9. The Electrical Generator

A generator produces electricity. It is made of two main parts, the Stator and the Rotor. The speed of the generator must be kept constant .
This sign on Generator 4 warns of the intense magnetic field produced by the stator - Image: Heurisko Ltd.
A manufacturer's plaque on Generator 4 showing the design specifications - Image: Heurisko Ltd.

The Stator

The Stator stays still and surrounds the rotor.

  • It has large coils of wire
  • Its coils create electricity when a magnetic field "cuts" them.

The Rotor

The Rotor rotates and is in the centre of the generator.

  • It is on a steel shaft that spins
  • It is made to spin by the steam turbine
  • It has coils of wire which become a magnet

A generator can be made more powerful by

  • increasing the number of turns of wire
  • increasing the strength of the magnetic field, or flux
  • spinning the rotor faster

At Waikarei the speed of the turbine is controlled by ‘governors’. If a great deal of electricity is needed the governor supplies extra steam. The extra steam drives the generator harder producing more electricity.

Some factors that affect the electricity supply are

  • The time of day and demand for electricity
  • The seasons
  • Weather changes
  • What other power stations are doing
  • The Cook Strait cables
  • Damage to the National Grid

It is a constant juggling act, between all the power stations in NZ to keep the electricity supply the same.