Transmission and Distribution Systems MCQs (Part-6)
What is the primary role of conductors in a power transmission system?
A Carry current
B Control frequency
C Insulate current
D Regulate voltage
Conductors are used to carry electrical current from one location to another in power transmission systems. They are typically made of materials like aluminum or copper, which provide good conductivity and ensure efficient power flow.
What material is commonly used for power transmission line conductors?
A Copper
B Aluminum
C Silver
D Steel
Aluminum is the most commonly used material for power transmission line conductors due to its lightweight, good conductivity, and cost-effectiveness. It also has a lower density, making it suitable for overhead lines and long-distance transmission.
What is the primary function of insulators in a transmission system?
A Store energy
B Reduce voltage loss
C Support conductors
D Prevent electrical faults
Insulators are used in transmission lines to support the conductors while preventing them from touching the ground or other structures. They also provide electrical isolation, ensuring that the current flows only through the conductors.
Why are insulators essential in preventing power system faults?
A Enhance conductivity
B Reduce resistance
C Prevent leakage
D Provide insulation
Insulators prevent electrical faults by providing insulation between the conductors and supporting structures. This ensures that electricity does not leak to the ground, reducing the risk of short circuits and maintaining the system’s integrity.
What is the purpose of substations in a power distribution network?
A Step-down voltage
B Store power
C Increase voltage
D Convert DC to AC
Substations are used to step down high voltage from transmission lines to lower, usable voltage for distribution. This is essential for providing electricity to homes and businesses safely and efficiently, ensuring the correct voltage is delivered.
What component in a substation is responsible for changing voltage levels?
A Circuit breaker
B Insulator
C Transformer
D Capacitor
Transformers in substations are responsible for changing voltage levels. A step-down transformer reduces the high voltage from the transmission lines to lower levels suitable for residential and commercial use, while a step-up transformer increases voltage for long-distance transmission.
What happens if the conductor material has high resistance?
A Increased voltage
B Higher power loss
C Reduced current
D Improved insulation
High resistance in conductors leads to higher power loss due to heat generation. The power loss is proportional to the square of the current, so increasing resistance significantly reduces transmission efficiency and increases energy costs.
What is the effect of line impedance on a transmission system?
A Stabilizes frequency
B Reduces voltage
C Reduces sag
D Increases power loss
Line impedance, which is the resistance and reactance in the transmission line, contributes to power losses. Higher impedance causes more energy to be dissipated as heat, reducing the overall efficiency of the transmission system.
What type of insulator is commonly used in high-voltage transmission lines?
A Glass
B Composite
C Ceramic
D Paper
Ceramic insulators are commonly used in high-voltage transmission lines because of their durability and ability to withstand high electrical stress. They are also resistant to weathering, which makes them suitable for outdoor environments.
What causes a transformer in a substation to overheat?
A High current
B Insufficient cooling
C Low voltage
D High impedance
Transformers overheat when high currents flow through them beyond their rated capacity. This excess current generates heat, which can damage the transformer’s insulation and components. Proper cooling and protection devices are necessary to prevent overheating.
What is the role of a circuit breaker in a substation?
A Increase current
B Prevent overloading
C Isolate power
D Step down voltage
Circuit breakers in substations protect the system from overloads and faults by automatically disconnecting the power when the current exceeds safe levels. This helps prevent damage to transformers, conductors, and other equipment in the network.
What is the function of a busbar in a substation?
A Control frequency
B Insulate conductors
C Distribute power
D Step-up voltage
A busbar in a substation is used to distribute electrical power from the incoming transmission lines to various outgoing lines. It serves as a common point where multiple circuits are interconnected, ensuring proper distribution of electricity.
How does temperature affect the resistance of conductors?
A Decreases with temperature
B Unaffected by temperature
C Fluctuates with temperature
D Increases with temperature
The resistance of conductors increases with temperature. As the temperature rises, the atoms in the conductor vibrate more, impeding the flow of electrons, which increases resistance and reduces the efficiency of power transmission.
What is the function of a transformer’s core?
A Provide magnetic flux
B Decrease resistance
C Control current
D Increase voltage
The core of a transformer is designed to provide a path for magnetic flux. It concentrates and directs the magnetic field generated by the primary winding, which induces voltage in the secondary winding, enabling the transformer to change voltage levels.
What is the primary cause of conductor sag in overhead lines?
A Conductor material
B High voltage
C Temperature changes
D Wind pressure
Conductor sag is primarily caused by temperature changes. As the temperature increases, the conductor expands and sags, while cooler temperatures cause it to contract. Proper sag calculation is essential to avoid line contact with the ground or objects.