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POWER TRANSMISSION:
Transmission means transmitting process of something from one place to another. Similarly electrical power transmission is nothing but the process of electrical power transmitting from one place to another. Generally in electrical power transmission, it transmits electrical power from generating station to different load centers.

So, the first question is why generating station situated away from load centers?
Because there are several factors to be considered for constructing a generating station. There are several types of generating station are available. Main types are thermal power station, hydro power station and nuclear power station. The factors are:
(i) In case of thermal power plant, easy availability of water is primary requirement.
(ii) As thermal power station require huge area, so huge amount of land also required.
(iii) Availability of fuel as well as transporting of fuel is also a key factor in thermal station.
(iv) As pollution should be considered, power station should situate away from populated area.
(v) In hydro power plant, a river with dam is primary requirement. So proper place of river is needed to construct a dam.
(vi) In nuclear station, it should be situated far away from locality due to minimize health effect from nuclear reaction.
(vii) Heavy electrical requirement also required to construct a power station. So train and road communication should be good.
(viii) All points should be considered under economical point of view.
Besides these, there are several points which indicate the power station normally situated away from the locality as well as load centers.

How electric power transmits?
Generally the electric power generated at power station in low voltage level. This low voltage power then stepped up to high voltage level and transmitted. Again in receiving end the high voltage power stepped down to low voltage at desired level and distributed to different distribution sub-station as well as consumers.
Here a question is arising that why electric power is generated at low voltage level?
The generation of electric power at low voltage level is quite economical. In case of low voltage level the size and weight of alternator is less than high voltage level as well as much less insulation is required as low voltage require less insulation. So power generation at low voltage is cheaper than high voltage power generation. Normally generation voltages are around 11 to 33 KV.

Why low voltage electrical power is not transmitted to load center?
In case of power transmission if voltage becomes low, the current should increase as the power is the product of voltage and current. So if current increases ohmic loss that is I2R loss also increases. With increasing current, the cross section of the conductor should also increase which have greater monetary value. The regulation of transmission system decreases with increasing current. These are the main cause for which electrical power transmission is not economical at low voltage level.

Are there any limitations of high transmission voltage?
In case of high transmission voltage, higher insulation of conductor also required which increases the cost of conductor. Also cost of transformer, switch-gear and other terminal apparatus also increased. But still high voltage transmission is economical because of saving in cost of conductor material.

Why in distribution line, low and medium voltages are used?
At consumer level the voltage level is 415 volt (line to line) but in transmission line, voltage is nearly 132 kilo volt or more. So it is tough to step down voltage from 132 kilo volt to 415 volt by step down transformer. Beside these high voltage lines are also risky in heavy populated area. In distribution voltage stepped down to 33 or 11 kilo volt and distributed through distribution sub-station, which also stepped down by distribution transformer at 415 volt to consumer end. It carries higher current but as the distance between two distributions transformers are not long, conductor resistance is not high, so power loss is low.

Transmission network:
As per previous discussion, we can conclude that electrical energy generated from a generating plant and transmitted to an electrical substation. The whole interconnected lines for transmitting energy from power plant to substation are called transmission network.
These transmission networks sometimes called grid. In India, Malaysia, U.K this grid is known as national grid or power grid. In combination of transmission and distribution is known as power grid in North America.
On previous day electrical generation, transmission and distribution were under same company but now in maximum countries, transmission and distribution companies are separated and doing business separately.

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