Explanation - Modern full‑scale converters use a high‑voltage DC link to reduce current and improve efficiency.
Correct answer is: 1 kV to 1.5 kV
Q.64 Which grid code parameter defines the allowable rate of change of frequency (RoCoF) that the system must tolerate?
Voltage dip depth
Frequency deviation limit
Rate of Change of Frequency (RoCoF) limit
Harmonic distortion limit
Explanation - RoCoF limits protect equipment from rapid frequency excursions caused by large disturbances.
Correct answer is: Rate of Change of Frequency (RoCoF) limit
Q.65 A "synchronous condenser" is primarily used in renewable‑rich grids to:
Generate active power
Provide reactive power and inertia
Store DC energy
Convert AC to DC
Explanation - Synchronous condensers are rotating machines that supply reactive power and contribute inertia without generating active power.
Correct answer is: Provide reactive power and inertia
Q.66 In a grid‑connected inverter, the "feed‑forward” control technique is used to:
Compensate for known disturbances such as grid voltage variations
Increase the switching frequency
Detect islanding events
Control battery charging
Explanation - Feed‑forward control adds a corrective term based on measured disturbances, improving dynamic performance.
Correct answer is: Compensate for known disturbances such as grid voltage variations
Q.67 Which of the following best describes the function of a "Power‑to‑X" (P2X) system in renewable integration?
Convert excess electricity into hydrogen, synthetic fuels, or heat
Increase the voltage level of the grid
Provide frequency regulation using mechanical inertia
Store energy in large batteries only
Explanation - P2X technologies enable flexible use of surplus renewable electricity for various energy carriers.
Correct answer is: Convert excess electricity into hydrogen, synthetic fuels, or heat
Q.68 The term "grid‑forming inverter" differs from a "grid‑following inverter" because it:
Can operate without a pre‑existing grid voltage reference
Has lower efficiency
Requires a transformer
Only works with wind turbines
Explanation - Grid‑forming inverters establish voltage and frequency autonomously, while grid‑following inverters rely on the grid’s waveform.
Correct answer is: Can operate without a pre‑existing grid voltage reference
Q.69 Which of the following is NOT a typical ancillary service provided by inverter‑based resources?
Voltage regulation
Frequency regulation
Inertia provision
Physical line switching
Explanation - Ancillary services involve power control, not mechanical switching of lines.
Correct answer is: Physical line switching
Q.70 In power system stability, the term "small‑signal stability" refers to:
System response to large disturbances like faults
Ability to maintain synchronism after minor perturbations
Voltage rise due to high generation
Battery charging efficiency
Explanation - Small‑signal stability concerns the system's ability to damp oscillations caused by small disturbances.
Correct answer is: Ability to maintain synchronism after minor perturbations
Q.71 Which renewable technology typically uses a "DC‑link capacitor" of several millifarads to filter voltage ripple?
Solar PV inverter
Wind turbine full‑scale converter
Hydroelectric generator
Geothermal plant
Explanation - Full‑scale converters employ a high‑voltage DC link with large capacitors to smooth the DC voltage.
Correct answer is: Wind turbine full‑scale converter
Q.72 What is the main purpose of a "Phase‑Shifting Transformer" in a renewable‑rich transmission network?
Reduce line losses by shifting voltage phase angle
Control power flow between parallel paths
Increase short‑circuit current
Store energy during peak generation
Explanation - Phase‑shifting transformers adjust the phase angle to direct power along desired transmission corridors.
Correct answer is: Control power flow between parallel paths
Q.73 Which of the following best describes the term "distributed energy resource" (DER)?
Large central power plant
Any small‑scale generation or storage located close to the load
Only solar PV systems
Transmission line equipment
Explanation - DER includes solar, wind, battery storage, micro‑turbines, and demand‑response resources at the distribution level.
Correct answer is: Any small‑scale generation or storage located close to the load
Q.74 In a grid‑connected PV system, the "Reactive Power Capability Curve" shows:
Maximum reactive power that can be supplied at each active power level
Battery state of charge
Sunlight intensity over time
Inverter switching frequency
Explanation - The curve defines the trade‑off between active and reactive power that the inverter can deliver.
Correct answer is: Maximum reactive power that can be supplied at each active power level
Q.75 Which of the following is a primary reason for installing "series reactors" in a renewable‑integrated feeder?
To limit fault currents
To increase active power flow
To provide frequency support
To store energy
Explanation - Series reactors add inductance, reducing the magnitude of short‑circuit currents and protecting equipment.
