Electricity - a
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
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.