Perpustakaan Digital ITB

Power transformers in electric power systems play a very important role, stepping up electrical voltage for transmission or down for distribution. Thermal, electrical, ambient and mechanical stress on the transformer leads to faster ageing of the insulation system. When there is an evolving fault in a power transformer, it forms gases in the insulation oil, which can be recognized with the right kind of measurement methods. DGA is a method of condition assessment and monitoring, it can be done to detect faults that occur. The accuracy of the dissolved gas analysis is influenced by many factors, including diffusion, gas properties, oil samples, etc. The gas properties, as well as the solubility of the gas is greatly influenced by temperature, pressure, oil conditions, and type of insulating oil. Dissolved gases in transformers move in the insulating liquids through diffusion, natural temperature-dependent oil circulations and forced convection. In a system, dissolved gases tend to reach an equilibrium state throughout the entire system. When an equilibrium state is reached between the gas and the liquid phases, the correlation between the concentration of dissolved gases in the liquid and the partial pressure in the gas phase can be described using Henry’s law. In the first part of this thesis, a measuring method for the solubility of gases in mineral oil insulation is developed. The second part deals with key gases, which are measured at different oil temperatures and the corresponding Henry constants, which are to be determined. The main focus here is on the two gases: CH4 and C2H6 measured at different temperatures (25 °C, 50 °C, 75 °C and 90 °C). The objective of this study is to determine Henry's constants from the gas solubility in mineral oil at specified temperature and at an equilibrium state. The experiment have been successfully carried out to determine the Henry's constant using a state-of-the-art test method. The Henry constants of the CH4 are decreasing and of C2H6 are increasing with increasing temperature. C2H6 is more easily dissolved in mineral oil compared to CH4.