Correct answer is: To limit fault currents
Q.76 The "grid‑code compliant" reactive power requirement for an inverter at 0.8 pu voltage is typically:
±0.5 p.u.
±0.2 p.u.
0 p.u. only
±1.0 p.u.
Explanation - Many grid codes demand that inverters can supply or absorb reactive power up to 0.5 p.u. to support voltage regulation.
Correct answer is: ±0.5 p.u.
Q.77 Which of the following best defines "Power Quality" in the context of renewable integration?
The ability to maintain voltage, frequency, and harmonic limits within standards
The total amount of energy generated per year
The mechanical reliability of wind turbines
The size of the solar array
Explanation - Power quality encompasses voltage sag, swell, flicker, harmonics, and frequency deviations.
Correct answer is: The ability to maintain voltage, frequency, and harmonic limits within standards
Q.78 In a hybrid renewable system, the term "DC‑bus" refers to:
The common DC connection point for multiple converters
A high‑voltage transmission line
The AC output terminal of the inverter
A protective relay
Explanation - The DC‑bus links PV arrays, batteries, and other DC sources before conversion to AC.
Correct answer is: The common DC connection point for multiple converters
Q.79 Which of the following is a key advantage of using a "Modular Multilevel Converter" (MMC) for HVDC links in renewable integration?
Reduced number of semiconductor devices
High scalability and lower harmonic distortion
Elimination of cooling requirements
Simplified control algorithms
Explanation - MMC architecture allows modular scaling and produces a near‑sinusoidal output with low harmonics.
Correct answer is: High scalability and lower harmonic distortion
Q.80 The "energy yield" of a solar PV plant is typically expressed in:
kWh per kW installed per year
MW per hour
VA per meter
Hz per kilowatt
Explanation - Energy yield normalizes annual production to the installed capacity, allowing comparison across sites.
Correct answer is: kWh per kW installed per year
Q.81 During a three‑phase short‑circuit, which component of the fault current is most responsible for triggering over‑current relays?
Zero‑sequence component
Positive‑sequence component
Negative‑sequence component
Harmonic component
Explanation - Positive‑sequence current dominates symmetrical faults and is used by most over‑current protection schemes.
Correct answer is: Positive‑sequence component
Q.82 Which renewable energy technology is most suited for providing continuous baseload power?
Solar PV
Onshore wind
Geothermal
Wave energy
Explanation - Geothermal plants can deliver stable, continuous power irrespective of weather conditions.
Correct answer is: Geothermal
Q.83 In grid integration studies, the term "load flow analysis" is used to:
Determine voltage magnitude and phase angles throughout the network
Calculate the frequency response of generators
Predict solar irradiance
Design inverter switching patterns
Explanation - Load flow (or power flow) computes steady‑state operating conditions of the power system.
Correct answer is: Determine voltage magnitude and phase angles throughout the network
Q.84 Which of the following is a primary cause of "reverse power flow" in distribution networks?
High consumer demand
Large amounts of distributed generation exporting power to the grid
Faulty transformers
Low voltage at the substation
Explanation - When local generation exceeds local demand, power flows back toward the transmission system.
Correct answer is: Large amounts of distributed generation exporting power to the grid
Q.85 A "grid‑supportive" inverter can provide which of the following services during normal operation?
Active power curtailment only
Reactive power injection/absorption, voltage regulation, and frequency support
Island operation
Automatic transformer tap changing
Explanation - Grid‑supportive (or smart) inverters are capable of multiple ancillary services while connected to the grid.
Correct answer is: Reactive power injection/absorption, voltage regulation, and frequency support
Q.86 In an HVDC link, the term "commutation failure" refers to:
Inability of the thyristors to turn off properly due to insufficient voltage
Loss of synchronization with the grid
Overheating of the converter cooling system
Failure of the DC cable insulation
Explanation - Commutation failure occurs when the voltage across a thyristor falls below the required value to extinguish its current.
Correct answer is: Inability of the thyristors to turn off properly due to insufficient voltage
Q.87 Which of the following is a typical control objective for a battery energy storage system participating in a frequency regulation market?
Maintain a constant state of charge
Provide a predetermined amount of power in response to frequency deviations
Operate at unity power factor at all times
Limit inverter switching frequency to 2 kHz
Explanation - BESS must quickly inject or absorb power proportional to the measured frequency error to help stabilize the grid.
