Power System: Transmission Line Components and Design Considerations
Power is an essential commodity for the advancement of every community. The level of development of any country can be weighed on the scale "how stable her power supply is". No matter the effort the government of a country put in to ensure development of that country, in vain is the effort if there exist power instability in that country. Personally, I have done some analysis and research, and discovered that all developed countries have stable power supply. Here in Africa, countries like Ghana, South Africa and some other countries which are progressive in terms of development, are enjoying some degree of constant power supply.
IntroductionPower system is a network or arrangement of components designed with for the purpose of generation, transmission, distribution and utilization of electrical energy. Electricity can be generated in different ways ranging from thermal means to hydro means, however, the main purpose of generating electricity is for consumption or utilization by country people or neighboring country. Hence, we can say that without utilization, the purpose of generation of electricity is incomplete. This brings in the question "how does electricity generating companies ensure that consumers utilize the electric energy generated?" ___ Unlike the sick patient that has to visit a doctor in hospital before getting some treatments(services), the consumers or utilizes of electricity do not have to go directly to electricity generating companies to utilize electricity; even if there is an option of going to these companies directly, would you stay in your apartment without light? As a solution to this the electricity generating companies has to deploy a means which ensures that electrical power is readily available for the consumers. Because of the distance between electricity generating company and the potential consumers, stages has to be employed to filled in the gap between electricity generation and electricity utilization.This stages that fill in the gap are the transmission stations and the distribution company.
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Depending on country, different level of voltage is generated and steeped up using transformers before transmitting. Here in Nigeria, most electricity generating companies generate voltages of magnitude 11KV and step it up to 33KV, 132KV or 330KV which are the transmission voltages. The transmission of such a high magnitude of voltage is to account for the losses encountered in the transmission line, this means before the voltage gets to the transmission companies, it must have dropped to some extent. All the transmission company and generating company are interconnected in a ring system, which is somewhat like a loop.
The electric power now in transmission company has not yet gotten to the consumers; so transmission company(substation) still has their own part to play in ensuring this electrical energy gets to the consumers. Transmission substation steps down the different voltages to 11KV then transmit to distribution companies(substation). The distribution companies step down the voltage further to 415V before sending it to distribution line, finally the available transformers steps down the voltage to 220V or 110V depending on country. Power system ensures all these operations are carried out successfully.
Transmission Line ComponentsComponents are otherwise the subsystem of a system. So, components of a power system implies the subsystem that make up a power system.
ConductorsConductors are dielectrics that allow the flow of electricity with a very little resistance under a given range of frequency, of-course frequency has effect on the conductance of a dielectric. Conductors are the actual line of transmission or medium of transmission. The over head thick non-insulated cables are among the conductors transmission company transmits power through. Conductor come in different form ranging from solid conductor to composite conductor.
Solid conductors are one thick wire which is not flexible. A better alternative is the stranded conductor which is made up of relatively tiny conductors superimposed on the other. Stranded conductor has the advantage of flexibility. Another is the composite conductor; this conductor is somewhat a stranded conductor but has being reinforce(a different material added to it for tensile strength). An example of this is the Aluminum conductor Steel Supported(ACSS); this composite conductor is made up of strings or strands of aluminium intertwined on steel for the purpose of strength, another example is the Aluminium Conductor Alloy Reinforced(ACAR).
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Bundled conductor means two or more separated conductors carrying a single phase voltage. Taking your AC source in the wall of your house as an example, you used two different wires to tap from the wall socket to your electrical extension. That is to say, you have two wires plugged in to the LIVE and two wires plugged in to the Neutral, the two separate conductors carrying one phase is simply a bundle of conductor. This has the advantage of low resistance as it increases the surface area of the path available for the flow of current. Such is also employed in transmission of extra high voltages, bundle of conductor are the six wires you see on a single support structure, each two wire is carrying a phase. In bundling, the two wires are not touching each other along the line, this helps in reducing the magnetic field. bundling also minimizes corona effect which is responsible for the humming sound heard close to active transformers
InsulatorsInsulators are opposite of dielectrics. It opposes the flow of current under specified conditions.
