'National Grid' power supply
Doc Brown's Physics Revision
Suitable for GCSE/IGCSE Physics/Science courses or
Methods we use to generate electricity
energy (fuel) => heat energy (steam) => kinetic energy (turbine blades)
=> electrical energy (generator)
Appreciate that various energy sources can be used to generate the electricity we need.
Appreciate the need to
carefully consider the advantages and disadvantages of using each energy source before
the decision to decide which
energy source(s) would be best to use in any particular situation.
Know that electricity is distributed via the
You are expected to use your skills, knowledge and understanding to:
evaluate different methods of generating electricity,
you should be able to evaluate
different methods of generating electricity given data including start-up
times, costs of electricity generation and the total cost of generating
electricity when factors such as building and decommissioning (removing
everything of an old power station) are taken into
You must also be able to consider the reliability of different
There are other general issues
such as environmental impact - pros and cons for the local community (eg
jobs versus environmental damage, visual impact), how long will it take to
build?, at what cost versus eventual power output?, planning delays etc.
Ideally you would want to site a
large fossil fuel/nuclear power station as near as possible to the
major/bulk users AND in the case of coal, near a coal mine, since power line
transmission involves wasted energy (see National Grid section).
Large scale tidal and river/lake
hydroelectric schemes and geothermal power plants all need very specific
For safety reasons, nuclear
power plants are sited in remote locations, often near the coast.
Small scale power generation
with solar cells and wind turbines can be sited anywhere, but larger wind
farms need to be in a windy area eg on low hills or out at sea.
Knowledge of the actual values
of start-up times and why they are different is not needed, but you must
appreciate that the implications of such differences in start-up times are
evaluate ways of matching supply with demand, either by increasing supply or decreasing demand,
you should be aware of the fact that, of
the fossil fuel power stations, gas-fired have the shortest start-up time.
Power station generator start up
times: Nuclear >> coal fired > gas-fired
By coincidence (or maybe not?),
this order is also paralled by the capital costs, decommissioning costs,
you should also be aware of the advantages of pumped storage systems in
order to meet peak demand, and as a means of storing energy for later use.
See the section on hydroelectricity.
compare the advantages and disadvantages of overhead power lines and underground cables.
Know and understand that the
flow of water and wind can be
used to drive turbines directly.
renewable energy sources used in
this way include, but are not limited to, wind, waves, tides and the falling
of water in hydroelectric schemes and all involve converting FREE kinetic
energy into electrical energy using a generator. None of these schemes needs
a fuel, or produces any kind of chemical pollution on the site, and all are
'green' in terms of not consuming fossil fuels ie carbon dioxide, but they
may have quite an environmental impact. All these methods can contribute to
National Grid of electricity supply.
Know and understand that small-scale production of
electricity may be useful in some areas and for some uses, eg
hydroelectricity in remote areas, solar cells for roadside signs, remote
You should know and
appreciate that using different energy
resources has different effects on the environment and these effects include:
the release of substances into the atmosphere,
the production of waste
noise and visual pollution,
the destruction of wildlife
Also, you should know and
understand that carbon capture and storage is a rapidly evolving technology.
To prevent carbon dioxide building up in the atmosphere we can catch and
Know that some of the best natural containers are old oil and gas
fields, such as those under the North Sea.
The idea is to capture the
carbon dioxide from fossil fuel burning before it is released into the
atmosphere and pump it to some suitable storage location.
Is it possible to feed the
carbon dioxide to algae from which to derive a biofuel?
There are other ways to reduce
carbon dioxide, principally by reducing electricity demand, so less fossil
fuel is burned. You can reduce electricity demand in the home by insulation,
better designed and more energy efficient appliances like washing machines,
low energy light bulbs, turning off all devices/appliances not in use.
Know that electricity is distributed
from power stations to consumers along the National Grid.
You should be able to identify
and label the essential parts of the National Grid.
The National Grid consists of a
vast network of pylons and cables (power lines) insulated and suspended from
You see them stretching for
miles and miles across the landscape to supply you, the consumer, very
conveniently with a constant (well nearly!) supply of electricity to your
city, town or village across the vast majority of the country.
power station ==> step-up
transformer ==> grid system ==> step-down transformer ==> user/consumer
For a given power increasing
the voltage reduces the current required and this reduces the energy losses
in the cables.
You should know why transformers
are an essential part of the National Grid.
So that you can transmit
(transfer) the very large quantities of electrical energy needed you need to
use, either, a very high current or a very high voltage or both.
the four possible choices are
(i) low current/low voltage, (ii) high current/low voltage, (iii) low
current/high voltage and (iv) high current/high voltage.
(i) couldn't deliver what is
needed, but (iii) is the actual choice.
So why is 'low current/high
voltage' the desired choice for electrical power line transmission.
The greater the current flowing
through a wire, the greater the heat generated, which in the context of
power lines means waste heat energy, which is why (ii) and (iv) are not
However, power = current x
voltage, so to deliver a particular power rating, you can increase one
of the two variables and decrease the other.
Therefore by using a very
high voltage (eg 400 000 V, 400 kV) and relatively low current
you maximise power transmission for the minimal heat loss of wasted energy.
Use of these extremely high
voltages (1667 x your domestic voltage of 240 V), means health and safety
issues arise and you need lots of big ceramic insulators on pylons and
transformers and lots of barbed wire to deter people from climbing up
You should know and
understand the uses of step-up and
step-down transformers in the National Grid.
You do not need to know the details of the
structure of a transformer and how a transformer works.
Now, (i) since the national
power transmission uses 400 kV, you can hardly use this in the home, and
(ii) generators themselves cannot deliver 400 kV, you need a way of
increasing (for efficiency), and then decreasing (for safety), the voltage
in power lines.
A transformer is a means
of changing an input voltage in one circuit, into another output voltage in
a separate circuit.
At the power station end is a
step-up transformer to increase the voltage for power line transmission.
At the user end is a
step-down transformer, to reduce the voltage that is a safe level for
factories, domestic homes, street lighting etc.
Comparing the advantages and disadvantages of overhead power lines and underground cables.
- visual impact
- the land itself
Overhead power lines
lower, simple erection of
pylons and linking cables carrying the high voltage
relatively easy, simple
considerable, miles of
pylons and cables stretching across the countryside -
controversial in designated areas of outstanding natural
slight - foundations of
much more needed and much
less reliable - weather damage eg from frost, snow,
corrosion of structure
much higher, costly trenches
and insulated cables
much more work, all that
digging and filling!
minimal, not really seen at
considerable, but temporary
- digging trenches is disturbing the land, but no
much less and more reliable,
not affected by weather BUT not as easy to trace and
access if fault develops
Energy and power
supplies revision notes index
Energy resources and their uses - a general survey
Renewable energy (1) Wind power and
Renewable energy (2) Hydroelectric power and
Renewable energy (3) Wave power and tidal power
Biofuels, renewables and non-renewables
The 'National Grid' power supply
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