Study on Down-sizing Inverter Transformers in Solar Farms

The unique operation mode of inverter transformers, typically characterized with no load during night and non-heavy load during daytime, in solar farms lead to considerably low usage and insignificant ageing. This motivates us to investigate the possibility of down-sizing inverter transformers in this paper. Based on relevant standards, thermal and loss of life (LOL) limits of the inverter transformers are defined to ensure safe overloading operation. Also, three loading cases: worst, ideal and measured cases are defined based on one-year data from a solar farm. The results show that hot-spot temperature (HST) is the limiting factor rather than LOL when inverter transformers are overloading. Further comparative study of three thermal models confirms that irrespective of the differences in the estimated HST, there are still considerable margins to increase the ratio factor, i.e., ratio of the rating of the inverter to that of the inverter transformer.