engleski

Comparative Investigation on Ester Insulating Liquids forHigh Voltage Applications

Ester based insulating fluids have entered the market and are the insulating liquids of choice in the case of application of high fire or environmental susceptibility. A lot of experiences in applications in traction and wind farm transformers are available. In recent times it has been shown that also large power transformers can perform with these liquids successfully. Along the relatively oxidation stable synthetic esters (e.g. such described in IEC 61099), also natural esters with intrinsic lower oxidation stability and designed for closed type applications find broader use successfully. Although ester insulating fluids necessarily need additives to protect them from rapid oxidation, these additives are not declared in detail and there are no standardized methods for their determination and monitoring during operation. The user, however, should be aware of the concentrations of such additives and their possible degradation during operation, in order to develop an appropriate maintenance concept. In this study an investigation on new methods for the determination of oxidation stability reflecting real conditions has been carried out in consideration of properties like: - Method for combined thermal and oxidation stability for esters simulating real behaviour and by means of thermal gravimetric analysis (TGA). - A high pressure liquid chromatography (HPLC) method has been developed to determine the additive content in synthetic and natural esters, since the commonly used infrared method does not deliver reliable results. - On the basis of real experience and laboratory methods some values for possible limit values in service have been proposed.

Synthetic ester insulating liquids ; natural ester insulating liquids ; oxidation stability methods ; thermal

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