Recent Trends in Emerging 765kV/800kV Power Transformers

Abstract

Bulk power transmission economically over long distances requires upgradation of transmission line voltage from existing 400kV to 765kV EHV (Extra High voltage AC) or 800 kV HVDC (High Voltage DC). This requires large size power transformers with capacity to handle EHV/UHV voltages. The specific modifications are therefore required in procedures of design, manufacturing, testing and site activities of 765kV/800kV transformers in comparison to procedures being practiced for 400kV transformers. Because of massive size and complicated design of such transformers, the modified procedures require consideration of appropriate material, manufacturing process, and benchmarking of on-site Erection & Commissioning (E&C) and Operation & Maintenance (O&M) practices for enhanced reliability. The present paper is unique and useful in the Indian context with the commissioning of 765kV Sipat-Seoni and 800kV Agra-North East lines and recent government emphasis to extend these lines farther. The paper, in addition to have discussion on some aspects of material, manufacturing & design, also brings out results of recent testing of equipment at site during installation & commissioning or while in-service.