Q.1 What is the main purpose of primary frequency control in a power system?
To balance supply and demand instantly
To change the voltage level
To switch power plants on and off
To measure the temperature of generators
Explanation - Primary frequency control, also known as droop control, reacts automatically to small changes in system frequency to maintain supply–demand balance.
Correct answer is: To balance supply and demand instantly
Q.2 Which component in a generator is responsible for adjusting its speed to maintain frequency?
Governor
Transformer
Capacitor bank
Breaker
Explanation - The governor senses frequency deviations and changes the turbine input to keep the generator speed and system frequency steady.
Correct answer is: Governor
Q.3 What unit is used to measure electric power in a power system?
Volt
Ampere
Watt
Hertz
Explanation - Power is measured in watts (W), representing the rate of energy transfer per unit time.
Correct answer is: Watt
Q.4 In a simple electric circuit, the voltage is the difference in which of the following?
Current
Resistance
Potential energy
Pressure
Explanation - Voltage (or electric potential difference) is the amount of electric potential energy per charge between two points.
Correct answer is: Potential energy
Q.5 What happens to system frequency when the load suddenly increases?
It rises
It falls
It stays the same
It oscillates randomly
Explanation - An increase in load reduces frequency because generators cannot instantly provide additional power.
Correct answer is: It falls
Q.6 Which device helps maintain the voltage level in a transformer?
Capacitor bank
Reactor
Tapered tap changer
Motor
Explanation - The tap changer adjusts the transformer's turns ratio to regulate output voltage.
Correct answer is: Tapered tap changer
Q.7 What is the unit of electrical frequency?
Volt
Watt
Hertz
Ohm
Explanation - Frequency is measured in hertz (Hz), indicating cycles per second.
Correct answer is: Hertz
Q.8 Which of the following is NOT a source of reactive power?
Inductive loads
Capacitive loads
Resistive loads
Capacitor banks
Explanation - Resistive loads consume real power but do not generate reactive power.
Correct answer is: Resistive loads
Q.9 What is the typical frequency of the North American power grid?
50 Hz
60 Hz
30 Hz
70 Hz
Explanation - North America uses a standard grid frequency of 60 Hz.
Correct answer is: 60 Hz
Q.10 When a power plant increases its output, which of the following will happen?
The frequency will increase
The voltage will drop
The current will decrease
The resistance will increase
Explanation - Increasing generation adds power, causing system frequency to rise if not balanced by load changes.
Correct answer is: The frequency will increase
Q.11 What is the role of a capacitor bank in voltage control?
It reduces the voltage
It increases the voltage
It supplies reactive power to support voltage
It supplies real power to support voltage
Explanation - Capacitors provide leading reactive power, helping maintain voltage levels during load changes.
Correct answer is: It supplies reactive power to support voltage
Q.12 Which control strategy is used to regulate generator output in response to frequency deviations within 10 seconds?
Primary control
Secondary control
Tertiary control
Quaternary control
Explanation - Primary control (droop control) acts within seconds to balance supply and demand locally.
Correct answer is: Primary control
Q.13 What is droop in the context of governor control?
The amount of voltage that can be changed
The percentage drop in frequency per unit of power change
The change in temperature of the turbine
The slope of the voltage–current curve
Explanation - Droop defines how much the governor will reduce speed as frequency rises, proportional to power output changes.
Correct answer is: The percentage drop in frequency per unit of power change
Q.14 Which device is used to change the voltage ratio in a power transformer?
Tap changer
Capacitor bank
Regulator
Reactor
Explanation - A tap changer adjusts the transformer's turns ratio, changing the output voltage.
Correct answer is: Tap changer
Q.15 What does the term 'voltage regulation' refer to?
The ability to change frequency
The ability to maintain constant voltage under load changes
The ability to increase power output
The ability to regulate temperature
Explanation - Voltage regulation measures how well a system keeps voltage steady when load varies.
Correct answer is: The ability to maintain constant voltage under load changes
Q.16 Which component supplies leading reactive power to help raise system voltage?
Inductors
Capacitors
Resistors
Turbines
Explanation - Capacitors provide leading reactive power, which helps raise voltage levels.
Correct answer is: Capacitors
Q.17 During a frequency dip, what is the immediate action taken by a governor?
It reduces fuel input
It increases fuel input
It disconnects the generator
It shuts down the turbine
Explanation - The governor raises turbine input to increase generator output and counteract the frequency drop.
Correct answer is: It increases fuel input
Q.18 What does the term 'reactive power' refer to?
Power that does useful work
Power that circulates but does not do useful work
Power measured in watts
Power measured in hertz
Explanation - Reactive power (VAR) is the power that oscillates between source and load, sustaining electric and magnetic fields.
Correct answer is: Power that circulates but does not do useful work
Q.19 Which control method is known as 'automatic voltage regulator' (AVR) in a generator?
Frequency control
Voltage control
Load control
Temperature control
Explanation - AVR adjusts the excitation of the generator to keep terminal voltage at a set level.
Correct answer is: Voltage control
Q.20 Which of the following best describes the role of the 'secondary' frequency control?
It corrects frequency deviations within seconds
It balances frequency over a longer time period using the governor setpoint
It shuts down generators during faults
It manages transformer tap changes
Explanation - Secondary control (AGC) adjusts the reference frequency to bring the system back to its nominal value.
Correct answer is: It balances frequency over a longer time period using the governor setpoint
Q.21 What is the typical range of frequency deviation allowed in most power systems?
±5 Hz
±1 Hz
±0.1 Hz
±10 Hz
Explanation - Power systems are designed to keep frequency within ±0.1 Hz of the nominal value for stability.
Correct answer is: ±0.1 Hz
Q.22 Which device in a power system provides a rapid supply of reactive power during voltage sags?
Synchronous condenser
Synchronous generator
Capacitor bank
Inductor bank
Explanation - A synchronous condenser can quickly provide or absorb reactive power to support voltage levels.
Correct answer is: Synchronous condenser
Q.23 What does the acronym 'AGC' stand for in power system control?
Automatic Grid Controller
Automatic Generation Control
Advanced Grid Computation
Auxiliary Grid Circuit
Explanation - AGC is the secondary frequency control that adjusts the output of generating units to maintain system frequency.
Correct answer is: Automatic Generation Control
Q.24 When the system voltage rises above its set point, what action does an AVR take?
Increases excitation voltage
Decreases excitation voltage
Increases generator speed
Decreases generator speed
Explanation - The AVR lowers the field excitation to reduce terminal voltage when it exceeds the target.
Correct answer is: Decreases excitation voltage
Q.25 Which of these is a primary cause of voltage instability in a power system?
Excessive load growth without reactive support
High frequency deviations
Low generator inertia
Faults in the transmission network
Explanation - When loads increase without adequate reactive power, voltages can collapse, leading to instability.
Correct answer is: Excessive load growth without reactive support
Q.26 What type of control is used to schedule large generator output adjustments over hours?
Primary control
Secondary control
Tertiary control
Quaternary control
Explanation - Tertiary control manages economic dispatch and scheduling of generators over longer periods.
Correct answer is: Tertiary control
Q.27 Which phenomenon describes the increase in frequency due to a sudden loss of generation?
Frequency dip
Frequency rise
Frequency drop
Frequency oscillation
Explanation - When generation drops, remaining generators run faster, raising frequency before controls intervene.
Correct answer is: Frequency rise
Q.28 What is the typical value of the droop coefficient for large thermal generators?
0.05
0.5
1.0
2.0
Explanation - Large generators often have droop coefficients around 0.5%, meaning a 1% frequency change produces a 0.5% change in power output.
Correct answer is: 0.5
Q.29 Which component can be used to supply both reactive and real power for voltage support?
