10. Wairakei Turbines and Generators
There
are four different turbine- generator types at the Wairakei Power Station.
These four types are needed because natural steam varies so much.
Generator
G4 is painted green and the Intermediate Pressure steam turbine that
drives it is painted red. The exciter that produces the magnetic field
in the stator of the generator is on the right and is blue - Image: Heurisko Ltd.
A
single condenser in a mixed pressure turbine is painted green to
show it contains cool river water. The water enters through the two
pipes and is sprayed into the round chamber - Image: Heurisko Ltd.
Generators
G7, G8 and G9 with their low pressure steam turbines (painted grey
and red) to drive them. Notice the maintenance in the foreground being
done on the exciter for the stator's magnetic field - Image: Heurisko Ltd.
The things that affect steam are
- the amount of steam
- the pressure of the steam
- the amount of steam compared to the amount of hot water
- the age of a well
- old or new well technology
- environmental factors
The variety of these ‘turbine – generator’ pairs is shown below.
Note: There are now 10 generators, with an 11th being built. The 11th is a new type called 'Binary Plant'.
| Generator Number |
Location | Turbine | Generator |
| G1 |
Station A | Intermediate Pressure | 11.2 MW 3000 rpm 2pole |
| G2 |
Station A | taken out of service in 1984 | - |
| G3 |
Station A | Taken out of service in 1984 | - |
| G4 |
Station A | Intermediate Pressure | 11.2 MW 3000 rpm 2pole |
| G5 | Station A |
Removed to Ohaaki in 1984 | - |
| G6 | Station A |
Removed to Ohaaki 1984 | - |
| G7 |
Station A | Low Pressure | 11.2 MW 3000 rpm 2pole |
| G8 |
Station A | Low Pressure | 11.2 MW 3000 rpm 2pole |
| G9 |
Station A | Low Pressure | 11.2 MW 3000 rpm 2pole |
| G10 |
Station A | Low Pressure | 11.2 MW 3000 rpm 2pole |
| G11 |
Station B | Mixed Pressure | 30 MW 1500 rpm 4 pole |
| G12 |
Station B | Mixed Pressure | 30 MW 1500 rpm 4 pole |
| G13 |
Station B | Mixed Pressure | 30 MW 1500 rpm 4 pole |
| G14 | Stand Alone |
Intermediate Low Pressure | 4 MW 1500 rpm 4 pole Uses an asynchronous, induction generator |
| Binary Plant | Stand Alone | High Pressure | 14 MW Under construction |
The Types of Wairakei Turbines
1. Low Pressure Turbines
- Wairakei has 4 Low Pressure steam turbines.
- Low Pressure means that the steam is only just above normal air pressure
- In each the steam enters in the middle of the turbine and flows out to both ends.
- Each has five different sets of blades then a condenser
- The steam is able to drive the turbine because the condenser creates a vacuum which is so powerful it sucks the steam through.
2. Intermediate Pressure turbines
- Wairakei has 2 Intermediate Pressure steam turbines
- Intermediate Pressure means that the steam is at 3.5 times normal air pressure
- The steam enters the turbine from the front and flows to the rear
- There are 3 different types of blade
3. Mixed Pressure Turbines
- Mixed Pressure means that the same turbine is driven by one steam pressure and then another. The first pressure is 3.5 times air pressure. The second pressure is 1.1 times air pressure.
- Wairakei has 3 Mixed Pressure steam turbines
- The first stage has 8 different types of blades. The second stage has 7 different types of blades.
- A condenser creates a vacuum which sucks the steam through
4. High Pressure Turbines
- High Pressure means that the steam turbines is 12 to 20 times the pressure of normal air
- Wairakei no longer has these turbines because it no longer has the steam to run them
- These turbines are now used at the Ohaaki Power Station.
5. The Binary Plant
- The Binary Plant will use the heat energy in waste hot water to drive.
- It is being built during 2005
- It will produce 14 MW of electricity which is enough to supply about 10,000 homes.
- The weather will have a big effect on output because it is air cooled.
- It will being able to generate 4MW more on a frosty night than a hot summer's day
- Does not affect the supply of geothermal water used by others.
The Binary Plant uses hot water to heat the liquid Pentane which
boils at only 29°C.
The Pentane gas is used to drive the turbine.
This is done by
- Heating the Pentane with hot water
- Allowing the Pentane to boil
- Using the Pentane gas to turn a turbine
- Cooling and condensing the Pentane
- Repeating the process
Condensers
- Condensers rapidly condense the steam that is leaving the turbine.
- This causes a vacuum that 'sucks ' the steam through the turbine,
- A Condenser doubles the power output of the turbines and generators.
- At Wairakei the Condensers are simple chambers into which river water is sprayed
- It takes 40kg of cool Waikato River water to condense each kg of steam.
- To create a good vacuum some gases in the steam and water have to be removed.