Power capacitors are highly reliable equipment due to their completely enclosed configuration. They have usually worked without almost any trouble for a long time. Their dielectric strength can be however reduced due to some stresses such as over-voltage application or thermal degradation of the insulation material during their long period of operation and these events can result in the dielectric breakdown of the capacitors in extreme cases.
Power capacitors with oil-impregnated paper-film are commonly used in substation. Therefore, it is very important to diagnose the deterioration and predict the remaining service life of such equipment, to assist in plant maintenance. To establish the diagnostic method of the deterioration of the capacitors with oil-impregnated paper-film, we have conducted thermally-and electrically-accelerated deterioration tests and investigated the changes of their characteristics. Based on the experimental results we obtained, it can be concluded that the behavior of the oil-dissolved gases can be used as a useful index to diagnose the insulation deterioration of these capasitors.
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