Q.1 Which of the following represents the primary cause of transient stability issues after a fault is cleared?
Increased line reactance
Loss of synchronism due to sudden change in power angle
Voltage regulator failure
Reduced load damping
Explanation - Transient stability problems arise when a fault causes a sudden change in the power angle between generators, potentially leading to loss of synchronism.
Correct answer is: Loss of synchronism due to sudden change in power angle
Q.2 Small-signal stability analysis typically uses which of the following mathematical tools?
Power flow equations
Eigenvalue analysis of the system Jacobian
Harmonic distortion charts
Transient response plots
Explanation - Small‑signal stability is assessed by linearising the system equations around an operating point and analysing the eigenvalues of the Jacobian matrix.
Correct answer is: Eigenvalue analysis of the system Jacobian
Q.3 Which type of damper is most effective for damping electromechanical oscillations in a synchronous generator?
Shunt damper winding
Static Var Compensator (SVC)
Series capacitor bank
Phase‑shifting transformer
Explanation - A shunt damper winding provides negative reactance to counteract rotor angle oscillations, thus improving electromechanical stability.
Correct answer is: Shunt damper winding
Q.4 What is the main purpose of a Flexible AC Transmission System (FACTS) device in enhancing system stability?
Reducing line losses
Providing dynamic reactive power support
Increasing transformer tap ratio
Stabilising frequency by mechanical means
Explanation - FACTS devices like STATCOMs and SVCs supply or absorb reactive power quickly, improving voltage profiles and stability margins.
Correct answer is: Providing dynamic reactive power support
Q.5 Which parameter in the swing equation is directly proportional to the generator inertia constant (H)?
Mechanical power input
Electrical power output
Angular acceleration
Frequency deviation
Explanation - In the swing equation \(2H \dot{\delta} = P_m - P_e\), the inertia constant H scales the angular acceleration of the rotor.
Correct answer is: Angular acceleration
Q.6 A large, sudden increase in load causes which of the following phenomena?
Positive power factor
Under‑frequency load shedding
Voltage collapse
Dynamic load increase
Explanation - When load suddenly rises, system frequency drops; protective relays may disconnect loads to maintain stability, known as under‑frequency load shedding.
Correct answer is: Under‑frequency load shedding
Q.7 Which of these is a key indicator of voltage instability?
High short‑circuit ratio
Low damping of electromechanical oscillations
Small voltage dips after a fault
High reactive power demand near the limit
Explanation - When reactive power demand approaches the capability of generators, voltage collapse becomes likely.
Correct answer is: High reactive power demand near the limit
Q.8 In the context of frequency stability, what role does the governor play?
Regulating reactive power
Maintaining voltage levels
Controlling turbine power output to match load changes
Adjusting transformer taps
Explanation - The governor modulates turbine input to keep generator output synchronized with the system frequency.
Correct answer is: Controlling turbine power output to match load changes
Q.9 Which of the following best describes 'ro‑ro' (rotor–rotor) interaction in a power system?
Interaction between two synchronous generators on a shared network
Interaction between rotor and stator fields within one generator
Interaction between a generator and a motor
Interaction between two machines connected through a back‑to‑back converter
Explanation - Rotor–rotor interaction refers to the electromechanical coupling between generators connected to the same network.
Correct answer is: Interaction between two synchronous generators on a shared network
Q.10 What is the main advantage of using an Active Power Filter (APF) for stability control?
Improving power factor
Reducing harmonic distortion
Providing fast voltage support
Stabilising rotor angle oscillations
Explanation - APFs can supply dynamic reactive power, which helps dampen rotor angle oscillations, enhancing stability.
Correct answer is: Stabilising rotor angle oscillations
Q.11 Which of the following is NOT a typical symptom of a power system approaching voltage collapse?
Rapid voltage rise on some buses
Sluggish voltage response to load changes
Reduced voltage stability margin
High load‑current ratio at generators
Explanation - Voltage collapse is characterized by voltage sag, not rise; the other options indicate typical signs of impending collapse.
Correct answer is: Rapid voltage rise on some buses
Q.12 In a two‑area power system, which phenomenon occurs when inter‑area electromechanical oscillation is poorly damped?
Synchronous speed drift
Inter‑area oscillations
Intra‑area oscillations
Voltage instability
Explanation - Inter‑area oscillations involve relative motion between generators of different areas and are a key small‑signal stability concern.
Correct answer is: Inter‑area oscillations
Q.13 What effect does increasing the turbine governor droop constant have on system frequency response?
Faster frequency restoration
Slower frequency restoration
No effect on frequency
Improved voltage regulation
Explanation - A higher droop constant reduces the governor’s sensitivity, leading to slower frequency recovery after disturbances.
Correct answer is: Slower frequency restoration
Q.14 Which of the following best characterises a ‘steady‑state’ stability issue?
Sudden loss of synchronism after a fault
Slow drift of system frequency over time
Voltage collapse due to excessive reactive power demand
Fast oscillations of generator speed
Explanation - Steady‑state stability relates to the ability to maintain equilibrium under constant conditions, often limited by reactive power capabilities.
Correct answer is: Voltage collapse due to excessive reactive power demand
Q.15 Which control technique is most effective for mitigating low-frequency oscillations in a large power system?
Automatic voltage regulator (AVR) tuning
Power system stabiliser (PSS)
Load shedding schemes
Frequency‑based load control
Explanation - A PSS adds a damping signal to the governor to counteract low‑frequency oscillations.
Correct answer is: Power system stabiliser (PSS)
Q.16 The ‘short‑circuit ratio’ of a bus is defined as:
Rated power / short‑circuit power
Short‑circuit power / rated power
Short‑circuit voltage / rated voltage
Rated voltage / short‑circuit voltage
Explanation - Short‑circuit ratio (SCR) = \(S_{SC}/S_{rated}\) and indicates the bus’s ability to tolerate disturbances.
Correct answer is: Short‑circuit power / rated power
Q.17 Which parameter in a generator’s internal model is most directly related to the speed droop characteristic?
Excitation voltage
Inertia constant H
Governor droop R
Armature resistance R_a
Explanation - Governor droop defines the change in power output per unit change in frequency.
Correct answer is: Governor droop R
Q.18 Which of these best represents a typical ‘over‑excitation’ scenario?
Generator operating below its synchronous speed
Generator operating with excessive field current
Generator operating with no reactive power
Generator operating at nominal voltage
Explanation - Over‑excitation occurs when the field current exceeds the level needed for the desired reactive power output.
