Influence of trace components contained in transformer insulating oil on various characteristics over time

To operate power transformers long-term, as well as ensuring their insulating reliability, adequate consideration must also be paid to the age-related decline in various insulating oil characteristics. Previous studies could roughly clarify the key components causing the insulating oil characteristics to decline by adding the components contained in field transformer insulating oil to oil with few impurities. On the other hand, this degradation causing components are trace components not present in the new oil. To clarify the insulating oil degradation mechanism over time, the components determined as the sources of the degradation causing components (source components) must be investigated. Accordingly, in this paper, a study is conducted on the influence of the trace components present in new oil on the degradation of the characteristics over time. In addition, since the breakdown characteristics of insulating oil are influenced by the water content in oil, the influence of the combined effect of various components and water etc. is also studied. Consequently, it emerged that sulfide (octyl sulfide), or sulfur compounds detected in new oil increased the copper content in oil, showing a tendency toward an increasing dissipation factor and declining volume resistivity characteristics. Conversely, no influence of additives was observed on the increase in water content and the relationship between breakdown voltage and water content remained almost unchanged, regardless of the presence or absence of additives. Following the study of the change based on interaction with water content, no influence of the presence or absence of the additives was observed on the characteristics (acidity, interfacial tension, and breakdown voltage). Based on the above, it was clarified that, among the trace components existing in oil used in the present experiment, octyl sulfide had impact on the insulating oil characteristics over time.