This month’s Featured Technical Paper is from the Proceedings of the 2018 International Conference of Doble Clients. The paper is titled: Field Diagnostics for Bad Transformer Bushing without Test Tap.
This paper discusses the use of field diagnostic techniques to rapidly locate a fault in a power transformer after it tripped out of service by a differential protection relay. These diagnostic techniques and methods involved the insulation Power Factor, Hot-Collar, Cross-Check, Sweep Frequency Response Analysis (SFRA) tests, and a visual inspection. The insulation power factor test shows clearly a ground fault on LV winding equipped with bushings with no test taps. The challenging tasks of the owner were to determine whether the fault occurred in the winding or in one of the bushings. This information is critical for guiding an action plan and the scope of repair. The use of field diagnostic techniques led to a complete understanding of the health and operational status of the failed unit and allowed to pinpoint the fault location to a LV bushing and to quickly return the unit to service. The paper also describes the data analysis and the correlation between the tests in order to identify the failed bushing.
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