Development and design of a compact and mobile oil drying and degassing system
The main application area of liquid insulations are power transformers. In general oils are insulating high voltage parts against each other and against the ground, dissipating the heat and impregnating solid insulating components made out of paper or pressboard. Insulating fluids are characterized by electrical and dielectric properties, e.g. high breakdown voltage, low dielectric loss factor and the low conductivity. These properties are influenced by various factors, e.g. the purity of the oil, the water content or the amount of dissolved gases in the oil. In particular, water dissolved in the oil leads to an increased dielectric loss factor and to a reduced dielectric strength. For this reason, insulating fluids are subjected to a special conditioning process. In this process, the oil is to be freed of impurities and dried using vacuum and heat. Due to the importance of the insulating liquids and the emergence of more and more new oils, various tests need to be carried out in the laboratory. Since many properties of the oil are determined e.g. by moisture and impurities, it must be ensured that the same conditions, with regard to the oil parameters, are always available. Thus it is necessary to condition the oil, i.e. to filter, dry and degas the oil. Therefore special systems are needed, which require less throughput than those, which can be used for large transformers. The reduction of moisture, impurities and gases has to be particularly thorough. As commercial systems are not available for this use, a separate system has been developed and designed.
In this contribution the development and design of a new conditioning system for insulating liquids for laboratory use is presented. The basic principle for the drying and degassing of the oils is the thin film degasification. First, the oil is filtered to remove fine particles. In order to reduce the viscosity, the oil is heated and is led to a column filled with glass rings with high surface area, where the oil is distributed over the thin layers. Under the influence of vacuum and temperature, the water evaporates from the oil and is extracted. With this system, two different oils can be simultaneously cleaned, dried and degassed independently of each other. Furthermore, the construction is designed in such a way that only one drying column is provided for each oil circuit. The system has an adjustable heating system and an automatic quick disconnect system with ventilation of the oil circuit in the case of a fault, e.g. the impending overflow of the drying columns. Furthermore, the oil drying and degassing system is installed compactly in a safe, closed and mobile housing. The developing process and the received results are presented in form of pictures, tables and diagrams.
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