Correct answer is: Generator operating with excessive field current
Q.19 In a power system stability context, what is the purpose of ‘load‑frequency characteristics’ (LFC)?
To maintain voltage stability at all times
To regulate load voltage by adjusting tap changers
To describe how load power changes with system frequency
To compute power system losses
Explanation - LFC expresses the dependence of load consumption on frequency, aiding in frequency regulation design.
Correct answer is: To describe how load power changes with system frequency
Q.20 Which of the following is a sign of a well‑damped small‑signal system?
All eigenvalues lie in the right‑hand plane
All eigenvalues have negative real parts
Eigenvalues are purely imaginary
All eigenvalues have large magnitude
Explanation - Negative real parts indicate stability; the magnitude and imaginary parts determine damping ratio.
Correct answer is: All eigenvalues have negative real parts
Q.21 In the context of ‘electromechanical oscillation’ damping, what role does the ‘damping coefficient’ play?
It determines the system’s voltage limit
It controls the size of the fault
It quantifies how quickly oscillations decay
It sets the speed of the turbine
Explanation - A higher damping coefficient results in faster decay of oscillations, improving stability.
Correct answer is: It quantifies how quickly oscillations decay
Q.22 Which of the following is NOT a typical cause of voltage instability in a transmission system?
High loading of transmission lines
Large shunt capacitor banks
Poor voltage regulator settings
Insufficient reactive power support
Explanation - Shunt capacitor banks add reactive power, typically improving voltage stability, not causing instability.
Correct answer is: Large shunt capacitor banks
Q.23 The ‘critical clearing time’ (CCT) refers to:
The maximum permissible time to clear a fault before instability occurs
The time needed to recover the generator rotor angle
The interval between successive faults
The delay in relay operation
Explanation - CCT is the fault clearance time beyond which the system may lose synchronism.
Correct answer is: The maximum permissible time to clear a fault before instability occurs
Q.24 A power system stabiliser (PSS) typically uses which type of signal to provide damping?
Voltage magnitude
Rotor speed deviation
Frequency deviation
Power flow direction
Explanation - PSS processes the speed deviation signal to generate a stabilising torque via the governor.
Correct answer is: Rotor speed deviation
Q.25 Which of the following statements is true regarding ‘frequency‑droop’ characteristic of a turbine‑governor system?
It is independent of generator inertia
It defines the slope of the power‑frequency curve
It is irrelevant for large‑area oscillations
It only affects reactive power
Explanation - Frequency‑droop determines how much power changes in response to frequency deviations.
Correct answer is: It defines the slope of the power‑frequency curve
Q.26 Which type of converter is most suitable for fast reactive power support in a high‑voltage transmission system?
Static Var Compensator (SVC)
Voltage Source Converter (VSC)
Current Source Converter (CSC)
Single‑phase inverters
Explanation - VSCs can quickly supply or absorb reactive power, aiding voltage stability.
Correct answer is: Voltage Source Converter (VSC)
Q.27 In the swing equation, the term \(P_m - P_e\) is referred to as:
Accelerating power
Power imbalance
Damping torque
Reactance load
Explanation - The difference between mechanical and electrical power generates acceleration or deceleration of the rotor.
Correct answer is: Accelerating power
Q.28 Which of the following best defines 'system inertia' in power engineering?
The capacity of the system to absorb reactive power
The aggregate kinetic energy stored in rotating masses
The ratio of active to reactive power
The speed at which the system frequency changes
Explanation - System inertia is the total kinetic energy of all rotating components, resisting frequency changes.
Correct answer is: The aggregate kinetic energy stored in rotating masses
Q.29 During a large fault, which protective relay action is most critical for preventing a wide‑area collapse?
Load tap changer operation
Generator over‑excitation limiter
Under‑frequency load shedding
Voltage regulator reset
Explanation - Removing load during a fault helps stabilize the system and prevent collapse.
Correct answer is: Under‑frequency load shedding
Q.30 What is the main reason for using a ‘static synchronous condenser’ in a transmission grid?
To supply mechanical power
To provide dynamic voltage support
To reduce transmission losses
To increase system inertia
Explanation - Static synchronous condensers act as adjustable reactive power sources, aiding voltage stability.
Correct answer is: To provide dynamic voltage support
Q.31 Which of the following best describes a ‘load‑shedding scheme’?
A method of adjusting transformer taps automatically
A strategy of disconnecting portions of load to restore frequency
A technique to reduce reactive power demand
A system for balancing power generation
Explanation - Load‑shedding disconnects parts of the load to relieve the system during disturbances.
Correct answer is: A strategy of disconnecting portions of load to restore frequency
Q.32 Which parameter in a PSS controller is directly responsible for the phase shift introduced to the speed signal?
Gain K
Time constant T
Phase shift \(\varphi\)
Deadband
Explanation - The phase shift determines how the PSS output aligns with the speed deviation signal.
Correct answer is: Phase shift \(\varphi\)
Q.33 What is the typical effect of increasing the series capacitor in a transmission line?
Decrease line impedance
Increase reactive power absorption
Increase voltage drop
Decrease fault current
Explanation - Series capacitors reduce line reactance, improving power transfer capability.
Correct answer is: Decrease line impedance
Q.34 Which of the following indicates a ‘low‑frequency’ oscillation in a power system?
Period of 0.1–0.5 s
Period of 1–5 s
Period of 10–30 s
Period of 0.001–0.01 s
Explanation - Low‑frequency oscillations (inter‑area) typically have periods between 1–5 s.
Correct answer is: Period of 1–5 s
Q.35 A generator’s excitation system typically includes which of the following components?
Turbine governor and AVR
Static VAR compensator
Power system stabiliser
Phase‑shift transformer
Explanation - The excitation system comprises the AVR controlling field voltage, often linked to the governor for frequency regulation.
Correct answer is: Turbine governor and AVR
Q.36 Which of the following best describes a ‘dead‑band’ in a governor controller?
Range where no control action is taken
Range of acceptable voltage deviations
Range of frequency deviations that trigger load shedding
Range where the system is fully stable
Explanation - A dead‑band prevents the governor from responding to very small deviations, reducing chatter.
Correct answer is: Range where no control action is taken
Q.37 The term ‘damping ratio’ in small‑signal stability analysis is defined as:
Ratio of real to imaginary part of an eigenvalue
Magnitude of the eigenvalue
Inverse of the damping coefficient
Ratio of reactive to active power
Explanation - Damping ratio ζ = -Re(λ)/|λ| gives the degree of damping of an eigenmode.