Correct answer is: Provide a predetermined amount of power in response to frequency deviations
Q.88 The "grid impedance" seen by a renewable inverter most directly affects:
The inverter’s maximum active power capability
The harmonic distortion at the point of interconnection
The inverter’s ability to ride through voltage dips
The inverter’s thermal rating
Explanation - Higher grid impedance limits the current that can be supplied during low‑voltage events, influencing LVRT performance.
Correct answer is: The inverter’s ability to ride through voltage dips
Q.89 Which of the following best describes the function of a "Phase‑shifting transformer" used in a renewable‑heavy grid?
Regulate voltage magnitude
Control power flow by altering phase angle between interconnected networks
Increase frequency stability
Convert DC to AC
Explanation - By shifting the phase, these transformers steer active power along desired transmission paths.
Correct answer is: Control power flow by altering phase angle between interconnected networks
Q.90 In the context of renewable integration, the term "firm capacity" refers to:
The maximum instantaneous power output of a plant
The guaranteed power that can be delivered with high reliability
The nameplate capacity of the plant
The amount of energy stored in a battery
Explanation - Firm capacity accounts for variability and is the amount of power that can be counted on with a certain confidence level.
Correct answer is: The guaranteed power that can be delivered with high reliability
Q.91 Which of the following control methods is commonly used to improve the voltage stability of a high‑penetration PV system?
Droop control of active power
Volt‑Var control (VVC)
Frequency droop control
Current limiting
Explanation - VVC adjusts reactive power based on local voltage, helping to maintain voltage within limits.
Correct answer is: Volt‑Var control (VVC)
Q.92 The term "Island Mode" in inverter operation means:
The inverter continues to feed power to the grid after a fault
The inverter operates autonomously, supplying a local load without grid support
The inverter shuts down completely
The inverter only provides reactive power
Explanation - Island mode allows the inverter to form a microgrid, delivering power to local loads when the main grid is unavailable.
Correct answer is: The inverter operates autonomously, supplying a local load without grid support
Q.93 Which of the following is a typical consequence of high solar PV penetration on the night‑time load curve?
Increased peak demand
Reduced net load during the day and a steep evening ramp‑up
Constant load throughout the day
Elimination of base load generation
Explanation - Solar generation lowers daytime load, but as the sun sets, the net load rises sharply, creating a ramp challenge.
Correct answer is: Reduced net load during the day and a steep evening ramp‑up
Q.94 In a grid‑connected inverter, the "PWM carrier frequency" influences:
The amount of active power produced
The magnitude of switching losses and harmonic content
The frequency of the grid
The battery charging speed
Explanation - Higher carrier frequencies reduce harmonic distortion but increase switching losses.
Correct answer is: The magnitude of switching losses and harmonic content
Q.95 Which of the following devices can provide fast reactive power support without any moving parts?
Synchronous condenser
Static VAR compensator (SVC)
Hydraulic turbine
Flywheel storage
Explanation - SVCs use power electronics to inject or absorb reactive power rapidly, aiding voltage regulation.
Correct answer is: Static VAR compensator (SVC)
Q.96 The term "DC‑link voltage ripple" in a wind turbine converter is primarily caused by:
Fluctuations in wind speed
Switching actions of the inverter
Variations in grid frequency
Battery temperature changes
Explanation - The high‑frequency switching of the converter creates voltage ripples on the DC link, which are filtered by capacitors.
Correct answer is: Switching actions of the inverter
Q.97 Which of the following is a key metric used to assess the reliability of a renewable energy plant?
Capacity factor
Mean Time Between Failures (MTBF)
Solar irradiance
Wind speed histogram
Explanation - MTBF quantifies the average time between successive failures, indicating plant reliability.
Correct answer is: Mean Time Between Failures (MTBF)
Q.98 In a power system with high renewable penetration, "frequency containment reserve" (FCR) is primarily provided by:
Synchronous generators and fast‑acting battery storage
Passive filters
Transformers with on‑load tap changers
Static VAR compensators
Explanation - FCR requires rapid active power response; batteries and conventional generators are the main sources.
Correct answer is: Synchronous generators and fast‑acting battery storage
Q.99 Which of the following statements about "grid‑forming converters" is FALSE?
They can operate in island mode without a grid reference
They provide voltage and frequency reference for the network
They rely on the grid voltage to set their output frequency
They can support voltage and frequency during disturbances
Explanation - Grid‑forming converters generate their own voltage and frequency reference, unlike grid‑following converters that depend on the grid.
Correct answer is: They rely on the grid voltage to set their output frequency
Q.100 What is the typical response time (in seconds) for a battery energy storage system to provide frequency regulation after a grid disturbance?
