What is the main advantage of overhead lines compared to underground cables?
A Lower installation cost
B Easier to maintain
C Higher power capacity
D Reduced sag
Overhead lines have a lower installation cost compared to underground cables due to reduced excavation and material expenses.
Which type of transmission line is typically used for interconnecting power grids?
A Medium voltage lines
B Low voltage lines
C High voltage lines
D Superconducting lines
High voltage lines are used to interconnect power grids as they minimize power losses during long-distance transmission.
What is the primary purpose of a conductor in a transmission line?
A To support insulators
B To transmit electric power
C To maintain mechanical tension
D To provide insulation
Conductors are the metallic wires that carry electrical power from one point to another in a power system.
Which type of insulator is most commonly used in high-voltage overhead transmission lines?
A Pin insulator
B Suspension insulator
C Shackle insulator
D Stay insulator
Suspension insulators are used in high-voltage lines because they can handle high mechanical stress and electrical load.
What is the purpose of maintaining proper sag in overhead lines?
A To reduce conductor resistance
B To prevent snapping during temperature changes
C To reduce corona losses
D To increase the current-carrying capacity
Sag allows for the expansion and contraction of the conductor due to temperature changes, preventing excessive tension and snapping.
What is the term used for the loss of electrical power due to resistance in the transmission line?
A Corona loss
B Dielectric loss
C Copper loss
D Eddy current loss
Copper loss refers to the power dissipated as heat due to the resistance of the conductor when current flows through it.
Why are high-voltage lines preferred for long-distance power transmission?
A To reduce the size of the conductors
B To reduce current and minimize losses
C To eliminate the need for transformers
D To improve insulation
High voltage reduces current for a given power level, minimizing resistive losses in the transmission line.
What is the function 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 commonly used as an insulator for overhead transmission lines?
A Aluminum
B Steel
C Porcelain
D Copper
Porcelain is a widely used insulator material due to its high dielectric strength and resistance to environmental conditions.
What is the effect of using conductors with larger diameters in transmission lines?
A Increases resistance
B Reduces corona loss
C Decreases current flow
D Increases inductance
Larger diameter conductors reduce the electric field intensity, thereby minimizing corona discharge and associated losses.
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.