Correct answer is: Ratio of real to imaginary part of an eigenvalue
Q.38 What is the main purpose of a ‘phase‑shifter transformer’?
To change the voltage level
To adjust the phase angle between bus voltages
To supply reactive power
To damp voltage oscillations
Explanation - Phase‑shifter transformers modify phase angles to control power flows.
Correct answer is: To adjust the phase angle between bus voltages
Q.39 Which of the following is a characteristic of a ‘weak’ system in terms of stability?
High inertia constant
High short‑circuit ratio
Low short‑circuit ratio
High load damping
Explanation - A weak system has low short‑circuit ratios, making it more susceptible to disturbances.
Correct answer is: Low short‑circuit ratio
Q.40 In voltage stability analysis, which method is commonly used to compute the maximum loadability?
Load flow analysis
Continuation power flow
Harmonic analysis
Small‑signal eigenvalue study
Explanation - Continuation power flow tracks system limits and determines maximum loadability.
Correct answer is: Continuation power flow
Q.41 What role does the ‘inverter‑based’ renewable generator play in system stability?
Providing mechanical inertia directly
Offering fast reactive power support
Increasing fault current levels
Regulating frequency by mechanical means
Explanation - Inverters can rapidly change reactive power output, assisting voltage and frequency stability.
Correct answer is: Offering fast reactive power support
Q.42 Which of the following best explains a ‘frequency nadir’?
Highest frequency reached after a fault
Lowest frequency reached before recovery
Average system frequency over a day
Frequency at which generators start to over‑excite
Explanation - The frequency nadir is the lowest point of frequency deviation after a disturbance.
Correct answer is: Lowest frequency reached before recovery
Q.43 During a fault, the ‘short‑circuit current’ is primarily limited by:
Generator reactive power output
Generator mechanical torque
System impedance between fault and source
Load demand at the fault location
Explanation - Short‑circuit current equals fault voltage divided by the network impedance to the source.
Correct answer is: System impedance between fault and source
Q.44 What is the typical impact of adding a capacitor bank at a load bus on voltage stability?
Reduces voltage level
Increases voltage level
Decreases short‑circuit ratio
Increases load damping
Explanation - Capacitor banks supply reactive power, raising bus voltage levels and improving stability.
Correct answer is: Increases voltage level
Q.45 Which of the following best describes an ‘inertial response’ in a power system?
Change in load power with frequency
Immediate frequency deviation after a disturbance
Gradual frequency change due to governor action
Voltage swing due to reactive power imbalance
Explanation - Inertia causes an immediate frequency change following a sudden power imbalance.
Correct answer is: Immediate frequency deviation after a disturbance
Q.46 The ‘steady‑state’ power flow equations are solved using which numerical method?
Newton‑Raphson
Fast Fourier Transform
Finite element analysis
Runge‑Kutta
Explanation - Newton‑Raphson is the standard method for solving non‑linear power‑flow equations.
Correct answer is: Newton‑Raphson
Q.47 A PSS with a high time constant typically provides:
Fast damping of low‑frequency oscillations
Slow damping of high‑frequency oscillations
No effect on oscillations
Damping only of voltage oscillations
Explanation - A larger time constant delays the response, suitable for higher‑frequency modes.
Correct answer is: Slow damping of high‑frequency oscillations
Q.48 Which of the following is an example of a ‘voltage‑swing’ problem?
Fast frequency rise after a generator trip
Slow voltage decay following a large load increase
Immediate increase in power factor
Rapid loss of synchronism between two generators
Explanation - Voltage‑swing refers to gradual voltage decline after a disturbance.
Correct answer is: Slow voltage decay following a large load increase
Q.49 Which of the following best describes the ‘critical power angle’?
Angle at which a generator’s reactive power is maximum
Angle at which the mechanical power equals electrical power
Angle beyond which generators lose synchronism
Angle at which the governor stops working
Explanation - The critical power angle defines the stability limit; exceeding it can cause loss of synchronism.
Correct answer is: Angle beyond which generators lose synchronism
Q.50 What is the effect of increasing the governor time constant on frequency response?
Faster frequency recovery
Slower frequency recovery
No change in frequency response
Immediate frequency overshoot
Explanation - A larger time constant reduces governor responsiveness, slowing frequency restoration.
Correct answer is: Slower frequency recovery
Q.51 Which of the following devices can provide fast‑acting voltage regulation at a high‑voltage substation?
Synchronous condenser
Shunt capacitor bank
SVC
Series reactor
Explanation - A Static Var Compensator (SVC) can rapidly adjust reactive power to regulate voltage.
Correct answer is: SVC
Q.52 A generator’s ‘exciter’ primarily controls which of the following?
Field current and reactive power output
Mechanical power input
Turbine speed
Transformer tap ratio
Explanation - The exciter supplies field current to the generator, controlling voltage and reactive power.
Correct answer is: Field current and reactive power output
Q.53 In a power system, ‘damping factor’ is related to which parameter of the swing equation?
Inertia constant H
Governor droop R
Speed governor time constant
Electrical damping coefficient D
Explanation - The damping coefficient D appears in the swing equation to represent energy dissipation.
Correct answer is: Electrical damping coefficient D
Q.54 Which of the following is a direct consequence of high load‑frequency sensitivity?
Reduced frequency swings during disturbances
Increased load shedding likelihood
Enhanced voltage stability
Lower system inertia
Explanation - High load‑frequency sensitivity means loads respond sharply to frequency changes, potentially leading to shedding.
Correct answer is: Increased load shedding likelihood
Q.55 A ‘dead‑band’ in a voltage regulator is used to:
Prevent over‑excitation
Eliminate voltage ripple
Avoid continuous small adjustments
Control generator speed
Explanation - The dead‑band reduces unnecessary controller activity for tiny voltage variations.
Correct answer is: Avoid continuous small adjustments
Q.56 Which of the following is a key feature of ‘dynamic load models’?
Fixed power consumption
Time‑dependent reactive power requirement
Static voltage drop
Instantaneous frequency response
Explanation - Dynamic loads can change their reactive power consumption over time, affecting stability.
Correct answer is: Time‑dependent reactive power requirement
Q.57 What is the purpose of a ‘load‑line method’ in voltage stability analysis?
To find maximum reactive power
To locate the point of voltage collapse
To calculate short‑circuit currents
To determine damping ratios
Explanation - The load‑line method helps identify the critical point where the system loses voltage stability.
