Investigation of Transformer Oil Properties with advanced Multidimensional Methods

Power Transformers are basic elements in electric power systems. In case of an unplanned outage due to failure at the transformer not only to the costs reflected to the repair costs but also the costs related to interrupted power supply or the stop of production will occur. Therefore, it is necessary to assess the condition of power transformers and to identify risks early. For this, different diagnostic techniques were developed. In this context oil test, such as the measurement of the oil properties and the DGA, are well established and easy to perform methods.With the help of the insulation oil properties, possible aging of the oil can be identified and the remaining capability withstand dielectric stresses can be investigated. Because some parameters indicate the same properties (such as ageing state) it could be possible that there are pairs or groups of parameters, which give redundant results. Therefore, in this contribution it is investigated if a correlation between different insulation oil properties can be found. Furthermore, it was investigated if relationships between insulation oil properties and DGA results can be found.Both investigations were based on a huge number of oil test results of real transformers of different voltage levels, applications, age, and manufacturers.