Critical Design Aspects for Reliability of 1200 kV UHV AC Capacitor Voltage Transformer under Severe System Conditions

摘要

Indian Power system is expanding at an accelerated pace due to rapid industrialization. The PlanningCommission projections indicated 3 times increase in peak demand by 2021-22. Power generatingunits are being installed more and more at remote places due to unevenly distributed energy sources inthe country. Right of Way, High Transmission losses, economical transmission of bulk power overlong distances etc are the main factors for considering the up-gradation of existing transmissionsystem voltage in a country like India having dense population. 1200 kV is considered as the nextlevel transmission voltage to overcome the above challenges. [1]Capacitor Voltage Transformer (CVT) is used in the power system for measurement of voltage,protection of Bus Bar against over voltage and PLCC (Power Line Carrier Communication)application. It is one of the most complicated equipment in the switchyard because of its sensitivity tothe system transients. This paper discusses the critical design aspects of a reliable CVT considering thesystem severity and all system transient conditions like ferroresonance, Electrostatic field distribution,Air saturation at high switching transient voltages, Corona Suppression etc. This paper also illustratesthe anticipated problems for reliable operation of the equipment and recommendations to overcomethese problems. Some of the unique features of 1200 kV CVT discussed in this paper are internal andexternal design of Capacitor voltage divider, various methods of ferroresonance damping and themethod adopted in 1200 kV CVT, electrostatic field distribution and design of corona shields.Apart from the above unique features, the 1200 kV CVT has to withstand many system transients inthe system which can affect its performance. As the solid state relays are used, the CVT has tofaithfully reproduce the changes on the primary voltage but this is also the time at which transients areproduced in the systems. The CVT needs to be designed to take care of these transients, so that muchsuperior transient response is guaranteed.Finally the approach for successful development and testing of 1200 kV Capacitor VoltageTransformer is illustrated in this paper.