10–30 s
1–5 s
0.1–0.5 s
60–120 s
Explanation - BESS can respond within hundreds of milliseconds, offering ultra‑fast frequency regulation.
Correct answer is: 0.1–0.5 s
Q.101 Which of the following is a common technique to reduce the size of the DC‑link capacitor in a photovoltaic inverter?
Increase the switching frequency
Decrease the MPPT voltage
Use larger transformer
Add series reactors
Explanation - Higher switching frequency reduces the required ripple current, allowing smaller capacitance values.
Correct answer is: Increase the switching frequency
Q.102 In the context of renewable integration, the term "curtailment ratio" indicates:
The proportion of generated energy that is not exported to the grid
The ratio of active to reactive power
The efficiency of the inverter
The amount of storage capacity relative to generation
Explanation - Curtailment ratio = (energy curtailed) / (total available generation).
Correct answer is: The proportion of generated energy that is not exported to the grid
Q.103 Which of the following is a primary benefit of using "virtual inertia" from inverter controls compared to physical inertia?
Zero cost
Instantaneous response without mechanical delay
Higher energy storage capacity
Reduced need for transformers
Explanation - Virtual inertia can be activated in milliseconds, faster than the mechanical response of rotating masses.
Correct answer is: Instantaneous response without mechanical delay
Q.104 A "grid‑supportive" PV inverter operating under low‑voltage conditions must primarily:
Increase active power output
Inject reactive power to raise local voltage
Switch off to protect the grid
Operate at unity power factor
Explanation - Injecting reactive power helps lift the voltage during low‑voltage events, satisfying LVRT requirements.
Correct answer is: Inject reactive power to raise local voltage
Q.105 Which of the following components in a renewable energy system is most directly responsible for converting variable mechanical speed into a fixed AC frequency?
Transformer
DC‑link capacitor
Full‑scale power electronic converter
MPPT controller
Explanation - Full‑scale converters decouple the generator speed from the grid frequency, delivering fixed‑frequency AC.
Correct answer is: Full‑scale power electronic converter
Q.106 In power system protection, the "distance relay" calculates impedance based on:
Voltage and current measurements at its location
Frequency deviation
Reactive power flow
Temperature of the conductor
Explanation - Distance relays estimate line impedance from local voltage and current to determine fault location.
Correct answer is: Voltage and current measurements at its location
Q.107 Which of the following best describes the role of "synthetic inertia" in a renewable‑rich grid?
Providing physical rotating mass
Emulating inertial response via fast active power adjustments
Storing energy as chemical fuel
Increasing line reactance
Explanation - Synthetic inertia uses inverter control to mimic the kinetic energy response of rotating generators.
Correct answer is: Emulating inertial response via fast active power adjustments
Q.108 The "Maximum Power Point (MPP)" of a solar panel depends primarily on:
Grid voltage
Solar irradiance and cell temperature
Battery state of charge
Inverter switching frequency
Explanation - MPP varies with the amount of sunlight and temperature, influencing the optimal voltage and current.
Correct answer is: Solar irradiance and cell temperature
Q.109 In a high‑voltage transmission system, "Series FACTS devices" such as STATCOMs are used to:
Provide reactive power support in series with the line
Increase active power generation
Store large amounts of energy
Switch off the line during faults
Explanation - Series FACTS devices inject series voltage to control power flow and improve voltage stability.
Correct answer is: Provide reactive power support in series with the line
Q.110 Which of the following is an advantage of using a "microgrid" with high renewable penetration?
Elimination of all grid codes
Improved resilience and ability to operate autonomously
Guaranteed zero curtailment
Reduced need for any storage
Explanation - Microgrids can island during disturbances, maintaining power supply for critical loads.
Correct answer is: Improved resilience and ability to operate autonomously
Q.111 The term "Phase Angle Difference" between two generators is important for:
Ensuring synchronism and power sharing
Measuring harmonic distortion
Determining transformer tap settings
Calculating battery state of charge
Explanation - Phase angle differences determine active power flow and stability between synchronized generators.
Correct answer is: Ensuring synchronism and power sharing
Q.112 Which of the following is typically the most limiting factor for the size of a renewable‑based inverter connected to a weak grid?
Thermal rating of the transformer
Grid short‑circuit ratio (SCR)
Battery capacity
Solar irradiance
Explanation - A low SCR indicates a weak grid, limiting the amount of inverter‑sourced current that can be safely injected.
Correct answer is: Grid short‑circuit ratio (SCR)