Q.1 What is the primary purpose of a high‑voltage transmission line?
To step down voltage for local use
To step up voltage to reduce line losses
To provide protection against lightning
To isolate power plants from substations
Explanation - Transmission lines operate at high voltage (often 115‑765 kV) to reduce current for a given power level, thereby minimizing I²R losses and allowing efficient long‑distance transfer.
Correct answer is: To step up voltage to reduce line losses
Q.2 Which component is used to increase voltage in a transmission system?
Transformer
Capacitor
Resistor
Inductor
Explanation - Transformers raise (step up) the voltage at a generator or substation to the high transmission level, reducing current and losses.
Correct answer is: Transformer
Q.3 A transmission line that carries 500 MVA at 230 kV has how many conductors per phase if it is a 3‑phase system?
1
2
3
4
Explanation - In a 3‑phase line, each phase normally has one conductor. 500 MVA at 230 kV requires 3 conductors (one per phase) in a typical 3‑phase transmission line.
Correct answer is: 3
Q.4 Which of the following best describes a 'cable' in a transmission system?
An overhead line with three conductors
A buried or submerged line made of insulated conductors
A device that steps up voltage
A type of transformer
Explanation - Cables are underground or underwater conductors with insulation, used where overhead lines are impractical.
Correct answer is: A buried or submerged line made of insulated conductors
Q.5 Which of the following is NOT a typical cause of voltage sag on a transmission line?
Fault on the line
Load changes
Wind gusts
Sunrise
Explanation - Voltage sag occurs due to faults, heavy loads, or mechanical disturbances. Sunrise is unrelated.
Correct answer is: Sunrise
Q.6 What is the primary reason for using AC over DC in long‑distance transmission?
AC can be stepped up/down with transformers easily
DC has lower losses
AC is cheaper to generate
DC cannot be transmitted through cables
Explanation - AC allows simple voltage transformation using transformers, making long‑distance transmission more economical despite higher losses than DC in some cases.
Correct answer is: AC can be stepped up/down with transformers easily
Q.7 What type of fault is characterized by a short circuit between one phase and the ground?
Line‑to‑line fault
Line‑to‑neutral fault
Three‑phase fault
Open circuit fault
Explanation - A line‑to‑neutral (or ground) fault involves a single phase touching ground or a conductive surface.
Correct answer is: Line‑to‑neutral fault
Q.8 In a 230 kV transmission line, the line impedance per km is approximately 0.3 Ω/km. What is the total impedance of a 120 km line?
36 Ω
28.8 Ω
30 Ω
45 Ω
Explanation - Impedance = 0.3 Ω/km × 120 km = 36 Ω.
Correct answer is: 36 Ω
Q.9 Which protective device is typically installed at a substation to isolate faults on the transmission line?
Surge arrester
Shunt reactor
Circuit breaker
Static VAR compensator
Explanation - Circuit breakers disconnect the line during fault conditions, protecting equipment and preventing damage.
Correct answer is: Circuit breaker
Q.10 What is the main advantage of a Flexible AC Transmission System (FACTS) device like a STATCOM?
It steps up voltage
It reduces line resistance
It dynamically controls reactive power
It eliminates line faults
Explanation - STATCOMs supply or absorb reactive power quickly, improving voltage stability and power transfer capability.
Correct answer is: It dynamically controls reactive power
Q.11 Which phenomenon causes a periodic variation in the voltage amplitude on a transmission line during load changes?
Resonance
Harmonic distortion
Synchronous operation
Load flow imbalance
Explanation - Resonance between line inductance and capacitance can amplify voltage variations during transient load changes.
Correct answer is: Resonance
Q.12 What is the function of a shunt reactor in a high‑voltage transmission line?
Provide reactive power support
Reduce voltage sag during high load
Increase line inductance to limit fault current
Step up voltage at the transmission terminal
Explanation - Shunt reactors absorb reactive power during peak loads, raising the system voltage and limiting over‑current.
Correct answer is: Reduce voltage sag during high load
Q.13 Which of the following is NOT a typical cause of insulation breakdown in a transmission line?
Overvoltage
Moisture ingress
Mechanical damage
Proper maintenance
Explanation - Proper maintenance prevents breakdown; the other factors increase risk.
Correct answer is: Proper maintenance
Q.14 How does a power‑line carrier (PLC) system communicate?
Using magnetic fields only
By modulating high‑frequency signals over existing lines
Through fiber optics installed along the line
With wireless radio signals
Explanation - PLC transmits data by superimposing high‑frequency carrier signals on the DC or AC power line.
Correct answer is: By modulating high‑frequency signals over existing lines
Q.15 Which component of a transmission system primarily limits the amount of power that can be transferred?
Line resistance
Line reactance
Transformer rating
Capacitor banks
Explanation - Line reactance governs the power transfer capability via the transmission equation P = (V1*V2/X) sinθ.
Correct answer is: Line reactance
Q.16 In a three‑phase system, if the line voltage is 230 kV, what is the phase voltage in a wye connection?
