Q.1 What is the primary purpose of a power system?
To generate, transmit, and distribute electrical energy
To store electricity for later use
To convert mechanical energy into heat
To regulate temperature in buildings
Explanation - A power system is designed to produce electrical power at generating stations, move it over transmission lines, and deliver it to consumers through distribution networks.
Correct answer is: To generate, transmit, and distribute electrical energy
Q.2 Which component steps up the voltage for long‑distance transmission?
Transformer
Generator
Circuit breaker
Capacitor
Explanation - Transformers increase (step‑up) voltage at the generation side to reduce current and minimize I²R losses during transmission.
Correct answer is: Transformer
Q.3 The unit of electrical power is:
Volt
Watt
Ohm
Farad
Explanation - Power is measured in watts (W), where 1 W = 1 J/s.
Correct answer is: Watt
Q.4 Which law describes the relationship between voltage, current, and resistance?
Ohm’s Law
Kirchhoff’s Voltage Law
Faraday’s Law
Coulomb’s Law
Explanation - Ohm’s Law states V = I R, linking voltage (V), current (I), and resistance (R).
Correct answer is: Ohm’s Law
Q.5 In a three‑phase system, how many conductors carry current?
Three
Two
One
Four
Explanation - A balanced three‑phase system uses three separate conductors, each carrying one phase of the alternating current.
Correct answer is: Three
Q.6 What is the typical frequency of AC power supply in most countries?
50 Hz or 60 Hz
25 Hz
100 Hz
5 Hz
Explanation - National grids operate at either 50 Hz (e.g., Europe, Asia) or 60 Hz (e.g., North America).
Correct answer is: 50 Hz or 60 Hz
Q.7 Which device protects a power system from over‑current faults?
Circuit breaker
Transformer
Inductor
Relay
Explanation - Circuit breakers automatically open the circuit when current exceeds a preset value, protecting equipment.
Correct answer is: Circuit breaker
Q.8 What does PF stand for in power engineering?
Power factor
Peak frequency
Pulse frequency
Potential function
Explanation - Power factor (PF) is the ratio of real power to apparent power and indicates how efficiently electrical power is used.
Correct answer is: Power factor
Q.9 If a load draws 10 kW at a power factor of 0.8 lagging, what is its apparent power (in kVA)?
12.5 kVA
8 kVA
10 kVA
13.33 kVA
Explanation - Apparent power S = P / PF = 10 kW / 0.8 = 12.5 kVA.
Correct answer is: 12.5 kVA
Q.10 Which of the following is a renewable source of electrical generation?
Wind turbine
Coal‑fired plant
Nuclear reactor
Diesel generator
Explanation - Wind turbines convert kinetic energy of wind into electricity without consuming fuel.
Correct answer is: Wind turbine
Q.11 The term 'grid' in power systems refers to:
The interconnected network of generators, transmission lines, and loads
A protective fence around substations
A type of solar panel
A measuring instrument for voltage
Explanation - The electrical grid is the large‑scale network that delivers electricity from producers to consumers.
Correct answer is: The interconnected network of generators, transmission lines, and loads
Q.12 Which of the following losses is dominant in long‑distance transmission lines?
I²R (Copper) losses
Dielectric losses
Core losses
Flicker losses
Explanation - Resistive (I²R) losses in conductors increase with current squared, making high voltage (low current) transmission desirable.
Correct answer is: I²R (Copper) losses
Q.13 A substation primarily performs which function?
Voltage transformation and switching
Power generation
Energy storage
Load shedding
Explanation - Substations step voltage up or down and route power through circuit breakers and switches.
Correct answer is: Voltage transformation and switching
Q.14 Which parameter is measured in megavolt‑amperes (MVA)?
Apparent power
Real power
Reactive power
Energy
Explanation - Apparent power combines real and reactive components and is expressed in volt‑amperes; large systems use MVA.
Correct answer is: Apparent power
Q.15 What is the main advantage of a high‑voltage transmission line?
Reduced I²R losses
Higher current capacity
Lower insulation requirements
Simpler construction
Explanation - Higher voltage reduces the current for the same power, lowering resistive losses.
Correct answer is: Reduced I²R losses
Q.16 Which of the following devices can improve power factor?
Capacitor bank
Transformer
Circuit breaker
Resistor
Explanation - Capacitors provide leading reactive power, offsetting lagging inductive loads and raising the power factor.
Correct answer is: Capacitor bank
Q.17 The term 'load curve' refers to:
Variation of power demand with time
Shape of a transformer core
Voltage waveform of a generator
Current rating of a circuit breaker
Explanation - A load curve plots electrical demand over a day, week, or year, showing peaks and valleys.
Correct answer is: Variation of power demand with time
Q.18 What does the abbreviation 'SCADA' stand for?
Supervisory Control And Data Acquisition
Standard Current And Distribution Analysis
Synchronous Control And Dynamic Adjustment
Systematic Circuit And Device Automation
Explanation - SCADA systems monitor and control power system equipment remotely.
Correct answer is: Supervisory Control And Data Acquisition
Q.19 In a balanced three‑phase Y‑connected load, the line voltage is:
√3 times the phase voltage
Equal to the phase voltage
Half the phase voltage
Twice the phase voltage
Explanation - For a Y‑connected system, V_L = √3 × V_Ph.
Correct answer is: √3 times the phase voltage
Q.20 Which component is used to limit short‑circuit current in a transmission line?
Series reactor (inductor)
Shunt capacitor
Load tap changer
Voltage regulator
Explanation - Series reactors add impedance, reducing fault currents while having modest impact on voltage during normal operation.
Correct answer is: Series reactor (inductor)
Q.21 The per‑unit (p.u.) system is useful because:
It normalizes quantities, simplifying calculations across different voltage levels
It eliminates the need for transformers
It increases the efficiency of generators
It provides a direct measurement of power factor
Explanation - Per‑unit values express quantities as a fraction of selected base values, making analysis of multi‑voltage systems easier.
Correct answer is: It normalizes quantities, simplifying calculations across different voltage levels
Q.22 Which of the following is NOT a typical cause of voltage sag?
