Electrical Transmission and Distribution Quiz

Why is alternating current used for transmission in the UK rather than direct current?

• A.C. can easily be increased and decreased in pressure (voltage) whereas d.c. cannot.

• D.C. is more efficient for long distances.

• A.C. is cheaper to produce.

• D.C. is safer for household use.

Answer explanation

A.C. is preferred for transmission in the UK because it can be easily transformed to higher or lower voltages, making it more efficient for long-distance transmission compared to D.C., which lacks this flexibility.

Which two voltages are used for transmission in the UK?

• 400kV and 275kV

• 66kV and 33kV

• 11kV and 6.6kV

• 230V and 110V

Answer explanation

In the UK, high voltage transmission is primarily done at 400kV and 275kV. These voltages are used for efficient long-distance electricity transmission, while lower voltages are used for distribution.

What are two reasons for using high voltage transmission and distribution?

• Reduces cable size and power loss

• Increases current carried

• Increases pylon size

• Reduces efficiency

Answer explanation

Using high voltage transmission reduces cable size because higher voltage allows for lower current, which means thinner wires can be used. It also reduces power loss due to lower resistive losses in the conductors.

Name three voltages which could be used in a distribution system.

• 66kV, 33kV, 11kV

• 400kV, 275kV, 230V

• 110V, 220V, 330V

• 500kV, 600kV, 700kV

Answer explanation

The correct choice, 66kV, 33kV, and 11kV, are commonly used voltages in electrical distribution systems, suitable for medium voltage applications, ensuring efficient power delivery.

Why are sub-stations used in distribution systems?

• To increase the voltage

• To interconnect the network and provide isolation points

• To decrease the current

• To store electricity

Answer explanation

Sub-stations are crucial in distribution systems as they interconnect different parts of the network and provide isolation points for maintenance and safety, ensuring reliable electricity distribution.

Name three cooling methods used in power transformers.

• Natural air, oil, and gas (SF6)

• Water, ice, and steam

• Fans, radiators, and coolants

• Refrigeration, air conditioning, and fans

Answer explanation

The correct choice, 'Natural air, oil, and gas (SF6)', includes common cooling methods for power transformers. Natural air and oil are widely used, while SF6 gas is effective for high-voltage applications due to its excellent insulating properties.

What is an advantage of overhead supply systems?

• Easier to identify fault position

• Less exposed to environmental factors

• Cheaper than underground systems

• Aesthetically pleasing

Answer explanation

An advantage of overhead supply systems is that they make it easier to identify fault positions. This is because the lines are visible and accessible, allowing for quicker diagnosis and repair compared to underground systems.

What is a disadvantage of overhead supply systems?

• Exposed to lightning strikes

• More expensive than underground systems

• Difficult to repair

• High risk of contact

Answer explanation

Overhead supply systems are exposed to lightning strikes, which can cause significant damage and safety hazards. This is a key disadvantage compared to underground systems, which are better protected from such natural events.

What is an advantage of underground supply systems?

• No impact on environment (visual)

• Cheaper than overhead systems

• Easier to repair

• Less efficient

Answer explanation

Underground supply systems have a significant advantage of having no visual impact on the environment, making them more aesthetically pleasing compared to overhead systems. This helps preserve the natural landscape.

What is a disadvantage of underground supply systems?

• Cables are more expensive

• High risk of contact

• Aesthetically unpleasant

• Difficult to identify faults

Answer explanation

A disadvantage of underground supply systems is that cables are more expensive to install and maintain compared to overhead systems. This higher cost can be a significant drawback for utility companies.