However it is not generated at volts because the current in amps A needed to push the energy through extremely large cables would be huge.
Big currents need thick cables that get hot. In our power stations electricity is generated at 25, volts at a current of , amps. Outside power stations there are huge step-up transformers that take the voltage from 25, volts to , volts Kv. The voltage can be as high as , volts in the super grid.
It was Nikola Tesla who established the principles of three-phase high-voltage electric power distribution while he was working for Westinghouse in the United States in the early 19th Century.
The transformer is a vital part of the National Grid in terms of limiting energy losses. Electrical energy that is generated in power stations at a potential of 25 kV, is first stepped up to kV by a transformer and then transmitted across the country in aluminium cables roughly 2 cm in diameter.
High voltages are used because the power loss per kilometre I2R for a given power output will be much less at high voltage and low current than at low voltage and high current. Despite this, even after the current has been reduced many transmission lines carry up to amps. In Britain the grid system can meet a simultaneous demand of 56 MW supplied through some km of high-voltage transmission line. In the early days of E generation Direct Current DC was used because generating plants were normally more local.
Annual energy used in the UK is around TWh 1. Natural gas power stations are the cheapest to build and relatively rapid start-up time. Nuclear power stations are the most costly to build and have the longest start-up time. The National Grid system of electricity supply MUST work off an alternating current ac for several reasons, and one important factor is that transformers only work using ac.
With alternating current ac , the current changes direction in a cycle e. With direct current dc there is no reversal in current direction, it flows one way with a constant voltage.
Note that some devices in the home work off a dc current - but the output from e. In the UK the generator output at the power station is 25 kV. A step-up transformer increases the p. The main power transition p. T ransmission of electricity, need for transformers, use of very high p. A step-down transformer decreases the p. The transformer sites are referred to as sub-stations. A substation will decrease the p. Explanation of transformers is given in the last section on this page.
See Generator effect, applications e. Both the function of generators and transformers depend on the electromagnetic effect. The scheme described above is similar for most generation, except that initially for hydroelectric, tidal and wind power generation, the turbine is rotated directly by these renewable energy resources of water or wind - no fuel required.
The only kind of power generation that does not require a turbine and generator is the solar panel. Renewable energy 1 Wind power and solar power, advantages and disadvantages. Renewable energy 2 Hydroelectric power and geothermal power, advantages and disadvantages. Renewable energy 3 Wave power and tidal barrage power, advantages and disadvantages.
All of these renewable energy sources can contribute to the National Grid system. More detail on the transmission of electricity, need for transformers in the National Grid system. 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. You also need to know why the long distance power lines use a very high p. So that you can transmit transfer the very large quantities of electrical energy per unit time needed, you need to use either a very high current or a very high voltage or both. The theoretical four possible choices are i low current and low voltage, ii high current and low voltage, iii low current and high voltage or iv high current and high voltage So why is ' low current and 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 more waste heat energy the higher the current, which is why ii and iv are not employed. This is a good numerical argument for minimising the current I.
Therefore by using a very high voltage eg V, kV and relatively low current you maximise power transmission for the minimal heat loss of wasted electrical energy. So for a given power transmission increasing the p. See the equations in the transformer section. However, use of these extremely high voltages x your domestic voltage of 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 pylons!
You should know and understand the uses of step-up and step-down transformers in the National Grid. With cables with a p. In some places the cables run underground, but this is more expensive see later comparison discussion. Now, i since the national power transmission uses kV, you can hardly use this in the home,. 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. The demand for electricity varies through the day e. Peak times are associated with cooking and transport needs and demands will increase in the winter when more energy is used for heating. Power companies know the demand patterns and can adjust to society's needs. Power stations do not run at their maximum output, there must be spare capacity most of the time, so if there is suddenly a huge increase in demand, it can be taken care of.
There might be an unplanned shut-down of a power station due to unforeseen circumstances. There are smaller power stations on standby that can be quickly brought into use. There are also pumped-storage systems that are very useful to meet electricity demands at peak times. See Renewable energy 2 including Hydroelectric power. Check out your practical work you did or teacher demonstrations you observed , all of this is part of good revision for your module examination context questions and helps with 'how science works'.
More detailed notes on the theory and structure of transformers. A transformer is a device that can change the potential difference p. It is another example of electromagnetic induction - the effect of magnetic fields inducing an ac current in a coil. A basic transformer consists of two coils of insulated wire , a primary coil and a secondary coil independently wound on an iron core - see the diagram further down. The wire is usually made of copper with a thin coating of insulation material.
Iron is used as because it is easily temporarily magnetised. Single-phase power is what you have in your house. You generally talk about household electrical service as single-phase, volt AC service. If you use an oscilloscope and look at the power found at a normal wall-plate outlet , what you will find is that the power at the wall plate looks like a sine wave , and that wave oscillates between volts and volts.
The peaks are indeed at volts; it is the effective rms voltage that is volts. The rate of oscillation for the sine wave is 60 cycles per second. Oscillating power like this is generally referred to as AC, or alternating current. The alternative to AC is DC, or direct current. Batteries produce DC: A steady stream of electrons flows in one direction only, from the negative to the positive terminal of the battery.
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