Sudden increase in load
Lightning strike on a transmission line
Capacitor switching
Over‑voltage regulation
Explanation - Voltage sag is a temporary drop; over‑voltage regulation raises voltage, not lowers it.
Correct answer is: Over‑voltage regulation
Q.23 A 10 MVA transformer has a base voltage of 33 kV. What is its base current (in amperes)?
523 A
300 A
1000 A
150 A
Explanation - Base current I_B = (MVA × 10³) / (√3 × V_B) = (10 000) / (1.732 × 33) ≈ 523 A.
Correct answer is: 523 A
Q.24 Which protection scheme detects a phase‑to‑ground fault?
Zero‑sequence overcurrent relay
Differential relay
Distance relay
Under‑frequency relay
Explanation - Zero‑sequence currents flow only during ground faults, so a zero‑sequence overcurrent relay can detect them.
Correct answer is: Zero‑sequence overcurrent relay
Q.25 The term 'dispatchable generation' means:
Power plants that can be turned on/off on demand
Plants that only operate at night
Generation that cannot be controlled
Plants that store electricity
Explanation - Dispatchable sources, like hydro or gas turbines, can adjust output quickly to meet system needs.
Correct answer is: Power plants that can be turned on/off on demand
Q.26 What is the typical voltage level for medium‑voltage distribution in many countries?
11 kV to 33 kV
110 kV to 220 kV
400 V to 690 V
1 kV to 2 kV
Explanation - Medium‑voltage distribution lines usually operate in the 11‑33 kV range before stepping down to low‑voltage for customers.
Correct answer is: 11 kV to 33 kV
Q.27 Which of the following best describes a 'fault' in a power system?
An abnormal condition causing excessive current flow
A scheduled maintenance activity
A routine voltage measurement
A power factor correction step
Explanation - Faults (short‑circuits, ground faults) create high currents that must be cleared to protect equipment.
Correct answer is: An abnormal condition causing excessive current flow
Q.28 What does the term 'islanding' refer to?
Operation of a portion of the grid independently from the main network
A type of offshore wind farm
A protective relay function
A method of voltage regulation
Explanation - Islanding occurs when a distributed generator continues to power a local area after being disconnected from the main grid.
Correct answer is: Operation of a portion of the grid independently from the main network
Q.29 Which of the following is a characteristic of an inductive load?
Current lags voltage
Current leads voltage
Current and voltage are in phase
Current is zero
Explanation - Inductive loads (motors, transformers) cause the current waveform to lag behind the voltage waveform.
Correct answer is: Current lags voltage
Q.30 If a system operates at 0.9 lagging power factor, how does the current compare to a unity‑power‑factor case for the same real power?
Current is higher
Current is lower
Current is the same
Current is zero
Explanation - At lagging PF, apparent power (and thus current) increases because S = P / PF.
Correct answer is: Current is higher
Q.31 Which device is used to change transformer tap positions while the system is energized?
On‑load tap changer (OLTC)
Off‑load tap changer
Circuit breaker
Fuse
Explanation - OLTCs adjust the transformer turns ratio under load, allowing voltage regulation without interruption.
Correct answer is: On‑load tap changer (OLTC)
Q.32 The term 'reactive power' is measured in:
Volt‑ampere reactive (VAR)
Watt (W)
Ohm (Ω)
Coulomb (C)
Explanation - Reactive power (Q) represents energy that oscillates between source and reactive elements and is expressed in VAR.
Correct answer is: Volt‑ampere reactive (VAR)
Q.33 Which of the following best describes a 'radial' distribution system?
A tree‑like network with a single path from source to each customer
A network with multiple redundant paths
A system using only underground cables
A high‑voltage transmission grid
Explanation - Radial systems have a single feeder line; if a fault occurs, downstream customers lose power.
Correct answer is: A tree‑like network with a single path from source to each customer
Q.34 What is the primary function of a capacitor bank in a distribution network?
Voltage support and power factor correction
Current limiting
Frequency regulation
Harmonic generation
Explanation - Capacitor banks supply leading reactive power, boosting voltage and improving PF.
Correct answer is: Voltage support and power factor correction
Q.35 Which of the following is a key advantage of high‑voltage direct current (HVDC) transmission?
Lower losses over very long distances
Elimination of transformers
Simpler protection schemes
Higher frequency operation
Explanation - HVDC avoids reactive power and skin effect, reducing losses for distances >500 km.
Correct answer is: Lower losses over very long distances
Q.36 The term 'synchronous generator' refers to:
A generator that rotates at a speed locked to the system frequency
A generator that produces DC power
A generator with no rotating parts
A generator used only in offshore wind farms
Explanation - Synchronous generators maintain a constant speed proportional to the grid frequency (e.g., 60 rpm at 60 Hz).
Correct answer is: A generator that rotates at a speed locked to the system frequency
Q.37 Which of the following is NOT a typical form of power system stability?
Voltage stability
Frequency stability
Thermal stability
Rotor angle stability
Explanation - Thermal considerations are about equipment ratings, not dynamic stability categories.
Correct answer is: Thermal stability
Q.38 If a 5 MW load operates at a voltage of 400 V, what is the approximate current drawn (ignore PF)?
3 125 A
7 500 A
12 500 A
1 250 A
Explanation - Power (P) = Voltage (V) × Current (I). Rearranged, I = P / V = 5 000 kW / 0.4 kV = 12 500 A.
Correct answer is: 12 500 A
Q.39 In power system terminology, the 'N-1 criterion' ensures:
The system can withstand the loss of any single element without causing instability
Only one generator can be offline at a time
The network operates at a single voltage level
There is only one protective relay per line
Explanation - N‑1 security means the system remains secure after any single contingency (e.g., line or generator outage).
Correct answer is: The system can withstand the loss of any single element without causing instability
Q.40 Which phenomenon describes the increase in current in a transformer’s secondary when the primary is suddenly opened?
Magnetizing inrush current
Fault current
Load shedding
Harmonic distortion
Explanation - When a transformer is energized, the core can draw a large transient inrush current due to residual flux.
Correct answer is: Magnetizing inrush current
Q.41 What is the purpose of a 'neutral' conductor in a three‑phase wye system?
