Method to evaluate the degradation condition of transformer insulating oil - experimental study on the hydrophilic and dissociative properties of degradation products

To operate power transformers long-term, as well as ensuring their insulating reliability, it is also important to study the age-related decline in various insulating oil characteristics and the method used to evaluate the same in an adequate manner. In the present paper, focusing on the oxidation degradation process of insulating oil, an experimental study was conducted on the influence of the hydrophilic and dissociative properties of oxidation degradation products on the insulating oil characteristics. Consequently, it emerged that, in the presence of highly hydrophilic degradation products, the influence of the water content on the breakdown voltage was likely to be less significant because the saturated water content increased. In the presence of oxidation degradation products with dissociation properties, the characteristic dissipation factor and volume resistivity values were likely to decline due to the influence of water content and heating. Based on the above results, the data in preceding studies were organized. As a result, there was a correlation between the breakdown voltage and the water saturation rate (actual water content in oil/saturated water content). In addition, it emerged that the dissociation property of insulating oil could be potentially determined based on correlation between the 80 °C values of the dissipation factor and the zero-minute values of volume resistivity at room temperature. These results pertain to the evaluation method used to diagnose the degradation condition of actual field-aged oil.