Def. – A transmission line basically consists of 2 or more
parallel conductors used to connect a source to a load.
What is a transmission line?
•Uniform transmission line is one which has its electrical
parameters remaining constant along its length of the line.
•In which voltage to current ratio does not vary with distance
if the line is terminated in its characteristics impedance.
•Electrical parameters of lines are R-L-C-G (ResistanceInductance-Capacitance-Conductance).
•These parameters are defined per unit length of the conductor
and are called Primary constants of the line.
Uses of Transmission lines:-
•To transfer the energy or signal or power from the
transmitter to the receiver.
•It acts as communication media.
•In most cases, transmission lines are metallic
•Few e.g. of Transmission lines are: Parallel wires
Twisted pair wires
REASONS FOR AC GENERATION AND TRANSMISSION
Due to ease of transformation of voltage levels and rough collector
cage motors, ALTERNATING CURRENT is universally utilised.
Both for GENERATION and LOADS and hence for
Generators are at distant places, away from the populated areas i.e.
the load centers
They are either PIT HEAD THERMAL or HYDEL
Turbines drive synchronous generators giving an output at 15-25
To reach the loads at homes/industry at required safe levels,
transformers step down voltage.
COMPARISION OF HVAC & HVDC SYSTEMS
– CONVENTIONALLY POWER TRANSMISSION IS EFFECTED THROUGH HVAC
SYSTEMS ALL OVER THE WORLD.
– HVAC TRANSMISSION IS HAVING SEVER LIMITATIONS LIKE LINE LENGTH ,
UNCONTROLLED POWER FLOW, OVER/LOW VOLTAGES DURING LIGHTLY /
OVER LOADED CONDITIONS,STABILITY PROBLEMS,FAULT ISOLATION ETC
– CONSIDERING THE DISADVANTAGES OF HVAC SYSTEM AND THE ADVANTAGES
OF HVDC TRANSMISSION , POWERGRID HAS CHOOSEN HVDC TRANSMISSION
FOR TRANSFERRING 2000 MW FROM ER TO SR
ADVANTAGES OF HVDC OVER HVAC
COST: AC vs DC Transmission
Line Cost AC
Line Cost DC
Terminal Cost DC
Terminal Cost AC
Break Even Distance
HVDC IN INDIA
HVDC LINK CONNECTING CAPACITY
North – West
2 x 250
West – South
2 x 500
Vizag – I
East – South
East – North
Vizag – II
East – South
USE OF DC
Direct current is put to use in common life for driving our
portable devices, UPSs, battery systems and vastly in railway
DC AS A MEANS OF TRANSMISSION
This has been possible with beginning of
High power/ high current capability thyristor.
Fast acting computerized controls
If DC is required to be used for transmission
since our primary source of power is A.C,
The following are three basic steps:1. Convert AC into DC (rectifier)
2. Transmit DC
3. Convert DC into AC ( inverter)