Transmission and Distribution Systems MCQs (Part-11)
What causes corona discharge in transmission lines?
A High voltage
B Low resistance
C High current
D High temperature
Corona discharge occurs when the electric field around a conductor exceeds the dielectric strength of the surrounding air, causing ionization. This typically happens at high voltages and leads to power losses, electromagnetic interference, and potential damage to equipment.
What is the primary effect of corona discharge on transmission lines?
A Increased resistance
B Voltage drop
C Reduced current
D Power loss
Corona discharge leads to power loss as energy is dissipated in the form of heat and light. This loss increases with higher voltage levels and can cause additional issues, such as radio interference and equipment degradation.
How can corona discharge be reduced in high voltage transmission lines?
A Lower voltage
B Use larger conductors
C Use insulators
D Increase current
Using larger conductors or conductors with rounded shapes can help reduce corona discharge by spreading the electric field more evenly. This reduces the likelihood of ionizing the air around the conductor and minimizes energy losses.
What is sag in transmission lines?
A Voltage fluctuation
B Load imbalance
C Conductor displacement
D Frequency variation
Sag refers to the downward displacement of transmission line conductors caused by their weight and environmental factors, such as temperature and wind. Proper design accounts for sag to ensure safe clearance from the ground and maintain reliable system performance.
What causes sag in transmission lines?
A Line length
B Conductor weight
C Wind pressure
D High voltage
Sag is mainly caused by the weight of the conductors, which causes them to droop under gravity. Environmental factors like temperature changes and wind pressure can exacerbate sag, requiring careful calculation to maintain safe distances and ensure system reliability.
How does temperature affect the sag of transmission lines?
A Decreases sag in heat
B Increases sag in cold
C No effect
D Increases sag in heat
As temperature increases, transmission line conductors expand, leading to greater sag. High temperatures cause the conductors to become more flexible and elongate, increasing the downward displacement, which must be accounted for during system design to avoid ground clearance issues.
What is the role of earthing in electrical systems?
A Protect against faults
B Regulate voltage
C Improve efficiency
D Control power flow
Earthing provides a safe path for fault currents to flow into the ground, preventing electrical shocks and equipment damage. Proper earthing ensures that electrical systems remain safe, even during fault conditions, by directing excess electrical energy safely away from users.
What is the purpose of an earthing system in power distribution?
A Prevent electrical fires
B Control frequency
C Prevent electric shock
D Improve voltage stability
The primary purpose of an earthing system is to prevent electric shock by providing a direct path to the ground for fault currents. This reduces the risk of injury and damage to electrical equipment by ensuring safety during fault conditions.
Which type of earthing system is commonly used for electrical installations?
A Loop earthing
B Resistance earthing
C Direct earthing
D Solid earthing
Solid earthing is commonly used for electrical installations where the neutral point of the system is directly connected to the earth. This provides a low‐resistance path for fault currents and ensures the safety of the electrical installation.
What is the effect of improper earthing in an electrical system?
A Increased voltage stability
B Increased risk of electric shock
C Reduced current
D Increased power factor
Improper earthing increases the risk of electric shock as it may fail to provide a safe path for fault currents. Without proper earthing, electrical equipment and installations can become dangerous, posing a significant safety hazard to individuals and equipment.
How is the tension in a transmission line affected by sag?
A No change
B Decreases
C Increases
D Depends on voltage
As sag increases, the tension in the transmission line also increases. The conductor must withstand both the weight (which causes sag) and the mechanical forces from wind, temperature changes, and other environmental factors, all of which affect line tension.
What does the term “grounding” refer to in an electrical system?
A Connection to a neutral point
B Connecting to an active phase
C Providing a path to earth
D Ensuring proper insulation
Grounding refers to the process of connecting parts of an electrical system to the earth, creating a path for fault currents to flow safely into the ground. It helps protect people and equipment from electrical hazards by ensuring a safe dissipation of electrical energy.
How does corona discharge affect the transmission system’s efficiency?
A Reduces efficiency
B Increases current flow
C No impact
D Increases efficiency
Corona discharge reduces the efficiency of the transmission system by causing energy loss in the form of heat, light, and sound. This occurs due to ionization of the air around conductors, especially in high‐voltage systems, leading to a waste of electrical energy.
What is the primary factor that influences the sag in a transmission line?
A Voltage levels
B Conductor diameter
C Conductor material
D Temperature
The material used for the conductor significantly influences sag because different materials have different thermal expansion coefficients and mechanical properties. Materials like aluminum have lower tensile strength and are more prone to sag compared to other materials like steel.
What happens to transmission lines during a fault condition if earthing is absent?
A Equipment damage
B Power flow stops
C Voltage rises
D Power is increased
Without proper earthing, fault currents cannot be safely directed to the ground, leading to potential damage to electrical equipment. The fault condition can cause overheating, fires, and even destruction of the electrical infrastructure, posing a serious safety risk.