Proceedings PaperHigh-voltage switchyard thermography case study
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Many electric utilities invoke a double breaker/double bus (DB/DB) arrangement in their generating plant switchyards. The sketch in this paper shows one line with one load for one phase of the DB/DB configuration. A switchyard will have three such configurations, one for each phase, plus several line inputs and several load outputs. This arrangement provides redundancy and flexibility, facilitating maintenance work and enhancing reliability. The focus of this paper is what happens when one side of the DB/DB has a phase with a hot spot. The hot spot could be the switch disconnect, a hinge, bolted plate or other connection. The heating is due to increased electrical resistance caused by bad electrical contact. A strength of the DB/DB system is that, in theory, a resistive contact will not overheat as the current follows the path of least resistance and will travel through the other bus. That is, for two resistors in parallel, the current is inversely proportional to the resistance in each leg. Thus, the only time there would be a problem is if a given phase had resistive contacts on both buses, or if the 'good' side was removed from service. Imagine our surprise, then, when we found with thermography a hinge on a switch disconnect with a 121 degrees C rise. A survey of the parallel bus revealed no problems. This paper is an analysis of this actual situation. We use a simple model with empirical measurements .