115 kV
230 kV
400 kV
115√3 kV
Explanation - Phase voltage = line voltage / √3 for a wye connection: 230 kV / √3 ≈ 133 kV; but typical nominal values use 115 kV for line‑to‑neutral in 230 kV lines.
Correct answer is: 115 kV
Q.17 What is the term for a condition where a transmission line loses its ability to transfer power due to thermal limits?
Thermal overload
Voltage collapse
Resistive heating
Current limitation
Explanation - When line temperature exceeds safe limits, the conductor’s resistance rises, and power transfer capacity drops.
Correct answer is: Thermal overload
Q.18 Which of the following is a typical characteristic of a 'smart grid' in relation to transmission systems?
Fixed voltage levels across all regions
No real‑time monitoring
Dynamic line rating and automated fault isolation
Exclusion of renewable energy sources
Explanation - Smart grids use sensors and control systems to adjust line ratings based on temperature and isolate faults automatically.
Correct answer is: Dynamic line rating and automated fault isolation
Q.19 Which parameter is most critical when determining the maximum power transfer over a transmission line?
Line resistance
Line inductance
Transmission voltage
Load impedance
Explanation - Inductive reactance limits power transfer; the higher the reactance, the lower the maximum transferable power for a given voltage.
Correct answer is: Line inductance
Q.20 What is the primary function of a voltage‑sag compensator?
Reduce transmission losses
Prevent over‑voltage
Maintain voltage during transient load changes
Increase fault current
Explanation - A voltage‑sag compensator injects reactive power to keep system voltage within limits during sudden load changes.
Correct answer is: Maintain voltage during transient load changes
Q.21 Which of these is a common type of high‑voltage insulator?
Ceramic insulator
Copper insulator
Steel insulator
Aluminum insulator
Explanation - Ceramic or porcelain insulators are standard for high‑voltage overhead lines due to their high dielectric strength.
Correct answer is: Ceramic insulator
Q.22 What is the main reason for using a three‑phase line instead of a single‑phase line for power transmission?
Increased mechanical strength
Better voltage regulation
Higher power transfer capability per conductor
Simplified fault detection
Explanation - A three‑phase system transfers more power with fewer conductors compared to single‑phase, reducing costs.
Correct answer is: Higher power transfer capability per conductor
Q.23 A fault current of 200 kA is detected on a 345 kV line. Which protective relay setting is most appropriate for coordination?
Fast time‑delay with 1‑second open time
Inverse time setting with 5‑second delay
Inverse time setting with 0.5‑second delay
Fixed time setting with 10‑second delay
Explanation - Inverse time relays reduce opening time for higher fault currents; 200 kA requires a fast setting, hence 0.5 s.
Correct answer is: Inverse time setting with 0.5‑second delay
Q.24 Which of the following is a disadvantage of using DC for long‑distance power transmission?
Requires expensive converters
Higher line losses compared to AC
Limited ability to step voltage
Incompatibility with renewable sources
Explanation - Converting AC to DC and back requires large, costly equipment, which is a major drawback compared to AC.
Correct answer is: Requires expensive converters
Q.25 The term 'dynamic line rating' refers to:
The static rating of a line based on design
The adjustable rating of a line based on real‑time conditions
The maximum rating before the line is dismantled
The rating determined during the summer months
Explanation - Dynamic line rating uses real‑time data (temperature, wind, etc.) to adjust the permissible current, increasing efficiency.
Correct answer is: The adjustable rating of a line based on real‑time conditions
Q.26 Which of these is NOT a typical protection scheme for a transmission line?
Distance protection
Over‑current protection
Under‑frequency protection
Impedance protection
Explanation - Under‑frequency protection is used in generators, not lines; line protection uses distance, over‑current, impedance, etc.
Correct answer is: Under‑frequency protection
Q.27 What does the term 'voltage collapse' mean?
Voltage permanently dropping below the minimum operating level
Voltage oscillating rapidly in the grid
Voltage sag during a fault
Voltage increase during a surge
Explanation - Voltage collapse is a cascading event where voltage falls below acceptable levels and cannot be restored.
Correct answer is: Voltage permanently dropping below the minimum operating level
Q.28 Which of the following is a key advantage of using a ‘T‑type’ line configuration?
Lower cost per conductor
Reduced corona loss
Higher mechanical stability
Improved power factor
Explanation - A T‑type line has a grounded neutral that reduces sag and increases mechanical strength.
Correct answer is: Higher mechanical stability
Q.29 Which component is commonly used to reduce electromagnetic interference (EMI) on a transmission line?
Grounding transformer
Shielded cable
Surge arrester
Cable sheath
Explanation - Shielded cables contain metallic layers that absorb EMI, protecting sensitive equipment.
Correct answer is: Shielded cable
Q.30 What is the typical operating frequency for AC transmission systems worldwide?
50 Hz
60 Hz
50/60 Hz
Both 50 Hz and 60 Hz depending on region
Explanation - 50 Hz is standard in most of the world, 60 Hz in North America; some countries use both.
Correct answer is: Both 50 Hz and 60 Hz depending on region
Q.31 Which type of fault is the most severe for transmission lines?
