A Novel De-rating Practice for Distributed Photovoltaic Power (DPVP) Generation Transformers

Abstract

Transformers are habitually designed and manufactured for operation at a fundamental frequency of 50Hz and sinusoidal load current. Transformers are susceptible to non-linear loads. The inception of switching action characterises Non-linear loads and consequently nonsinusoidal load current which brings about higher transformer service losses, hotspot temperature rise, and degradation of cellulosic and liquid insulation, and consequently untimely failure of transformers during service. This phenomenon yield current with different components that are multiples of the fundamental frequency of the distributed photovoltaic power (DPVP) generation system. In order to obviate these challenges, the continuous power rating of the transformer, which is intended to facilitate non-linear loads must be minimised using procedure ascribed by the standards as de-rating. This work, an extension of previous work, proposes a novel procedure by means of Finite Element Method (FEM) for the de-rating of DPVP transformers serving non-linear loads during their service life. The proposed procedure considers parameters such as skin effect, proximity effect, and the magnetic flux leakage on the windings that were not included in the IEEE recommended de-rating procedure. The theoretical examination is substantiated on a 500kVA, three-phase, oil-filled transformer.