Investigations on Distribution of Gases and Water in the Vessel Oil of GSU Transformers

Project Number 291

GSU transformers contain mineral oil as dielectric agent and coolant. The oil has to conform to the defined quality parameters and is thus sampled periodically and tested following laboratory methods as per VDE 0370.

For sampling, in general three sampling lines of the tank are available. Since the early 70s the oil is also used as medium for diagnosis by measuring and evaluating the fault gases dissolved in the oil. Sampling, analysis and evaluation of the fault gases dissolved in the oil are based upon DIN IEC 60567/60599. There are no regulations for sampling points in any of the standards. Obviously, homogeneous gas distribution in the transformer oil is supposed due to the rather high oil rotation performance.

In practice, however, the analysis results vary in relation to the sampling points; the results are to be used for further findings, in particular on

  • localisation of the fault by comparison of the fault gas concentration,
  • determination of accelerated oxidation reactions by comparison of oxygen concentration.

Further, knowledge on suitable sampling points is of utmost importance for application of online analyzers.

By means of the research project, findings on the gas distribution and gas management in the transformer tank (as well as their oil-filled assemblies) of large power transformers are to be made.

The task is to be solved headed by Dr. Eckhard Bräsel, Gatron GmbH, Greifswald, in co-operation with the Grohnde and Brokdorf Nuclear Power Plants by utilisation of existing and installation of additional online devices (TGM). Moreover, the main laboratory of the E.ON Engineering GmbH is involved. Besides the Gatron TGM, existing Unisensor devices are used.

The research results expected can be applied regardless of the manufacturer. Detailed analytical results are achieved through comparison with measuring results of online devices with different laboratory methods.

The research project helps to improve the reliability of diagnostic statements and thus to achieve positive impacts on the state evaluation and the operation- and age management of large power transformers.

The project is supported by the Technical Committee “Electrical Engineering, I&C, and IT”. The final report will be available in autumn 2008.