The National Grid
The National Grid is the high-voltage transmission system of cables and transformers in pylons or undersea interconnections. It connects power stations and sub-stations so that electricity generated is distributed throughout a country.
Electricity produced by power station generators has a voltage of around 25,000 V. However this push is not enough to send it long distances, so a step-up transformer (see slide) at the power station boosts the voltage to 275,000 or 400,000 V for efficient transfer.
Power (Watts), Current ( Amperes or Amps) and Voltage (Volts) are related in the equation:
Watts = Amps x Volts
So for a given power, increasing the voltage reduces the current required and this reduces heat energy loss in the cables.
Step-down transformers adjust voltages according to the customer requirements.
E.g. In UK 240 V is needed in homes/offices,
hospitals and light industries need 11,000 V
while heavy industries need 30,000 V .