What is Transmission line?Large Generating station are used fir the economical power generation. Recently capacities of generating set have gone up.Generating set in the range of 10 MW ,210 MW and 500 MW are manufactured in the world .generating station are obviously located at the sites where water and other resources are available and sufficient head are available .A vast network of transmission system has been created so that power generated at one station may fed to grid system and may be distributed over large areas.The Transmission and distribution system comprises a network of three –phase circuit with transforming and switching substation at various junctions
Various Generating station are interconnected .The benefit or advantages of interconnection are
- Its reduced the number of spare plant required as one station can assist the other at the time of emergency.
- At the time of light load one station can shutdown which effect the operational cost of generating station
High voltage of the order of 66kv ,132kv ,220kv and 400kv are used for transmitting power by 3 phase 3 wire overhead system
The primary voltage is reduce to low values of the order of 3.3kv,11kv.or 33kv for secondary transmission .
The transmission line terminated at large main substation from which the power is distributed to small secondary substation which is located all over the load areas .The voltage of primary distribution may be 11kv to 132kv
The network is laid along the street, localities and the consumer areas. From these secondary distribution line connection are provided for individual .For this purpose 3 phase ,4 wire ,440v/220v circuit are used from which 3 phase 440v or single phase 220v power supply may be provided to the consumers.
Classification of Overhead Lines
1-Short Transmission Line
When the length of the overhead transmission line is up to 50 km and the line voltage is less than 20kv ,it is known as short transmission line .The Capacitive effect of short transmission line is neglected due to small length and low voltages. Thus resistance and inductance are the major parameter which is considered for these lines .
2-Medium Transmission Lines
When the lenth of overhead transmission line are 50 km to 150 km and the voltage range is 20 kv to 100 kv , it is known as medium transmission line .Due to sufficient length and voltages of the line ,the capacitive effect are considered .
3-Long transmission Lines
These are more than 150 km in length and carry voltage more than 100kv.
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