Synchronous condenser
Synchronous generator
Capacitor bank
Inductive load
Explanation - Unlike a generator, a synchronous condenser is operated without a shaft and can provide variable reactive power.
Correct answer is: Synchronous condenser
Q.30 What is the main objective of the secondary frequency control (AGC) in a multi-area power system?
To maintain voltage within ±10%
To equalize frequency and tie-line power flows among areas
To regulate temperature of generators
To synchronize transformers
Explanation - AGC coordinates power generation among areas to keep frequency and inter‑area power exchange on target.
Correct answer is: To equalize frequency and tie-line power flows among areas
Q.31 Which of the following is NOT a type of voltage regulator?
Static voltage regulator
Dynamic voltage regulator
Thermal voltage regulator
Automatic voltage regulator
Explanation - Voltage regulators adjust voltage electronically; there is no standard 'thermal' regulator.
Correct answer is: Thermal voltage regulator
Q.32 What is the function of a 'step‑down transformer' in a distribution network?
To increase voltage
To decrease voltage
To control current
To regulate frequency
Explanation - Step‑down transformers reduce high transmission voltages to safer levels for local use.
Correct answer is: To decrease voltage
Q.33 Which element in a power system is primarily responsible for delivering reactive power to the grid?
Reactors
Capacitor banks
Transformers
Turbines
Explanation - Capacitor banks provide leading reactive power to support voltage levels throughout the grid.
Correct answer is: Capacitor banks
Q.34 What is the typical frequency of the European power grid?
50 Hz
60 Hz
45 Hz
55 Hz
Explanation - Europe and many other regions use a standard grid frequency of 50 Hz.
Correct answer is: 50 Hz
Q.35 Which of these best describes 'voltage collapse'?
A temporary surge in voltage
A rapid decrease in voltage due to loss of reactive power
An increase in frequency
A change in transformer tap ratio
Explanation - Voltage collapse occurs when the system can no longer maintain voltage due to insufficient reactive support.
Correct answer is: A rapid decrease in voltage due to loss of reactive power
Q.36 Which parameter is critical for assessing voltage stability margins?
Short‑circuit voltage
Load factor
Power factor
Thermal rating
Explanation - Short‑circuit voltage levels influence how much voltage drop a system can tolerate before collapsing.
Correct answer is: Short‑circuit voltage
Q.37 In a power system, what is the relationship between real power, reactive power, and apparent power?
S = P + Q
S = P × Q
S² = P² + Q²
S = P ÷ Q
Explanation - Apparent power (S) is the vector sum of real (P) and reactive (Q) power: S² = P² + Q².
Correct answer is: S² = P² + Q²
Q.38 Which control strategy adjusts generator output based on load forecasts over a day?
Primary control
Secondary control
Tertiary control
Quaternary control
Explanation - Tertiary control schedules generation over long periods using load forecasting and economic dispatch.
Correct answer is: Tertiary control
Q.39 Which of the following is an indicator of poor voltage regulation?
Voltage drop of more than 5% under load
Frequency fluctuation of 0.05 Hz
Temperature rise in generators
High power factor
Explanation - Significant voltage drop under load indicates inadequate voltage support or regulation.
Correct answer is: Voltage drop of more than 5% under load
Q.40 What is the main function of the Automatic Voltage Regulator (AVR) in synchronous generators?
Regulate frequency
Control reactive power injection
Maintain terminal voltage within set limits
Adjust generator speed
Explanation - AVR adjusts the field excitation to keep terminal voltage at the desired setpoint.
Correct answer is: Maintain terminal voltage within set limits
Q.41 Which of these best describes 'frequency response' of a power system?
The speed at which voltage changes
The change in frequency following a disturbance
The response time of a transformer tap changer
The reaction of load to voltage changes
Explanation - Frequency response describes how the system frequency changes after a disturbance and how control devices react.
Correct answer is: The change in frequency following a disturbance
Q.42 Which control loop uses a governor and a turbine to adjust mechanical power output?
Voltage control loop
Frequency control loop
Thermal control loop
Load control loop
Explanation - The frequency control loop adjusts mechanical power via the governor-turbine system to maintain frequency.
Correct answer is: Frequency control loop
Q.43 Which of the following is a typical application of a synchronous condenser?
Providing real power during peak loads
Stabilizing system voltage by injecting reactive power
Increasing system frequency during brownouts
Cooling power transformers
Explanation - Synchronous condensers supply leading reactive power, helping maintain voltage stability.
Correct answer is: Stabilizing system voltage by injecting reactive power
Q.44 What does the term 'synchronism' mean in power system operation?
Matching of voltage magnitudes
Matching of frequency, voltage magnitude, and phase angle among generators
Matching of thermal ratings
Matching of generator types
Explanation - Synchronism ensures all generators operate in harmony, preventing circulating currents and instability.
Correct answer is: Matching of frequency, voltage magnitude, and phase angle among generators
Q.45 Which of the following best describes the 'tie‑line power flow' in a multi‑area power system?
Power flow between generators in the same area
Power flow across boundary lines connecting different control areas
Power flow within a transformer
Power flow between load and generation within one area
Explanation - Tie‑line power flow represents the exchange of power between two control areas through interconnections.
Correct answer is: Power flow across boundary lines connecting different control areas
Q.46 In a droop controller, if the droop slope is increased, what happens to the system's frequency response to a load change?
Faster frequency response
Slower frequency response
No change
Frequency overshoot
Explanation - A higher droop slope means the governor allows less change in power for a given frequency deviation, slowing the response.
Correct answer is: Slower frequency response
Q.47 Which parameter is crucial for the design of a capacitor bank for voltage support?
Capacitance value in Farads
Number of turns in transformer
Voltage rating of the lines
Thermal rating of the generator
Explanation - The capacitance determines how much reactive power the bank can provide to support voltage.
Correct answer is: Capacitance value in Farads
Q.48 What is the primary reason for using a 'reactive power controller' in an industrial plant?
To increase real power output
To maintain power factor close to unity
To control generator speed
To regulate system frequency
Explanation - Reactive power controllers adjust capacitor or reactor banks to keep the plant's power factor near 1, minimizing losses.
Correct answer is: To maintain power factor close to unity
Q.49 Which of these best explains 'load frequency control' (LFC)?
The adjustment of load to keep frequency constant
The control of generator frequency to match load frequency
The use of load variations to regulate system frequency
The measurement of frequency during load changes
Explanation - LFC uses changes in load and generation to balance frequency, ensuring it stays at the nominal value.
Correct answer is: The use of load variations to regulate system frequency
Q.50 Which of the following is a direct consequence of having insufficient reactive power support during a fault?
System frequency rises
Voltage collapse
Generator speed increases
Load shedding is prevented
Explanation - Lack of reactive power leads to a voltage drop that can trigger a voltage collapse if not corrected.
Correct answer is: Voltage collapse
Q.51 What is the main difference between a step‑up transformer and a step‑down transformer?
Step‑up increases voltage, step‑down decreases voltage
Step‑up decreases voltage, step‑down increases voltage
Step‑up uses a tap changer, step‑down does not
Step‑up is used only in transmission, step‑down only in distribution
Explanation - Step‑up transformers increase voltage for efficient transmission; step‑down transformers reduce voltage for local use.
Correct answer is: Step‑up increases voltage, step‑down decreases voltage
Q.52 Which of the following devices directly controls the output voltage of a power transformer?
Tap changer
Capacitor bank
Turbine governor
Reactive power controller
Explanation - The tap changer modifies the transformer's turns ratio to adjust its output voltage.
Correct answer is: Tap changer
Q.53 What is the primary role of a synchronous condenser in a power grid?
Generate real power
Provide reactive power to support voltage
Increase system frequency
Control transformer tap settings
Explanation - A synchronous condenser supplies or absorbs reactive power without producing real power, helping maintain voltage levels.
