The journey of electricity
Electricity made at a power station must travel long distances to reach towns and homes. This is done through the National Grid Network, a system of cables carried on tall pylons and buried underground. Along the way, transformers change the voltage several times.
Why high voltage?
Cables have resistance, so some energy is always lost as heat as current flows. The power wasted as heat is given by P = I²R, which depends strongly on the current. To keep the loss small, the current must be kept low. A step-up transformer at the power station raises the voltage to very high values (for example 132 kV or more). Because power = V × I, a higher voltage means a much lower current, so far less energy is wasted in the cables.
Key idea
High voltage → low current → small heat loss (P = I²R). This is why electricity is transmitted at high voltage.
Bringing it back down
Very high voltage is dangerous and unsuitable for homes. Near towns, step-down transformers at substations lower the voltage in stages. In Malaysia, homes finally receive electricity at about 240 V. Cables are usually made of aluminium or copper because these metals are good conductors and, for aluminium, light and cheap.
Remember
- Transmit at high voltage to reduce heat loss in cables.
- Step-up near the station, step-down near consumers.
- Homes in Malaysia use about 240 V.