In my work I deal with transformer diagnostics and one of its special methods, currently not applied in Hungary, UHF partial discharge measurement. My goal is to introduce this method and its application on various oil samples.
Transformers are the most important and expensive parts of the distribution and transmission network. Their failure may endanger the energy supply of large areas. Therefore their maintenance and condition monitoring is of utmost importance, so that the defects can be eliminated before they grow to a failure. The most important part of a transformer with respect to reliability is its oil-paper insulation. Local defects formed here can be detected and located by the means of UHF partial discharge measurement. The applicability of the method relies heavily on the signals to propagate to the sensors via the oil. To determine this, the high frequency behavior of the oil must be understood. The presented method relies on the measurement of the impedance of the oil at high frequency. With this, the (complex) frequency dependent dielectric constant of the oil can be determined. This allows the calculation whether the PD signals can be measured or not.
During the measurements oils of various types has been compared. In the High Voltage Laboratory, measurements have been carried out on mock-ups in order to validate the models.