Line‑to‑ground fault
Line‑to‑line fault
Three‑phase fault
Open circuit fault
Explanation - Three‑phase faults produce the highest fault currents and are the most destructive.
Correct answer is: Three‑phase fault
Q.32 A 500 kV line has a per‑phase impedance of 0.2 Ω. What is the maximum power transfer assuming a 30° phase shift?
2500 MW
4000 MW
5000 MW
6000 MW
Explanation - Using Pmax = (V² / X) * sinθ, V = 500/√3 kV ≈ 288 kV; X = 0.2 Ω. Pmax ≈ (288² / 0.2) * sin30° ≈ 4000 MW.
Correct answer is: 4000 MW
Q.33 In a transmission line, the line charge per unit length is 10 pF/km. Which of the following is an effect of this capacitance?
It increases the line's inductive reactance
It causes voltage rise in long lines
It reduces the power transfer capacity
It limits the maximum voltage
Explanation - The line’s capacitive charging current raises the voltage along the line during heavy loading.
Correct answer is: It causes voltage rise in long lines
Q.34 What is the purpose of a ‘remote terminal unit’ (RTU) in a transmission system?
To step up voltage
To monitor and control equipment remotely
To provide reactive power support
To isolate faults automatically
Explanation - RTUs collect data from field devices and send commands to protect and control equipment over communication networks.
Correct answer is: To monitor and control equipment remotely
Q.35 Which of the following best describes the concept of 'grid frequency stability'?
Maintaining voltage above 100 V
Keeping power system frequency within a narrow range (e.g., 50 ± 0.5 Hz)
Ensuring equal phase angles
Balancing reactive and active power
Explanation - Grid frequency stability refers to the ability to keep frequency close to the nominal value despite disturbances.
Correct answer is: Keeping power system frequency within a narrow range (e.g., 50 ± 0.5 Hz)
Q.36 In a transmission line, what is the effect of increasing the conductor diameter?
Increase line resistance
Decrease line resistance
No effect on resistance
Increase line inductance
Explanation - A larger diameter conductor has lower resistance, reducing I²R losses.
Correct answer is: Decrease line resistance
Q.37 Which device is used to inject capacitive reactive power into a transmission system?
Shunt reactor
Shunt capacitor bank
Synchronous condenser
Static VAR compensator
Explanation - Capacitor banks supply reactive power, reducing line current and improving voltage profile.
Correct answer is: Shunt capacitor bank
Q.38 The 'skin effect' in conductors causes:
Current to flow through the center only
Current to flow near the surface only
Reduction of conductor resistance
Increase in inductance
Explanation - At high frequencies, AC current concentrates near the surface, increasing effective resistance.
Correct answer is: Current to flow near the surface only
Q.39 Which of the following is a typical characteristic of a 'dead‑end' transmission line?
It terminates at a substation with no further lines
It has a low voltage rating
It uses only a single conductor
It is used exclusively for renewable integration
Explanation - A dead‑end line ends at a substation or plant; it is not part of a continuous network.
Correct answer is: It terminates at a substation with no further lines
Q.40 What does 'HVDC' stand for?
High Voltage Direct Current
High Voltage Digital Circuit
High Voltage Data Control
High Voltage Dynamic Converter
Explanation - HVDC is a method of transmitting power over long distances using direct current.
Correct answer is: High Voltage Direct Current
Q.41 Which of the following is a benefit of using a 'three‑wire' transmission line?
Reduces the number of conductors needed
Increases voltage rating
Allows for easier grounding of each phase
Enables more flexible fault isolation
Explanation - A three‑wire line includes a neutral conductor, allowing for better fault handling and lower voltage differences.
Correct answer is: Enables more flexible fault isolation
Q.42 Why are high‑voltage lines usually strung on tall pylons?
To reduce line sag
To minimize electromagnetic fields
To keep the line away from the ground and obstacles
To increase conductor cross‑section
Explanation - Tall pylons elevate the conductors, ensuring clearance from obstacles and minimizing interference.
Correct answer is: To keep the line away from the ground and obstacles
Q.43 Which component is primarily responsible for stepping down voltage from 345 kV to 132 kV in a substation?
Shunt capacitor bank
Step‑down transformer
Voltage regulator
Synchronous condenser
Explanation - Transformers change voltage levels, stepping down high transmission voltages to distribution levels.
Correct answer is: Step‑down transformer
Q.44 In a transmission line, what is the 'current‑carrying capacity' dependent on?
Line voltage only
Conductor size, ambient temperature, and soil thermal resistivity
Number of conductors per phase
Transformer rating
Explanation - The capacity is determined by the conductor’s ability to dissipate heat under operating conditions.
Correct answer is: Conductor size, ambient temperature, and soil thermal resistivity
Q.45 Which of the following is NOT typically a part of a transmission line system?
Pylons
Conductors
Transformers
Generators
Explanation - Generators supply power but are not components of the transmission line itself.
Correct answer is: Generators
Q.46 What is the effect of increasing the number of conductors per phase from one to two in a transmission line?
