DC POWER TRANSMISSION TECHNOLOGY

InTrOduCtIoN :

                        The industrial growth of a nation increased consumption of energy , particularly electrical energy. this has led to increase in the generation and transmission facilities to meet the increasing demand.In U.S.A, till the early seventies,the demand doubled every ten years.in developing countries,like india , the demand doubles every seven years which requires considerable investment in electric power sector. 

                     The Imperative of supplying energy at reasonable costs coupled which the depleting re-serves of non - renewable energy sources has led to the establishment of remote generating stations - predominantly fossil-fuel fired thermal stations at pit head . Environmental considerations also some times dictate the sitting of power stations at remote locations . Large hydro stations are invariably at distances of hundred of kilometers from load centers . The need to economize on costly investments in generations reserves , sharing of benefits in utilizing variability in generation mixes and load patterns have given rise to inter connection of neighbouring systems and development of large power grids .

             The HDVC transmission made a modest beginning in 1954 when a 100 KV,  20MW DC link was established between Swedish main land and the island of Gotland.Until 1970,the converters stations utilised mercury arc valves for rectification. the successful use of thyristors for power control in industrial devices encouraged its adoption in device rating is now in the range of 5 kv , 3000A. 
          The relative merits of AC and DC transmission  are reviewed in the next section.