Seneca
Sign up

Energy in Transformers

Physics: Cambridge International GCSE Supplement, topic 4.16.5

High-Voltage Transmission and Transformers

Electricity is generated at voltages of around 15,000 V. It is transmitted at 400,000 V before a transformer is then used to decrease the voltage to 230 V to be used in plug sockets in homes.

Long distances

Long distances

  • Transformers are used to increase the voltage of electricity, so it can be transmitted long distances through cables.
  • A step-up transformer is used to increase the voltage to around 400,000 V to be transmitted long distances.
  • Transmitting electricity at high voltages reduces the energy that is lost as heat due to the resistance of the cables.

Important Equations

IpVp IsVs

IpVp = IsVs

  • In electricity transmission, energy is carried from power stations to homes through long cables.
  • A transformer is used to step up the voltage before transmission.
  • which means power in the primary = power in the secondary (ignoring losses).
  • If the voltage is increased at the secondary, the current in the secondary must decrease to keep the same power transmitted.
  • Example: To transmit 1000 W, using 10 V would require 100 A, but using 1000 V requires only 1 A.
Ploss I2R

Ploss = I2R

  • Power lost in transmission cables is due to the resistance of the wires.
  • This means power loss depends on the square of the current and the resistance of the cable.
  • When the current is large, I2R becomes very large, so significant energy is wasted as heat in the cables.
  • By transmitting at a high voltage, the current is reduced, so the I2R losses become very small.
  • At the receiving end, transformers step the voltage down again to safe levels (e.g. 230 V for homes).
  • This method ensures efficient energy transfer with minimal losses in long-distance power distribution systems.

Test yourself on Energy in Transformers

  • Which type of transformer is used to increase voltage for transmission over long distances?

  • At what voltage is electricity transmitted over long distances?

  • Suggest a reason why DC (direct current) is not used for the National Grid.

  • Pick the correct values.

  • A transformer steps up the voltage from 500 V to 5000 V to transmit 10 kW of power. What is the secondary current?

Practise this topic for free