Generating Electricity
Hydro Tasmania generates alternating current (AC). This means that instead of the electrons flowing in one direction down the wires they move backwards and forwards. To understand how this works we can use a comparison with a railway engine and railway cars.
Each generator can be compared to a railway engine connected to huge rows of railway cars (the electrons) running down a railway track (the transmission line). As the engine moves forward it pushes the first of the railway cars. The force exerted by the engine is transferred progressively down the row as each car bumps the next. In a similar way electrical energy is transferred progressively along a conducting wire as moving electrons dislodge other electrons nearby. This shunting effect travels at almost 300,000 kilometres per second but any individual electron moves only a short distance.
The generation of alternating current means that the engine (generator) is not continually pushing electrons in one direction down the track. It pushes and pulls the electron backwards and forwards 50 times every second. This is known as the frequency, and is the same for all Hydro Tasmania's generators (50 hertz or cycles per second).
The pushing and pulling effect on electrons is caused by the alternation of north and south magnetic poles inside the generator. As different poles spin past the coils the electrons are sent first one way then the other.
It is important to maintain a constant frequency of 50 cycles per second. This means the speed at which the turbine spins needs to be kept constant. This function is performed by a machine called a governor. The governor can adjust the amount of water used to spin the turbine. The governor allows for such changes as reductions in the water pressure due to low water levels in the storage lake.
The strength of the magnets in a generator is controlled by a machine called an exciter.
The greater the strength of the magnets, the greater the electric pressure or voltage produced by the generator. The majority of Hydro Tasmania's generators produce electricity at a pressure of 11,000 volts.
Exciters at Tungatinah
Power Station
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