What is the main purpose of cross-arms in overhead lines?
A To insulate the line
B To support conductors
C To carry current
D To reduce sag
Cross-arms are structural components that hold the conductors at a safe distance from the pole and each other.
What is the common spacing between phases in high-voltage transmission lines determined by?
A Voltage level
B Current level
C Line length
D Cross-arm spacing
The spacing between phases increases with voltage to prevent flashover and ensure safety.
What is the main disadvantage of overhead transmission lines?
A High installation cost
B Vulnerability to weather conditions
C Limited current carrying capacity
D High corona loss
Overhead lines are exposed to environmental factors such as wind, rain, and lightning, making them more prone to damage.
Which factor primarily affects the selection of conductor material in transmission lines?
A Cost and conductivity
B Weight and color
C Tensile strength only
D Environmental resistance only
Conductor materials are selected based on their cost, conductivity, mechanical strength, and resistance to environmental factors.
What is the main cause of power loss in underground cables?
A Dielectric loss
B Corona loss
C Copper loss
D Eddy current loss
Dielectric loss occurs in underground cables due to the heating of the insulating material under alternating voltage.
Which type of conductor arrangement is used to minimize skin effect?
A Solid conductor
B Stranded conductor
C Twisted pair conductor
D Bundled conductor
Stranded conductors distribute current more uniformly across the strands, reducing the impact of the skin effect.
What is the purpose of a distribution board in a power system?
A To transmit high voltage
B To divide electrical power into multiple circuits
C To generate electrical power
D To store energy
A distribution board divides electrical power into subsidiary circuits, providing control and protection for each circuit.
What is the primary reason for using transmission towers instead of wooden poles for high-voltage lines?
A Higher current carrying capacity
B Greater mechanical strength
C Better insulation
D Lower installation cost
Transmission towers provide the mechanical strength required to support high-voltage conductors over long spans.
What is the primary factor that determines the voltage drop in a transmission line?
A Conductor material
B Conductor length and resistance
C Insulator material
D Cross-arm spacing
Voltage drop in a transmission line is directly proportional to the line’s length and the resistance of the conductor.
What is the purpose of earthing in a transmission system?
A To provide insulation
B To ensure safety and fault current dissipation
C To stabilize voltage levels
D To reduce resistance
Earthing provides a safe path for fault currents to flow into the ground, protecting equipment and personnel.
What is the primary purpose of a step-up transformer in a power system?
A To reduce power losses during transmission
B To decrease voltage levels
C To balance loads
D To improve power factor
Step-up transformers increase voltage levels, which decreases current for the same power level. Lower current reduces resistive losses in the transmission lines.
What is the main function of a step-down transformer?
A To increase voltage for long-distance transmission
B To provide suitable voltage for end users
C To regulate power factor
D To balance reactive power
Step-down transformers reduce high transmission voltages to levels suitable for residential, commercial, and industrial usage.
Which property of conductors directly affects the efficiency of a transmission line?
A Conductivity
B Tensile strength
C Weight
D Insulation
Conductivity determines how well a material allows the flow of electric current. Higher conductivity reduces resistive losses, improving efficiency.
What is the primary purpose of voltage regulation in a power system?
A To reduce transmission losses
B To maintain consistent voltage levels at the load
C To improve insulation of conductors
D To balance the current
Voltage regulation ensures that the voltage supplied to consumers remains stable despite variations in load demand or transmission conditions.
What is the role of insulators in transmission systems?
A To conduct electricity
B To prevent leakage of current to supporting structures
C To increase conductor strength
D To reduce corona loss
Insulators are placed between the conductors and their supporting structures to prevent electrical leakage and ensure safety.
What is the main purpose of a capacitor bank in a power system?
A To step up voltage
B To improve power factor
C To regulate frequency
D To reduce load
Capacitor banks supply reactive power, compensating for lagging power factors caused by inductive loads and improving overall system efficiency.
Which material is most commonly used as a conductor in overhead transmission lines?
A Steel
B Aluminum
C Copper
D Iron
Aluminum is lightweight, cost-effective, and has good conductivity, making it the preferred material for overhead transmission lines.
