Online acoustic PD-measurements of oil/paper-insulated transformers- methods and results

Abstract: Online acoustic PD measurement methods have the benefit that electrical disturbances like broadcasting stations or corona have little or no influence and a PD detection can be managed by one sensor. However, a fundamental understanding and knowledge of the whole acoustical transmission system of the transformer is needed. Beside the mechanical disturbances on site, found in or at the transformer itself, such as 50 Hz components, magnetostriction or external loose parts, also the mechanics of the tank have to be considered in a modal analysis. The adaptation of the sensors and hardware on the various propagation paths in the insulating system, determining the signal damping, is the basis for sensitive capturing of PD signals. With the aid of sophisticated digital signal processing algorithms, like the newly developed “FFT2D”, a detection and more important a distinction between mechanical disturbances and PD`s can be reached easily. Comparisons to other signal processing techniques show the improvement in the ability of PD recognition. The resulting sensitivity on site is furthermore demonstrated using recent online-measurements of various oil/paper insulated devices. Several examples of measurements on transformers will be discussed. 1