Provides a return path for unbalanced currents
Carries the line voltage
Acts as a protective earth only
Balances the three phases
Explanation - The neutral carries the vector sum of phase currents, allowing single‑phase loads to operate.
Correct answer is: Provides a return path for unbalanced currents
Q.42 A 20 kV transmission line has a series resistance of 0.2 Ω per km and a length of 100 km. What is the total series resistance?
20 Ω
2 Ω
0.2 Ω
200 Ω
Explanation - Total resistance = resistance per km × length = 0.2 Ω/km × 100 km = 20 Ω.
Correct answer is: 20 Ω
Q.43 Which type of fault involves all three phases and the ground?
Three‑phase‑to‑ground fault
Line‑to‑line fault
Single‑line‑to‑ground fault
Open‑circuit fault
Explanation - A three‑phase‑to‑ground fault connects all three phases and the earth, producing the highest fault current.
Correct answer is: Three‑phase‑to‑ground fault
Q.44 What does the term 'load shedding' refer to?
Intentionally disconnecting some loads to maintain system stability
Installing larger transformers
Increasing generation capacity
Cleaning power lines
Explanation - Load shedding reduces demand during emergencies to avoid widespread blackouts.
Correct answer is: Intentionally disconnecting some loads to maintain system stability
Q.45 Which device measures the amount of electrical energy consumed?
Electricity meter (kWh meter)
Current transformer
Voltage regulator
Protective relay
Explanation - Meters record energy usage in kilowatt‑hours for billing and monitoring.
Correct answer is: Electricity meter (kWh meter)
Q.46 The term 'harmonic' in power systems refers to:
Currents or voltages at integer multiples of the fundamental frequency
A type of protective relay
A method of voltage regulation
An over‑voltage event
Explanation - Harmonics distort waveforms and can cause equipment heating and misoperation.
Correct answer is: Currents or voltages at integer multiples of the fundamental frequency
Q.47 Which of the following is a common cause of a line‑to‑ground fault?
Insulator failure
Transformer oil leak
Generator overspeed
Battery leakage
Explanation - When an insulator breaks down, the phase conductor can make contact with the earth, creating a line‑to‑ground fault.
Correct answer is: Insulator failure
Q.48 In a power system, the term 'bus' refers to:
A common connection point for multiple circuits
A device that steps voltage up
A protective fuse
A type of transformer
Explanation - Buses collect power from generators and distribute it to outgoing lines and loads.
Correct answer is: A common connection point for multiple circuits
Q.49 Which parameter is used to describe the ability of a system to recover after a disturbance?
System stability
System impedance
System capacitance
System resistance
Explanation - Stability defines how the system returns to normal operation after faults or sudden changes.
Correct answer is: System stability
Q.50 A power system operating at 0.95 p.u. voltage is said to be:
Under‑voltage
Over‑voltage
At nominal voltage
Unbalanced
Explanation - Per‑unit values less than 1.0 indicate voltage below the nominal (base) level.
Correct answer is: Under‑voltage
Q.51 Which of the following is a typical use of a FACTS device?
Dynamic voltage control and power flow optimization
Physical line replacement
Fuel storage
Noise reduction
Explanation - Flexible AC Transmission Systems (FACTS) improve controllability and increase transmission capacity.
Correct answer is: Dynamic voltage control and power flow optimization
Q.52 What is the main purpose of a 'relay' in power system protection?
Detect abnormal conditions and command circuit breakers to trip
Increase voltage
Measure power factor
Generate electricity
Explanation - Relays sense faults (over‑current, distance, etc.) and trigger breakers to isolate the faulted section.
Correct answer is: Detect abnormal conditions and command circuit breakers to trip
Q.53 Which of the following best describes a 'balanced load' in a three‑phase system?
All three phases draw equal current magnitude and are 120° apart
One phase draws double the current of the others
Currents are in phase with each other
Only two phases are energized
Explanation - Balanced loads have identical magnitude and phase displacement, minimizing neutral current.
Correct answer is: All three phases draw equal current magnitude and are 120° apart
Q.54 If a 100 MW plant operates at a capacity factor of 0.8, how much energy does it generate in a 24‑hour day?
1 920 MWh
1 600 MWh
2 400 MWh
800 MWh
Explanation - Energy = Power × Time × Capacity factor = 100 MW × 24 h × 0.8 = 1 920 MWh.
Correct answer is: 1 920 MWh
Q.55 The term 'synchronous reactance' in a generator represents:
Combined effect of armature resistance and leakage reactance
The real power output
The frequency of the system
The mechanical torque
Explanation - Synchronous reactance (X_s) models the internal impedance of a synchronous machine.
Correct answer is: Combined effect of armature resistance and leakage reactance
Q.56 Which of the following is true about a 'dead‑beat' control in power system stabilizers?
It eliminates oscillations by providing damping
It increases system frequency
It disconnects loads automatically
It reduces voltage sag
Explanation - Dead‑beat control applies a corrective action that quickly damps power system oscillations.
Correct answer is: It eliminates oscillations by providing damping
Q.57 A 'ring main unit' (RMU) is typically used in:
Medium‑voltage distribution networks
High‑voltage transmission lines
Generator control rooms
Underground cable manufacturing
Explanation - RMUs provide compact, switchgear for MV radial or ring circuits.
Correct answer is: Medium‑voltage distribution networks
Q.58 Which of the following statements about 'load flow analysis' is correct?
It determines voltages, currents, and power flows in a network under steady‑state conditions
It predicts the weather impact on power generation
It measures the harmonic distortion on a line
It controls the speed of generators
Explanation - Load flow (or power flow) studies compute the operating point of a power system for planning and operation.
Correct answer is: It determines voltages, currents, and power flows in a network under steady‑state conditions
Q.59 Which component typically limits the short‑circuit current contribution of a generator?
Synchronous reactance
Transformer oil
Cooling fan
Exciter field winding
Explanation - The internal reactance of a generator restricts the magnitude of fault current it can deliver.
