Step-up Transformers for Intermittent Renewable Sources: Natural Ester Fluid Helping to Surpass the Challenges of this Application

The share of renewable energy generation has been increasing significantly over the years, and a further global acceleration is expected for the near future. While clean electrification is bringing several advantages, mainly reducing the greenhouse gas emissions in the electricity sector, renewables are also associated with some very specific requirements. Restrictions derived from the variability and unpredictability (intermittency) of wind and sun, have caused additional hurdles not typically found in traditional generation. These issues, resulted from an incomplete understanding of all requirements, include high content of harmonics that are not always properly filtered. Harmonics and dielectric stresses have crucial influence in the transformer operation and need to be very well specified for the equipment manufacturer. Natural ester insulating liquid can offer more than fire safety and environmental benefits. This paper brings a review in the thermal class and dielectric properties of natural ester where the Partial Discharge Inception Voltage of natural ester is compared with synthetic ester and mineral oil. A real case of a 7350 kVA transformer with high temperature insulation materials for solar application will be evaluated with data from dissolved gases analysis. This paper will show how natural ester can helps the generator step-up transformers for the renewable energy application to face issues like harmonics from the inverters and high heat operation, avoiding problems like partial discharges in the active part.