Electrical Power
Assignment 1

Task 3 – Q4

3 Phase Transformer Construction
Diagram

Description
As shown in the diagram above, a three phase has three sets of iron cores instead of the one of a single phase transformer. Each ‘leg’ of the transformer has its own primary and secondary windings. Each primary winding will have the same amount of coils as will each secondary winding.

The three primary windings (shown above as P1, P2 and P3) and the secondary windings (shown above as S1, S2 and S3) can be connected in either a star or delta arrangement to give a required output. Also the output could be wired in a zigzag arrangement for special purposes where a phase shift of 30° is required.

Core Types
There are a few different types of core that are used in transformers, some are described below:

Solid Cores
Solid cores are just made of solid iron and are used in circuits such as switch mode power supplies which operate above mains frequencies and even up to a few kHz. The materials used in these cores combine high magnetic permeability with high electrical resistivity.

Laminated Steel Cores
These cores are made from layers of high permeability silicon steel and are usually used at power and audio frequencies. They are used because in a solid core at high frequencies ‘eddy currents’ are formed. The laminations confine eddy currents inside each lamination and so decrease the losses.

Air Cores
An air core is simply a transformer without any core at all, the windings are just arranged close to each other. The leakage inductance however is very high and has very poor regulations and therefore unsuitable for power distribution.

Windings
Different materials could be used for the windings but ultimately it depends on the application of the transformer, whatever material is used each separate winding should always be insulated from the next winding. Small transformers which use relatively small currents are usually wound from enameled magnet wire, whereas much larger transformers could be wound from rectangular copper strip insulated by oil-impregnated paper and blocks of pressboard.

Coolant
Some larger transformers that use high voltages can get very hot and may damage the windings, therefore a coolant is required. The transformer would be immersed in a highly refined mineral oil known as transformer oil that cools and insulates the windings. The tank that the transformer is contained by, often has radiators that circulate the oil by natural convection and sometimes by an electric pump.

Connections
There are many ways that a 3 phase transformer may be connected, this could be:

• Delta to Delta – Used in industrial applications
• Delta to Star – This is the most common connection and is used in commercials and industrial applications
• Star to Delta – This is used in high voltage power transmissions
• Star to Star – Very rare as it causes harmonics and balancing problems
• Zigzag – Used to derive an earth reference point in an underground electrical system, or used to control harmonics
Also depending on how each winding is connected the phase shift will alter for different applications. Task 3 – Q5

Task 4 – Q6

Utilising a 3 phase system in terms of economic benefits:

Economic Factor Benefit of 3 phase over single phase
Cost of Cabling The conductors of a three phase system are ¾ of the size of conductors of a single phase system, therefore the same power can be transferred through much smaller and hence cheaper cable. Also 6 conductors would have to be used in single phase system in comparison to 4 conductors being used in a three phase system.
Cost of Distribution By using the point above in regards to smaller conductors it means that the pylons need to be able to hold less weight (for the smaller 3 phase cables) and so making them cheaper by the fact of having to use fewer materials for the actual construction of them, and they would can to be placed further apart. Also the erection of the pylons would be considerably easier and therefore take less man hours to erect a whole distribution system.
Cost of Switchgear The cost of the switchgear would also be considerably less as a three phase system would use a smaller current than a single phase system. Therefore the cost of switchgear would be cheaper in regards to the parts required for the much smaller 3 phase switchgear.
Energy Losses The energy losses in a single phase system would be greater than when utilising a 3 phase system, therefore when distributing power over longer distances there will be less energy losses, therefore saving money.

Example Calculation (figures used are non-representative of the actual costs or sizes)

Economic Factor Three Phase Single Phase Saving
Cost of Cabling £100/meter @100m
4 conductors
¾ size of single phase
4 x 100m x £100 x 0.75
= £30,000 £100/meter @100m
6 conductors
6 x 100m x £100
= £60,000 £30,000
Cost of Distribution 3 phase pylon = £6500
Every 150m
Need 67 for 10KM
£6500 x 67
= £435,000 Single phase pylon = £10,000
Every 100m
Need 100 for 10KM
£10000 x 100
= £1,000,000 £565,000
Cost of Switchgear From BS7671:2008(+A1:2011)
Copper conductor, Multicore, PVC
70mm2 (approx ¾ less than single phase @ 95mm2) current carrying capacity 192A
Therefore only 1 200A, 4 pole (3ph + N) Breaker required
1 x £300 = £300 From BS7671:2008(+A1:2011)
Copper conductor, Multicore, PVC
95mm2 current carrying capacity 269A
Therefore only 3 280A, 2 pole (1 ph + N) Breaker required
3 x £150 = £450 £150 (for each way)

