Entwicklung eines innovativen Sensorsystems zur Alterungsanalyse von Papierisolierungen in Leistungstransformatoren

authored by: Tobias Münster
supervised by: Peter Werle
Abstract: For a reliable supply of electrical energy, transformers are essential as the interface between producer and consumer. Most of these components, especially the cost-intensive power transformers, are electrically insulated with a mixed dielectric of liquid and paper. These materials are organic materials, which are subject to a continuous ageing process during operation and a resulting deterioration of their properties. In view of the increasing average operating age of transformers and the advancing energy revolution, reliable monitoring of the ageing condition to increase operational safety and efficiency is of increasing importance. For this reason, this thesis presents various ageing investigations and the development of an innovative optical sensor to improve the condition assessment of transformers.

With regard to liquid-solid insulated power transformers, a distinction is made between free breathing transformers with an oil expansion vessel and hermetically sealed transformers with a gas cushion. In order to simulate the service life of these devices, thermally accelerated ageing tests were carried out using various insulating liquids, whereby the typical insulating system of these transformers is simulated. Samples of the insulating paper as well as of the insulating liquid were examined at different points in time, whereby different ageing markers were evaluated. It turned out that certain ageing markers or a combination of these are suitable to allow an indirect estimation of the ageing condition.

As a further step in view of the advancing digitalisation, a new type of patented and cost-effective optical sensor was developed to precisely determine the ageing of the insulating paper, which can be used both in the laboratory and as a monitoring system. By means of a light source and the use of fibre optic cables, it is possible to determine the ageing progress by recording the reflection spectra of the insulating paper, which could be confirmed with various insulating paper samples from real transformers. By specifically analysing characteristic wavelengths of the reflected light, a precise measurement can be carried out non-destructively and within seconds, which considerably extends and improves the state of the art in ageing assessment compared to previous methods. The knowledge gained in this work and the sensor system developed sustainably expand the existing diagnostic methods and thus ultimately contribute to a reliable energy supply.
Organisation(s): High Voltage Engineering and Asset Management Section (Schering Institute)
Type: Doctoral thesis
No. of pages: 285
Publication date: 02.06.2025
Publication status: Published
Electronic version(s): https://doi.org/10.15488/19063 (Access: Open)