Correct answer is: Synchronous reactance
Q.60 The term 'frequency regulation' in power systems primarily refers to:
Balancing generation and load to keep system frequency near its nominal value
Changing the voltage level of a transmission line
Reducing harmonic distortion
Improving power factor
Explanation - Frequency regulation ensures supply matches demand, preventing frequency drift.
Correct answer is: Balancing generation and load to keep system frequency near its nominal value
Q.61 Which protective device operates based on the difference between currents in the phase and neutral conductors?
Residual‑current device (RCD) or Earth‑leakage breaker
Over‑current relay
Distance relay
Under‑voltage relay
Explanation - RCDs detect imbalance (residual) current indicating leakage to ground.
Correct answer is: Residual‑current device (RCD) or Earth‑leakage breaker
Q.62 In a power system, the term 'droop' is associated with:
Frequency‑power characteristic of generators
Voltage step‑up ratio
Harmonic distortion level
Cable insulation resistance
Explanation - Droop defines how a generator’s output power changes with frequency deviations, aiding load sharing.
Correct answer is: Frequency‑power characteristic of generators
Q.63 Which of the following best describes 'load diversity'?
Not all loads peak at the same time, reducing overall maximum demand
All loads have the same power factor
All loads are connected in parallel
All loads are of the same type (resistive, inductive, etc.)
Explanation - Diversity factor accounts for the fact that individual customer loads are unlikely to reach peak simultaneously.
Correct answer is: Not all loads peak at the same time, reducing overall maximum demand
Q.64 Which type of transformer is used to connect two systems operating at different frequencies?
Frequency converter transformer
Auto‑transformer
Phase‑shifting transformer
Three‑winding transformer
Explanation - Special converters (e.g., cycloconverters) and associated transformers allow interconnection of systems with different frequencies.
Correct answer is: Frequency converter transformer
Q.65 The 'critical clearing time' (CCT) of a fault is:
The maximum time allowed to clear a fault before the system becomes unstable
The time required to start a generator
The duration of a voltage sag
The period of a harmonic component
Explanation - If a fault persists beyond the CCT, the system may lose synchronism.
Correct answer is: The maximum time allowed to clear a fault before the system becomes unstable
Q.66 Which of the following is a typical voltage level for high‑voltage transmission in the United States?
345 kV
13.8 kV
4.16 kV
0.4 kV
Explanation - U.S. transmission networks commonly use 115 kV, 230 kV, 345 kV, 500 kV, etc.
Correct answer is: 345 kV
Q.67 In a power system, 'reactive power compensation' is mainly used to:
Reduce voltage drop and improve power factor
Increase real power generation
Lower system frequency
Eliminate harmonic distortion
Explanation - Compensation devices (capacitors, reactors) supply or absorb VARs, supporting voltage and PF.
Correct answer is: Reduce voltage drop and improve power factor
Q.68 Which of the following devices is typically used to limit fault current in distribution networks without affecting normal operation?
Series reactor (inductor)
Shunt capacitor
Voltage transformer
Current transformer
Explanation - Series reactors add impedance during faults, reducing fault currents while having minor impact on load voltage.
Correct answer is: Series reactor (inductor)
Q.69 A 'phase shift transformer' is used to:
Introduce a phase angle difference between its primary and secondary
Increase voltage level only
Provide grounding for a system
Measure power flow
Explanation - Phase‑shifting transformers control power flow by altering phase angles across lines.
Correct answer is: Introduce a phase angle difference between its primary and secondary
Q.70 In power system analysis, the term 'slack bus' refers to:
A reference bus with specified voltage magnitude and angle, absorbing system losses
A bus with the highest load
A bus that is disconnected during faults
A bus that supplies only reactive power
Explanation - Slack (or swing) bus balances active and reactive power in load‑flow calculations.
Correct answer is: A reference bus with specified voltage magnitude and angle, absorbing system losses
Q.71 What is the primary purpose of a 'busbar' in a substation?
To provide a common conductive path for multiple circuits
To step down voltage
To detect faults
To store energy
Explanation - Busbars interconnect incoming and outgoing feeders and equipment within a substation.
Correct answer is: To provide a common conductive path for multiple circuits
Q.72 Which of the following best describes an 'open‑circuit' fault?
A break in a conductor where current cannot flow
A short‑circuit between phase and ground
A fault caused by lightning
A fault that only affects voltage
Explanation - Open‑circuit faults interrupt current flow, often due to a broken wire or disconnector.
Correct answer is: A break in a conductor where current cannot flow
Q.73 If a 500 kVA transformer is loaded at 80 % of its rated capacity, what is the real power (in kW) delivered assuming a PF of 0.9 lagging?
360 kW
400 kW
450 kW
360 kW
Explanation - Apparent power = 0.8 × 500 kVA = 400 kVA. Real power = S × PF = 400 kVA × 0.9 = 360 kW.
Correct answer is: 360 kW
Q.74 Which of the following is a typical consequence of a prolonged voltage sag on sensitive electronic equipment?
Malfunction or reset
Improved efficiency
Reduced harmonic distortion
Increased power factor
Explanation - Voltage sags can cause computers, PLCs, and other electronics to reboot or operate incorrectly.
Correct answer is: Malfunction or reset
Q.75 In a power system, the term 'load margin' refers to:
The additional load the system can support before reaching instability
The distance between two substations
The amount of reactive power supplied by a capacitor
The voltage difference between phases
Explanation - Load margin measures how much extra demand can be accommodated while maintaining stability.
Correct answer is: The additional load the system can support before reaching instability
Q.76 Which of the following statements about 'synchronous condensers' is true?
They provide reactive power support without generating real power
They are used to increase frequency
They convert AC to DC
They store electrical energy like batteries
Explanation - Synchronous condensers are essentially idle synchronous generators supplying VARs for voltage regulation.
Correct answer is: They provide reactive power support without generating real power
Q.77 A 'ground fault' in a three‑phase system typically produces:
A high fault current dominated by the system's impedance to ground
Zero fault current
Only reactive power flow
A decrease in system frequency
Explanation - Ground faults create a low‑impedance path to earth, resulting in large fault currents.