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In transmission line, insulators does not only the conductors from electrically contacting the support structures, but also holds the conductor in a required position. Insulators come in different types like the suspension type, the shackle type insulators among others
Shield WiresShield wires are made from high conducting dielectrics and are earthed. Its function is to protect the transmission conductors in the event of lightening. Whenever lightening bolt hits the transmission system, the shield wires provide a safe path for it to the earth. This ensures that the conductors are protected.
Support structuresSupport structures are the towers on which the the transmission line rest upon through the aid of an insulator. Support structure ensures that the conducting wires is far above sudden contact with human.
This corresponds to safety also. Support structures comes broadly in two types which are the poles and towers. In high voltage transmission, the tower type of support structure is used. It can be self supporting(does not require extra support) or stayed tower(requires additional support).
Design ConsiderationTo design a new transmission line for a community or to extend transmission of electrical energy to remote communities, some factors has to be considered. Electrical construction companies consider some factors before putting a new extension of transmission line on ground.
Electrical FactorsBefore construction a new transmission line, Engineers consider some electrical analysis like the magnitude of power generated and the expected maximum current in order to calculate the cross section of the conductor to use and even the type of conductor to use.More power means a better with a relatively bigger cross sectional area. The type of insulation to use ; the spacing between the conductors and the resultant magnetic field due to that spacing; the[ reliability of the transmission](https://steemit.com/steemstem/@ikchris/deep-thought-reliabi-1552497914) line and the type of earthing material to use are all considered under this.
Mechanical FactorsThis deals with the mechanism of the transmission line. Before constructing a new transmission line, engineers consider things like, the maximum pressure or weight each support structure can bear, the tensile strength of the support structures and its form of expansion of the towers under different temperatures. The best support tower to use(whether horizontal or vertical); the spacing of the different support structures and the depth of ground to dig for each location of the tower . Ways of improving the mechanical strength especially for swampy area is also considered. Finally the mechanical factor also entails the vibration of the tower due to the force on a conductor carrying high magnitude of voltage/current.
Environmental FactorFault might arise in a transmission line, if such a fault arise how does it affect the environment, people living in it and even wildlife?. This factor considers such and hence, an overhead transmission line should not pass through a densely populated areas; underground system should be an option. Transmission are not built over house roofs and people are always advises to stay clear off from transmission line towers not just because of the risk of electric shock, but also for the risk of some radiations from the high voltage carrying conductor. Also some towers and overhead lines have the tendency of making a geographical area rough and appalling to see, this is resolved by designing a tower which blends with specific region
Economic FactorAchieving the best at the possible minimum cost makes any construction firm unique. While construction a new transmission line, it is good to spend minimal but also build the best that can withstand pressures and vibrations
ConclusionThe importance of electrical power to human can not be over emphasized. Hence, electrical power is generated,transmitted, distributed and utilized, this forms a complete cycle of electrical power flow . This cycle is achieved through power system . All the stages of the cycle are important.
References* [Electrical power generation](https://en.wikipedia.org/wiki/Electricity_generation)
* [Electrical power transmission](http://edisontechcenter.org/Transmission.html)
* [Electrical power distribution](https://en.wikipedia.org/wiki/Electric_power_distribution)
* [Enviromental effect of transmssion lines](https://www.fingrid.fi/en/grid/land-use-and-environment/environmental-impacts-of-transmission-lines/)
* [Over head power line](https://en.wikipedia.org/wiki/Overhead_power_line)
* [The purpose of insulators in transmission line](https://www.quora.com/Why-is-an-insulator-used-in-a-transmission-line)
* [conductors used in transmssion line](http://www.electricalpowerenergy.com/2014/02/11/types-of-conductors-use-for-transmission-line/)
* [Composite conductor, strand and bundled conductor](https://engineeringtutorial.com/difference-solid-conductor-stranded-conductor/)