Increases the line’s reactance
Decreases the line’s capacitance
Reduces the line’s resistance
Has no effect on line parameters
Explanation - Parallel conductors lower the overall resistance, improving efficiency.
Correct answer is: Reduces the line’s resistance
Q.47 Which phenomenon can cause a sudden drop in voltage at a load end of a transmission line?
Resonance
Harmonic distortion
Fault current surge
Temperature rise
Explanation - A fault introduces a high current that causes a voltage drop across the line impedance.
Correct answer is: Fault current surge
Q.48 Which of the following is a typical purpose of a 'phase‑shifting transformer' in a transmission system?
To increase line voltage
To adjust power flow direction
To reduce line sag
To step down voltage
Explanation - Phase‑shifting transformers change the phase angle between supply and demand, controlling power flow.
Correct answer is: To adjust power flow direction
Q.49 Which type of insulator is commonly used for underground cables?
Ceramic insulator
Glass insulator
Plastic (PVC) insulator
Steel insulator
Explanation - PVC or polyethylene insulators provide good dielectric strength for underground cables.
Correct answer is: Plastic (PVC) insulator
Q.50 What is the purpose of a 'copper‑clad steel' conductor in high‑voltage lines?
To reduce electromagnetic interference
To improve mechanical strength and conductivity
To increase thermal resistance
To lower cost compared to aluminum
Explanation - Copper provides good conductivity; steel gives strength; the combination balances both properties.
Correct answer is: To improve mechanical strength and conductivity
Q.51 Which of the following best describes 'power system resilience'?
The ability to recover from a fault quickly
The capacity to handle high voltage spikes
The ability to withstand weather conditions
The use of renewable energy sources
Explanation - Resilience refers to the system’s ability to withstand disturbances and recover operations.
Correct answer is: The ability to recover from a fault quickly
Q.52 What does 'line‑to‑neutral voltage' refer to in a wye‑connected system?
Voltage between two phases
Voltage between a phase and ground
Voltage across all phases
Voltage at the substation transformer
Explanation - Line‑to‑neutral voltage is the voltage from each phase conductor to the neutral conductor.
Correct answer is: Voltage between a phase and ground
Q.53 Which of the following is a key benefit of using 'liquid‑filled' (LF) transformers in transmission substations?
Lower cost
Higher insulation level
Reduced electromagnetic emissions
Faster voltage regulation
Explanation - LF transformers provide excellent dielectric strength, allowing higher voltage ratings.
Correct answer is: Higher insulation level
Q.54 Which parameter is most critical in determining the thermal limit of a transmission line?
Conductor resistance
Ambient temperature
Line voltage
Capacitance per unit length
Explanation - Ambient temperature directly affects heat dissipation; higher temperatures reduce the current rating.
Correct answer is: Ambient temperature
Q.55 A transmission line is said to operate in 'dead‑band' when?
Voltage is within ±5 % of nominal
Current is below the protection threshold
Power flow is zero
Frequency is exactly 50 Hz
Explanation - Dead‑band is a protection setting where minor current variations do not trigger action.
Correct answer is: Current is below the protection threshold
Q.56 What is the main reason for using 'z‑type' pylons?
To reduce construction cost
To allow higher voltage levels
To provide better mechanical strength with fewer towers
To lower electromagnetic field strength
Explanation - Z‑type pylons have a cross‑section resembling a Z, providing high strength and reducing number of towers needed.
Correct answer is: To provide better mechanical strength with fewer towers
Q.57 Which type of fault is most commonly detected by 'distance protection' relays?
Line‑to‑neutral faults
Three‑phase faults
Line‑to‑line faults
All of the above
Explanation - Distance protection calculates fault distance based on impedance, detecting all fault types.
Correct answer is: All of the above
Q.58 In transmission systems, what does the term 'reactive power' refer to?
Power that does useful work
Power stored and released by inductors and capacitors
Power lost as heat
Power transferred across a line at zero phase angle
Explanation - Reactive power is associated with energy oscillation, not real work output.
Correct answer is: Power stored and released by inductors and capacitors
Q.59 Which of the following is an advantage of using 'air‑insulated' cables?
Lower cost compared to XLPE
Higher temperature capability
Better mechanical strength
Higher dielectric strength
Explanation - Air‑insulated cables can operate at higher temperatures than XLPE, reducing losses.
Correct answer is: Higher temperature capability
Q.60 The term 'short‑circuit current' refers to:
Maximum current that can flow when a fault occurs
Current flowing in a healthy line
Current needed to energize a transformer
The normal operating current of a line
Explanation - Short‑circuit current is the peak current during a fault, used for protective relay settings.
Correct answer is: Maximum current that can flow when a fault occurs
Q.61 Which of the following is NOT a factor that influences the voltage rise in long transmission lines?
Line inductance
Line capacitance
Line resistance
Line current
Explanation - Voltage rise is primarily due to inductive and capacitive effects; resistance mainly causes voltage drop.
Correct answer is: Line resistance
Q.62 What does 'power system operator' primarily do?
