- Discuss how the National Grid is used - Explain the advantages of providing electricity through the National Grid
Below is diagram that will help you understand how the whole process flows. Click to enlarge.
Still a bit shaky?
Bitesize has a useful page on the National Grid. Click on the logo so it can re-direct you to their page.
What do I actually need to know for the exam?
Well, you should aim to know the general idea of what the National Grid does. But something does keep crawling up in the exams ...
- What is a step-up transformer? This is usually a 2mark question. You need to state
For the first mark - That it increases voltage and or decreases current
For the second mark - reducing energy losses (through the cables)
QUESTION TIME! (Click to enlarge image)
(b) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.
Over the next 10 years, more than 300 kilometres of new high voltage transmission cables are to be added to the National Grid. Most of the new cables will be suspended from pylons and run overhead while the rest will be buried underground. Outline the advantages and disadvantages of both overhead transmission cables and underground transmission cables. (6marks)
(c)When an electric current flows through a transmission cable, a magnetic field is produced.The graph shows how the strength of the magnetic field varies with distance from both overhead and underground transmission cables that carry the same current.
What conclusions may be drawn from this graph? (2 marks)
Have you ever seen those metallic things on the motorway that look a bit like the Eiffel tower? Well they are called pylons and they make up a small part of what is called the National Grid. The National Grid is a network of cables and transformers that links power stations to consumers. The electricity is charged in units which is equivalent to one kilowatt of electricity used in one hour.
The Power Station
The power station is where it all starts. The fuel is brought and used. The power stations generate the energy. Power stations produce electrity at around 25,000 volts (V).
Step-up transformers
Step-up transformer increases voltage and decreases current. The lower the decrease in current the less (heat) energy that escapes from the cables. The current needs to be as low as possible as the energy loss (due to the friction of currents) could lose the company money.
Pylons
This rather attractive pink pylon is one of a collection of pylons that transports the electricity to consumers. When a current flows through a wire, it can lose energy in the form of heat. To prevent this as much as possible, they transfer the electricity at a low current.
Step-down transformers
The electricity from the wires were at a voltage of about 250,000V which is way too dangerous to be used in homes. Step-down transformers lower the voltage so it is safer to use. There are also substations which further decrease the voltage.
Mark Scheme! Click to enlarge!
Don't like reading? Below is a video that is quite good at summing this all up.