High Voltage Transmission (Edexcel GCSE Physics)

Higher Tier Only

• When a current passes through a wire, the current creates a heating effect which means the wires warm up
• This means they lose electrical energy as heat which reduced the efficiency of the transformer
  • This is due to electrical resistance which is present in all wires

• The power (energy per second) lost in the wire is given by the following equation

P = I²R

• Where:
  • P = power in watts (W)
  • I = current in amps (A)
  • R = resistance in ohms (Ω)

• Since the power is the energy lost per second, the total energy lost in a time t will be:

E = P × t

• Where:
  • E = energy in joules (J)
  • t  = time in seconds (s)

• A step-up transformer may be used to increase the voltage of a power supply from the power station to the transmission wires
• The number of turns and voltage for the transformer is related by the following equation:

• Where:
  • V_p = potential difference (voltage) across the primary coil in volts (V)
  • V_s = potential difference (voltage) across the secondary coil in volts (V)
  • n_p = number of turns on the primary coil
  • n_s = number of turns on the secondary coil

• A step-up transformer has more turns on the secondary coil, N_s, than on the primary coil, N_p
• Since a transformer cannot output more power than is put into it, increasing the voltage must result in the current being lowered

I_pV_p = I_sV_s

• Where:
  • I_p = current in the primary coil in amps (A)
  • I_s = current in the secondary coil in amps (A)

• Lower current results in less power and energy loss in the cables
  • This makes the transfer of electrical energy through the wires more efficient