Correct answer is: To locate the point of voltage collapse
Q.58 Which of the following best represents the ‘damping ratio’ of a mode with eigenvalue \(-0.1 + j0.8\)?
0.1
0.8
0.96
0.5
Explanation - Damping ratio ζ = -Re(λ)/|λ| = 0.1/√(0.1²+0.8²) ≈ 0.96.
Correct answer is: 0.96
Q.59 The ‘critical clearing time’ for a fault on a high‑voltage line is typically:
Between 0.1 and 0.5 s
Between 1 and 5 s
Between 0.01 and 0.02 s
Above 10 s
Explanation - High‑voltage faults usually have critical clearing times in the range of 0.1–0.5 s.
Correct answer is: Between 0.1 and 0.5 s
Q.60 Which of the following is NOT a typical function of an AVR?
Maintain generator terminal voltage
Adjust field excitation
Set system frequency
Provide reactive power support
Explanation - AVRs regulate voltage, not frequency; governors control frequency.
Correct answer is: Set system frequency
Q.61 A ‘high‑frequency’ oscillation in a power system typically has a period of:
0.05–0.2 s
0.5–1.5 s
5–10 s
20–30 s
Explanation - High‑frequency oscillations, such as intra‑area, occur in the 0.05–0.2 s range.
Correct answer is: 0.05–0.2 s
Q.62 Which of the following is a consequence of having a large ‘reactive power deficiency’?
Voltage rise
Voltage sag
Frequency increase
Reduced damping
Explanation - A lack of reactive power causes bus voltage to drop (sag).
Correct answer is: Voltage sag
Q.63 In a dynamic security assessment, the ‘transient stability margin’ is defined as:
Maximum permissible fault clearance time
Maximum power transfer capacity
Minimum load angle before collapse
Maximum permissible voltage swing
Explanation - Transient stability margin measures the time margin between actual and critical clearing times.
Correct answer is: Maximum permissible fault clearance time
Q.64 Which component of a power system can provide ‘synthetic inertia’?
Synchronous condensers
FACTS devices
Power‑electronic converters
Load tap changers
Explanation - Converters can emulate inertia by adjusting power output in response to frequency changes.
Correct answer is: Power‑electronic converters
Q.65 A generator’s ‘damping factor’ is most effectively improved by:
Increasing field excitation
Adding a damper winding
Reducing generator inertia
Short‑circuiting the stator
Explanation - Damper windings provide negative reactance, increasing electromagnetic damping.
Correct answer is: Adding a damper winding
Q.66 Which of the following best represents the ‘critical power angle’ for a generator operating at full load?
Zero degrees
90 degrees
180 degrees
Between 30 and 60 degrees
Explanation - Full‑load critical angles typically range from 30° to 60° depending on system parameters.
Correct answer is: Between 30 and 60 degrees
Q.67 In a two‑area system, which relay typically initiates inter‑area load shedding?
Under‑frequency relay
Under‑voltage relay
High‑frequency relay
Over‑current relay
Explanation - Under‑frequency relays detect frequency drop and disconnect load to prevent collapse.
Correct answer is: Under‑frequency relay
Q.68 Which of the following is a direct consequence of reducing the system’s short‑circuit capacity?
Improved voltage stability
Higher fault currents
Increased inertia
Lower system voltage
Explanation - Reduced short‑circuit capacity implies higher impedance, leading to lower fault current levels, which may affect protection coordination.
Correct answer is: Higher fault currents
Q.69 A ‘transient stability study’ typically uses which of the following simulation approaches?
Static power‑flow analysis
Dynamic time‑domain simulation
Harmonic analysis
Small‑signal eigenvalue analysis
Explanation - Transient stability requires time‑domain simulation of generator dynamics.
Correct answer is: Dynamic time‑domain simulation
Q.70 What is the effect of a ‘high short‑circuit ratio’ on a transmission line’s voltage stability?
It decreases voltage stability margin
It increases voltage stability margin
It has no effect
It reduces system inertia
Explanation - High SCR indicates a strong source, providing better voltage support.
Correct answer is: It increases voltage stability margin
Q.71 Which of the following is an example of ‘electromechanical damping’?
Resistive losses in the stator winding
Reactive power compensation
Mechanical friction in the turbine
Voltage regulation by AVR
Explanation - Mechanical friction provides a damping torque that reduces rotor oscillations.
Correct answer is: Mechanical friction in the turbine
Q.72 In a power system, a ‘high‑frequency’ disturbance typically requires:
Fast‑acting voltage regulators
Slow‑acting load‑shedding schemes
Long‑duration governor response
Large‑step phase angle adjustments
Explanation - High‑frequency oscillations demand rapid damping via fast‑acting devices.
Correct answer is: Fast‑acting voltage regulators
Q.73 Which of the following parameters is most directly affected by a change in the governor time constant?
Generator inertia
Voltage regulation range
Frequency response speed
Power flow magnitude
Explanation - The governor time constant determines how quickly the turbine adjusts power.
Correct answer is: Frequency response speed
Q.74 A ‘dynamic load model’ that includes frequency dependence is also known as a:
Voltage‑dependent load
Frequency‑dependent load
Time‑varying load
Load‑line model
Explanation - Such models capture load changes in response to frequency variations.
Correct answer is: Frequency‑dependent load
Q.75 Which of the following is a typical cause of ‘low‑frequency inter‑area oscillations’?
Short‑circuit fault on a single line
Sudden loss of a large generator
Large change in load at a single bus
Over‑excitation of a small generator
Explanation - Removing a large generator disrupts power flows between areas, inducing low‑frequency oscillations.
Correct answer is: Sudden loss of a large generator
Q.76 A ‘load‑shedding relay’ is most commonly triggered by:
Voltage below a threshold
Frequency below a threshold
Over‑current
Under‑voltage at a transformer tap
Explanation - Load‑shedding relays monitor frequency and disconnect load when it falls below a setpoint.
Correct answer is: Frequency below a threshold
Q.77 Which of the following best represents a ‘critical clearing time’ that is too short for a low‑voltage system?
0.5 s
0.05 s
1 s
10 s
Explanation - Low‑voltage faults often have critical clearing times in the tens of milliseconds.
Correct answer is: 0.05 s
Q.78 In the context of voltage stability, which of the following is a measure of the system’s ability to withstand voltage collapse?
Short‑circuit ratio (SCR)
Maximum loading factor
Load‑frequency characteristic
Power flow angle
Explanation - Higher SCR indicates greater fault current capability, improving voltage stability margin.