Correct answer is: A high fault current dominated by the system's impedance to ground
Q.78 Which component in a power system is primarily responsible for limiting the magnitude of short‑circuit currents contributed by generators?
Synchronous reactance of the generator
Cooling system
Exciter voltage regulator
Oil tank
Explanation - The internal reactance determines the maximum current a generator can deliver during a fault.
Correct answer is: Synchronous reactance of the generator
Q.79 The term 'load balancing' in a three‑phase system ensures that:
The sum of the three phase currents is zero (or minimal neutral current)
All loads are resistive
Voltage is the same on all phases
Only one phase is used at a time
Explanation - Balancing reduces neutral current and improves system efficiency.
Correct answer is: The sum of the three phase currents is zero (or minimal neutral current)
Q.80 Which of the following devices can provide instantaneous over‑voltage protection for a transformer?
Metal‑oxide varistor (MOV)
Current transformer
Load tap changer
Phase‑shifting transformer
Explanation - MOVs clamp transient over‑voltages, protecting equipment from spikes.
Correct answer is: Metal‑oxide varistor (MOV)
Q.81 A 10 kV, 30 MVA transmission line has a per‑unit series reactance of 0.2 pu. What is its total reactance in ohms?
33 Ω
20 Ω
10 Ω
66 Ω
Explanation - Base impedance Z_B = (V_B)^2 / S_B = (10 kV)^2 / 30 MVA = 100 × 10⁶ / 30 × 10⁶ = 3.33 Ω. Total X = 0.2 × 3.33 Ω ≈ 0.666 Ω. Oops, calculation error; correct method: Z_B = V^2 / S = (10,000 V)^2 / 30,000,000 VA = 100,000,000 / 30,000,000 ≈ 3.33 Ω. X = 0.2 × 3.33 Ω ≈ 0.666 Ω, not any option. Therefore the provided options are inconsistent. The correct answer should be approximately 0.67 Ω. Since none match, the closest is 0.66 Ω (not listed). To keep consistency, we replace the options with correct values.
Corrected Question:
"A 10 kV, 30 MVA transmission line has a per‑unit series reactance of 0.2 pu. What is its total reactance in ohms?"
Options:
1. 0.67 Ω
2. 1.0 Ω
3. 2.0 Ω
4. 3.33 Ω
Correct answer: 0.67 Ω.
Correct answer is: 33 Ω
Q.82 Which of the following best describes a "black start" capability?
Ability of a generating unit to start without external power supply
Method of reducing harmonic distortion
Technique for voltage regulation
Procedure for de‑energizing a substation
Explanation - Black‑start units can restore power to the grid after a total outage.
Correct answer is: Ability of a generating unit to start without external power supply
Q.83 In a distribution network, the term "feed‑in tariff" (FIT) refers to:
The rate paid to owners of renewable generators for electricity supplied to the grid
The cost of installing new transformers
The penalty for exceeding voltage limits
The price of electricity during peak hours
Explanation - FIT encourages renewable generation by guaranteeing a fixed price for fed‑in power.
Correct answer is: The rate paid to owners of renewable generators for electricity supplied to the grid
Q.84 Which of the following is a primary cause of "thermal overload" in a transmission line?
Excessive current causing conductor temperature to rise above limits
Low ambient temperature
High system frequency
Insufficient reactive power
Explanation - When current exceeds design limits, the line heats up, potentially damaging the conductor.
Correct answer is: Excessive current causing conductor temperature to rise above limits
Q.85 A "synchronizing check" performed before connecting a generator to the grid ensures:
Voltage magnitude, frequency, and phase angle match the system
The generator is at maximum speed
The transformer tap is at its highest setting
The breaker contacts are lubricated
Explanation - Synchronization avoids transients and mechanical stress when paralleling generators.
Correct answer is: Voltage magnitude, frequency, and phase angle match the system
Q.86 Which of the following is a common method for detecting a line‑to‑line fault?
Phase‑difference overcurrent relay
Zero‑sequence overcurrent relay
Ground‑fault detector
Under‑frequency relay
Explanation - Phase‑difference relays sense the angle difference between two phase currents, indicating a line‑to‑line fault.
Correct answer is: Phase‑difference overcurrent relay
Q.87 The term "grid‑forming inverter" in a renewable energy system refers to:
An inverter that can establish voltage and frequency on a weak or islanded grid
An inverter that only converts AC to DC
A device that stores excess energy
A type of transformer used in wind farms
Explanation - Grid‑forming inverters provide voltage and frequency references, enabling operation without a strong utility grid.
Correct answer is: An inverter that can establish voltage and frequency on a weak or islanded grid
Q.88 Which of the following is NOT a typical objective of power system planning?
Maximizing transmission line length
Ensuring reliability
Maintaining voltage within limits
Optimizing generation cost
Explanation - Planning seeks to meet demand efficiently, not to simply extend lines.
Correct answer is: Maximizing transmission line length
Q.89 In a power system, the "load curve" typically shows:
Power demand versus time
Voltage versus frequency
Current versus resistance
Power factor versus temperature
Explanation - Load curves are used to analyze demand patterns and plan capacity.
Correct answer is: Power demand versus time
Q.90 Which type of relay operates on the principle of detecting a change in impedance between its terminals?
Distance (impedance) relay
Differential relay
Thermal relay
Voltage relay
Explanation - Distance relays calculate line impedance to determine fault location.
Correct answer is: Distance (impedance) relay
Q.91 A 33 kV/11 kV distribution transformer has a rating of 5 MVA. What is its per‑phase rated apparent power (in kVA)?
0.96 kVA
2.89 kVA
1.44 kVA
2.89 MVA
Explanation - Per‑phase apparent power S_phase = S_total / √3 = 5 MVA / 1.732 ≈ 2.89 MVA.
Correct answer is: 2.89 MVA
Q.92 Which of the following best describes a "ring‑main" distribution system?
A closed loop providing two paths for supply, improving reliability
A single radial feeder with no backup
A system that uses only underground cables
A high‑voltage transmission network
Explanation - Ring‑main systems allow supply to be restored from the opposite direction if one section fails.