Designs new transmission lines
Monitors real‑time grid conditions
Builds transformers
Manufactures insulators
Explanation - Operators ensure balanced load, voltage, and frequency across the system.
Correct answer is: Monitors real‑time grid conditions
Q.63 Which component is used to isolate a faulted section of a transmission line while keeping the rest of the network energized?
Breaker‑switch
Load‑break switch
Sectionalizer
Bus‑bar
Explanation - A sectionalizer allows the operator to isolate a faulted portion of a line.
Correct answer is: Sectionalizer
Q.64 The 'line‑to‑line voltage' in a three‑phase system is:
The voltage between any two phases
The voltage between a phase and neutral
The voltage across all three phases
The same as phase voltage
Explanation - Line‑to‑line voltage is measured between any two phase conductors.
Correct answer is: The voltage between any two phases
Q.65 Why are 'high‑temperature low‑smoke' (HTLS) cables preferred for underground transmission?
They are cheaper
They provide better insulation and are fire‑safe
They allow higher voltage
They are lighter
Explanation - HTLS cables resist fire and provide high insulation, reducing risk in underground environments.
Correct answer is: They provide better insulation and are fire‑safe
Q.66 Which type of transformer is commonly used in HV transmission substations to provide a step‑down ratio of 1:1?
Autotransformer
Isolation transformer
Regulating transformer
Bifilar transformer
Explanation - Isolation transformers provide a 1:1 ratio and electrical isolation between windings.
Correct answer is: Isolation transformer
Q.67 The 'magnetic field' around a transmission line is strongest when?
Current is low
Current is high
Voltage is high
Voltage is low
Explanation - Magnetic field strength is proportional to current, not voltage.
Correct answer is: Current is high
Q.68 Which of these is a primary function of a 'voltage regulator' in a transmission system?
Maintain constant line voltage
Control reactive power
Isolate faults
Reduce line sag
Explanation - Voltage regulators adjust tap settings to keep the system voltage within limits.
Correct answer is: Maintain constant line voltage
Q.69 The 'phase angle difference' between two nodes in a transmission network determines:
Voltage magnitude at each node
The direction and magnitude of power flow
The line impedance
The transformer tap position
Explanation - Power flow is proportional to the sine of the phase angle difference between nodes.
Correct answer is: The direction and magnitude of power flow
Q.70 What is the main purpose of installing a 'grounding electrode' at a substation?
To increase voltage
To provide a reference potential and dissipate fault currents
To step up voltage
To support the substation tower
Explanation - Grounding electrodes provide a path for fault currents to earth and maintain system reference.
Correct answer is: To provide a reference potential and dissipate fault currents
Q.71 Which of the following is NOT a typical type of insulation for high‑voltage overhead lines?
Air
Oil
XLPE
Water
Explanation - Water is not used as insulation for overhead lines; air or solid dielectrics are used.
Correct answer is: Water
Q.72 What does 'line charging current' refer to in a long transmission line?
Current due to line resistance
Current that charges line capacitance
Current supplied by the generator
Current that flows during a fault
Explanation - Line charging current is the capacitive current that flows to charge the line’s capacitance.
Correct answer is: Current that charges line capacitance
Q.73 A 'Synchronous Condenser' in a transmission system primarily provides:
Active power
Reactive power
Grounding
Voltage regulation
Explanation - A synchronous condenser supplies or absorbs reactive power without delivering real power.
Correct answer is: Reactive power
Q.74 Which of the following best describes a 'transmission corridor'?
A path between two generators
A protected route for power lines over a large distance
The route of a single conductor
The area around a substation
Explanation - A corridor is a defined route that houses multiple transmission lines.
Correct answer is: A protected route for power lines over a large distance
Q.75 Why is 'copper' commonly used in transformer windings?
It is inexpensive
It has high electrical conductivity
It has low thermal expansion
It is lighter than aluminum
Explanation - Copper provides lower resistance and thus lower I²R losses.
Correct answer is: It has high electrical conductivity
Q.76 Which of these is a consequence of 'corona discharge' in a transmission line?
Decreased line voltage
Increased power losses
Improved transmission efficiency
Lower line impedance
Explanation - Corona discharge consumes power, creating losses and radio interference.
Correct answer is: Increased power losses
Q.77 The 'thermal rating' of a transmission line is expressed in terms of:
Maximum voltage
Maximum current
Maximum temperature
Maximum power
Explanation - Thermal rating indicates the maximum conductor temperature the line can sustain.
Correct answer is: Maximum temperature
Q.78 Which type of line is most suitable for very long distances (>600 km) due to its low losses?
AC HV transmission line
DC HV transmission line
Low‑voltage AC line
High‑frequency AC line
Explanation - HVDC has lower line losses over very long distances, making it efficient for >600 km.
Correct answer is: DC HV transmission line
Q.79 What is the purpose of a 'dead‑center' transformer in a transmission system?
To isolate ground faults
To step down voltage
To provide a neutral point
To increase line current capacity
Explanation - A dead‑center transformer offers a neutral connection for balanced loads.
Correct answer is: To provide a neutral point
Q.80 Which of the following is a common cause of 'transient over‑voltage' on a transmission line?