Correct answer is: Provide reactive power to support voltage
Q.54 Which of the following statements about voltage regulation is FALSE?
It measures the change in voltage from no load to full load
Better regulation means a higher voltage drop
It is expressed as a percentage
It depends on transformer tap settings
Explanation - Better voltage regulation results in a smaller voltage drop between no load and full load.
Correct answer is: Better regulation means a higher voltage drop
Q.55 Which part of a generator is adjusted by the Automatic Voltage Regulator (AVR) to control terminal voltage?
Stator winding
Rotor field excitation
Turbine speed
Generator housing
Explanation - AVR changes the field current in the rotor, altering the generated EMF and thereby controlling voltage.
Correct answer is: Rotor field excitation
Q.56 What is the typical speed of a large synchronous generator in a 60 Hz power system?
3000 rpm
1800 rpm
600 rpm
2400 rpm
Explanation - A 60 Hz, 3‑phase synchronous generator running at 4 poles rotates at 3000 rpm.
Correct answer is: 3000 rpm
Q.57 Which of the following best describes the concept of 'voltage stability margin'?
The amount of voltage that can be lost before collapse
The time it takes for voltage to recover after a fault
The maximum voltage the transformer can handle
The difference between high and low voltage sides
Explanation - Voltage stability margin indicates how close the system is to voltage collapse; larger margins mean greater stability.
Correct answer is: The amount of voltage that can be lost before collapse
Q.58 Which parameter is directly affected by increasing the number of turns in the transformer’s secondary winding?
Voltage ratio
Current ratio
Resistance
Frequency
Explanation - Increasing secondary turns raises the secondary voltage relative to the primary.
Correct answer is: Voltage ratio
Q.59 Which control method provides the fastest response to a sudden load change?
Primary control (droop)
Secondary control (AGC)
Tertiary control (economic dispatch)
Quaternary control (manual operation)
Explanation - Primary control reacts within seconds to counteract frequency changes caused by load fluctuations.
Correct answer is: Primary control (droop)
Q.60 What is the function of a 'reactive power compensation system' in an industrial plant?
To increase real power output
To maintain voltage and reduce losses
To stabilize frequency
To control generator speed
Explanation - Reactive compensation supplies or absorbs reactive power, keeping voltage within limits and decreasing transmission losses.
Correct answer is: To maintain voltage and reduce losses
Q.61 Which of the following is a typical measure of frequency deviation in a power system?
Hz
V
A
Ω
Explanation - Frequency is measured in hertz (Hz), representing cycles per second.
Correct answer is: Hz
Q.62 A capacitor bank can be switched into the system to provide what type of power?
Real power
Reactive power
Both real and reactive power
Neither real nor reactive power
Explanation - Capacitors provide leading reactive power, which supports system voltage.
Correct answer is: Reactive power
Q.63 Which of the following is NOT a function of a governor in a power system?
Maintain generator speed
Control fuel flow
Adjust transformer taps
React to frequency changes
Explanation - Governors control mechanical input; tap changers are separate devices for voltage regulation.
Correct answer is: Adjust transformer taps
Q.64 Which of the following describes the effect of a sudden fault on system voltage?
Voltage rises
Voltage drops
Frequency rises
Current decreases
Explanation - A fault creates a large short‑circuit current, causing the voltage to collapse at the fault point.
Correct answer is: Voltage drops
Q.65 What is the main purpose of a step‑down transformer in residential distribution?
To increase voltage to 110 V
To decrease voltage to 110 V
To regulate frequency
To control current flow
Explanation - Step‑down transformers lower high transmission voltages to safe residential levels (~110 V).
Correct answer is: To decrease voltage to 110 V
Q.66 In a power system, which of these is an example of 'primary frequency control'?
Automatic Voltage Regulator
Generator governor adjusting turbine input
Tertiary dispatch of generators
Load shedding program
Explanation - Primary frequency control involves governors reacting to frequency changes by adjusting turbine power output.
Correct answer is: Generator governor adjusting turbine input
Q.67 Which of the following components supplies leading reactive power to support voltage during a load increase?
Synchronous generator
Capacitor bank
Transformer tap changer
Turbine governor
Explanation - Capacitors provide leading reactive power, which raises voltage when load increases.
Correct answer is: Capacitor bank
Q.68 The 'short‑circuit voltage' of a generator is defined as the voltage produced when:
No load is applied
Maximum load is applied
The generator is short‑circuited at the terminals
The governor is turned off
Explanation - Short‑circuit voltage is the voltage across the generator terminals under a short‑circuit condition.
Correct answer is: The generator is short‑circuited at the terminals
Q.69 What is the effect of increasing the droop slope in a governor?
Faster frequency response
Slower frequency response
No change in response time
Instantaneous response
Explanation - A larger droop slope reduces the change in power for a given frequency deviation, slowing the response.
Correct answer is: Slower frequency response
Q.70 Which of these devices can be used to change the transformer's voltage ratio in real time?
Tap changer
Capacitor bank
Generator governor
Reactor
Explanation - A tap changer modifies the transformer's turns ratio to adjust voltage during operation.
Correct answer is: Tap changer
Q.71 In a power system, the 'load‑frequency characteristic' (LFC) is best described as:
The relationship between load and voltage
The relationship between load and frequency
The relationship between voltage and frequency
The relationship between load and power factor
Explanation - LFC studies how changes in load affect system frequency and how control actions can compensate.
Correct answer is: The relationship between load and frequency
Q.72 Which of the following is a direct indicator of the system's ability to resist a frequency change?
Inertia constant
Thermal rating
Voltage stability margin
Power factor
Explanation - The inertia constant determines how much kinetic energy is stored in rotating masses, affecting frequency stability.
Correct answer is: Inertia constant
Q.73 Which of the following best explains the concept of 'voltage dip'?
A sudden rise in voltage
A temporary reduction in voltage due to load changes or faults
A permanent voltage increase
A change in frequency
Explanation - Voltage dips occur when a fault or load change causes a brief voltage sag.
Correct answer is: A temporary reduction in voltage due to load changes or faults
Q.74 What is the main advantage of using a synchronous condenser over a capacitor bank for voltage support?
Higher real power output
Variable reactive power with speed control
Lower cost
No need for control systems
Explanation - Synchronous condensers can change reactive power by adjusting speed, offering dynamic voltage support.
Correct answer is: Variable reactive power with speed control
Q.75 Which of the following is an example of tertiary control in a power system?
Governor droop adjustment
Automatic Frequency Control (AGC)
Economic dispatch scheduling
Load shedding during a blackout
Explanation - Tertiary control involves long‑term scheduling of generator outputs based on economic criteria.
Correct answer is: Economic dispatch scheduling
Q.76 Which of the following is a typical measurement used to assess voltage regulation at a transformer?
Voltage drop percentage
Power factor angle
Frequency deviation
Load factor
Explanation - Voltage regulation is expressed as the percentage change in voltage from no load to full load.
Correct answer is: Voltage drop percentage
Q.77 What is the main cause of frequency oscillations in a power system?
Load fluctuations
Generator governor lag
Transformer tap changes
Capacitor bank operation
Explanation - Sudden changes in load can cause the system to oscillate in frequency until controls restore balance.
Correct answer is: Load fluctuations
Q.78 Which of these is a typical method to increase system voltage in a distribution network?
Adding a step‑up transformer
Adding a capacitor bank
Adding a load tap changer
Adding a synchronous condenser
Explanation - Capacitor banks provide reactive power, which raises system voltage.
Correct answer is: Adding a capacitor bank
Q.79 Which component in a power system is primarily responsible for delivering reactive power to the grid during a fault?
Capacitor bank
Synchronous condenser
Synchronous generator
Turbine governor
Explanation - Synchronous condensers can quickly provide reactive power to support the voltage during faults.