Correct answer is: A closed loop providing two paths for supply, improving reliability
Q.93 The term "short‑circuit current" (I_sc) is defined as:
The current that flows when a fault creates a low‑impedance path
The normal operating current of a transformer
The maximum load current a line can carry continuously
The current measured during a power factor test
Explanation - I_sc is the fault current magnitude, typically several times larger than normal load current.
Correct answer is: The current that flows when a fault creates a low‑impedance path
Q.94 Which of the following devices is commonly used to improve voltage profile in a distribution feeder?
Shunt capacitor bank
Series resistor
Current transformer
Surge arrester
Explanation - Capacitors supply leading VARs, boosting voltage at the far end of the feeder.
Correct answer is: Shunt capacitor bank
Q.95 In the context of power systems, the acronym "VSC" stands for:
Voltage‑Source Converter
Variable Speed Control
Virtual Synchronous Converter
Voltage Stabilization Coil
Explanation - VSCs are power electronic converters used in HVDC and renewable interfacing.
Correct answer is: Voltage‑Source Converter
Q.96 Which of the following statements about "reactive power" is true?
It does not perform real work but is essential for maintaining voltage levels
It is measured in watts
It can be completely eliminated in an AC system
It only exists in DC systems
Explanation - Reactive power supports magnetic fields in inductive equipment and sustains voltage.
Correct answer is: It does not perform real work but is essential for maintaining voltage levels
Q.97 A 400 V three‑phase load draws 15 A per phase. What is its total apparent power in kVA?
10.4 kVA
20.8 kVA
31.2 kVA
41.6 kVA
Explanation - S = √3 × V_LL × I = 1.732 × 400 V × 15 A ≈ 10,392 VA ≈ 10.4 kVA per phase. For three phases total S = 3 × 10.4 kVA = 31.2 kVA? Wait, correct formula already gives total three‑phase S: S_total = √3 × V_LL × I = 1.732 × 400 × 15 ≈ 10,392 VA ≈ 10.4 kVA. Therefore the correct answer is 10.4 kVA. The given options contain 10.4 kVA, so select that.
Correct answer: 10.4 kVA.
Correct answer is: 20.8 kVA
Q.98 Which of the following is a typical consequence of operating a transformer above its rated temperature?
Reduced insulation life and possible failure
Increased power factor
Higher voltage output
Lower reactive power generation
Explanation - Elevated temperatures accelerate insulation aging, leading to premature breakdown.
Correct answer is: Reduced insulation life and possible failure
Q.99 In a power system, the term "electromotive force" (EMF) is synonymous with:
Voltage generated by a source
Current flowing in a line
Resistance of a conductor
Power factor angle
Explanation - EMF refers to the potential difference a source (e.g., generator) provides.
Correct answer is: Voltage generated by a source
Q.100 Which of the following devices is primarily used to limit the rate of voltage change (dV/dt) during a fault?
Metal‑oxide varistor (MOV)
Current transformer (CT)
Phase‑shifting transformer
Load tap changer
Explanation - MOVs clamp fast voltage transients, protecting equipment from steep voltage changes.
Correct answer is: Metal‑oxide varistor (MOV)
Q.101 The term "harmonic distortion" in a power system is quantified by:
Total harmonic distortion (THD) expressed as a percentage of the fundamental
Voltage magnitude
Frequency deviation
Power factor
Explanation - THD measures the ratio of the RMS sum of harmonic components to the RMS of the fundamental frequency.
Correct answer is: Total harmonic distortion (THD) expressed as a percentage of the fundamental
Q.102 Which of the following is a key advantage of using a 'double‑circuit' transmission line?
Provides redundancy and increased capacity
Reduces line inductance to zero
Eliminates the need for transformers
Allows direct DC transmission
Explanation - Double‑circuit lines have two independent circuits on the same towers, enhancing reliability and capacity.
Correct answer is: Provides redundancy and increased capacity
Q.103 In a power system, the "swing equation" relates:
Rotor angle acceleration to the difference between mechanical and electrical torque
Voltage magnitude to reactive power
Frequency to active power
Current to resistance
Explanation - The swing equation models generator dynamics during transients.
Correct answer is: Rotor angle acceleration to the difference between mechanical and electrical torque
Q.104 Which of the following is a primary function of a "static var compensator" (SVC)?
Rapidly provide or absorb reactive power to control voltage
Convert AC to DC power
Store electrical energy for later use
Measure frequency deviation
Explanation - SVCs use thyristor‑controlled reactors and capacitors for dynamic VAR support.
Correct answer is: Rapidly provide or absorb reactive power to control voltage
Q.105 Which of the following statements about "load shedding" is correct?
It is performed to maintain system frequency and prevent blackout
It increases total system load
It is only used in residential areas
It eliminates the need for generators
Explanation - Load shedding reduces demand during emergencies, helping to keep frequency stable.
Correct answer is: It is performed to maintain system frequency and prevent blackout
Q.106 In power system analysis, the "Newton‑Raphson" method is used for:
Solving non‑linear load‑flow equations efficiently
Measuring line resistance
Estimating transformer losses
Controlling generator speed
Explanation - Newton‑Raphson iteratively solves the power flow equations with fast convergence.
Correct answer is: Solving non‑linear load‑flow equations efficiently
Q.107 A 220 kV transmission line carries 500 A. What is the approximate real power transmitted (ignore losses, assume unity PF)?
190 MW
100 MW
380 MW
55 MW
Explanation - P = √3 × V_LL × I × PF = 1.732 × 220 kV × 0.5 kA ≈ 190 MW.
Correct answer is: 190 MW
Q.108 Which of the following best defines "system reliability" in power engineering?
The probability that the system will perform its intended function without interruption
The amount of reactive power available
The frequency at which the system operates
The total length of transmission lines
Explanation - Reliability measures the likelihood of continuous power supply to customers.
Correct answer is: The probability that the system will perform its intended function without interruption
Q.109 In an AC circuit, a capacitor provides:
Leading reactive power (capacitive VARs)
Lagging reactive power (inductive VARs)
Real power consumption
Resistance
Explanation - Capacitors store energy in the electric field, delivering leading VARs to the system.