Sudden load drop
Fault clearance
Inrush current
Increased line sag
Explanation - When a load drops, the line voltage can rise rapidly due to line capacitance.
Correct answer is: Sudden load drop
Q.81 The 'voltage stability margin' is defined as the difference between:
Maximum load and minimum load
System voltage and nominal voltage
Maximum and minimum line impedance
Maximum and minimum current ratings
Explanation - Voltage stability margin indicates how far the system voltage can fall before instability.
Correct answer is: System voltage and nominal voltage
Q.82 Which of the following is NOT a typical use of a 'shunt capacitor' in a transmission line?
To increase line voltage
To reduce reactive power consumption
To improve power factor
To step up voltage
Explanation - Capacitors supply reactive power but do not step up voltage.
Correct answer is: To step up voltage
Q.83 Which of the following best describes the term 'line impedance'?
Resistance only
Reactance only
Combined resistance and reactance
Combined resistance, reactance, and capacitance
Explanation - Impedance is the complex sum of resistance and reactance; capacitance is usually represented separately.
Correct answer is: Combined resistance and reactance
Q.84 A 400 kV transmission line has a per‑phase resistance of 0.1 Ω and a reactance of 0.3 Ω. What is its impedance magnitude?
0.316 Ω
0.4 Ω
0.6 Ω
0.5 Ω
Explanation - Impedance = √(R²+X²) = √(0.1²+0.3²) ≈ 0.316 Ω.
Correct answer is: 0.316 Ω
Q.85 Which of the following is an effect of a high ‘grounding resistance’ in a substation?
Reduced fault currents
Increased fault currents
Improved voltage stability
Higher line losses
Explanation - Higher grounding resistance limits the fault current flow into earth, potentially prolonging fault conditions.
Correct answer is: Reduced fault currents
Q.86 In a power transmission system, the term 'feed‑forward' control refers to:
Adjusting voltage in response to a fault
Predicting load changes and adjusting accordingly
Controlling current in the line
Using reactive power to stabilize voltage
Explanation - Feed‑forward control anticipates changes and modifies settings pre‑emptively.
Correct answer is: Predicting load changes and adjusting accordingly
Q.87 Which of the following is a key design consideration for a 'high‑voltage direct current' (HVDC) link?
Transformer tap settings
Converter station placement
Line sag
Cable insulation type
Explanation - HVDC requires converter stations at each end; their location and design are critical.
Correct answer is: Converter station placement
Q.88 A 'dead‑end' transmission line can be safely energized if:
The terminal substation is grounded
All downstream loads are disconnected
A fault detector is installed
All of the above
Explanation - Energizing a dead‑end requires proper grounding, load isolation, and fault detection.
Correct answer is: All of the above
Q.89 Which of the following is NOT a type of transmission line topology?
S‑type
Z‑type
Y‑type
X‑type
Explanation - Common topologies include S, Z, Y, and T; X‑type is not used.
Correct answer is: X‑type
Q.90 The 'short‑circuit impedance' of a transmission line is used to determine:
The line’s resistance only
The fault current magnitude
The line's capacitance
The transformer tap ratio
Explanation - Short‑circuit impedance directly influences the fault current that can flow.
Correct answer is: The fault current magnitude
Q.91 Which of the following is a typical application of 'static VAR compensators' (SVCs) in a transmission network?
To step up voltage
To absorb fault currents
To provide dynamic reactive power support
To isolate the line from faults
Explanation - SVCs rapidly adjust reactive power to maintain voltage levels.
Correct answer is: To provide dynamic reactive power support
Q.92 Which of the following is an example of a 'neutral‑point fault' in a transmission line?
Ground fault on one phase
Short between two phases
Fault between phase and neutral
Open circuit in the neutral conductor
Explanation - A neutral‑point fault involves a phase conductor contacting the neutral.
Correct answer is: Fault between phase and neutral
Q.93 What is the main advantage of 'direct current (DC) transmission' over 'alternating current (AC) transmission' for submarine cables?
Higher voltage operation
Lower losses due to capacitive charging
Simpler control mechanisms
Lower installation cost
Explanation - DC eliminates line charging currents, reducing losses in submarine cables.
Correct answer is: Lower losses due to capacitive charging
Q.94 A 'synchronous generator' in a power system is primarily connected to the grid via:
A transformer
A capacitor bank
A DC link
A resistive load
Explanation - Synchronous generators are usually stepped down by a transformer before connecting to the grid.
Correct answer is: A transformer
Q.95 Which of the following is an effect of 'line sag' in a transmission line?
Increased electromagnetic interference
Higher mechanical tension
Reduced voltage at the load
Higher line impedance
Explanation - Sag increases the mechanical tension in conductors due to longer span length.
Correct answer is: Higher mechanical tension
Q.96 In a transmission system, which of the following parameters is most critical for determining the 'thermal limit' of a line?
Line resistance
Line impedance
Conductor cross‑sectional area
Conductor temperature rise
Explanation - The thermal limit is based on allowable temperature rise in the conductor under load.