Correct answer is: Short‑circuit ratio (SCR)
Q.79 Which of the following devices is specifically designed to provide fast reactive power support to maintain voltage during transients?
SVC
Series capacitor bank
Under‑frequency relays
Turbine governor
Explanation - SVCs can quickly change reactive power output, aiding voltage control during disturbances.
Correct answer is: SVC
Q.80 The term ‘steady‑state stability’ refers to:
The ability to maintain synchronism after a transient disturbance
The ability to recover from a fault within 0.1 s
The ability to keep system frequency within ±0.5 Hz
The ability to avoid voltage collapse at any operating point
Explanation - Steady‑state stability concerns the system’s ability to settle to a new equilibrium after a large disturbance.
Correct answer is: The ability to recover from a fault within 0.1 s
Q.81 Which of the following is a common technique to improve the ‘critical clearing time’ in a power system?
Increase generator inertia
Reduce load frequency sensitivity
Add a large shunt capacitor bank
Install a voltage regulator
Explanation - Higher inertia slows the frequency change, giving more time to clear faults.
Correct answer is: Increase generator inertia
Q.82 Which of the following best describes the ‘electrical damping factor’ in a generator’s swing equation?
Damping due to mechanical friction
Damping due to resistive losses in the stator
Damping due to the generator’s field current
Damping due to reactive power imbalance
Explanation - Electrical damping arises from resistive elements in the machine that dissipate energy.
Correct answer is: Damping due to resistive losses in the stator
Q.83 The ‘critical power angle’ can be calculated for a two‑area system using which of the following relationships?
δc = sin⁻¹(Pm / E1E2/X)
δc = tan⁻¹(Pe / Pm)
δc = 0.5 × (δmax + δmin)
δc = (Pmax - Pmin) / (X1 + X2)
Explanation - Critical power angle is derived from the power‑angle equation of a synchronous machine.
Correct answer is: δc = sin⁻¹(Pm / E1E2/X)
Q.84 Which of the following best describes an ‘under‑frequency load shedding (UFLS) scheme’?
Selective disconnection of high‑priority loads when frequency falls below a threshold
Automatic voltage regulation using SVCs
Dynamic adjustment of generator excitation
Fast‑acting protective relays for fault clearance
Explanation - UFLS schemes aim to maintain frequency by shedding non‑essential loads.
Correct answer is: Selective disconnection of high‑priority loads when frequency falls below a threshold
Q.85 Which of the following is a characteristic of a ‘weak’ system in terms of transient stability?
High critical clearing time
High short‑circuit ratio
Low damping of electromechanical modes
Large system inertia
Explanation - Weak systems tend to have low damping, making them more vulnerable to instability.
Correct answer is: Low damping of electromechanical modes
Q.86 The ‘critical clearing time’ for a fault at a generator terminal is influenced by:
Generator inertia constant
Load level at the faulted bus
Governor time constant
All of the above
Explanation - All listed factors affect the time margin before loss of synchronism.
Correct answer is: All of the above
Q.87 Which of the following statements about ‘voltage stability margin’ is true?
It is independent of load level
It can be increased by adding shunt capacitors
It is determined by the short‑circuit ratio alone
It is unaffected by reactive power compensation
Explanation - Adding capacitors supplies reactive power, raising voltage levels and increasing stability margin.
Correct answer is: It can be increased by adding shunt capacitors
Q.88 In a power system, which of the following devices can provide both voltage support and damping of electromechanical oscillations?
Shunt capacitor bank
Static VAR compensator (SVC)
Turbine governor
Under‑frequency relay
Explanation - SVCs can supply reactive power for voltage regulation and also add damping via control.
Correct answer is: Static VAR compensator (SVC)
Q.89 Which of the following best describes the ‘damping factor’ of an electromechanical mode?
The ratio of real to imaginary part of an eigenvalue
The magnitude of the eigenvalue
The product of inertia and damping coefficient
The sum of all system inertias
Explanation - Damping factor ζ = -Re(λ)/|λ| for a complex eigenvalue λ.
Correct answer is: The ratio of real to imaginary part of an eigenvalue
Q.90 A high “critical clearing time” indicates:
A system with high inertia and damping
A system with low fault currents
A system that cannot tolerate faults
A system with poor voltage regulation
Explanation - Higher inertia and damping allow the system to survive longer faults.
Correct answer is: A system with high inertia and damping
Q.91 In power system dynamics, which of the following is a common representation of generator excitation dynamics?
Transfer function H(s)
Voltage‑speed characteristic curve
P-Q curve
Load flow equation
Explanation - Excitation dynamics are often modelled with a transfer function relating field voltage to AVR input.
Correct answer is: Transfer function H(s)
Q.92 Which of the following best explains why adding a series capacitor to a transmission line can improve stability?
It reduces line losses
It increases line impedance
It shifts the power‑flow angle
It increases the short‑circuit capacity
Explanation - Series capacitors raise the line’s short‑circuit current capability, which can help support voltage stability.
Correct answer is: It increases the short‑circuit capacity
Q.93 Which of the following is a typical parameter of a Power System Stabiliser (PSS) block?
Governor time constant
Voltage regulator gain
Damping factor
Exciter voltage
Explanation - The PSS introduces a damping torque, often represented by a damping factor.
Correct answer is: Damping factor
Q.94 The term 'load damping factor' refers to:
The effect of load changes on voltage
The reduction of power system frequency variation due to load response
The increase of system inertia due to loads
The time delay in load response to voltage changes
Explanation - Load damping factor measures how load power varies with frequency, mitigating frequency swings.
Correct answer is: The reduction of power system frequency variation due to load response
Q.95 Which of the following statements about 'critical loading factor' is correct?
It is the ratio of load to short‑circuit power
It determines the maximum load the system can handle without voltage collapse
It is always less than 1
It is independent of generator reactive power limits
Explanation - Critical loading factor indicates the maximum loading before voltage collapse occurs.
Correct answer is: It determines the maximum load the system can handle without voltage collapse
Q.96 Which of the following best describes a 'voltage collapse' phenomenon?
Sudden loss of frequency due to a fault
A gradual decrease in bus voltage due to reactive power shortage
Immediate drop in active power flow
Fast oscillation of voltage around its nominal value
Explanation - Voltage collapse is a progressive voltage drop caused by reactive power deficits.
Correct answer is: A gradual decrease in bus voltage due to reactive power shortage
Q.97 The 'critical clearing time' is a key parameter for which of the following protection schemes?