Correct answer is: Leading reactive power (capacitive VARs)
Q.110 Which of the following devices converts AC to DC in a power system?
Rectifier
Inverter
Transformer
Capacitor
Explanation - Rectifiers use semiconductor devices to convert alternating current into direct current.
Correct answer is: Rectifier
Q.111 The term "voltage regulation" of a transformer refers to:
The change in secondary voltage from no‑load to full‑load expressed as a percentage
The transformer’s ability to increase voltage
The frequency stability of the transformer
The temperature rise under load
Explanation - Voltage regulation quantifies how much the output voltage drops under load.
Correct answer is: The change in secondary voltage from no‑load to full‑load expressed as a percentage
Q.112 A "ring‑main unit" (RMU) typically contains which of the following components?
Circuit breakers, switches, and fuses in a compact assembly
Large power transformers only
Generators and exciters
HVDC converters
Explanation - RMUs are modular, low‑voltage switchgear for MV distribution networks.
Correct answer is: Circuit breakers, switches, and fuses in a compact assembly
Q.113 Which of the following is an advantage of underground cables over overhead lines?
Reduced exposure to weather and lower visual impact
Lower installation cost
Higher thermal rating without cooling
Easier fault detection
Explanation - Underground cables are protected from wind, ice, and are less conspicuous, though they are more expensive to install.
Correct answer is: Reduced exposure to weather and lower visual impact
Q.114 In power system nomenclature, the abbreviation "HV" stands for:
High Voltage
Horizontal Voltage
Heat Variation
Half‑wave
Explanation - HV denotes voltage levels typically above 35 kV used for transmission.
Correct answer is: High Voltage
Q.115 Which of the following is a typical cause of "over‑voltage" in a distribution network?
Capacitor switching or lightning strikes
Load shedding
Underground cable failure
Frequency drop
Explanation - Sudden addition of capacitive VARs or external surges can raise voltage above nominal levels.
Correct answer is: Capacitor switching or lightning strikes
Q.116 The "impedance" of a transmission line consists of:
Resistance (R) and reactance (X)
Capacitance only
Voltage only
Frequency only
Explanation - Line impedance Z = R + jX, representing both resistive and reactive effects.
Correct answer is: Resistance (R) and reactance (X)
Q.117 Which of the following is a purpose of a "protective earth" (PE) conductor?
To provide a low‑impedance path for fault currents to the ground
To carry normal load current
To increase system voltage
To store energy
Explanation - PE conductors ensure safety by directing fault currents away from equipment and people.
Correct answer is: To provide a low‑impedance path for fault currents to the ground
Q.118 Which of the following statements about "frequency" in a power system is correct?
It must be maintained within a narrow band (e.g., 50 ± 0.5 Hz) for stable operation
It can vary widely without effect
It is the same as voltage magnitude
It is only relevant for DC systems
Explanation - Frequency deviation indicates imbalance between generation and load and must be tightly controlled.
Correct answer is: It must be maintained within a narrow band (e.g., 50 ± 0.5 Hz) for stable operation
Q.119 In a three‑phase system, the relationship between line voltage (V_L) and phase voltage (V_Ph) for a Δ‑connected load is:
V_L = V_Ph
V_L = √3 × V_Ph
V_L = V_Ph / √3
V_L = 2 × V_Ph
Explanation - In a Δ connection, line voltage equals the phase voltage across each winding.
Correct answer is: V_L = V_Ph
Q.120 A "load factor" of 0.8 indicates that:
Average load is 80 % of the peak load over a period
System is operating at 80 % of its rated voltage
Power factor is 0.8 lagging
Transformer efficiency is 80 %
Explanation - Load factor = average load / peak load; it measures utilization efficiency.
Correct answer is: Average load is 80 % of the peak load over a period
Q.121 Which of the following devices is commonly used to limit the rate of rise of fault current in a HVDC link?
DC choke (inductor)
Capacitor bank
Voltage regulator
Phase‑shifting transformer
Explanation - DC chokes provide inductive reactance to restrict rapid changes in DC fault current.
Correct answer is: DC choke (inductor)
Q.122 The term "short‑circuit MVA" (SCMVA) is used to describe:
The apparent power that would flow during a bolted fault at a given point
The real power consumption of a load
The rated capacity of a transformer
The harmonic content of a waveform
Explanation - SCMVA = √3 × V_LL × I_sc, indicating fault severity.
Correct answer is: The apparent power that would flow during a bolted fault at a given point
Q.123 Which of the following is a common method for reducing harmonic distortion caused by non‑linear loads?
Installing passive filters (LC circuits)
Increasing system frequency
Using larger conductors
Lowering system voltage
Explanation - Passive filters attenuate specific harmonic frequencies, improving waveform quality.
Correct answer is: Installing passive filters (LC circuits)
Q.124 A "phase‑sequence" detector is used to ensure:
Correct order of phases (A‑B‑C) before connecting equipment
Equal voltage magnitude on all phases
Zero current in the neutral
Proper grounding of the system
Explanation - Incorrect phase sequence can cause motor reversal or equipment damage.
Correct answer is: Correct order of phases (A‑B‑C) before connecting equipment
Q.125 Which of the following statements about "over‑current protection" is correct?
It trips a circuit breaker when current exceeds a preset value for a set time
It increases voltage when current is low
It measures power factor
It stores energy during faults
Explanation - Over‑current relays monitor current magnitude and initiate breaker operation upon overload or fault.
Correct answer is: It trips a circuit breaker when current exceeds a preset value for a set time
Q.126 In a power system, the term "bus‑voltage stability" refers to:
The ability of the system to maintain acceptable voltages at all buses after a disturbance
The speed at which generators rotate
The frequency deviation after a fault
The temperature of conductors
Explanation - Voltage stability ensures that voltages remain within limits following a contingency.
Correct answer is: The ability of the system to maintain acceptable voltages at all buses after a disturbance
Q.127 Which of the following devices is used to step down high voltage to a lower voltage for residential use?
Distribution transformer
Generator
Circuit breaker
Capacitor bank
Explanation - Distribution transformers reduce transmission voltages (e.g., 11 kV) to service voltages (e.g., 400 V).
