Representation of Transmission Line
A conductive line which is used for the transmission f the electrical power from one place to the another place is known as transmission line.Electrical power is generated in power station. By using transmission line we can deliver that gendered power to the load.Flow of power from the power station to the main distribution station is called the transmission network.
Conductor is used to the transmit the electrical power from one place to the another place. That conductor has its internal resistance and reactance. Same as generator is used for generate the energy. Generator has resistance and reactance.Hence the generator and the conductor line both are connected in series and represented by an impedance. Generator impedance is connected in series with the generated emf of each phase.
Fig shows the three phase star connected generator connected with a three phase balanced star connected load through the conductive transmission line.
Current is flowing through all phases, the sum of the all current in balanced three phase system is zero. It means that the current passing through the conductor between the neutral of the system and star point of load is zero.So the tree phase system can be analyzed based on single phase.
Fig shows the equivalent circuit of single phase representation of line.
Classification of Transmission line:-
Transmission line is classified in three ways,
Short transmission line :-
Length of these line is less then 80km and operating voltage is less or equal then 11kv.
Performance of this line is depending upon the resistance and inductance only. Because due to low distance and low voltage capacitance effect is negligible.
Medium transmission line:-
Length of these line is between 80km and 240km and the operating voltage is between 11kv and 66kv. Due to sufficient voltage of line and length, charging current is applicable and therefore capacitance effect can be considered.
Long transmission line:-
If the transmission line has length above 240km and line voltage is above 66kv are considered as the long transmission Line. Line constants are considered uniformly distributed over entire length of line.
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