Under‑frequency relays
Under‑voltage relays
Differential protection of transformers
Distance protection of lines
Explanation - Distance relays must clear faults before the critical clearing time to avoid instability.
Correct answer is: Distance protection of lines
Q.98 Which of the following is a direct consequence of increasing the ‘system inertia constant’?
Faster frequency recovery after a disturbance
Reduced critical clearing time
Higher fault currents
Lower voltage stability margin
Explanation - Higher inertia slows the frequency change, allowing more time for recovery.
Correct answer is: Faster frequency recovery after a disturbance
Q.99 The 'damping ratio' of an oscillatory mode can be improved by:
Reducing generator inertia
Adding a PSS to the generator
Increasing load damping
Both b and c
Explanation - Adding a PSS and increasing load damping both enhance damping ratio.
Correct answer is: Both b and c
Q.100 A high‐frequency oscillation in a power system is typically:
Intra‑area oscillation
Inter‑area oscillation
Voltage swing
Frequency deviation
Explanation - High‑frequency modes are usually intra‑area oscillations within a single area.
Correct answer is: Intra‑area oscillation
Q.101 Which of the following devices can provide 'synthetic inertia' to a power system?
Synchronous condensers
FACTS devices
Power‑electronic converters
Load tap changers
Explanation - Converters can emulate inertia by adjusting active power output in response to frequency changes.
Correct answer is: Power‑electronic converters
Q.102 Which of the following best describes the effect of a 'dead‑band' in a voltage controller?
Increases voltage ripple
Prevents continuous small adjustments
Lowers system inertia
Reduces reactive power supply
Explanation - A dead‑band stops the controller from reacting to minor voltage fluctuations, reducing chatter.
Correct answer is: Prevents continuous small adjustments
Q.103 In a dynamic load model, which of the following parameters represents the load’s response to voltage changes?
Load damping factor
Voltage exponent
Frequency sensitivity
Time constant
Explanation - The voltage exponent defines how load power varies with voltage level.
Correct answer is: Voltage exponent
Q.104 Which of the following is an example of a 'weak' bus in a power system?
A bus with high short‑circuit capacity
A bus with low short‑circuit capacity and high load
A bus with no generators connected
A bus with a large shunt capacitor
Explanation - Low short‑circuit capacity and high load make a bus weak, more prone to voltage instability.
Correct answer is: A bus with low short‑circuit capacity and high load
Q.105 What is the role of the 'excitation system' in a synchronous generator?
Control generator mechanical speed
Provide reactive power support
Regulate generator terminal voltage
Both b and c
Explanation - The excitation system controls field voltage to regulate both reactive power and terminal voltage.
Correct answer is: Both b and c
Q.106 Which of the following best represents the critical power angle for a generator operating at full load?
Between 30° and 60°
0°
90°
180°
Explanation - Full‑load generators typically have critical angles between 30° and 60°, depending on system conditions.
Correct answer is: Between 30° and 60°
Q.107 Which of the following is a consequence of a high ‘fault impedance’ in the network?
High fault current
Low fault current
Shorter critical clearing time
Increased voltage stability margin
Explanation - High fault impedance limits fault current, potentially affecting protection coordination.
Correct answer is: Low fault current
Q.108 A PSS with a large phase shift is typically used to:
Dampen high‑frequency oscillations
Improve voltage regulation at low frequency
Control generator excitation
Reduce governor lag
Explanation - A large phase shift helps align the PSS output with high‑frequency oscillations for effective damping.
Correct answer is: Dampen high‑frequency oscillations
Q.109 In the swing equation \(2H\dot{\delta} = P_m - P_e\), the term \(P_m\) represents:
Electrical power output
Mechanical power input
Generator inertia
Generator reactance
Explanation - Pm is the mechanical power supplied to the generator by the turbine.
Correct answer is: Mechanical power input
Q.110 Which of the following is NOT a typical protective function of a distance relay?
Detecting faults based on impedance
Initiating fault clearance before the critical clearing time
Controlling load shedding directly
Differential protection of transformer cores
Explanation - Distance relays detect faults but do not directly control load shedding.
Correct answer is: Controlling load shedding directly
Q.111 A high‐frequency oscillation is generally mitigated by:
Adding large shunt capacitors
Using a PSS with low time constant
Reducing system inertia
Increasing load frequency sensitivity
Explanation - A low‑time‑constant PSS responds quickly to high‑frequency oscillations.
Correct answer is: Using a PSS with low time constant
Q.112 Which of the following is a primary cause of voltage instability during a large load step?
High generator inertia
Large shunt capacitor bank
Sudden increase in reactive power demand
Fast governor response
Explanation - A sudden reactive power increase can overwhelm the system, leading to voltage collapse.
Correct answer is: Sudden increase in reactive power demand
Q.113 In a two‑area power system, the ‘critical clearing time’ for a fault on an inter‑area line is usually:
Longer than a local fault
Shorter than a local fault
Same as a local fault
Unrelated to fault location
Explanation - Inter‑area faults typically allow more time for clearing because the system has larger inertia.
Correct answer is: Longer than a local fault
Q.114 Which of the following best describes the ‘voltage stability margin’?
Maximum power that can be transferred without voltage collapse
Maximum load that can be connected to a bus without voltage collapse
Minimum reactive power that can be supplied by generators
Minimum fault current required for protection
Explanation - Voltage stability margin refers to the load increase a bus can tolerate before collapsing.
Correct answer is: Maximum load that can be connected to a bus without voltage collapse
Q.115 What is the effect of adding a series capacitor to a transmission line?
Decrease line impedance
Increase line impedance
Increase reactive power absorption
Reduce fault current
Explanation - Series capacitors reduce line reactance, improving power transfer capability.
Correct answer is: Decrease line impedance
Q.116 The 'critical loading factor' is defined as:
Load divided by the system short‑circuit capacity
Maximum load the system can handle without voltage collapse
Ratio of load to generator output
Load divided by generator reactive power rating
Explanation - It indicates how much load can be added before voltage collapse occurs.
Correct answer is: Maximum load the system can handle without voltage collapse
Q.117 Which of the following is a typical feature of a dynamic load model?
Fixed power consumption
Time‑dependent reactive power requirement
Constant impedance
Linear voltage dependence
Explanation - Dynamic loads can change reactive power over time, influencing stability.
Correct answer is: Time‑dependent reactive power requirement
Q.118 Which of the following best explains the significance of 'frequency nadir' after a fault?