Correct answer is: Synchronous condenser
Q.80 Which of the following best defines 'voltage stability'?
The ability of the system to maintain frequency
The ability of the system to maintain voltage within limits during disturbances
The ability of the system to deliver real power
The ability of the system to provide reactive power
Explanation - Voltage stability refers to the system's capability to sustain acceptable voltages following a disturbance.
Correct answer is: The ability of the system to maintain voltage within limits during disturbances
Q.81 Which of these devices can be used to increase the voltage in a power system by adjusting the transformer's turns ratio?
Tap changer
Capacitor bank
Synchronous condenser
Generator governor
Explanation - Tap changers change the transformer turns ratio, thereby altering the output voltage.
Correct answer is: Tap changer
Q.82 Which of the following is a direct consequence of a sudden load increase without any reactive power compensation?
System frequency rises
Voltage drop occurs
Real power output increases
Capacitor banks absorb more power
Explanation - Without reactive support, voltage tends to sag when load increases.
Correct answer is: Voltage drop occurs
Q.83 In a 3‑phase system, what is the phase shift between the voltage and the current in an ideal capacitor?
0°
90°
-90°
180°
Explanation - In a capacitor, the current leads the voltage by 90°, giving a -90° phase shift.
Correct answer is: -90°
Q.84 Which of the following is NOT a component of the secondary frequency control system (AGC) network?
Area Control Error (ACE)
Generation Control Center (GCC)
Load Shedding Algorithm (LSA)
Inter‑Area Tie‑Line
Explanation - LSA is part of contingency handling, not the core AGC network components.
Correct answer is: Load Shedding Algorithm (LSA)
Q.85 Which of these best describes the 'power flow direction' in a transmission line?
From low voltage to high voltage
From high voltage to low voltage
From the generator to the transformer
From the transformer to the load
Explanation - Power flows from higher to lower voltage levels to minimize losses.
Correct answer is: From high voltage to low voltage
Q.86 In a power system, a 'voltage dip' is also known as:
Voltage sag
Voltage swell
Voltage spike
Voltage rise
Explanation - A voltage dip is commonly referred to as a voltage sag.
Correct answer is: Voltage sag
Q.87 Which of the following devices can provide both real and reactive power to support voltage and frequency?
Capacitor bank
Synchronous condenser
Synchronous generator
Turbine governor
Explanation - Synchronous generators can generate real power and, by adjusting excitation, reactive power.
Correct answer is: Synchronous generator
Q.88 Which of these is the most important parameter in determining the system's inertial response to a disturbance?
Number of transformers
Inertia constant (H)
Load factor
Voltage regulator setting
Explanation - The inertia constant reflects stored kinetic energy, directly influencing frequency response.
Correct answer is: Inertia constant (H)
Q.89 What is the primary effect of a transformer tap changer on system voltage?
Increases resistance
Changes the phase angle
Adjusts the voltage level
Increases frequency
Explanation - Tap changers modify the transformer's turns ratio, thereby changing the output voltage.
Correct answer is: Adjusts the voltage level
Q.90 Which of the following best explains the term 'voltage regulation' for a transformer?
The change in voltage from no load to full load expressed as a percentage
The difference between primary and secondary voltage
The ability to maintain constant voltage under all conditions
The ratio of secondary to primary voltage
Explanation - Voltage regulation measures how much the voltage changes when the load increases.
Correct answer is: The change in voltage from no load to full load expressed as a percentage
Q.91 Which of the following is a key advantage of using a synchronous condenser for voltage support?
No need for any control system
Provides both active and reactive power
Provides reactive power with adjustable speed
Is cheaper than capacitor banks
Explanation - Synchronous condensers can change reactive output by adjusting speed, offering dynamic support.
Correct answer is: Provides reactive power with adjustable speed
Q.92 What is the typical operating frequency deviation allowed in a modern power grid during normal conditions?
±0.5 Hz
±0.1 Hz
±1 Hz
±5 Hz
Explanation - Modern grids limit frequency deviations to within ±0.1 Hz to preserve stability.
Correct answer is: ±0.1 Hz
Q.93 Which of the following best describes a 'step‑up transformer' in a transmission system?
Reduces voltage to a lower level
Increases voltage for efficient transmission
Controls frequency
Regulates current flow
Explanation - Step‑up transformers raise voltage levels, reducing transmission losses over long distances.
Correct answer is: Increases voltage for efficient transmission
Q.94 What is the main function of the Automatic Voltage Regulator (AVR) in a synchronous machine?
Maintain generator speed
Adjust field excitation to keep terminal voltage constant
Control reactive power flow
Reduce frequency deviations
Explanation - The AVR modifies field current to stabilize the generator's terminal voltage.
Correct answer is: Adjust field excitation to keep terminal voltage constant
Q.95 In a power system, the 'frequency droop characteristic' relates:
Frequency to voltage
Load to power factor
Generator speed to power output
Reactive power to frequency
Explanation - Droop shows how a generator's power output changes with speed (or frequency) deviation.
Correct answer is: Generator speed to power output
Q.96 Which of the following is a direct result of increasing system load without reactive power support?
Frequency increases
Voltage increases
Voltage drop
Reduced system inertia
Explanation - Insufficient reactive power causes a voltage sag when load increases.
Correct answer is: Voltage drop
Q.97 What is the function of a 'reactive power controller' in an industrial plant?
To adjust real power output
To regulate voltage by switching capacitor banks
To control generator speed
To manage transformer tap settings
Explanation - The controller manages reactive power by turning capacitor banks on/off to keep voltage within limits.
Correct answer is: To regulate voltage by switching capacitor banks
Q.98 Which of the following is a typical indicator of a well‑regulated voltage in a distribution network?
Large voltage drop under load
Minimal voltage difference between peak and minimum
High reactive power consumption
Large frequency fluctuations
Explanation - Good voltage regulation results in small variations in voltage across the network.
Correct answer is: Minimal voltage difference between peak and minimum
Q.99 The 'load‑frequency characteristic' is represented by which of the following plots?
Power vs. voltage
Frequency vs. load
Current vs. voltage
Reactive power vs. frequency
Explanation - Load‑frequency characteristic shows how frequency changes with load variations.
Correct answer is: Frequency vs. load
Q.100 Which of the following best defines the term 'voltage collapse'?
A gradual increase in voltage due to load growth
An abrupt drop in voltage due to loss of reactive power
A rise in system frequency
A reduction in system inertia
Explanation - Voltage collapse happens when reactive power is insufficient, causing a rapid voltage drop.
Correct answer is: An abrupt drop in voltage due to loss of reactive power
Q.101 In a power system, which device can be used to provide rapid reactive power support during a voltage dip?
Synchronous condenser
Synchronous generator
Capacitor bank
Turbine governor
Explanation - Capacitor banks can be switched in quickly to supply reactive power during voltage dips.
Correct answer is: Capacitor bank
Q.102 Which of the following is a key component of a governor‑controlled droop system?
Power factor
Excitation system
Speed governor
Load tap changer
Explanation - The speed governor adjusts turbine input based on speed deviations for droop control.
Correct answer is: Speed governor
Q.103 What is the primary function of a 'power system stabilizer' (PSS)?
To control reactive power
To damp oscillations in system frequency
To regulate voltage
To maintain generator temperature
Explanation - PSS reduces oscillations by adding damping signals to the governor and AVR systems.
Correct answer is: To damp oscillations in system frequency
Q.104 Which of the following is NOT typically used to increase system voltage?
Capacitor bank
Synchronous condenser
Step‑up transformer
Generator governor
Explanation - The governor controls speed; voltage increases are achieved via capacitors or transformer taps.
Correct answer is: Generator governor
Q.105 In the context of voltage control, what is a 'load tap changer' (LTC)?
