A measurement system for the on-line diagnostics of power transformer bushings

Several studies highlight that power transformer bushings are among the least reliable components in power systems. Furthermore, bushing failures are responsible for a very significant number of transformer breakdowns. This encouraged the research on continuous monitoring systems allowing the detection of incipient faults and thus the implementation of Condition Based Maintenance (CBM) techniques to power transformer bushings. Many on-line diagnostic techniques can be found in literature; however most part of them suffers from some limitations or high complexity. The authors have previously proposed a novel method allowing the early fault detection through the superimposition of a high frequency signal across the bushing tap and ground. In this paper it will be shown how this monitoring technique can be implemented. A prototype has been developed and its measurement performance has been evaluated.