Task 5 – Q7

Solar
Solar energy is basically converting sunlight into electricity. This can be done either:
• Directly by using photovoltiacs (PV)
• Indirectly by using concentrated solar power (CSP)
Photovoltiacs use the solar radiation from the sun to create DC electricity with semiconductors that exhibit the photoelectric effect.
The photoelectric effect in short, is that electrons are emitted from the matter as a consequence of absorbing the electromagnetic radiation from the very short wavelengths of visible or ultraviolet light.
To generate power by using the sun (solar) an array of solar cells containing a photovoltaic material such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, or copper indium gallium selenide/sulfide are used.
When the sun shines on a solar cell it produces an electrical field across the layers of the photovoltaic material, therefore the brighter the sunlight the more electricity is produced.
The other way of using solar radiation to create electricity is by using concentrated solar power systems. These CSP systems use arrays of mirrors or lenses to concentrate a large area of sunlight onto an area very small.
The electricity is then produced by using the light and converting it to heat which drives a steam turbine most commonly connected to an electrical power generator.
The current technologies for the concentration of sunlight are parabolic trough, dish stirlings, concentrating linear Fresnel reflector and solar power tower. They are all simple in design but the technology is far from reaching its maximum theoretical concentration.
Wind
Wind power is simply the conversion of the wind energy into a form of energy that can be used. Wind energy has actually been used for longer than it may seem, many years ago wind was being used in windmills to convert the wind energy to mechanical power. In the modern era the main way of using wind energy is to convert it to electrical power using a wind turbine, which could be a single turbine or part of a wind farm (a collection on wind turbines).
Wind turbines work by the wind pushing round the blades which in turn works as a conventional generator, with the blades turning the rotor to cut the flux to make the electrons flow.
There are many types of wind turbine that fall under two main categories that are vertical axis and horizontal axis. Water
Water power is otherwise known as hydropower and is the power converted from the kinetic energy of the water to a form of energy that can be used such as electricity. Before electricity it was used in a similar way to water in a mill and the water energy converted to mechanical energy.
Hydroelectricity is changing hydropower into electricity by the use of the gravitational force of the falling or flowing water to turn a turbine which in turn converts the kinetic energy into electric energy. Of all the renewable energy sources this is the most common, this is probably down the fact that once the hydroelectric complex has been built, it produces no direct waste. It is a very clean way of making electricity and produces very little carbon dioxide especially in comparison to fossil fuels. Environmental Impact
Type of Alternative Energy Environmental Impact Efficiency Capital Cost
Solar The main environmental impact of solar energy is the material and production costs of the equipment before any energy is even produced. After a few years however this should balance out and start to give a positive impact.
On a household scale with PV cells, the cost of the materials and production is the main negative environmental impact. Whereas on a commercial scale with large CSP farms the impact is the same, but in addition to this a large area of land is required to host all of the mirrors and lenses that concentrate the suns energy. Although placed out in the desert most of the time, some would consider this still to be a major environmental impact.
Using solar panels doesn't release carbon dioxide, nitrogen oxide, sulphur dioxide, or mercury into the atmosphere as many traditional forms of electrical generation do, and therefore do not contribute to global warming, acid rain or smog. The efficiency of solar panels depends on what the panels are manufactured from. But in general for a modern photovoltaic panel the energy payback time is typically from one to four years depending on the module type and location. Some of the new ‘thin-film’ technologies can achieve significantly shorter energy payback times than conventional systems often less than 1 year, this combined with a typical lifetime of 20 to 30 years this in consideration means that these cells produce significantly more energy over their lifespan.
Solar panels made of crystalline silicon are getting to their theoretical limiting efficiency of 29% and so can achieve an energy payback period of 1–2 years. The capital cost of solar panels are relatively high approximately £10000, but the energy payback would be achieved within 4 years. There are also schemes ran by certain companies that do all sorts of deals with the end customer.
As far as the commercial scale goes, the cost of the production of CSP farms is very large, but as it is producing electricity for free with limited maintenance costs it soon becomes a very cost effective way of producing energy.
New innovations in CSP technology are leading systems to become more and more cost-effective.

Wind Wind power is one of the largest growing of the renewable energy options. Nonetheless there are environmental concerns with wind energy, it can negatively affect wildlife habitat and individual species as well as create an eyesore, due to the massive size of the turbines.
Also because of the location of them, normally close to the coast as these are the areas with the most wind it could be deemed that they are ruining the countryside.
There is benefits that also come with using wind turbines as a alternative energy, it is very clean and once built the turbines need little maintenance and do not contribute to global warming. The efficiency of a wind turbine depends on the turbine itself as well as other factors such as wind speed, location and the aerodynamics of the blade.
But efficiency has very little relevance as the fuel is cost free and unlimited, so it is probably better to consider cost-effectiveness. So to apply this to a wind turbine is the aerodynamic efficiency of the blades of the turbine, so the amount of energy that’s can be extracted from the wind by the blades.
It does have a theoretical limit though, this is called the Betz Limit and is 59.3%. The efficiency will also change with wind speed depending on the style of blade used. A typical turbine with varying conditions will be approximately 30% efficient. The capital cost of a wind farm is made up of a number of different components, a typical breakdown of the costs is about 2 thirds is the wind turbines itself, a quarter is other necessary installations such as roads, foundations and electricity cables and the remaining made up of installation, planning and legal fees.
Costs of wind farms are site specific so will depends on the location and conditions, but typically these days the capital costs are around £700/kW.

Comparison The environmental impact of both of these types of alternative energies, when at a industrial size is mainly to do with the large size of the area that is required to locate them. Wind has a large impact as they are located in areas where many people live, whereas the solar farms are located in deserts where people live anyway.
From a domestic or small commercial point of view solar panels can be located on roofs of buildings and are less of an eyesore. But wind farms will last a lot longer as solar panels have a lifetime, so overall the environmental impact of wind farms is less. When comparing solar and wind in terms of efficiency it is very difficult as wind energy depends on the type of blade, wind speed, location and then solar power depends on the type of application as well as location.
But in terms of a commercial property with a small series of panels or a small turbine they are both going to have a similar efficiency of roughly 30%. The capital cost between the two types of alternative energy is however relatively different. If placed on a small commercial property a wind turbine would cost considerably less, about a 1/5th of the price. But the solar energy would generate more electricity over a set period of 10 years for instance. But it depends on how long a company wants to be based there, because if its more than the lifespan of a solar panel, wind power would probably be better suited. Alternative for Small Commercial Property
Based on the comparison above, I would say for a small commercial property because of how much more electricity it could generate over a set period, I would go with a series of solar panels. Although the capital cost is higher I think in the long run, the panels would generate a more significant cost saving to the company.