What is the purpose of load balancing in a power distribution system?
A To equalize the load on all phases
B To reduce the need for transformers
C To increase voltage levels
D To decrease conductor resistance
Load balancing ensures even distribution of power across phases, reducing stress on the system and improving efficiency.
What is reactive power in an electrical power system?
A Power used to perform useful work
B Power associated with magnetic and electric fields
C Power lost due to resistance
D Power that reduces voltage
Reactive power is the component of power used to establish magnetic and electric fields in inductive and capacitive loads. It does not perform useful work but is essential for system operation.
What is the primary function of a substation in a power system?
A To generate power
B To step up or step down voltage levels
C To store energy
D To improve power factor
Substations transform voltage levels to facilitate efficient transmission and distribution of power.
Which type of insulator is used for low-voltage distribution lines?
A Suspension insulator
B Pin insulator
C Shackle insulator
D Strain insulator
Shackle insulators are compact and suitable for low-voltage distribution lines, providing effective insulation and mechanical support.
How does high voltage reduce power losses in transmission lines?
A By increasing resistance
B By reducing current flow
C By decreasing line capacitance
D By increasing frequency
High voltage reduces current for the same power level, minimizing resistive losses (IĀ²R) in the transmission line.
What is the main purpose of a stay wire in overhead lines?
A To support the conductor mechanically
B To carry the current
C To insulate the line
D To increase line voltage
Stay wires provide mechanical support to poles or structures, maintaining stability against wind and other forces.
Which material is most commonly used as a conductor in high-voltage transmission lines?
A Copper
B Aluminum
C Steel
D Iron
Aluminum is lightweight, cost-effective, and has good conductivity, making it the preferred material for high-voltage transmission lines.
What is the primary cause of power loss in distribution systems?
A Copper loss
B Dielectric loss
C Eddy current loss
D Radiation loss
Copper loss occurs due to the resistance of conductors, causing energy dissipation as heat during current flow.
What is the typical range of efficiency for step-up and step-down transformers?
A 50-60%
B 70-80%
C 95-99%
D 100%
Transformers are highly efficient devices, with efficiencies typically ranging from 95% to 99%, depending on design and operating conditions.
What is the main purpose of a lightning arrester in a substation?
A To step down voltage
B To protect equipment from overvoltage due to lightning
C To reduce sag in lines
D To improve power factor
Lightning arresters divert the surge caused by lightning strikes to the ground, preventing damage to electrical equipment.
What is the main factor that affects the size of a conductor in a transmission line?
A Voltage level
B Current-carrying capacity
C Frequency
D Power factor
The conductor size is determined by its ability to carry the maximum expected current without overheating.
What is the purpose of an earthing system in substations?
A To increase voltage levels
B To provide a safe path for fault currents
C To reduce resistance in conductors
D To increase insulation strength
Earthing systems ensure the safety of equipment and personnel by safely dissipating fault currents into the ground.
What does power factor represent in a power system?
A The ratio of active power to apparent power
B The ratio of reactive power to apparent power
C The efficiency of the system
D The frequency of the system
Power factor measures the efficiency of power usage in a system. A higher power factor indicates more efficient utilization of electrical power.
What is the primary purpose of a conductor in a power system?
A To reduce current flow
B To transmit electrical energy
C To regulate voltage
D To generate power
Conductors are materials, typically metals like aluminum or copper, that carry electrical energy from generation stations to consumers with minimal losses.
What is the purpose of insulating material in transmission lines?
A To increase current
B To protect against voltage leakage
C To reduce sag
D To decrease resistance
Insulating materials prevent electrical leakage, ensuring that the current flows only through the conductor and protecting the surroundings from electrical hazards.
What type of transformer is used in substations to increase voltage for long-distance transmission?
A Step-up transformer
B Step-down transformer
C Isolation transformer
D Auto-transformer
Step-up transformers increase voltage, which reduces current for a given power level, minimizing resistive losses during long-distance transmission.
Which component is responsible for reducing voltage levels for residential and commercial usage?
A Substation transformer
B Step-down transformer
C Voltage regulator
D Capacitor bank
Step-down transformers reduce high transmission voltage to safe levels for end users, such as homes and businesses.
