Multidimensional Investigation of Transformer Oil Properties

Abstract

The investigation of the oil properties is one of the most basic, but also one of the most powerful methods of condition assessment on power transformers. With the standard oil test (SOT) it can be tested if the oil is still able to withstand the stresses occurring during operation. In order to do a standard oil test different parameters are measured. With some of these parameters for example the breakdown voltage mainly the capability to withstand dielectric stresses can be investigated. Other parameters such as acidity or dielectric dissipation factor can help to assess the aging of the insulating liquid. Because some parameters indicate the same properties (such as ageing state) it could be possible that there are pairs or groups pf parameters, which give redundant results. With other words: it could be possible that some parameters indicate each other. In this case it would be possible to reduce the number of parameters, which were measured during the SOT. To investigate if such behaviour can be observed in real oil properties of real transformers, the different parameters of oil properties of a huge database were analysed with correlation analysis. Additionally it is shown how often the different oil properties can be classified as good, fair or poor according to the applicable standard IEC 60422. Using these information operators of power transformer are able to evaluate the results of the SOT of their own transformers not only according to the standard, but also according to the performance of other real transformers.