Science & Technology in Action

3rd Edition

The Science of Electricity Generation


By recovering the heat from exhaust gases the overall efficiency of an oil or gas-fired generator can be increased.
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Lesson excerpt

The Irish electricity market opened to full competition for business users in 2001 and for domestic users in 2005. This meant that new suppliers could obtain a licence to generate electricity. Energia is a well known licensed supplier, currently serving about 25% of the all-island business market. In order to do this Energia must operate a power station and feed electricity into the national grid for distribution to customers.

Early one the morning in October 2006, a convoy about 107 metres long left Dublin docks and started on a slow careful trip up the M50. The 372 tonne load being carried that day was a Mitsubishi combined cycle gas turbine generator. It was being delivered to Energia for installation in their power station at Huntstown, Co. Dublin. In this lesson we take a closer look at the new turbine and see how it brings physics and chemistry, electrical engineering and mechanical engineering together to produce electricity more efficiently and connect to the grid.

What is a generator?
First we need to review a fundamental principle that was discovered and demonstrated by Michael Faraday in 1831. If aconductor moves in a magnetic field, cutting through the lines of force, a potential difference (emf) is produced across the conductor. The principle involved is called electromagnetic induction. This discovery led to astounding changes in society. It underpins the development of the electric motor and the ability to generate electricity and distribute it across long distances. The earliest generators were called dynamos and the term still applies to small ones such as those often used on bicycles.

So, in essence, agenerator is a machine that can move conductors though a magnetic field to produce the required potential across the output terminals. In fact, large modern generators actually move the magnetic field, while the conductors remain stationary. They do this by rotating electromagnets on a spindle so that the field cuts through a series of conductors. These conductors are arranged in coils on the inside of a cylinder surrounding the spindle. The spinning part with the magnets is called the rotorwhile the cylinder and coils surrounding the spindle is the stator. This whole assembly is often called an alternator because it produces AC.

True or False?

  1. It is more efficient to transmit DC rather than AC over long distances.
  2. A transformer can step a voltage up but not down.
  3. The unit of magnetic flux density is the tesla or weber/m2 ( 1 T = 1 Wb/m2 )
  4. Electromagnetic induction is the only way to produce electricity.
  5. The highest voltage in the national grid is 220 kV.
  6. Natural gas is one of the dirtiest hydrocarbon fuels.
  7. An alternator is a generator.
  8. In the Energia Mitsubishi generator the magnets are on the stator.
  9. A watt is a unit of power.
  10. Energia owns the national grid.