Transformer Inefficiencies (AQA A Level Physics): Revision Note

Inefficiencies in a transformer

• Inefficiencies in a transformer appear not from just the core, but also in the wires

• The coils of wire have resistance

  • This causes heat energy to be lost from the current flowing through the coils

  • The larger the current, the greater the amount of heat energy lost

• In the core, the inefficiencies appear from:

  • induced eddy currents

  • the reversal of magnetism

  • poor insulation between the primary and secondary coil

• Ways to reduce energy loss in a transformer are:

  • making the core from soft iron or iron alloys to allow easy magnetisation and demagnetisation and reduce hysteresis loss

  • laminating the core

  • using thick wires, especially in the secondary coil of step-down transformers

  • using a core that allows all the flux due to the primary coil to be linked to the secondary coil

Power loss in transmission lines

• Energy losses due to the heating of transmission lines in the National Grid are significant

• This is because the electrical energy is transmitted across long distances from power stations to buildings

  • This is not just within the UK, but also to other countries such as France and the Netherlands

• Transformers are used to step up the voltage generated in power stations

• Since power transmitted is the product of the voltage and current, stepping up the voltage reduces the current

  • Smaller currents have a smaller heating effect on the wires

  • This reduces energy loss to the surroundings from the wires

  • Therefore, this improves the efficiency of the electrical energy and power transmitted through the wires

• Power losses from the current are calculated using the equation:

$P=I^{2}R$

• Where:

  • $P$ = power (W)

  • $I$ = current (A)

  • $R$ = resistance (Ω)

• The equation shows that:

  • $P\propto I^2$

  • This means doubling the current produces four times the power loss

• Therefore, step-up transformers are used to increase the voltage which decreases the current through transmission lines

  • This reduces the overall heat energy lost in the wires during transmission

• A step-down transformer is then used to decrease the voltage to that required in homes and buildings