Tennessee Valley Authority's 500-kY System - Step-Down Substation Design

The determining factor, used by the Tennessee Valley Authority, in selecting the insulating system for extra-high-voltage (EHV) substations, is the long-duration switching surge. investment in lines and substations makes outages for maintenance economically undesirable; consequently, TVA has designed its stations so that some changes and maintenance can be performed while the equipment is energized. Employment of vertical reach switches is a TVA design feature, which provides an arrangement whereby mechanical equipment can be used to repair breakers and disconnect switches without outage time. The ring bus switching scheme is applicable except in cases where more than three lines and one bank are likely to be involved; then, the main and transfer scheme is adopted.