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Chromatographic analysis of gases from condenser bushings containing insulating oil
The text describes practical experience with chromatographic analysis of gases from condenser bushings. The gas was not obtained in common way, i.e. by degassing of the insulating oil, but by a direct withdrawer of gas through an adjusted drain valve screw from a hermetic bushing (with a gas-proof syringe).
The introduction describes risks of occurrence of possible errors and how they may affect the reproducibility of measuring. It treats also the detection sensitivity of chromatograph and its influence on results of analysis. It is stated that the limiting sensitivity of a common device is not a hindrance as it is sufficient at a bushing with a beginning defect. In case of a bushing without a defect, it is not important to detect a trace presence of decomposition gases.
To be able to apply the known ratio criteria, it is necessary to recalculate the measured gas concentrations as if they were obtained from degassed oil. It is also recommended to correct the results with regard to temperature. The studies have shown that due to the specific construction of bushings in comparison with insulating system of transformers it is not possible to use criteria for transformers. It was also found that in cases of possibility of withdrawal of an oil sample for traditional degassing, the measured values are considerably influenced after ventilation of the bushing.
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