Generation, Transmission and Distribution of Electric Power
Q. Line Diagram of Generation, Transmission and Distribution of Electric Power.
Introduction :
- In the beginning of 19th century, the use of electrical power was limited. Due to little demand, small power stations were built to supply simple lighting and heater load. And these power stations were built near the load. So transmission of electricity was restricted to small distances.
- Later on in the beginning of 20th century, widespread of electrical power necessitated to produce bulk electrical power.
- The big power stations were located at suitable site. For example, hydro power plant is located where ample storage of water is available.
- Thermal power plant is located where sufficient supply of coal alongwith transport facility is available.
- Thus, the necessity of long transmission line arised because now the big power stations may not be near the load.
- The electricity from generating stations is to be brought to the consumers through conductors. And the system through which it is brought is called transmission and distribution system.
Single Line Diagram of A.C. Power Supply Scheme
- The electrical power produced in generating station is transmitted over large distance through transmission lines. Then it is distributed to various consumers through a distribution network.
- Various stages are involved in between, in which this power is processed and sent further.
- A typical single line diagram of AC power supply scheme is shown in Figure A.
- Standard transmission voltages are 132 kV, 220 kV, 400 kV.
- This diagram gives a general idea about supply system.
Various Stages and Standard Voltage Levels
The various stages and standard voltage levels :
Generating Station : Power is generated at generating stations at 11 kV voltage level. (It may be 3.3 kv, 6.6 kV, 11 kV or 33 kV in some cases.) It is stepped upto 110 kV, 132 kV or 220 kV or 400 kV for primary transmission purpose. 3-phase stepup transformer is used to stepup the voltage. The advantage of transmitting power at high voltage are reduction in size of conductor, better performance of transmia process. The highest transmission voltage in India is 400 kV.
Main Classification : (1) Primary Transmission and (2) Secondary Transmission
- Primary Transmission : Power at high voltage i.e. 132 kV or 220 kV or 400 kV is transmitted by means primary transmission lines. It is 3-phase 3-wire system (overhead tower lines).
- Secondary Transmission : At receiving station the voltage is stepped down from 132 kV to 33 kV or 66 kV by means of step down transformer. From receiving station, electric power is transmitted to substation located at particular points in the city. The overhead 3-phase 3-wire system (tower line or iron poles) is used for this.
- Primary Distribution : The secondary transmission line terminates at receiving station where the voltage is stepped down to 11 kV or 6.6 kV or 3.3 kV by step down transformer and these 11 kV lines run along road sides of city or steel poles.
- Secondary Distribution : The distribution substations are located at consumer’s premises where voltage of 11 kV is stepped down to 4.5 volt (3-phase 4-wire) for secondary distribution. The advantages of using 3-phase 4-wire system (R, Y, B, N) are that both 3-phase and 1-phase supply can be used depending upon the load. Service lines are taken off from this line.