Abstract: Insulators for ultra-high voltage direct current (800 kV UHVDC) transmission line should meet the dual requirement of withstanding a peak high voltage defined by the nominal system voltage without flashover as well as sustain the mechanical load derived from the conductor. Generally the insulator suffers damage due to simultaneous action of mechanical load arising out of heavy wind, lightning, power arc and electrical switching surge current. Although the line losses are minimized while the transmission cost goes down in 800 kV DC line, pollution performance of the insulator assumes a decisive role due to fixed grid polarity. It is overcome by improvement in the shed profile, shape and size of insulator. Based on the experience of 500 kV DC grid, state-owned Powergrid used ball and socket type porcelain insulator for 800 kV Chiriapalli Agra, India (U)HVDC line. Cigre however recommends composite insulator made with epoxy-glass core with silicone rubber sheds which is found to have superior pollution performance initially due to intrinsic hydrophobicity that diminished in field over a period of time. In contrast puncture-proof porcelain longrod insulators provide an excellent hassle-free service with 3-5 fold increase in life. Additionally hydrophobic glaze can provide superior pollution performance over the entire life period. In this study we propose our design concepts and discuss the controls required on material and processing so as to prevent early aging of the porcelain longrod insulator in (U)HVDC.

Keywords: HVDC, Insulator, porcelain, polymer, longrod, Pollution, Electro-mechanical, Strength, Vibration, Aging.