A device that adjusts load size
A device that changes the transformer's turns ratio under load
A device that measures voltage
A device that regulates frequency
Explanation - LTCs allow voltage adjustment while the transformer remains energized, improving voltage regulation.
Correct answer is: A device that changes the transformer's turns ratio under load
Q.106 Which of the following describes the relationship between real power (P) and reactive power (Q) in a three‑phase system?
S = P + Q
S = P - Q
S² = P² + Q²
S = P × Q
Explanation - Apparent power is the vector sum of real and reactive power, given by the Pythagorean relationship.
Correct answer is: S² = P² + Q²
Q.107 What is the main advantage of using a 'synchronous condenser' over a capacitor bank for voltage control?
Higher power factor
Dynamic reactive power capability
No need for excitation control
Lower cost
Explanation - Synchronous condensers can adjust reactive output in real time by changing speed, providing dynamic support.
Correct answer is: Dynamic reactive power capability
Q.108 In a power system, which component provides both real and reactive power?
Capacitor bank
Synchronous generator
Transformers
Load tap changer
Explanation - Synchronous generators produce real power and, through excitation control, reactive power.
Correct answer is: Synchronous generator
Q.109 Which of the following best explains the term 'voltage stability margin'?
The difference between high and low voltage limits
The maximum allowable voltage fluctuation during operation
The ability of the system to withstand voltage sags without collapsing
The maximum reactive power the system can provide
Explanation - Voltage stability margin represents how close the system is to voltage collapse.
Correct answer is: The ability of the system to withstand voltage sags without collapsing
Q.110 Which of the following is a key component of the secondary frequency control system?
Area Control Error (ACE)
Load Shedding Algorithm (LSA)
Voltage regulator
Power factor controller
Explanation - ACE is used by the AGC to adjust generator outputs in each control area.
Correct answer is: Area Control Error (ACE)
Q.111 The 'inertia constant' (H) of a generator is defined as:
Stored kinetic energy per unit of rated power
Resistance of the stator
Reactance of the rotor
The difference between no-load and full-load voltage
Explanation - Inertia constant quantifies the kinetic energy stored in the rotating mass per unit power.
Correct answer is: Stored kinetic energy per unit of rated power
Q.112 Which of the following is NOT a typical effect of a step‑down transformer in a distribution network?
Reduce line losses
Increase voltage
Adjust voltage to usable levels
Provide voltage regulation under load
Explanation - A step‑down transformer reduces voltage from transmission to distribution levels.
Correct answer is: Increase voltage
Q.113 Which of the following devices can provide a rapid increase in reactive power during a fault?
Capacitor bank
Synchronous condenser
Load tap changer
Turbine governor
Explanation - Capacitors can be switched in quickly to supply leading reactive power during faults.
Correct answer is: Capacitor bank
Q.114 Which of the following statements about a 'voltage sag' is true?
It lasts for more than 10 seconds
It is caused by a fault or large load change
It always improves power quality
It increases frequency
Explanation - Voltage sags are temporary voltage drops typically caused by faults or large load changes.
Correct answer is: It is caused by a fault or large load change
Q.115 Which of the following best defines 'reactive power'?
Power that does useful work
Power that is lost as heat
Power that oscillates between source and load
Power measured in watts
Explanation - Reactive power supports magnetic and electric fields in AC systems but does not perform real work.
Correct answer is: Power that oscillates between source and load
Q.116 Which of the following is a common method to improve voltage regulation in a transformer?
Adding more taps to the tap changer
Installing a transformer with higher impedance
Using a lower-rated transformer
Increasing load at the secondary side
Explanation - More taps allow finer adjustment of the voltage ratio, improving regulation.
Correct answer is: Adding more taps to the tap changer
Q.117 Which of these components is responsible for providing both real and reactive power in a power system?
Capacitor bank
Synchronous generator
Transformer tap changer
Load tap changer
Explanation - Synchronous generators produce real power and can also supply or absorb reactive power via excitation control.
Correct answer is: Synchronous generator
Q.118 Which of the following is a primary consequence of a low system frequency?
Higher voltage levels
Reduced generator speed
Increased load shedding
Higher reactive power demand
Explanation - Low frequency indicates that generator speeds have dropped relative to the synchronous speed.
Correct answer is: Reduced generator speed
Q.119 Which of these is a characteristic of a 'reactive power controller' in a power system?
It switches capacitor banks to maintain voltage
It adjusts turbine speed
It regulates transformer taps
It balances power supply and demand
Explanation - A reactive power controller controls capacitor bank operation to keep voltage within limits.
Correct answer is: It switches capacitor banks to maintain voltage
Q.120 Which of the following best describes the primary function of a 'synchronous condenser' in a transmission system?
To generate real power
To provide reactive power support
To regulate system frequency
To increase system inertia
Explanation - Synchronous condensers supply leading reactive power, aiding voltage stability.
Correct answer is: To provide reactive power support
Q.121 Which of the following is an example of a frequency regulation strategy that operates on a timescale of minutes?
Primary droop control
Secondary AGC control
Tertiary economic dispatch
Load shedding
Explanation - Secondary AGC adjusts generator setpoints over minutes to bring frequency back to nominal.
Correct answer is: Secondary AGC control
Q.122 Which of the following statements about a 'voltage regulator' is true?
It controls the frequency of the generator
It adjusts the excitation of the generator to maintain voltage
It switches capacitor banks on/off
It measures the load factor
Explanation - A voltage regulator controls generator excitation to keep terminal voltage constant.
Correct answer is: It adjusts the excitation of the generator to maintain voltage
Q.123 Which of the following best describes the role of a 'load tap changer' (LTC) in voltage control?
It changes the load size
It adjusts transformer taps while the transformer is energized
It controls the generator governor
It measures the power factor
Explanation - An LTC changes the transformer’s turns ratio in real time to regulate voltage.
Correct answer is: It adjusts transformer taps while the transformer is energized
Q.124 Which of these is NOT a typical component of a frequency control system?
Governor
AVR
Power system stabilizer
Load tap changer
Explanation - Load tap changers regulate voltage, not frequency.
Correct answer is: Load tap changer
Q.125 In a power system, the 'load‑frequency characteristic' is often used to design which of the following?
Voltage regulators
Load‑frequency controller
Synchronous condensers
Turbine governors
Explanation - The load‑frequency characteristic helps design the controller that compensates frequency deviations.
Correct answer is: Load‑frequency controller
Q.126 What is the typical frequency of a 3‑phase synchronous generator operating at 50 Hz with 2 poles?
50 Hz
100 Hz
25 Hz
200 Hz
Explanation - The electrical frequency equals twice the mechanical speed for a 2‑pole machine at 50 Hz.
Correct answer is: 100 Hz
Q.127 Which of the following best describes the purpose of the Automatic Voltage Regulator (AVR) in a generator?
To maintain the generator's frequency
To maintain the generator's terminal voltage
To adjust the generator's speed
To monitor the generator's temperature
Explanation - The AVR controls field excitation to keep terminal voltage at its setpoint.
Correct answer is: To maintain the generator's terminal voltage
Q.128 Which of the following is an example of a dynamic voltage support device?
Capacitor bank
Synchronous condenser
Transformer tap changer
Turbine governor
Explanation - A synchronous condenser can adjust reactive power quickly, providing dynamic support.
Correct answer is: Synchronous condenser
Q.129 In a power system, what is the primary role of the 'Power System Stabilizer (PSS)?'
To regulate reactive power
To damp power oscillations
To control voltage
To control temperature
Explanation - PSS provides additional damping to reduce oscillations in generator and system frequency.
Correct answer is: To damp power oscillations
Q.130 Which of the following statements about frequency control is FALSE?
