Mehdi Moallem - Isfahan University of Technology

The persistant rapid growth in electricity consumptio n has been accompanid by an increare in the capacity and voltage of transmission lines. The reason for bulk transmission falls under several headings , each of which has a separate economical justification . Generally it is necessary to show that electricity transmission is cheaper than any other alternative . A saying in fuel costs results from the location of a generating plant at a source of cheap fuel such as coal mines or oil refinery . The cost of transmission must be less then the cost of fuel transportation. Natural resource exploitaion is the other reason for using long transmission lines. Finally , enviromental constraints restricts possible siting of thermal plants. For the reason cited above and the benefits of an interconnected power system,long EHV transmission lines are always necessary for transferring of power. Because of the technical problems with long EHV AC transmission lines and advent of high power switching devices,HVDC has been considerd for the transmission of electrical energy. This paper reviews the present status of HVDC transmission and its recent growth , the technical advantages of HVDC transmission over EHV lines will be discussed later and finally a method for deducing the cost of a HVDC line from the cost of a known EHV line is presented.