12-12-2012, 01:13 PM
HVDC TRANSMISSION SYSTEM
HVDC SYSTEM.ppt (Size: 694.5 KB / Downloads: 227)
INTRODUCTION
Now a days large blocks of power are needed to be transmitted.
There arises some technical problems of transmitting power to such a long distance using ac.
In the view of the draw backs of ac the HVDC transmission has come into picture.
The first dc link was set up in 1954 in between Swedish main land and the island of Gotland.
The use of an HVDC link in an ac system requires converter stations at each end of the line.
HISTORY
IN the initial stages dc used to be employed for generation ,transmission and distribution of electric power. The first 110V D C central electric station was installed by Edison in New York in1882.with the introduction of transformer and 3-phase ac system the situation changed in favors of ac .
But the supporters of DC carried out extensive research on dc field And found the advantages of dc in high and extra high voltage of transmission for long distance .
HVDC Transmission has also been introduced in India .A +-500kv ,1500mw,810km bipolar HVDC line has already been set up between Rihand and Delhi. it is designed to operate in bipolar ,monopolar ground return ,and Monopolar metallic return mode.
Vindhyachal HVDC back to back system for exchanging power between northern and western region in either direction .
PRINCIPLE OF OPERATION OF HVDC LINE
It required two ac system which are to be connected by dc link.
Step-up transformer at sending end and step-down transformer at receiving end.
Two Converter station one at sending end for converting ac to dc and other at receiving end for converting dc to ac.
By changing the firing angle it act as rectifier(0 to 90) deg. And inverter (90 to 180)deg. .so it can operate in bidirectional flow of power.
The dc out-put voltage magnitude can be controlled by changing the firing angle of the converter.
Economic advantages
DC lines and cables are cheaper than ac lines or cables.
The towers of the dc lines are narrower, simpler and cheaper compared to the towers of the ac lines.
Line losses in a dc line are lower than the losses in an ac lines.