Primary control responds within seconds
Secondary control operates over minutes
Tertiary control adjusts economic dispatch over hours
Frequency control is independent of load changes
Explanation - Frequency control is directly influenced by load changes; it aims to counteract them.
Correct answer is: Frequency control is independent of load changes
Q.131 In a power system, which of the following devices is used to quickly inject reactive power to mitigate a voltage sag?
Synchronous condenser
Capacitor bank
Transformer tap changer
Generator governor
Explanation - Capacitor banks can be switched on rapidly to provide leading reactive power during sag events.
Correct answer is: Capacitor bank
Q.132 Which of these best describes the term 'inertia constant' (H) in power systems?
The amount of reactive power a system can provide
The stored kinetic energy per unit of rated power
The time constant of the voltage regulator
The speed of a transformer tap changer
Explanation - Inertia constant quantifies how much kinetic energy is stored in the rotating masses per unit of rated power.
Correct answer is: The stored kinetic energy per unit of rated power
Q.133 What is the main benefit of using a 'synchronous condenser' in a transmission network?
To generate real power
To provide dynamic reactive power support
To reduce system inertia
To increase load factor
Explanation - Synchronous condensers can quickly adjust reactive power to support voltage and stability.
Correct answer is: To provide dynamic reactive power support
Q.134 Which of these components is responsible for providing the 'droop characteristic' in a governor system?
Excitation system
Governor
Load tap changer
Reactive power controller
Explanation - The governor implements the droop characteristic to control generator output with frequency changes.
Correct answer is: Governor
Q.135 Which of the following best describes the term 'voltage stability margin'?
The maximum voltage swing allowed in the system
The difference between the system voltage and the rated voltage
The ability of the system to withstand voltage sags without collapsing
The amount of reactive power the system can supply
Explanation - Voltage stability margin indicates how close the system is to voltage collapse.
Correct answer is: The ability of the system to withstand voltage sags without collapsing
Q.136 Which of the following devices can be used to adjust the voltage at the secondary side of a transformer while it remains energized?
Step‑up transformer
Capacitor bank
Load tap changer
Turbine governor
Explanation - A load tap changer (LTC) changes the transformer's turns ratio under load conditions.
Correct answer is: Load tap changer
Q.137 In a power system, which of the following is a key advantage of using a 'reactive power controller'?
It can provide real power output
It can regulate voltage by switching capacitor banks
It can control generator speed
It can reduce system inertia
Explanation - A reactive power controller manages the operation of capacitor banks to keep voltage within limits.
Correct answer is: It can regulate voltage by switching capacitor banks
Q.138 Which of these statements about frequency control is correct?
It only affects voltage
It is managed by the governor and turbine
It is not related to generator speed
It does not interact with load changes
Explanation - Frequency control relies on the governor-turbine system to adjust mechanical power output.
Correct answer is: It is managed by the governor and turbine
Q.139 In a power system, what is the typical range of frequency deviation that can be tolerated without automatic protection tripping?
±0.1 Hz
±0.5 Hz
±1.0 Hz
±2.0 Hz
Explanation - Modern grids allow only ±0.1 Hz deviation to maintain stability and protect equipment.
Correct answer is: ±0.1 Hz
Q.140 Which of the following devices can quickly provide reactive power to counteract a voltage dip?
Capacitor bank
Synchronous condenser
Transformers
Turbine governor
Explanation - Capacitor banks can be switched in quickly to provide leading reactive power during a voltage dip.
Correct answer is: Capacitor bank
Q.141 In a power system, the 'Area Control Error (ACE)' is used to:
Calculate the power factor
Measure the voltage drop
Balance tie‑line power flows and frequency in an area
Determine the load growth rate
Explanation - ACE is used by the AGC to adjust generator outputs to maintain nominal tie‑line flows and frequency.
Correct answer is: Balance tie‑line power flows and frequency in an area
Q.142 Which of the following is NOT typically a function of an Automatic Voltage Regulator (AVR)?
Maintain generator terminal voltage
Control reactive power
Adjust generator excitation
Regulate generator frequency
Explanation - The AVR regulates voltage, not frequency; frequency is controlled by the governor.
Correct answer is: Regulate generator frequency
Q.143 What is the purpose of a 'power system stabilizer' (PSS) in a power system?
To increase reactive power
To damp electromechanical oscillations
To regulate voltage
To control turbine speed
Explanation - PSS adds damping to the governor and AVR system to reduce oscillations in frequency.
Correct answer is: To damp electromechanical oscillations
Q.144 Which of the following best explains the term 'voltage sag' in a power system?
A gradual increase in voltage due to load growth
A sudden drop in voltage caused by a fault or large load change
An increase in frequency
A reduction in system inertia
Explanation - Voltage sag is a temporary voltage drop due to a fault or abrupt load change.
Correct answer is: A sudden drop in voltage caused by a fault or large load change
Q.145 Which of the following devices is used to maintain the system voltage during load changes?
Load tap changer (LTC)
Turbine governor
Automatic Voltage Regulator (AVR)
Generator breaker
Explanation - The LTC changes transformer taps under load to keep the voltage steady.
Correct answer is: Load tap changer (LTC)
Q.146 Which of the following best describes the role of a 'reactive power controller' in an industrial plant?
To manage the temperature of generators
To switch capacitor banks on and off to keep voltage stable
To adjust generator speed for frequency regulation
To monitor system inertia
Explanation - A reactive power controller manages capacitor banks to control voltage in the plant.
Correct answer is: To switch capacitor banks on and off to keep voltage stable
Q.147 Which of these statements about a 'step‑up transformer' is true?
It reduces voltage for efficient transmission
It increases voltage for efficient transmission
It regulates frequency
It controls reactive power
Explanation - Step‑up transformers raise voltage, reducing losses over long distances.
Correct answer is: It increases voltage for efficient transmission
Q.148 Which of the following best describes the purpose of the 'automatic generation control' (AGC) in a power system?
To provide real power only
To adjust generator outputs to maintain nominal frequency and tie‑line flows
To regulate voltage in individual transformers
To monitor system load
Explanation - AGC coordinates generator outputs to keep frequency and tie‑line power exchanges at their setpoints.
Correct answer is: To adjust generator outputs to maintain nominal frequency and tie‑line flows
Q.149 Which of the following is a key advantage of using a synchronous condenser over a capacitor bank for voltage control?
Lower cost
Dynamic reactive power capability
No need for excitation control
Higher reactive power rating
Explanation - Synchronous condensers can adjust reactive power rapidly through speed changes.
Correct answer is: Dynamic reactive power capability
Q.150 What is the main purpose of a 'synchronous condenser' in a transmission system?
To provide reactive power support
To generate real power
To increase system frequency
To reduce line losses
Explanation - Synchronous condensers supply leading reactive power to improve voltage stability.
Correct answer is: To provide reactive power support
Q.151 Which of the following best describes the 'voltage regulation' of a transformer?
The ability to maintain a constant voltage under all conditions
The change in voltage from no‑load to full‑load expressed as a percentage
The ratio of primary to secondary voltage
The change in phase angle under load
Explanation - Voltage regulation quantifies how much voltage changes as the load varies.
Correct answer is: The change in voltage from no‑load to full‑load expressed as a percentage
Q.152 Which of the following is NOT a function of the Automatic Voltage Regulator (AVR)?
Maintain generator terminal voltage
Adjust field excitation
Control generator speed
Regulate reactive power
Explanation - The AVR adjusts field excitation; generator speed is controlled by the governor.
Correct answer is: Control generator speed
Q.153 Which of these devices can quickly provide reactive power to counteract a voltage sag?
Capacitor bank
Synchronous condenser
Transformer tap changer
Turbine governor
Explanation - Capacitor banks can be switched in rapidly to supply reactive power during voltage dips.
Correct answer is: Capacitor bank
Q.154 Which of the following statements about frequency control is correct?
