At a time when the optimal utilization of resources is becoming ever more important, the condition monitoring of electrical equipment is also becoming increasingly essential. The dissolved gas analysis (DGA), an internationally accepted method for the condition assessment of transformers, plays a key role in this respect. By continuously monitoring the key gases in a transformer, incipient faults can be detected at an early stage and suitable maintenance measures can be initiated. This ability to plan maintenance measures may provide the key to cutting costs and increasing the overall system reliability. In free-breathing transformers, degassing or gas dissolving can occur over time, which may influence the interpretation basis of the DGA. The reason for this is that molecules always strive for equal distribution in a chemical-physical system. Various theories, which are based on the determination of physical and chemical material properties, can be used to describe these processes. Here, the Henry constants describe the concentration equilibrium at the phase interfaces and the diffusion coefficients describe the movement of the gas molecules dissolved in mineral oil. This paper presents mathematically or experimentally determined values and compares them with the literature. Furthermore, it describes the influence of the key gases investigated and the temperature dependence.
Dissolved gas analysis (DGA) is frequently used for the condition assessment and monitoring of transformers. In the case of free-breathing transformers, gas losses may occur at the phase interface due to the chaotic molecular movement of the dissolved gas molecules. These gas losses and the resulting distortion of the interpretation basis for the DGA can lead to a false assessment of the condition. Furthermore, the relative ratios may shift, which in turn can lead to the misclassification of the present defect. This paper deals with the influences on gas losses and describes a possible consideration for use in the condition assessment. It begins with an explanation of the gas losses problem in more detail based on theoretical considerations and summarised in hypotheses. In addition to the experimental methods used, theoretical model considerations for taking gas losses into account are described below. The results deal on the one hand with the influences on the gas losses (geometry and temperature) and the other hand with the application of the developed model for the consideration of the gas losses. In detail, the results of the gassing behaviour of different complex geometries -simple phase interfaces, a transformer model and a distribution transformer -are described in more detail and it is shown that a correction of the degassing with the model is possible within certain limits. Furthermore, the methodologies for determining the model are discussed in this paper.INDEX TERMS Transformer, dissolved gas analysis, gas losses, gas management, molecular movement.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.