8. Steam Turbines

In its first twenty years, the steam turbine cut the use of coal for electric generating stations by 75 percent. This is due to steam turbines spinning quickly which suits electrical generators. Today the steam turbine is still important in generating electricity worldwide.
Fitting new blades to the central shaft of Mixed Pressure turbine 11. This end of the shaft will finally carry 7 stages of blading - Image: Heurisko Ltd. Panorama.
An aerial view of the shaft of Mixed Pressure steam turbine 11 which is being rebladed. Notice the 8 stages on the left and 7 on the right. The person gives an idea of the scale as does the lathe which occupies the whole floor - Image: Heurisko Ltd.
A single blade from the low-pressure steam turbine that drives Generator 9. Others are stacked behind - Image: Heurisko Ltd. Panorama

The Science of Steam Turbines

The earliest use of a steam turbine in a power station was in 1888 in the North of England. Charles Parsons sketched the original design of this turbine on the back of an envelope. It took $300 000 of research and 25 years for engineers to improve its efficiency by just 2%.

This shows how very good Charles Parsons design was. He realised that this was because the steam had been expanded in a single step and he would use many small steps.

Within Charles Parsons' turbine each turbine blade was made larger.

This was done in three ways by

  1. increasing the height of each blade
  2. increasing the diameter of the drums
  3. altering the angles between the blades

Between each set of blades are diaphragms, Steam expands and speeds up through the diaphragms. The turbine blades spins by slowing down the steam.

These design ideas are still part of steam turbine’s today.

Heat to Kinetic Energy

This energy conversion occurs in the turbines of the Wairakei power station. Each of the 10 turbines is

  • made up of a shaft with blades around the outside
  • made efficient by shaping the blades
  • made to operate at one pressure
  • made to spin at one speed