It only affects voltage
It is managed by the governor and turbine
It does not interact with load changes
It is independent of generator speed
Explanation - Frequency control relies on governor‑turbine actions to adjust power output.
Correct answer is: It is managed by the governor and turbine
Q.155 In a power system, the 'Area Control Error (ACE)' is used to:
Calculate the power factor
Measure the voltage drop
Balance tie‑line power flows and frequency in an area
Determine the load growth rate
Explanation - ACE is used by the AGC to adjust generator outputs to maintain nominal tie‑line flows and frequency.
Correct answer is: Balance tie‑line power flows and frequency in an area
Q.156 Which of the following best describes the 'power system stabilizer' (PSS) function?
Increase reactive power
Damp electromechanical oscillations
Regulate voltage
Control turbine speed
Explanation - PSS adds damping to the system to reduce oscillations in frequency and voltage.
Correct answer is: Damp electromechanical oscillations
Q.157 Which of the following is a key advantage of using a synchronous condenser?
High reactive power rating
Dynamic reactive power capability
Low cost
No need for excitation control
Explanation - Synchronous condensers can adjust reactive power quickly through speed changes, providing dynamic support.
Correct answer is: Dynamic reactive power capability
Q.158 Which of these statements about a 'step‑up transformer' is correct?
It reduces voltage for efficient transmission
It increases voltage for efficient transmission
It regulates frequency
It controls reactive power
Explanation - Step‑up transformers raise voltage to reduce losses over long distances.
Correct answer is: It increases voltage for efficient transmission
Q.159 Which of the following best describes the role of a 'reactive power controller' in an industrial plant?
To switch capacitor banks on/off to keep voltage stable
To adjust generator speed for frequency regulation
To monitor system inertia
To manage transformer tap settings
Explanation - Reactive power controllers control the operation of capacitor banks to regulate voltage.
Correct answer is: To switch capacitor banks on/off to keep voltage stable
Q.160 Which of the following best describes the primary role of a 'voltage regulator' in a generator?
Maintain system frequency
Control reactive power output
Adjust field excitation to maintain terminal voltage
Regulate generator temperature
Explanation - A voltage regulator adjusts the generator's excitation to keep its terminal voltage constant.
Correct answer is: Adjust field excitation to maintain terminal voltage
Q.161 Which of the following devices is used to provide rapid reactive power support during a fault?
Capacitor bank
Synchronous condenser
Transformer tap changer
Turbine governor
Explanation - Capacitor banks can be switched in quickly to provide leading reactive power during faults.
Correct answer is: Capacitor bank
Q.162 Which of the following best describes a 'voltage sag' in a power system?
A sudden drop in voltage caused by a fault or large load change
A gradual increase in voltage due to load growth
An increase in frequency
A reduction in system inertia
Explanation - Voltage sag is a temporary drop in voltage resulting from faults or load changes.
Correct answer is: A sudden drop in voltage caused by a fault or large load change
Q.163 Which of these best describes the function of a 'synchronous condenser' in a transmission network?
Generate real power
Provide dynamic reactive power support
Increase system inertia
Reduce load factor
Explanation - Synchronous condensers can quickly adjust reactive power to improve voltage stability.
Correct answer is: Provide dynamic reactive power support
Q.164 Which of the following devices is typically used to adjust the voltage at the secondary side of a transformer while it remains energized?
Step‑up transformer
Capacitor bank
Load tap changer
Turbine governor
Explanation - An LTC changes the transformer's turns ratio under load to regulate voltage.
Correct answer is: Load tap changer
Q.165 In a power system, which of these statements about the 'power system stabilizer (PSS)' is correct?
It increases reactive power
It provides voltage regulation
It damps electromechanical oscillations
It controls turbine speed
Explanation - PSS adds damping to the governor and AVR system to reduce frequency and voltage oscillations.
Correct answer is: It damps electromechanical oscillations
Q.166 Which of the following best describes the main function of the Automatic Voltage Regulator (AVR) in a generator?
To adjust generator speed
To maintain generator terminal voltage
To supply real power
To control system frequency
Explanation - AVR controls excitation to keep the generator's terminal voltage at its setpoint.
Correct answer is: To maintain generator terminal voltage
Q.167 Which of the following devices can quickly provide reactive power to counteract a voltage sag?
Capacitor bank
Synchronous condenser
Transformer tap changer
Turbine governor
Explanation - Capacitor banks can be switched in rapidly to provide leading reactive power during a voltage dip.
Correct answer is: Capacitor bank
Q.168 What is the main benefit of using a synchronous condenser in a power system?
To provide dynamic reactive power support
To generate real power
To reduce line losses
To increase system frequency
Explanation - Synchronous condensers can quickly adjust reactive power to support voltage and stability.
Correct answer is: To provide dynamic reactive power support
Q.169 Which of these best describes the purpose of a 'load tap changer' (LTC)?
It changes the load size
It adjusts the transformer's turns ratio while the transformer is energized
It controls generator speed
It measures the power factor
Explanation - An LTC changes transformer taps under load to regulate voltage.
Correct answer is: It adjusts the transformer's turns ratio while the transformer is energized
Q.170 Which of the following is a key advantage of using a synchronous condenser over a capacitor bank for voltage control?
Lower cost
Dynamic reactive power capability
No need for excitation control
Higher reactive power rating
Explanation - Synchronous condensers can adjust reactive power quickly through speed changes.
Correct answer is: Dynamic reactive power capability
Q.171 Which of the following best explains the term 'voltage stability margin' in a power system?
The maximum voltage swing allowed in the system
The difference between the system voltage and the rated voltage
The ability of the system to withstand voltage sags without collapsing
The amount of reactive power the system can supply
Explanation - Voltage stability margin indicates how close the system is to voltage collapse.
Correct answer is: The ability of the system to withstand voltage sags without collapsing
Q.172 Which of the following devices is used to adjust the voltage at the secondary side of a transformer while the transformer remains energized?
Step‑up transformer
Capacitor bank
Load tap changer
Turbine governor
Explanation - An LTC changes the transformer’s turns ratio under load to regulate voltage.
Correct answer is: Load tap changer
Q.173 Which of these statements about a synchronous condenser is FALSE?
It can be used for reactive power support
It has no rotating shaft
It can be switched on/off quickly
It can supply real power
Explanation - Synchronous condensers provide reactive power only; they have no shaft for real power generation.
Correct answer is: It can supply real power
Q.174 Which of the following best describes the function of a 'synchronous condenser' in a transmission network?
Provide real power
Reduce system inertia
Provide dynamic reactive power support
Increase load factor
Explanation - Synchronous condensers can quickly adjust reactive power to improve voltage stability.
Correct answer is: Provide dynamic reactive power support
Q.175 Which of the following devices can be used to regulate voltage under load conditions without interrupting supply?
Step‑up transformer
Load tap changer
Capacitor bank
Turbine governor
Explanation - Load tap changers change transformer taps while the transformer remains energized.
Correct answer is: Load tap changer
Q.176 Which of these best describes the purpose of a reactive power controller in a power system?
To manage generator temperature
To adjust capacitor bank operation to regulate voltage
To control generator speed
To monitor system inertia
Explanation - Reactive power controllers manage the operation of capacitor banks to keep voltage stable.
Correct answer is: To adjust capacitor bank operation to regulate voltage
Q.177 Which of the following best describes the role of a 'voltage regulator' in a generator?
Maintain generator frequency
Adjust field excitation to maintain terminal voltage
Control generator speed
Regulate generator temperature
Explanation - A voltage regulator controls the generator’s excitation to keep its terminal voltage at the setpoint.
Correct answer is: Adjust field excitation to maintain terminal voltage
Q.178 Which of these statements about frequency control is true?
