Abstract
Electrical system reliability is highly dependent on power transformers performance. Yet the transformer reliability is highly impacted by its cooling medium and the contaminants within the cooling medium. These contaminants account for roughly 15% of transformer failures. Contaminants such as water can be harmful to the transformer, will reduce its reliability, and, consequently, the electrical system reliability. Therefore, moisture must be eliminated from the cooling medium as well as the insulation paper of the transformer. In this paper, an online oil drying system technology is implemented on a 69/13.8 kV transformer with more than 35 years in service. The technology removes moistures from transformer's oil and the winding insulation paper. This paper also illustrate the working principle of this technology. The importance of this technology comes from the fact that the drying process is conducted while the power transformer is in service. Hence, no outage is required. The ultimate purpose of transformer dehydration is to increase the transformer reliability and extend its service life. This paper analyzes the performance of the online dehydration technology and compares it to offline methods. Actual oil analysis results show that this dehydration system reduced the water content in the insulation medium by 29%.