Diagnostics of transformer oil by elastic waves

Abstract

In the diagnostics of oil-immersed transformers, a chemical analysis of generated gases in the oil is generally performed, evaluating the kinds of gases and their quantities. This method, however, involves numerous procedures and is difficult to use in the field to diagnose the deterioration of oil. Considering the current state of the advanced information society, no deterioration in power apparatus should be permitted and the diagnosis of deterioration must be performed reliably while the equipment is energized. Therefore, we attempted to diagnose insulation oil based on analyses of elastic waves produced by a pulse discharge in the oil. This technique uses the behavior of elastic waves in liquid, in which an incident wave causes a high-frequency oscillation component with increasing gas content. In this investigation, elastic waves were detected on the outside surface of an oil tank at gas concentrations of 0 to 10%. The detected waves were analyzed by the fast Fourier transform. It was found that frequency spectra of 400 to 1000 kHz were increasingly evident when the gas concentration in oil was higher than ∼5%. This indicates that our new technique is useful for the diagnostics of oil-immersed transformers using the oscillation behavior of elastic waves produced by bubbles in oil. © 2001 Scripta Technica, Electr Eng Jpn, 135(1): 1–7, 2001