Harmonic distortion-based condition monitoring of distribution transformers in a solar farm

This paper presents a condition monitoring approach for distribution transformers in solar farms, focusing on analysing harmonic distortion. The methodology leverages the IEEE standard to evaluate the severity of harmonic pollution in the transformer's operating environment. Specifically, the research investigates Total Harmonic Distortion (THD), Total Demand Distortion (TDD), and Individual Harmonic Distortion (IHD) through real-time data measurements. These parameters are essentially the majority in distinguishing transformer degradation from increased losses, over-heating and insulation stress brought about by non-linear loads inrush currents. In this study, the operating characteristics of the six station transformers supplying converters as non-linear loads are examined and the influence of THD on voltage current power loss and transformer efficiency is rated. A case study is conducted on a 1400 kVA three-phase transformer feeding a rectifier connected to a symmetrical inductive load. The analysis compares the PCC and the measured harmonic levels based on the IEEE standard to identify thermal faults and evaluate the operating condition of the transformer. Transformers 3 and 6 are characterized as overheated due to elevated temperature in combination with high load percentages (86% and 84% respectively) and moderately high THDI values (10% to 12%). Transformers 1, 4 and 5 are labelled with a high THDI value because their current harmonic distortion values (between 11% and 14%) clearly exceed the recommended limits. By monitoring these harmonic indices, this approach provides a proactive method to detect and mitigate harmonic-related problems, extend transformer life and improve power system reliability. The results emphasize the importance of adhering to standard guidelines for maintaining optimal transformer performance and ensuring power quality in distribution networks.