Transmission and Distribution Systems MCQs (Part-4)
What is the typical voltage for medium voltage systems in power distribution?
A 230 V
B 400 V
C 1 kV
D 11 kV
Medium voltage systems typically operate at 11 kV, which is used for distribution from substations to areas close to consumers. It is higher than low voltage but lower than high voltage, making it suitable for local power distribution.
Which of the following is used to prevent overloading in transmission systems?
A Transformer
B Fuse
C Capacitor
D Inductor
A fuse is used to prevent overloading in transmission systems by disconnecting the circuit if the current exceeds safe levels. It protects the system from damage due to excessive current flow, ensuring safety and longevity.
Why is high voltage preferred for long-distance transmission?
A Stabilize voltage
B Decrease current
C Reduce loss
D Increase efficiency
High voltage is preferred for long-distance transmission because it reduces current. With lower current, the energy lost due to resistance (IĀ²R losses) decreases, making power transmission more efficient and reducing overall losses.
What is the purpose of a distribution transformer?
A Step-down voltage
B Convert AC to DC
C Regulate current
D Step-up voltage
A distribution transformer is used to step down the voltage from higher levels (e.g., 11 kV) to lower, usable levels (e.g., 230 V) for residential and commercial distribution. This makes the voltage safe for consumer use.
Which factor does not affect the resistance in transmission lines?
A Length
B Material
C Frequency
D Temperature
The resistance in transmission lines is affected by the material, temperature, and length of the line. However, frequency does not directly impact resistance, although it can influence inductive reactance and overall power quality.
What is the main function of line conductors?
A Regulate voltage
B Carry current
C Prevent faults
D Support insulators
Line conductors are primarily responsible for carrying electrical current from the power source to the distribution network. They are designed to handle high current levels efficiently while minimizing losses during transmission.
What causes the phenomenon of corona discharge in high voltage lines?
A High voltage
B Low current
C High resistance
D Low temperature
Corona discharge occurs when the voltage level in a transmission line is high enough to ionize the surrounding air. This leads to energy loss and electrical interference. It is more likely to occur in high voltage transmission systems.
What does “sag” refer to in transmission lines?
A Voltage drop
B Conductor tension
C Current fluctuation
D Conductor displacement
Sag refers to the downward displacement of transmission line conductors caused by their weight and environmental conditions, such as temperature changes. Proper sag calculation is important to ensure safe clearance from the ground.
Which system helps distribute power in remote areas?
A Smart grid
B Overhead lines
C Microgrid
D Underground system
Microgrids are designed to distribute power in remote or isolated areas. They can operate independently from the main grid, often using renewable energy sources, and provide reliable power even in areas without extensive infrastructure.
What is a common characteristic of overhead transmission lines?
A Low voltage
B High voltage
C High insulation
D High power loss
Overhead transmission lines typically operate at high voltage to efficiently transmit power over long distances. High voltage reduces current flow and minimizes energy losses due to resistance in the wires, ensuring efficient long-distance transmission.
What does a voltage regulator do in a distribution system?
A Increase current
B Reduce power loss
C Stabilize voltage
D Increase resistance
A voltage regulator maintains a constant voltage level in a distribution system, ensuring that electrical equipment receives stable power. This is crucial for preventing voltage fluctuations, which could damage sensitive devices or reduce system efficiency.
What is the primary function of a circuit breaker in transmission systems?
A Increase efficiency
B Control power flow
C Regulate voltage
D Prevent faults
A circuit breaker protects the transmission system by disconnecting the flow of electricity in the event of faults such as short circuits or overloads. This prevents damage to the system and ensures safety for the equipment and operators.
What is the most commonly used conductor material for transmission lines?
A Aluminum
B Iron
C Copper
D Steel
Aluminum is widely used in transmission lines due to its lightweight, cost-effectiveness, and good electrical conductivity. Its lower weight reduces mechanical stress on the support structures, making it ideal for overhead transmission lines.
What does a step-up transformer do in power transmission?
A Convert DC to AC
B Step down voltage
C Step up voltage
D Stabilize current
A step-up transformer increases the voltage for efficient long-distance transmission. Higher voltage reduces current, which minimizes energy loss through resistance in the transmission lines, ensuring that electricity reaches consumers efficiently.
Which of the following is not a power loss factor in transmission lines?
A Sag
B Conductor resistance
C Voltage drop
D Line impedance
Sag refers to the physical displacement of conductors due to their weight and environmental conditions. While it affects the safe clearance of lines, it does not directly cause power loss, unlike conductor resistance, line impedance, and voltage drop.