A New Low-Liquid-Content Current Transformer [includes discussion

Abstract

The importance of continuity of service in modern power systems demands that current transformers for operation of meters and control devices be properly applied and designed to give high accuracy, trouble-free operation, and long life. Unlike most other types of apparatus, current transformers have negligible reactance to limit short-circuit currents and therefore are occasionally subjected to exceedingly high overcurrents. Under such conditions, an internal failure may result in excessively high pressures within a fraction of a cycle. Improved materials, new manufacturing and testing techniques, and novel features of design are utilized in a new liquid-filled current transformer to meet these exacting requirements. The new transformer is designed to be stronger mechanically than previous models, in addition to having high metering accuracy, improved sealing against entrance of moisture, and higher corona-starting voltages. One of the features of this design is its ability to relieve excessive internal pressure, should it occur. This feature is so combined with other component parts of the transformer that they mutually co-operate to insulate, to hold mechanically in position, to reduce expansion, and to relieve excessive pressure.