Investigation of temperature and humidity effect on dielectric liquids behavior

Transformers play one of the most critical roles in the transmission and distribution of electricity. Oil-immersed transformers have a large share in the transmission and distribution of electrical energy in the network, with around 80-85% utilization. However, the importance of the oil used in transformers is even greater. Transformer oils play an important role in the protection and long-term operation of transformers. Environmental factors deteriorate the structure of transformer oil and adversely affect the operation of the transformer. It also shortens the life of the transformer. Breakdown voltage occurs when the dielectric strength of the transformer oil is exceeded. Puncture voltage occurs at the point where the insulation of the oil deteriorates. Two of the environmental factors that affect breakdown voltage are temperature and humidity. The first of these factors, temperature, adversely affects the dielectric properties of transformer oils, which is an insulating structure. Air bubbles in oil expand at high temperatures. This changes the volume of the air bubbles and negatively affects the breakdown voltage. Moisture, another environmental factor, is a parameter that reduces the dielectric properties of transformer oils and causes them to lose their dielectric properties. Therefore, its effect on the breakdown stress is also large. In this study, the effect of humidity and temperature as environmental factors on the puncture stress in transformer oils and the characteristic responses of transformer oils were investigated. For this purpose, 3 transformer insulating liquids were initially selected. These insulating liquids are mineral oil, synthetic ester liquid and natural ester liquid, which are the most commonly used oils in transformers. Then, a needle plane horizontal electrode design was made in which the puncture voltage is realized in the transformer oil. The design was used to create an experimental set for temperature and humidity experiments. Temperature experiments were carried out between 20ºC and 60ºC. Humidity experiments were carried out between 40% and 95% humidity. Temperature experiments were repeated every 5ºC. Humidity experiments were repeated at each 5% humidity level. The distance between the electrodes was increased by 1 mm from 1 mm to 5 mm for each experiment and repeated for each liquid dielectric for 5 different distances. As a result of the experiments, puncture voltage data were obtained for each liquid dielectric. In order to correctly interpret the puncture stress data, various methods were evaluated. The kurtogram method was preferred in this investigation and the data obtained for each experiment was analyzed using the kurtogram method. The results of the kurtogram method were analyzed by comparing the responses of temperature and humidity to the puncture stresses on oils. This analysis allowed the superiority and differences between the insulating liquids to be determined.