Most power transformer failures can be correlated with deterioration of the insulation system over time. The existing IEEE Std. C57.91-2011 gives a basic aging mechanism for simplified loading studies, which is based on hot-spot temperature rise alone. It also assumes an average useful life of 20 years for power transformers. There is a need for this useful life assessment to be updated based on practical considerations.
There has been extensive research conducted in the past decade towards incorporating markers such as moisture, cooling system performance, furan, and DGA test results for the life expectancy and loading study of service-aged power transformers. Insulation moisture content in power transformers is a major area of concern for utilities, operating such service-aged units.
With this background, the major objective of this project is to develop a comprehensive loading guide for in-service power transformers by incorporating the effect of dynamic parameters such as moisture, furan, CO2/CO, methanol, hot-spot temperature, oxygen, cooling system efficiency, and loading history. A secondary objective is to determine the useful remaining life and loss-of-life curves for service aged transformers based on the aforementioned factors.
To fully achieve the objectives of this assignment in the most cost-effective manner, a Subject Matter Expert (SME) intimately familiar with the best practices in loading service-aged power transformers was utilized, supported by an engineering team of two, to research and develop an improved dynamic loading model. An in-depth review of literature was conducted in analyzing industry standards and documents pertaining to IEEE, IEC, and CIGRE, in addition to incorporating expertise with loading service-aged power transformers. A much-improved loading model was implemented by utilizing the latest IEC Std. 60076-2018 as the baseline and incorporating the effect of dynamic aging markers. Utility case studies were conducted using the model to achieve better loading and estimation of the life expectancy of service-aged power transformer units.
Power transformers, transformer loading, insulation life expectancy, loss-of-life, remaining useful life