There is considerable experience on 500/600 kV dc system available world wide and lot of learning's are also available now during development and recent operation of 800 kV dc system. During 1970's and 80's, anticipating the next stage of high power HVDC transmission, considerable studies and field tests pertaining to Corona Studies, Insulation System Insulator Pollution Tests etc was taken up by EPRI/other international institutions up to ±1200kV dc system. However, due to saturation of load growth, further Research and Development in Ultra High Voltage (UHV) area were slowed down or virtually stopped. With high surge of Energy requirement of geographically large countries coupled with large population and steep economic development in countries like China, India, Brazil and Africa etc, the situation has changed and these developing countries have shown high interest for harnessing remote hydro resources. This necessitates large transmission systems with UHV dc and ac to transmit large block of power to a distant load centre. It is afact that dc phenomena is complex and different than UHVac in regard to it's pollution performance, reliability of converter transformers, harmonics, ground return mode operation etc. The existing knowledge of electrical withstand in air, oil and other materials for voltages 2000–3000 kV is not enough neither for AC, DC, lightning or switching impulse, particularly not at high altitudes(2000–4000 m) where some of the future potential transmissions are going to be built However, thanks to the ongoing development of better insulating materials for pollution, super thermal upgraded papers for transformer insulation, better quality transformer oils, split air core reactors, high energy capability surge arrestors and technology up gradation in civil engineering for cheaper in door switch yard etc which may facilitate 1000 kV development.