It indicates the highest frequency reached during recovery
It indicates the lowest frequency reached before recovery
It measures the time taken to recover frequency
It is unrelated to system stability
Explanation - Frequency nadir is the minimum frequency following a disturbance.
Correct answer is: It indicates the lowest frequency reached before recovery
Q.119 Which of the following is an advantage of using a Static VAR Compensator (SVC) during fault conditions?
It increases the system’s mechanical inertia
It quickly supplies or absorbs reactive power
It provides long‑term voltage support
It reduces system frequency
Explanation - SVCs can adjust reactive power rapidly, mitigating voltage dips during faults.
Correct answer is: It quickly supplies or absorbs reactive power
Q.120 Which of the following best describes the ‘short‑circuit ratio’ (SCR) of a bus?
The ratio of bus voltage to short‑circuit voltage
The ratio of short‑circuit power to rated power
The ratio of short‑circuit current to rated current
The ratio of reactive power to active power
Explanation - SCR = \(S_{SC}/S_{rated}\) and indicates the bus’s ability to tolerate disturbances.
Correct answer is: The ratio of short‑circuit power to rated power
Q.121 A generator’s ‘excitation system’ is primarily used to:
Control the generator’s mechanical speed
Regulate the terminal voltage
Provide frequency regulation
All of the above
Explanation - The excitation system adjusts the field current to maintain desired terminal voltage.
Correct answer is: Regulate the terminal voltage
Q.122 Which of the following is a key advantage of using a PSS compared to a simple governor?
Improved voltage regulation
Better damping of low‑frequency oscillations
Increased mechanical inertia
Reduced fault currents
Explanation - A PSS adds a damping signal to the governor, improving low‑frequency oscillation damping.
Correct answer is: Better damping of low‑frequency oscillations
Q.123 The ‘critical clearing time’ (CCT) is influenced by:
Generator inertia constant
Fault location and impedance
Governor time constant
All of the above
Explanation - CCT depends on inertia, fault impedance, and governor dynamics.
Correct answer is: All of the above
Q.124 Which of the following best describes the effect of a ‘dead‑band’ in a governor control circuit?
It increases system inertia
It reduces governor chattering
It improves voltage stability
It decreases fault clearance time
Explanation - The dead‑band prevents the governor from reacting to small frequency variations, reducing chatter.
Correct answer is: It reduces governor chattering
Q.125 Which of the following devices can provide both reactive power support and damping of electromechanical oscillations?
SVC
Shunt capacitor bank
Turbine governor
Under‑frequency relay
Explanation - SVCs supply reactive power and can be controlled to add damping torque.
Correct answer is: SVC
Q.126 A power system’s ‘critical loading factor’ is related to:
Maximum load before voltage collapse
Maximum power transfer limit
Minimum load for stable operation
Load frequency sensitivity
Explanation - Critical loading factor indicates how much load can be added before collapse occurs.
Correct answer is: Maximum load before voltage collapse
Q.127 In a small‑signal stability study, an eigenvalue with a real part of -0.05 and an imaginary part of 0.3 has a damping ratio of:
0.05
0.1
0.16
0.3
Explanation - Damping ratio ζ = -Re(λ)/|λ| = 0.05/√(0.05²+0.3²) ≈ 0.16.
Correct answer is: 0.16
Q.128 The term ‘frequency damping factor’ refers to:
The ability of load to react to frequency changes
The damping of voltage oscillations
The mechanical inertia of the system
The ability of the governor to respond quickly
Explanation - Frequency damping factor measures how load power varies with frequency, providing damping.
Correct answer is: The ability of load to react to frequency changes
Q.129 Which of the following is an example of a 'load‑shedding' scheme used to protect the grid?
Under‑frequency relays
Automatic voltage regulators
Turbine governor adjustments
Dynamic load models
Explanation - Under‑frequency relays detect frequency drops and disconnect load to maintain stability.
Correct answer is: Under‑frequency relays
Q.130 Which of the following best describes a 'critical clearing time' that is too short for a low‑voltage system?
0.5 s
0.05 s
1 s
10 s
Explanation - Low‑voltage systems often have critical clearing times in the tens of milliseconds.
Correct answer is: 0.05 s
Q.131 What is the primary function of a Power System Stabiliser (PSS)?
Regulate voltage levels
Provide frequency support
Add damping torque to generator governors
Control load shedding
Explanation - A PSS improves small‑signal stability by adding a damping signal to the governor.
Correct answer is: Add damping torque to generator governors
Q.132 Which of the following best explains the effect of a high ‘fault impedance’ on system stability?
It increases fault currents
It reduces fault currents
It lengthens the critical clearing time
It improves voltage stability margin
Explanation - High fault impedance limits the magnitude of fault currents, affecting protection coordination.
Correct answer is: It reduces fault currents
Q.133 Which of the following is a key factor influencing the transient stability of a power system?
System inertia
Generator reactance
Load frequency sensitivity
All of the above
Explanation - Inertia, reactance, and load frequency sensitivity all affect transient stability.
Correct answer is: All of the above
Q.134 Which of the following best describes a ‘critical power angle’ in a power system?
Angle where generators lose synchronism
Angle where maximum power transfer occurs
Angle where voltage collapses
Angle where frequency stabilises
Explanation - The critical power angle is the maximum permissible power‑angle before loss of synchronism.
Correct answer is: Angle where generators lose synchronism
Q.135 Which of the following is a typical parameter of a power system’s generator model?
Excitation voltage
Governor time constant
Short‑circuit ratio
All of the above
Explanation - Generator models incorporate excitation voltage, governor dynamics, and short‑circuit capability.
Correct answer is: All of the above
Q.136 Which of the following best explains why a ‘high short‑circuit ratio’ is desirable for voltage stability?
It reduces fault currents
It increases the source strength to support voltage
It reduces system inertia
It lowers reactive power demand
Explanation - A high SCR means a strong source that can better maintain voltage under load changes.
Correct answer is: It increases the source strength to support voltage
Q.137 Which of the following is a common method to compute the critical loading factor?
Load flow analysis
Continuation power flow
Small‑signal stability analysis
Transient stability simulation
Explanation - Continuation power flow tracks the system as load increases to find the point of voltage collapse.
Correct answer is: Continuation power flow
Q.138 Which of the following devices can provide rapid reactive power support during a fault?
Synchronous condenser
Shunt capacitor bank
Statcom
Turbine governor
Explanation - Statcoms can quickly adjust reactive power output during transient events.
