Induced Potential, Transformers & the National Grid (OCR GCSE Physics A (Gateway Science Suite)): Revision Notes
7.3.7 Alternating Current & High Voltage Transmission
Transformers
Transformers are used to change voltages and currents in transmission lines. A transformer is formed from two coils of wire around a magnetic core. The number of coils determines whether the transformers will step-up or step-down the voltage.
Key Points As the power transferred must stay the same:
- increasing voltage decreases the current
- decreasing voltage increases the current
In the National Grid, a step-up transformer is used to increase the voltage and reduce the current. The voltage is increased from about 25,000 Volts (V) to 400,000 V causing the current to decrease. Less current means less energy is lost through heating the wire.
To keep people safe from these high voltage wires, pylons are used to support transmission lines above the ground.
Before reaching the end user, a step-down transformer reduces the voltage from the transmission voltage to the safer voltage of 230 V for home use.