Transmission and Distribution Systems MCQs (Part-1)
What is the main purpose of a transmission line?
A Power loss reduction
B Voltage regulation
C Transfer power
D Power distribution
Transmission lines are primarily used to transfer electrical power from power plants to substations, where it can be further distributed. The purpose is to deliver high‐voltage electricity efficiently over long distances with minimal loss.
What is the typical voltage level of high voltage transmission lines?
A 400 kV
B 1 kV
C 11 kV
D 110 kV
High-voltage transmission lines typically operate at 400 kV or higher to reduce power losses over long distances. Higher voltage allows for efficient transmission of electricity by reducing the current and thus the resistance losses.
Which of the following materials is commonly used for overhead transmission line conductors?
A Copper
B Steel
C Iron
D Aluminum
Aluminum is widely used in overhead transmission line conductors because of its low weight, good conductivity, and cost-effectiveness. It is also less prone to corrosion compared to copper.
What is a step-down transformer used for?
A Regulate current
B Decrease voltage
C Maintain voltage
D Increase voltage
A step-down transformer reduces the voltage from high levels, making it suitable for distribution purposes. This is crucial for converting transmission voltage to lower, usable levels for consumers.
What is the main function of insulators in transmission lines?
A Support conductors
B Control voltage
C Transfer power
D Protect from overload
Insulators are used to support transmission line conductors and prevent them from coming into contact with the ground or other structures. They provide electrical insulation, ensuring that electricity only flows through the conductors.
What is the typical voltage for medium voltage distribution systems?
A 230 V
B 400 kV
C 11 kV
D 110 kV
Medium voltage distribution systems typically operate at 11 kV, which is used to distribute power over shorter distances from substations to local areas or industries. It is higher than low voltage, making it more efficient for transmission.
What is sag in transmission lines?
A Voltage fluctuation
B Conductor drop
C Line loss
D Line bending
Sag refers to the vertical drop of conductors in an overhead transmission line due to their weight and environmental factors like wind and temperature. Proper calculation of sag ensures safety and proper functioning of the transmission system.
Which of the following is used for underground power transmission?
A Switchgears
B Fiber cables
C Underground cables
D Overhead lines
Underground cables are used for power transmission in areas where overhead lines are not feasible, such as in urban environments or areas prone to storms. They are more expensive but offer better protection from weather-related disruptions.
What is the main purpose of a substation?
A Step-up voltage
B Convert AC to DC
C Store power
D Step-down voltage
A substation is primarily used to step down the high voltage from transmission lines to a lower voltage for distribution to homes and businesses. Some substations may also regulate voltage and ensure stable power supply.
What is the main factor contributing to power losses in transmission lines?
A Corona discharge
B Voltage fluctuations
C Line impedance
D Line inductance
Line impedance, which is the resistance to electrical flow in transmission lines, contributes to power losses in the form of heat. High current and long distances increase these losses, so efficient design aims to minimize line impedance.
What is the primary function of a voltage regulator in a distribution system?
A Stabilize voltage
B Increase frequency
C Control current
D Reduce power loss
A voltage regulator ensures that the voltage supplied to consumers remains within acceptable limits, despite variations in load. This is critical for protecting electrical equipment and ensuring reliable service.
What is reactive power in electrical systems?
A Power that does no work
B Power consumed by motors
C Power used by transformers
D Power used in resistive heating
Reactive power is the power that oscillates between the source and load, without performing any useful work. It is needed to maintain voltage levels and ensure the proper functioning of inductive loads like motors and transformers.
What is a major cause of corona discharge in transmission lines?
A High humidity
B Low voltage
C High voltage
D High temperature
Corona discharge occurs when the electric field around a conductor exceeds a certain threshold, causing ionization of the surrounding air. This is more likely to happen at high voltages and can lead to power loss and signal interference.
What is the role of earthing in electrical systems?
A Control reactive power
B Prevent overvoltage
C Improve current flow
D Protect from shocks
Earthing provides a safe path for fault currents to flow to the ground, preventing electric shock hazards. It ensures that if a fault occurs, the affected equipment is safely grounded, reducing the risk of electrical accidents.
What is the purpose of a step-up transformer?
A Decrease voltage
B Increase voltage
C Regulate frequency
D Increase current
A step-up transformer increases the voltage from a low value to a higher value, typically for efficient long-distance transmission. High voltage reduces current, which minimizes energy loss in the transmission process.