GCSE Combined Science (AQA)

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Transformer Equation in the National Grid

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Electricity Energy transfers

Transformer Equation in the National Grid

3:23 The National Grid
Spec 4.2.4.3
Previous Efficiency of the National Grid Next Cells, Tissues & Organs
  • Transformers in the national grid are designed for maximum efficiency.
  • Efficiency is achieved using low resistance wires and an insulating soft iron core.
  • Electrical power input to a transformer is assumed to be equal to the power output.
  • No energy is lost if power in equals power out.
  • Power is calculated as potential difference multiplied by current.
  • The equation for transformers is: VP * IP = VS * IS.
  • VP and IP are the primary coil's potential difference and current.
  • VS and IS are the secondary coil's potential difference and current.
  • Units for potential differences are volts, and for currents, amps.
  • Example: Electricity in the national grid is transported at 440,000 volts and 62.5 amps.
  • A transformer converts this to 1,100 volts for factory use.
  • To calculate the secondary current, rearrange the transformer equation.
  • Secondary current = (Primary potential difference * Primary current) / Secondary potential difference.
  • Calculation: (440,000 volts * 62.5 amps) / 1,100 volts = 25,000 amps used in the factory.

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