Correct answer is: Conductor temperature rise
Q.97 Which of the following is a characteristic of a 'dynamic line rating' system?
It uses fixed ratings based on design
It adjusts line capacity based on real‑time data
It ignores temperature changes
It only applies to overhead lines
Explanation - Dynamic line rating uses real‑time measurements (temperature, wind) to compute a safe current limit.
Correct answer is: It adjusts line capacity based on real‑time data
Q.98 Which of the following is a typical use of a 'copper‑clad conductor' in high‑voltage lines?
To reduce corona discharge
To lower cost of material
To increase mechanical strength while maintaining conductivity
To provide better insulation
Explanation - Copper cladding gives high conductivity; steel provides mechanical strength.
Correct answer is: To increase mechanical strength while maintaining conductivity
Q.99 The 'per‑unit system' is used in power engineering to:
Measure voltage in volts
Simplify calculations by normalizing values
Express only reactive power
Indicate thermal limits of a line
Explanation - Per‑unit normalizes parameters to a base, simplifying complex system calculations.
Correct answer is: Simplify calculations by normalizing values
Q.100 Which of the following is NOT a typical cause of 'transient over‑voltage' on a transmission line?
Sudden load addition
Fault clearance
Inrush current at energization
Long‑duration high load
Explanation - Transient over‑voltage occurs during sudden events, not sustained high loads.
Correct answer is: Long‑duration high load
Q.101 Which device is used to protect a transmission line by detecting changes in impedance?
Distance relay
Under‑current relay
Thermal relay
Over‑voltage relay
Explanation - Distance relays calculate the impedance to the fault location to initiate isolation.
Correct answer is: Distance relay
Q.102 What is the main function of a 'series reactor' on a transmission line?
Reduce line charging
Increase line inductance to control current
Improve voltage regulation
Lower line impedance
Explanation - Series reactors increase inductance, reducing fault currents and controlling load flow.
Correct answer is: Increase line inductance to control current
Q.103 The 'line impedance per km' is usually expressed in terms of:
Ohms per km
Kilohms per km
Milliohms per km
Megaohms per km
Explanation - Impedance is measured in ohms per unit length (ohms/km) for transmission lines.
Correct answer is: Ohms per km
Q.104 Which of the following is a typical use of 'static VAR compensators' in high‑voltage transmission?
To provide voltage support during transient events
To reduce line sag
To step up voltage
To isolate faults
Explanation - SVCs quickly supply reactive power, helping maintain voltage during disturbances.
Correct answer is: To provide voltage support during transient events
Q.105 Which of the following is an advantage of a 'tensile‑rated conductor'?
Lower cost
Higher mechanical strength for longer spans
Lower capacitance
Higher thermal limits
Explanation - Tensile‑rated conductors can span longer distances without sag.
Correct answer is: Higher mechanical strength for longer spans
Q.106 What is the primary function of a 'surge arrester' in a transmission line?
To step up voltage
To protect against lightning and switching surges
To supply reactive power
To increase line capacitance
Explanation - Surge arresters clamp voltage spikes to a safe level, protecting equipment.
Correct answer is: To protect against lightning and switching surges
Q.107 The 'transmission system operator' (TSO) is primarily responsible for:
Designing transformers
Maintaining grid security and reliability
Manufacturing insulators
Building substations
Explanation - TSOs manage the operation of the transmission network, ensuring reliability.
Correct answer is: Maintaining grid security and reliability
Q.108 Which of the following is NOT a typical type of 'over‑current protection' relay setting?
Inverse time
Inverse‑current
Fixed time‑delay
Exponential time‑delay
Explanation - The common settings are inverse time, fixed time‑delay, and sometimes exponential, not 'inverse‑current'.
Correct answer is: Inverse‑current
Q.109 Which of the following best describes a 'dead‑end line'?
A line that connects to a substation but has no downstream load
A line that is permanently de‑energized
A line that is used only for maintenance
A line that has no neutral conductor
Explanation - Dead‑end lines terminate at a substation or plant and carry no load to the rest of the grid.
Correct answer is: A line that connects to a substation but has no downstream load
Q.110 In a transmission line, the 'voltage regulation' of a transformer refers to:
The ratio of no‑load to full‑load voltage
The ability to step up voltage
The maximum fault current
The transformer’s impedance
Explanation - Voltage regulation indicates how much the voltage changes from no‑load to full‑load operation.
Correct answer is: The ratio of no‑load to full‑load voltage
Q.111 The 'short‑circuit power' of a transmission line is calculated using which formula?
S = V² / R
S = V² / X
S = V * I
S = (V² / Z) * sinθ
Explanation - Short‑circuit power is V² divided by the line’s reactance for a three‑phase fault.
Correct answer is: S = V² / X
Q.112 Which of the following is a major disadvantage of using a 'high‑voltage direct current' (HVDC) transmission line?
Higher line losses
Need for converter stations
Lower voltage levels
Incompatibility with AC distribution
Explanation - HVDC requires costly converter stations at both ends.
Correct answer is: Need for converter stations
Q.113 What is the primary purpose of 'shunt reactors' in transmission systems?
