Bushing Current Transformers for Oil Circuit Breakers [includes discussion]

A new line of improved bushing current transformers for modern oil circuit breakers has been developed incorporating increased knowledge in materials, manufacturing techniques, and construction methods. In the advancement of circuit breaker designs to meet the growing requirements of industry, the design of bushing current transformers has likewise been advanced to meet the demand for improved performance characteristics and for better construction features. This paper outlines the objectives established to guide the development program and describes the new line of bushing current transformers. Distributed windings and moisture resistant materials are the important new features of the transformers. A high degree of resistance to mechanical damage has been provided and impregnation processes have been eliminated. The new transformers are designed to meet American Standards Association (ASA) standards for multiratio transformers for class-L relaying accuracy. The performance characteristics and construction features have been proved by an extensive test program.