Modern Condition Assessment Techniques for Power Transformers Connected to Renewable Energy Sources

The ongoing integration of renewable energy sources such as wind and solar power is increasing the operational stress on ageing power transformers, particularly due to higher and more volatile loading conditions combined with limited grid expansion. Under these circumstances, accurate condition assessment and temperature control are essential to prevent accelerated ageing and unexpected failures. This paper presents an overview of modern on-site and online diagnostic techniques for power transformers connected to renewable energy sources. The contribution demonstrates how advanced methods such as Frequency Response Analysis (FRA), ultra-highfrequency partial discharge (UHF-PD) monitoring, online breakdown voltage monitoring in onload tap-changers, and fibre-optic hot-spot temperature measurements can significantly enhance condition-based asset management. The results show that these techniques enable earlier fault detection, more accurate failure localization, and improved thermal assessment under dynamic operating conditions. When properly applied, modern diagnostic technologies are neither overly complex nor impractical, and they provide a robust foundation for reliable and data-driven transformer operation in renewable-energy-dominated power systems.