Effects of Reduced Fault Duration Upon Power System Components: A Study of the Feasibility of a Greatly Simplified Alternative to the Fault Current Limiter. Final Report

摘要

Practical means are needed to extend the fault current capacity of transmission substations. Since industry efforts to develop a true fault current limiting device have encountered serious technical and economic problems, a simpler solution is sought. In this report, the current concept of a protective scheme based upon fault limitation after the first current loop is formulated and examined in some detail as a viable alternative. Quantitative information from utilities and workshops has been compiled on both the industry needs and on the characteristics of actual fault currents. Consensus has been obtained on criteria for an acceptable protective scheme. . A test program has evaluated the ability of diverse contact structures to handle currents in excess of rating. The information learned to date is summarized and a specific 69KV application of the concept is considered in some detail. The present assessment suggests that 160% of rating will meet the needs and is attainable provided that appropriate back-up protection can be devised. This conclusion is based upon the statistical nature of fault characteristics; the practicality of limiting severe faults to a single current loop; and upon characteristics of the substation equipment. It is shown that the likelihood of subjecting circuit breakers to instantaneous currents in excess of close and latch rating is exceptionally rare. Tests have demonstrated the ability of circuit breakers with multiple finger contact structures to accommodate this duty without any difficulty. Approximate, analytical methods have been devised to assist in the rational identification of systems to which the proposed protection scheme can be applied. It is recommended that future efforts involve in depth studies of specific potential applications with cooperating utilities, and the development of adequate back-up protection procedures. (ERA citation 08:014688)