Dielectric response of oil-impregnated paper by utilizing lightning and switching transients

On-line monitoring of insulation systems in power components such as power transformer bushings has significant value for their reliability. Dielectric spectroscopy is known as a powerful tool in condition assessment of power components´ solid insulation. However, it is difficult to apply it on-line. Therefore, a new approach of intended use for on-line diagnosis of oil-impregnated paper, as a major insulation component of power transformers and bushings, is presented. In this technique, natural transients such as lightning and switching impulses are used as stimuli for on-line dielectric response measurements. The wide frequency range of these transients is their advantage as stimuli for dielectric spectroscopy. The influence of moisture content and temperature on the dielectric response of oil-impregnated paper has been investigated for performance evaluation of the proposed technique. It is shown that this technique can track the changes caused by moisture content and temperature in the dielectric response of oil-impregnated paper. The results of both low and high voltage study cases have been verified by comparison with Frequency Domain Spectroscopy (FDS). According to the well-matched results with FDS, the proposed technique can offer a valuable approach for frequent monitoring of dielectric properties of oil-impregnated paper insulated systems such as those commonly encountered in power transformer bushings. However, the validity range of the results depends on the bandwidth of the applied transients and other discussed measurement considerations.