On Highlighting the Merits of Gas-to-Liquid Transformer Oil Under Accelerated Thermal Aging and Faults: Electrical and Physio- Chemical Properties

Mineral (MO) oil has long been utilized as a dielectric and cooling medium in high-voltage power transformers due to its low cost and availability. Recently, there has been a great trend toward the use of gas-to-liquid (GTL) oil due to its purity, chemical consistency, and better performance than conventional oils. This study aims to investigate the normal and abnormal thermal impacts on GTL and MO oil types. In this regard, this paper presents two parts. Firstly, it studies a comprehensive evaluation of the aging characteristics under normal conditions of GTL oil in comparison to conventional MO. Aged oil samples were obtained using a laboratory-based accelerated aging test, for simulating the thermal stress during the transformer’s operation. Hence, the two oil types are subjected to different aging durations (i.e., 3, 6, and 10 days). These aged and fresh samples were tested for AC breakdown voltage, dielectric dissipation factor, permittivity, and resistivity as electrical testing. Additionally, as chemical and physical testing, moisture and acidity are measured for fresh and aged samples of two of these oil types. Besides, optical spectroscopy measurements have been used for insulating oil assessment; these kinds of measurements point out the existence of overall aging byproducts, including sludge formation, which can negatively impact the oil properties including physio-chemical and electrical properties. The used optical techniques include Ultraviolet-visible absorption and photoluminescence tests. Secondly, thermal faults impact as abnormal conditions is generally evaluated through dissolved gas analysis as a chemical test, where it is utilized to measure the gas concentrations for the two oils under abnormal conditions test after the thermal heating test. This study concluded that the electrical and physio-chemical properties of GTL oil with aging have superior results compared to MO oil.