A method for calculating disconnector contact availability as a function of thermography inspection intervals and load current

摘要

This paper presents a practical method of quantifying and evaluating changes to existing thermography inspection schemes for disconnector contacts. The inspection interval availability is used to calculate disconnector contact average maintenance costs. Any changes to existing thermography schemes regarding load or inspection intervals are subsequently evaluated using these maintenance costs.rnThe proposed method is illustrated by a case study of three disconnectors in the Swedish 400-220kV transmission system. The three disconnectors represent different typical load characteristics. The result of the case study was that the new thermography inspection scheme would reduce the total average maintenance cost by a third, for the three disconnectors. In the study, the large reduction in maintenance cost was due to the specific load characteristics of the disconnectors. When applying the method to a larger disconnector population the cost reduction would depend on the actual loading characteristics of all disconnectors. The aim of the case study is to illustrate the usefulness of the proposed method when it comes to quantifying the effect of changes in thermography inspection schemes.rnThe only failure mode considered in this paper is contact over-heating. A disconnector contact that is found to be failed is assumed to be replaced by a new identical contact. Since the exact time of a hidden failure is unknown, the exponential distribution is used for the time to failure in order to adapt the model to the amount of information available to the network owner.rnThe proposed method provides a practical tool to quantify and evaluate the effect of different changes to the inspection scheme with respect to maintenance costs and availability.