Online Fault Gas Monitoring System for Hermetically Sealed Power Transformers

Transformer faults, depending on their nature, lead to decomposition of the insulating liquid or cellulose paper. In this process, dissolved fault gases are produced. Through Dissolved Gas Analysis (DGA) by means of gas chromatography, the gas mixture produced by the fault can be separated to its constituent gas elements. The concentration as well as the type of the gas is of interest in the evaluation of these key gases. Hermetically sealed oil filled power transformers are manufactured with a sealed and gastight tank that prevents any contact between the insulating liquid and ambient air. A gas cushion, usually compressed nitrogen or dry air, is maintained above the liquid. Therefore, the electrical properties of insulation liquid are not exposed to further aging factors, ensuring a longer life span of the transformer. In case of severe faults, generation of considerable amount of fault gases is expected, which will, in case of hermetically sealed power transformers, gradually escape from the insulating liquid and diffuse into the gas cushion. As a cost-effective and compact alternative to gas chromatography, the development of a semiconductor-based online monitoring system of undissolved fault gases is presented. The proposed monitoring system is based on a set of integrated sensors, tracking the concentration of fault gases in the gas cushion continuously, through which faults in the insulating system can be detected early. Furthermore, physical parameters such as temperature, pressure, and humidity are also recorded permanently.