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 Electricity - a beginner's guide

 

 

We are so accustomed to electricity that we never spare a thought about where it comes from. Now that there is not enough to go round, there is a lot of discussion about what we can do to help.

Most of South Africa's electricity comes from coal burning power stations. The best place to build them is near the coal mines and that's why most are in Mpumalanga. In the Western Cape we also have Koeberg which is a nuclear plant as well as some peak power stations that are used to help when the load is very high, there are two gas burning stations and four hydroelectric stations. The "load" that people talk about is the demand for electricity at any given time, it reaches a peak at about 38 000 Megawatts (MW). A megawatt is a million watts. One watt is not much but the average car produces about 25 000 watts so Eskom produces the same amount of power each morning and afternoon as 1,5 million cars.

But how do they create it?

Electricity is generated by spinning a magnet inside three coils of wire. Each time the magnet passes the wire it generates some electricity. Magnets have two poles and as they swing round the current they generate alternates or moves in opposite directions, this is why our electricity is called Alternating Current (AC). To generate lots of electricity the magnets and coils need to be very big and the problem there is how you turn such a big thing. The thing is called a generator and is driven by stream or water in the case of hydroelectric stations. Power stations work like big kettles boiling water to make steam which drives the generators. The heating either comes from coal crushed into a powder and then blown into a furnace or by the splitting of uranium atoms in a nuclear plant. When the steam is hot enough it is able to make the magnet spin 3000 times a minute or 50 times a second which you may have seen on appliances as 50 hertz (Hz). This is an important number as electrical appliances measure time by counting the direction changes in the current, every 50 switches is one second, however under heavy load conditions the power station can't create enough steam that is hot enough to keep the generators running at 50 spins a second and as a result your clocks slow down.

Where do we store it?

Electricity can't be effectively stored, which is why peak times are so problematic because when you run out, you simply run out. It is the main reason why Eskom forces some people to lose their electric supply. If there were too much or too little electricity flowing in the system it would cause the entire system to crash. This is even more of a problem because it takes time for a power station to start a boiler to create stream for the anticipated loads so they are running almost all the time. This leaves less time for maintenance and so faults are more likely. When faults do occur, they lose the ability to generate electricity and the lights go out.

How does it get to us?

South Africa generates the 38 000 megawatts (MW) of power it needs to get us through the day. Most is produced in Mpumalanga, but not used there, to get it to Cape Town, Joburg and Durban requires over 350 000 km of cable. In the same way your home water supply pressure drops as you open more taps, the same effect applies to electricity, you can only send so much at a time through a cable. Electric companies move the huge volumes of power by increasing the voltage as high as 400 000 volts when your home only uses 220 volts. This massive load is transferred by the really large power pylons you see around the country. There are two sets that deliver power to Cape Town and it was a problem on one of these lines back in 2006 that caused a lot of the problems keeping Cape Town's lights on. Once it arrives in Cape Town or Joburg the voltage is dropped down in stages as it is sent round the City until the final voltage that reaches you is the required 220 volts. Cable theft, illegal connections and not enough power supply all make the cable system vulnerable to shutting down. It is a prospect that even if there was enough electricity being generated, we might still wind up sitting in the dark because the power grid shut down. Cape Town got a taste of this recently when a sub station that converts the power from a higher to lower voltage, failed.
 

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