Effects of current harmonics on maximum loading capability for solar power plant transformers

Distribution transformers are commonly designed and manufactured to operate at fundamental frequency and to facilitate sinusoidal loads. The operation of loads that draw distorted currents culminate in higher losses, hotspot temperatures, degradation of insulation materials and declined service life. To avert these technical challenges, the continuous power rating of the transformer under current harmonics has to be reduced. This paper presents some analysis into the effect of current harmonics on the maximum loading capability of oil-filled transformers that are intended to operate within solar power plants. The harmonic spectrum derived by the presence of non-linear loads and seen by the transformer during service is presented. A recommended practice for derating the transformer described in the IEEE std. C57. 10-2018 is adopted in the study.