It only affects voltage
It is controlled by the governor and turbine
It is not affected by load changes
It is independent of generator speed
Explanation - Frequency control is performed by the governor-turbine system adjusting mechanical power output.
Correct answer is: It is controlled by the governor and turbine
Q.179 Which of these best describes the role of the Area Control Error (ACE) in an AGC system?
Measure the power factor
Measure voltage drop
Balance tie‑line power flows and frequency in an area
Determine load growth rate
Explanation - ACE is used by AGC to adjust generator outputs to maintain nominal tie‑line flows and frequency.
Correct answer is: Balance tie‑line power flows and frequency in an area
Q.180 What is the typical frequency range for a power system in North America?
30 Hz
40 Hz
50 Hz
60 Hz
Explanation - North American power systems operate at a standard frequency of 60 Hz.
Correct answer is: 60 Hz
Q.181 Which of the following statements about voltage regulation is FALSE?
It measures the change in voltage from no-load to full-load
A high voltage regulation value is desirable for a transformer
It is expressed as a percentage
It depends on transformer tap settings
Explanation - A low voltage regulation value is desirable; a high value indicates poor regulation.
Correct answer is: A high voltage regulation value is desirable for a transformer
Q.182 What is the main purpose of a governor in a generator?
Control generator voltage
Adjust the turbine input to maintain frequency
Switch capacitor banks on and off
Measure system load
Explanation - A governor regulates the turbine input to keep the generator’s speed and frequency steady.
Correct answer is: Adjust the turbine input to maintain frequency
Q.183 Which device in a power system supplies reactive power to maintain voltage levels?
Capacitor bank
Turbine governor
Load tap changer
Generator breaker
Explanation - Capacitor banks provide leading reactive power to support system voltage.
Correct answer is: Capacitor bank
Q.184 Which of the following is a primary effect of a frequency drop in a power system?
Increased system voltage
Decreased generator speed
Increased load shedding
Higher real power output
Explanation - A frequency drop indicates that generator speeds have fallen relative to the synchronous speed.
Correct answer is: Decreased generator speed
Q.185 Which of the following best describes a voltage sag in a power system?
A sudden increase in voltage due to a fault
A temporary drop in voltage due to a fault or load change
A permanent increase in voltage
A reduction in frequency
Explanation - A voltage sag is a short‑term voltage drop caused by a fault or large load change.
Correct answer is: A temporary drop in voltage due to a fault or load change
Q.186 What is the function of an Automatic Voltage Regulator (AVR) in a generator?
Control generator frequency
Regulate generator temperature
Adjust field excitation to maintain terminal voltage
Switch capacitors on and off
Explanation - The AVR controls the excitation current to keep the generator terminal voltage constant.
Correct answer is: Adjust field excitation to maintain terminal voltage
Q.187 Which of the following is a typical measure of voltage regulation at a transformer?
Voltage drop percentage
Power factor angle
Short‑circuit voltage
Load factor
Explanation - Voltage regulation is expressed as the percentage change in voltage from no‑load to full‑load.
Correct answer is: Voltage drop percentage
Q.188 Which of the following best explains the concept of reactive power in AC systems?
The power that does useful work
The power that is dissipated as heat
The power that oscillates between source and load
The power measured in watts
Explanation - Reactive power sustains electric and magnetic fields but does not perform useful work.
Correct answer is: The power that oscillates between source and load
Q.189 What is the typical function of a step‑down transformer in a distribution network?
Increase voltage for transmission
Reduce voltage to safer residential levels
Control system frequency
Regulate voltage under load
Explanation - Step‑down transformers lower high transmission voltages to safe levels for local use.
Correct answer is: Reduce voltage to safer residential levels
Q.190 Which of the following devices can provide reactive power to support system voltage during a fault?
Capacitor bank
Synchronous condenser
Transformer tap changer
Turbine governor
Explanation - Capacitor banks can be switched in rapidly to supply leading reactive power during a fault.
Correct answer is: Capacitor bank
Q.191 What does the term 'voltage regulation' refer to in the context of a transformer?
The change in voltage from no-load to full-load expressed as a percentage
The difference between primary and secondary voltage
The ability to maintain constant voltage under all conditions
The change in phase angle under load
Explanation - Voltage regulation indicates how much voltage changes from no-load to full-load operation.
Correct answer is: The change in voltage from no-load to full-load expressed as a percentage
Q.192 Which of the following is the correct formula for apparent power in a three‑phase system?
S = √(P² + Q²)
S = P + Q
S = P × Q
S = P ÷ Q
Explanation - Apparent power is the vector sum of real and reactive power: S = √(P² + Q²).
Correct answer is: S = √(P² + Q²)
Q.193 Which of the following best describes the role of a governor in a power system?
Regulate system frequency
Supply reactive power
Adjust transformer taps
Measure system load
Explanation - The governor adjusts turbine input to maintain system frequency by controlling generator speed.
Correct answer is: Regulate system frequency
Q.194 Which of the following devices is used to control the voltage of a transformer while it remains energized?
Step‑up transformer
Capacitor bank
Load tap changer
Turbine governor
Explanation - Load tap changers allow voltage adjustments without interrupting power delivery.
Correct answer is: Load tap changer
Q.195 Which of the following best describes a frequency sag in a power system?
A sudden drop in frequency caused by a fault or load change
A temporary increase in voltage due to a fault
An increase in system frequency
A reduction in system inertia
Explanation - A frequency sag is a short‑term decrease in frequency caused by a fault or load change.
Correct answer is: A sudden drop in frequency caused by a fault or load change
Q.196 Which of the following best explains the concept of 'reactive power' in AC circuits?
The power that does useful work
The power that is lost as heat
The power that oscillates between the source and load
The power measured in watts
Explanation - Reactive power supports the creation of magnetic fields and is necessary for inductive loads.
Correct answer is: The power that oscillates between the source and load
Q.197 Which of the following is the primary function of a capacitor bank in a power system?
Supply real power
Supply reactive power
Regulate frequency
Control transformer taps
Explanation - Capacitor banks provide leading reactive power to support voltage levels.
Correct answer is: Supply reactive power
Q.198 Which of the following is a typical measure of voltage regulation at a transformer?
Voltage drop percentage
Power factor angle
Short‑circuit voltage
Load factor
Explanation - Voltage regulation is expressed as the percentage change in voltage from no‑load to full‑load.
Correct answer is: Voltage drop percentage
Q.199 What is the main advantage of using a step‑up transformer in a power transmission system?
To reduce voltage for safer residential levels
To increase voltage for efficient transmission
To control system frequency
To regulate reactive power
Explanation - Step‑up transformers raise voltage levels, reducing losses over long distances.
Correct answer is: To increase voltage for efficient transmission
Q.200 Which of the following best describes a voltage drop due to a load increase?
The voltage rises
The voltage stays the same
The voltage drops
The voltage oscillates
Explanation - When load increases, voltage typically drops unless compensated by reactive power support.
Correct answer is: The voltage drops
Q.201 Which of the following devices is used to regulate voltage in a power system while it remains energized?
Load tap changer
Turbine governor
Capacitor bank
Transformer tap changer
Explanation - Load tap changers adjust transformer taps under load to maintain voltage levels.
Correct answer is: Load tap changer
Q.202 Which of the following is the best description of a voltage sag in a power system?
A sudden increase in voltage due to a fault
A temporary drop in voltage due to a fault or load change
A permanent increase in voltage
A reduction in frequency
Explanation - A voltage sag is a short‑term voltage drop caused by a fault or load change.
Correct answer is: A temporary drop in voltage due to a fault or load change
Q.203 Which of the following devices provides reactive power support to the grid?
Capacitor bank
Turbine governor
Load tap changer
Transformer tap changer
Explanation - Capacitor banks provide leading reactive power to help maintain voltage levels.
Correct answer is: Capacitor bank