The Evolution fo Standard Lines of Current Transformers for High Overcurrent Capacity

Modern switchgear requires, more and more frequently, special current transformers capable of carrying very high fault currents. In the past, the application engineer and the design engineer were not always close together in their work on the current-transformer problem; the application engineer has often had only an approximate idea of what the design engineer could produce, while the design engineer has had only an approximate idea as to general application requirements. The design engineer has not had too sound a basis for many of his designs. His costs were high on account of the multiplicity of special designs. This paper discusses the basis of design of current transformers for high overcurrents, and describes the co-ordination of mechanical parts with performance requirements to produce lines of current transformers in a definite and easily understood pattern of characteristics. The result is that selection of the proper current transformer is easily accomplished. The arrangement of the line of mechanical parts and performance characteristics is such that the expense involved in manufacturing these special transformers can be considerably reduced.