A Study on Condition Assessment Method of Gas-Insulated Switchgear. Part II. Influence of Moisture in the SF_6, Detection of a Partial Discharge on a Spacer, Repetition Discharge and Overheating by Incomplete Contact

摘要

Rationalization of the maintenance of gas-insulated equipment under operation and lifetime extension based on the results of appropriate diagnosis are necessary to reduce the cost of gas-insulated equipment. Therefore, condition-based maintenance (CBM) is required and accurate methods for observing the inside of equipment are important. In this report, we describe a diagnosis method that can be used for actual gas-insulated equipment, such as to assess the deterioration of the spacers made of epoxy resin and to detect loose connections in the central conductor. The principal results are summarized as follows: (1) The quantity of decomposition gases depends on the moisture and magnitude of the partial discharge. However, decomposition gases were detected even if SF_6 had low moisture content (less than 100 ppm) similar to that used in actual equipment. This means that our method can be applied to actual equipment. (2) It became clear that CF_4 is a typical gas generated by partial discharge on the spacer surface. Therefore, it is possible to diagnose spacer deterioration by monitoring CF_4. (3) Decomposition gases (SF_4, SO_2, SO_4, SO_2F_2) were generated by impulse breakdown, which was assumed to be due to repetition discharge caused by insulation failure and loose connections. (4) SF_6 gas was assumed to be exposed to a loose connection and was heated from room temperature to 800℃, and the generated decomposition gases were analyzed by FTIR in real time. As a result, the decomposition gases were generated at temperatures above approximately 500℃ in a heating time of 1.5 minutes. Therefore, a loose connection can be detected by analyzing the decomposition gas.