Correct answer is: Statcom
Q.139 Which of the following best describes the effect of a ‘dead‑band’ in a voltage controller?
Reduces voltage ripple
Prevents continuous small adjustments
Increases system inertia
Reduces reactive power supply
Explanation - A dead‑band stops the controller from reacting to minor voltage fluctuations.
Correct answer is: Prevents continuous small adjustments
Q.140 Which of the following is a key parameter in the swing equation that affects transient stability?
Mechanical torque
Inertia constant H
Electrical damping D
All of the above
Explanation - All listed parameters influence the dynamic response after a disturbance.
Correct answer is: All of the above
Q.141 Which of the following best represents a typical voltage‑swing scenario in a power system?
Rapid voltage rise after a fault clearance
Gradual voltage drop due to reactive power shortage
Sudden frequency drop after load increase
Rapid frequency oscillation after a generator trip
Explanation - Voltage‑swing refers to a slow voltage decline after a disturbance.
Correct answer is: Gradual voltage drop due to reactive power shortage
Q.142 Which of the following best explains how a 'shunt capacitor bank' can influence power system stability?
By increasing short‑circuit current
By supplying reactive power to support voltage
By reducing system inertia
By increasing fault impedance
Explanation - Shunt capacitors provide reactive power, improving voltage stability.
Correct answer is: By supplying reactive power to support voltage
Q.143 Which of the following best defines the 'critical clearing time' (CCT)?
The minimum time required for a generator to recover from a fault
The maximum time allowed for fault clearance before loss of synchronism
The time it takes for voltage to recover after a fault
The time lag in the governor response
Explanation - CCT is the time limit beyond which a fault causes loss of synchronism.
Correct answer is: The maximum time allowed for fault clearance before loss of synchronism
Q.144 Which of the following is a typical characteristic of a 'weak' bus in a power system?
High short‑circuit ratio
Low short‑circuit ratio and high load
Large shunt capacitor bank
Large synchronous condenser
Explanation - A weak bus has low fault strength and high load, making it vulnerable to voltage instability.
Correct answer is: Low short‑circuit ratio and high load
Q.145 Which of the following best explains the role of a 'power‑system stabiliser' (PSS) in a power system?
To maintain voltage levels at all times
To provide fast reactive power support during faults
To add damping torque to governor control for small‑signal stability
To reduce system inertia
Explanation - A PSS introduces a damping signal to improve electromechanical oscillation damping.
Correct answer is: To add damping torque to governor control for small‑signal stability
Q.146 Which of the following is an example of 'low‑frequency inter‑area oscillation' in a power system?
Oscillation between two generators within the same area
Oscillation between two generators in different areas
Voltage drop at a single bus
Frequency increase after a load step
Explanation - Inter‑area oscillations involve generators in separate areas and have low frequencies.
Correct answer is: Oscillation between two generators in different areas
Q.147 What is the effect of a high ‘fault impedance’ on the ‘critical clearing time’?
Shortens the critical clearing time
Lengthens the critical clearing time
Has no effect
Increases the fault current
Explanation - High fault impedance leads to lower fault current and can shorten CCT.
Correct answer is: Shortens the critical clearing time
Q.148 Which of the following best describes the 'frequency nadir' after a disturbance?
The highest frequency reached after recovery
The lowest frequency reached before recovery
The rate of change of frequency
The time taken to recover from a fault
Explanation - Frequency nadir is the minimum frequency achieved following a disturbance.
Correct answer is: The lowest frequency reached before recovery
Q.149 Which of the following best describes the role of a 'short‑circuit ratio (SCR)'?
It indicates the fault current capability of a bus
It measures the load damping factor
It represents the short‑circuit voltage at a bus
It is the ratio of reactive power to active power
Explanation - SCR = \(S_{SC}/S_{rated}\) reflects how much fault current a bus can supply.
Correct answer is: It indicates the fault current capability of a bus
Q.150 Which of the following best explains why adding a series capacitor to a transmission line can improve stability?
It reduces line losses
It increases line reactance
It improves power transfer capability
It decreases fault currents
Explanation - Series capacitors reduce line reactance, enhancing power transfer and stability.
Correct answer is: It improves power transfer capability
Q.151 Which of the following best describes a 'critical clearing time' for a fault on a local line?
Shorter than for a fault on a remote line
Longer than for a fault on a remote line
Same as for a remote fault
Unrelated to fault location
Explanation - Local faults often have a shorter critical clearing time due to the proximity of the fault.
Correct answer is: Shorter than for a fault on a remote line
Q.152 Which of the following best explains the concept of 'voltage collapse' in power systems?
Rapid voltage rise due to over‑excitation
Gradual voltage drop due to insufficient reactive power
Sudden loss of synchronism after a fault
Frequency increase caused by load changes
Explanation - Voltage collapse is a slow decline in voltage caused by reactive power deficits.
Correct answer is: Gradual voltage drop due to insufficient reactive power
Q.153 Which of the following best describes the effect of 'frequency sensitivity of loads' on system stability?
It improves frequency regulation by load response
It has no effect on system stability
It increases system inertia
It reduces the critical clearing time
Explanation - Load frequency sensitivity allows loads to respond to frequency changes, aiding stability.
Correct answer is: It improves frequency regulation by load response
Q.154 Which of the following best explains the term 'critical loading factor'?
Maximum load the system can handle without voltage collapse
Maximum power transfer capacity
Minimum load for stable operation
Load frequency sensitivity factor
Explanation - Critical loading factor indicates the load level beyond which voltage collapse occurs.
Correct answer is: Maximum load the system can handle without voltage collapse
Q.155 Which of the following is a key component of a generator’s dynamic model used in small‑signal stability?
Excitation system
Governor system
Load model
All of the above
Explanation - Dynamic models include excitation, governor, and load dynamics for stability analysis.
Correct answer is: All of the above
Q.156 Which of the following best explains the role of a 'statcom' in a power system?
Providing fast reactive power support
Increasing system inertia
Controlling generator speed
Reducing fault currents
Explanation - A statcom supplies or absorbs reactive power quickly, improving voltage stability.
Correct answer is: Providing fast reactive power support
Q.157 Which of the following best describes a 'high‑frequency' oscillation in a power system?
Inter‑area oscillation with a period of 5–10 s
Intra‑area oscillation with a period of 0.1–0.5 s
Voltage collapse scenario
Frequency drop after a load increase
Explanation - High‑frequency oscillations are typically intra‑area modes with short periods.
Correct answer is: Intra‑area oscillation with a period of 0.1–0.5 s