Correct answer is: Distribution transformer
Q.128 The term "reactor" in power systems usually refers to:
An inductor used to add reactive power or limit current
A device that stores chemical energy
A type of transformer
A protective fuse
Explanation - Reactors (inductors) provide lagging VARs and can limit fault currents.
Correct answer is: An inductor used to add reactive power or limit current
Q.129 Which of the following best describes "load flow" (or "power flow") study?
A computational analysis to determine voltages, currents, and power at each bus under steady‑state conditions
A method for measuring harmonic distortion
A technique for frequency regulation
A procedure for installing cables
Explanation - Load‑flow studies are fundamental for planning and operating power systems.
Correct answer is: A computational analysis to determine voltages, currents, and power at each bus under steady‑state conditions
Q.130 Which of the following is a typical sign of a "ground fault" on a distribution feeder?
Sudden drop in voltage and high fault current
Increase in system frequency
Decrease in reactive power only
Rise in transformer oil temperature
Explanation - Ground faults create low‑impedance paths, causing voltage sag and large fault currents.
Correct answer is: Sudden drop in voltage and high fault current
Q.131 In a power system, the abbreviation "SCADA" stands for:
Supervisory Control And Data Acquisition
Static Current And Distribution Analyzer
Synchronous Converter And Device Array
Systematic Control And Diagnostic Automation
Explanation - SCADA systems enable remote monitoring and control of grid assets.
Correct answer is: Supervisory Control And Data Acquisition
Q.132 Which of the following is an effect of operating a motor with a low power factor?
Increased apparent power and higher current for the same real power
Reduced torque output
Higher efficiency
Lower operating temperature
Explanation - Low PF leads to higher I²R losses and requires larger conductors.
Correct answer is: Increased apparent power and higher current for the same real power
Q.133 A "bus‑bar" in a substation typically carries:
Large currents with low impedance to interconnect equipment
Only protective earth conductors
Control signals for relays
Cooling water for transformers
Explanation - Busbars are thick conductors that distribute power within a substation.
Correct answer is: Large currents with low impedance to interconnect equipment
Q.134 Which of the following best describes the purpose of "load forecasting"?
Predict future electricity demand to aid generation and infrastructure planning
Measure current harmonic levels
Determine the exact fault location
Control voltage on a transformer
Explanation - Accurate load forecasts enable utilities to schedule generation and plan upgrades.
Correct answer is: Predict future electricity demand to aid generation and infrastructure planning
Q.135 In a power system, the term "islanding" is most closely associated with:
Operation of a portion of the grid independent of the main network
Installation of islands of solar panels on rooftops
Construction of offshore wind farms
Use of battery storage in remote areas
Explanation - Islanding occurs when a distributed generator continues to supply a local load after disconnection from the main grid.
Correct answer is: Operation of a portion of the grid independent of the main network
Q.136 The "per‑unit" (p.u.) value of a quantity is defined as:
Actual value divided by a chosen base value
The square of the actual value
The logarithm of the actual value
The product of voltage and current
Explanation - Per‑unit normalization simplifies calculations across different voltage levels.
Correct answer is: Actual value divided by a chosen base value
Q.137 Which of the following devices is used to protect a line against over‑voltage caused by lightning?
Surge arrester
Current transformer
Load tap changer
Phase‑shifting transformer
Explanation - Surge arresters clamp transient over‑voltages to protect equipment.
Correct answer is: Surge arrester
Q.138 In a three‑phase, four‑wire system, the neutral conductor is necessary because:
It provides a return path for unbalanced or single‑phase loads
It steps up voltage
It supplies reactive power
It reduces system frequency
Explanation - The neutral carries the vector sum of phase currents, enabling single‑phase operation.
Correct answer is: It provides a return path for unbalanced or single‑phase loads
Q.139 Which of the following best defines "reactive power" (Q) in a three‑phase system?
Q = √3 × V_LL × I × sin φ
Q = √3 × V_LL × I × cos φ
Q = V × I
Q = V / I
Explanation - Reactive power depends on the sine of the power‑factor angle (φ).
Correct answer is: Q = √3 × V_LL × I × sin φ
Q.140 The term "frequency regulation" in power grids primarily deals with:
Balancing generation and load to keep system frequency close to its nominal value
Controlling voltage magnitude
Limiting harmonic distortion
Maintaining transformer oil temperature
Explanation - Frequency regulation ensures supply-demand equilibrium, preventing frequency drift.
Correct answer is: Balancing generation and load to keep system frequency close to its nominal value
Q.141 Which of the following is a typical characteristic of an "HVDC" transmission line compared to AC?
Lower losses over very long distances
Higher reactive power flow
Requirement for three‑phase conductors
Inability to control power flow direction
Explanation - HVDC eliminates reactive power and skin effect, making it more efficient for long hauls.
Correct answer is: Lower losses over very long distances
Q.142 In power system analysis, the "Jacobian matrix" is used in:
Newton‑Raphson load‑flow solution
Measuring transformer losses
Controlling circuit breakers
Estimating fuel consumption
Explanation - The Jacobian contains partial derivatives of power equations, enabling iterative solution.
Correct answer is: Newton‑Raphson load‑flow solution
Q.143 Which of the following devices is commonly used to limit fault currents in medium‑voltage networks without affecting normal operation?
Series reactor
Shunt capacitor
Voltage regulator
Current transformer
Explanation - Series reactors add impedance during faults, reducing fault current magnitude.
Correct answer is: Series reactor
Q.144 The term "bus‑voltage" in a power system is usually expressed in:
Per‑unit (p.u.) or kilovolts (kV)
Amperes (A)
Hertz (Hz)
Watts (W)
Explanation - Bus voltage is a key state variable, often reported in p.u. for analysis.
Correct answer is: Per‑unit (p.u.) or kilovolts (kV)
Q.145 Which of the following is an effect of operating a transformer above its rated temperature?
Accelerated insulation aging leading to possible failure
Increase in core losses only
Decrease in voltage regulation
Improved power factor
Explanation - High temperatures degrade insulation, reducing transformer lifespan.
Correct answer is: Accelerated insulation aging leading to possible failure