Transformers for interconnecting high-voltage transmission systems: For feeding synchronous condensers from a tertiary winding

Owing to the advantages to be realized from the use of the star-star connection in interconnecting high-voltage transmission systems and from the fact that this connection requires the use of an auxiliary winding connected in delta to stabilize the neutral point or to decrease the inductance in the ground connection, a great majority of the transformers designed for interconnecting transmission lines are three-winding transformers. Another type of transformer which would be included in this general class would be that having an auxiliary winding for feeding a synchronous condenser used in controlling the voltage at the receiver end of the line. Many of the alternatives such as the choice between self-cooling or water-cooling, or between single-phase units and three-phase units, differ in no way from the same questions on transformers for ordinary service. However, there are a number of important features peculiar to three-winding transformers for these classes of service that complicate the design and operation to an extent that justifies special consideration of these problems. This paper will call attention to these special problems and indicate the way in which the design and performance of transformers for these classes of service are influenced by them.