To supply reactive power during peak demand
To absorb reactive power during heavy load
To step up voltage
To increase line sag
Explanation - Shunt reactors provide inductive reactive power, counteracting capacitive effects during high load.
Correct answer is: To absorb reactive power during heavy load
Q.114 Which of the following is a typical protective strategy for a 'transmission line section'?
Open‑cycle protection
Fault‑current relay with time delay
Over‑voltage relay only
Under‑current relay only
Explanation - Fault‑current relays with time delay isolate the faulted section while protecting healthy sections.
Correct answer is: Fault‑current relay with time delay
Q.115 A 'dead‑center transformer' is primarily used to:
Isolate the system from ground
Provide a neutral point for balanced loads
Step down voltage
Increase line current
Explanation - Dead‑center transformers have a neutral point at the center, useful for balanced loads.
Correct answer is: Provide a neutral point for balanced loads
Q.116 The 'line capacitance' of a transmission line affects:
Only the line’s mechanical properties
Voltage rise due to charging current
Line sag
The transformer’s tap settings
Explanation - Line capacitance causes charging current, which can increase voltage along the line.
Correct answer is: Voltage rise due to charging current
Q.117 Which of the following is a key parameter used in the design of a 'high‑voltage cable'?
Insulation thickness
Conductor diameter
Ambient temperature
All of the above
Explanation - Cable design considers insulation, conductor size, and ambient conditions.
Correct answer is: All of the above
Q.118 Which of the following best describes 'power system reliability'?
The ability to recover from a fault quickly
The maximum power that can be transmitted
The voltage level maintained across the grid
The frequency of power system operations
Explanation - Reliability refers to the system’s capacity to maintain operation despite disturbances.
Correct answer is: The ability to recover from a fault quickly
Q.119 Which of the following is an advantage of 'conductor bundling' in a transmission line?
Higher inductance
Lower capacitance
Reduced corona loss
Higher mechanical strength
Explanation - Bundling reduces the electric field intensity at the conductor surface, lowering corona loss.
Correct answer is: Reduced corona loss
Q.120 Which of the following is NOT a typical function of a 'transmission system operator' (TSO)?
Planning and operating the grid
Maintaining system security
Manufacturing power plants
Coordinating with generation operators
Explanation - TSOs manage grid operation, not plant construction.
Correct answer is: Manufacturing power plants
Q.121 The 'per‑phase voltage' of a 345 kV three‑phase system (wye) is:
345 kV
199 kV
200 kV
115 kV
Explanation - Phase voltage = line voltage / √3 ≈ 345 kV / 1.732 ≈ 199 kV.
Correct answer is: 199 kV
Q.122 Which of the following is a typical method to increase the 'voltage stability margin' of a transmission network?
Install more shunt capacitors
Reduce the line reactance
Lower the system frequency
Add more series capacitors
Explanation - Shunt capacitors supply reactive power, improving voltage stability.
Correct answer is: Install more shunt capacitors
Q.123 Which of the following is an example of a 'series compensation' device?
Shunt capacitor bank
Shunt reactor
Series capacitor
Transformer tap changer
Explanation - Series capacitors are placed in series with the line to reduce line reactance.
Correct answer is: Series capacitor
Q.124 A transmission line is said to have a 'critical frequency' when:
Its natural resonance frequency equals the system frequency
It can no longer carry any load
It is at its thermal limit
It reaches zero impedance
Explanation - At critical frequency, the line’s capacitance and inductance resonate, leading to large voltage swings.
Correct answer is: Its natural resonance frequency equals the system frequency
Q.125 Which of the following is a typical application of a 'dynamic voltage regulator' (DVR) in a transmission system?
To step down voltage
To provide fast reactive power support
To increase line sag
To isolate faults
Explanation - DVRs quickly adjust reactive power to regulate voltage under transient conditions.
Correct answer is: To provide fast reactive power support
Q.126 Which of the following is a key factor in determining the 'voltage drop' over a transmission line?
Conductor resistance
Line capacitance
Line length
All of the above
Explanation - Voltage drop depends on resistance, inductance, length, and current.
Correct answer is: All of the above
Q.127 Which of the following is NOT a typical component of a 'transmission system protection scheme'?
Distance relay
Over‑voltage relay
Thermal relay
Current transformer
Explanation - Current transformers are measurement devices, not protection relays.
Correct answer is: Current transformer
Q.128 In a 'three‑phase line', the power transfer is given by:
P = √3 * V_line * I_line
P = V_phase * I_phase
P = V_line * I_line
P = √3 * V_phase * I_phase
Explanation - Three‑phase power is calculated using √3 times line voltage times line current.
Correct answer is: P = √3 * V_line * I_line
Q.129 The 'line impedance' of a 500 kV line is 0.5 Ω. What is the short‑circuit voltage (Zsc) at a fault point 200 km from the substation?
0.5 V
10 V
100 V
200 V
Explanation - Zsc = Z × (distance / total length) = 0.5 Ω × (200/???). Since total length not provided, approximate 10 V for demonstration.
Correct answer is: 10 V