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What are the three major components of Electrical Power System?
The function of an electrical power system is to connect the power generating station to a large number of consumers by means of interconnected system of transmission and distribution networks.
Therefore, a typical electrical power system has three main parts, viz. −
The power generating station,
The transmission systems, and
The distribution systems.
The transmission system is the connecting link between the power generating station and the distribution system, while the distribution system is the connecting link between the consumer’s loads and the transmission systems.
The following figure shows a single-line diagram or one-line diagram of a simple electric power system.
Generally, the power generating station consists of two or more 3-phase alternators operated in parallel. Because of some technical reasons, the generation voltage usually is in the range of 11 kV to 25 kV. Generally, the power generating plants are located quite away from the load centres. Due to economic reasons, the electric power has to be transmitted through the transmission lines at a very high voltage.
Therefore, at the power generating station, the generated voltage is stepped up to a high value (say 132 kV) with the help of a step-up transformer. Then, the electric power is carried by the transmission lines at this high voltage.
At the outskirts of the city (also called transmission sub-station), the voltage is reduced to low value (say 11 kV) with the help of a step-down transformer.
Now, the feeder carries the electric power to the distribution sub-stations. At the distribution sub-station, the voltage is further reduced to 440 V with the help of a step-down transformer. Here, the voltage between two lines, also called line voltage, is 440 V while the voltage between any one line and neutral, called phase voltage, is 230 V. Finally, the distributers are employed to supply power to various consumers.
Points to Note
The important points about the structure of electric power systems are as follows −
For the sake of simplicity, the 3-phase electrical system is represented by a single-line diagram.
The 3-phase alternators at the power station are designed to produce balanced three phase supply. Because the single phase supply can easily be obtained from a three-phase system by using one of the three lines and the neutral. Actually, it is necessary to show the three phases and the neutral when drawing a diagram of the circuit. However, in order to simplify the diagram, the neutral wire is omitted and the circuit components are represented by their standard symbols instead of their equivalent circuits. Such a simplified diagram of an electrical power system is called the single line diagram or one-line diagram.
In an actual electrical power system, there are also various protective devices such as fuses, circuit breakers, etc. Thus, the information included in the single line diagram depends on the purpose for which the diagram is drawn.
The power demanded by the consumers is supplied by the power station through the transmission and distribution systems. When the power demanded by the consumers change, the power supplied by the power station changes accordingly.
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