How electricity gets from a power station to your home, why the cables run at hundreds of kilovolts, and the transformer equation.
What you will learn
- Put the parts of the National Grid in order
- Explain why a high p.d. makes the grid efficient, using P = VI and P = I²R
- Calculate the power wasted in cables
- Use Vp × Ip = Vs × Is (Physics only, Higher)
From power station to plug
The National Grid is the network of cables and transformers that links power stations to homes, shops and factories.
- Power station: generates at about 25 kV
- Step-up transformer: raises the p.d. to hundreds of kV (400 kV on the main lines)
- Transmission cables: carry the energy across the country
- Step-down transformers: lower the p.d. in stages near the towns
- Homes: 230 V
A step-up transformer makes the p.d. bigger; a step-down transformer makes it smaller.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- From power station to plug
- Why such a high potential difference?
- The transformer equation (Physics only, Higher)
- Try it: See how the waste depends on current
- Try it: Power wasted in cables
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
National Grid, Step-up, Step-down
In this unit: Mains electricity, the National Grid and static
Direct and alternating current, the three-core cable and plug, electrical power and energy, the cost of electricity, the National Grid and transformers, and static charge and electric fields.