What is the purpose of a substation in a power system?
A To store energy
B To regulate voltage and distribute power
C To generate electricity
D To measure current
Substations transform voltage levels, control power flow, and facilitate the distribution of electricity to consumers.
What is the main reason for using reactive power management in power systems?
A To increase system frequency
B To stabilize voltage levels
C To reduce active power losses
D To increase transformer efficiency
Reactive power helps maintain voltage levels within a power system, ensuring the proper operation of equipment and reducing system instability.
Which type of insulator is used for supporting transmission lines with high mechanical tension?
A Suspension insulator
B Strain insulator
C Pin insulator
D Shackle insulator
Strain insulators are designed to bear high mechanical tension in transmission lines, especially at sharp bends or terminations.
What is the unit of reactive power in a power system?
A Watt
B VAR (Volt-Ampere Reactive)
C Volt
D Joule
Reactive power, associated with magnetic and electric fields, is measured in VAR, which denotes the non-working power in the system.
Why are aluminum conductors preferred over copper in transmission lines?
A Higher conductivity
B Lower cost and lightweight
C Higher resistance
D Easier to insulate
Aluminum is more cost-effective and lighter than copper, making it ideal for overhead transmission lines despite slightly lower conductivity.
What is the primary purpose of voltage regulation in a distribution system?
A To decrease conductor resistance
B To maintain consistent voltage at the load
C To increase transformer efficiency
D To reduce reactive power
Voltage regulation ensures the voltage remains stable at the consumer’s end despite variations in load or transmission distances.
What causes power loss in a transmission line?
A High voltage levels
B Conductor resistance
C Insulation strength
D Reactive power
Power loss occurs due to the resistance in the conductor, which converts part of the electrical energy into heat.
What is the purpose of load balancing in a three-phase distribution system?
A To reduce power factor
B To evenly distribute the load across phases
C To increase current flow
D To regulate system frequency
Load balancing minimizes phase imbalances, reducing losses and ensuring the system operates efficiently.
What is the function of a lightning arrester in a power system?
A To step up voltage
B To prevent overvoltage due to lightning strikes
C To regulate reactive power
D To balance loads
Lightning arresters divert the high-voltage surge caused by lightning to the ground, protecting the system from damage.
What is the effect of increasing the diameter of a conductor in a transmission line?
A Increases resistance
B Reduces corona loss
C Decreases current carrying capacity
D Increases power factor
Larger conductor diameters reduce the electric field intensity, minimizing corona discharge and its associated losses.
What type of insulator is commonly used for low-voltage distribution systems?
A Pin insulator
B Suspension insulator
C Strain insulator
D Shackle insulator
Shackle insulators are compact and commonly used in low-voltage distribution systems, providing effective insulation and mechanical support.
What is the main advantage of using high-voltage transmission for long distances?
A Reduces power factor
B Minimizes power losses
C Eliminates conductor resistance
D Improves insulation
High voltage reduces current for the same power level, minimizing resistive losses in the transmission line.
What is power quality in a power system?
A The ratio of reactive power to apparent power
B The reliability and stability of voltage and frequency
C The efficiency of power transmission
D The amount of power lost in transmission
Power quality refers to maintaining stable voltage, frequency, and waveform to ensure proper operation of electrical equipment.
What is the purpose of a capacitor bank in a power distribution system?
A To reduce voltage levels
B To improve power factor by providing reactive power
C To increase current flow
D To reduce insulation requirements
Capacitor banks provide leading reactive power, compensating for inductive loads and improving the system’s power factor.
What is the main function of a circuit breaker in a substation?
A To step up voltage
B To interrupt fault currents
C To store energy
D To regulate frequency
Circuit breakers isolate faulty sections of the system by interrupting the flow of current during abnormal conditions, protecting the system and equipment.
What does energy efficiency in a power system mean?
A Minimizing energy losses and using power effectively
B Increasing system frequency
C Reducing conductor size
D Decreasing insulation strength
Energy efficiency focuses on reducing losses in transmission and distribution and optimizing power usage for better performance and reduced costs.