Analyzing Harmonic Current Effect on Distributed Photovoltaic Power Generation System Transformers

Abstract

Untimely failures of Distributed Photovoltaic Power Generation System (D2PGS) Transformers has been reported by various utility owners in spite of designing in accordance to the technical criteria and practices of the existing technical standards during the design phase and manufactured units passing the Factory Acceptance Tests (FATs) to corroborate the newly manufactured and packaged D2PGS transformers meet their intended purpose. These accentuate the need to perform comprehensive studies in relation to analyzing the effects of harmonic currents in D2PGS transformers, specifically on the winding Eddy losses and structural stray losses. The aforementioned is crucial in examining the capability of these transformers under the operational requirements of D2PGS. This work investigates the capability of an oil-filled D2PGS transformer in a harmonically contaminated Point of Common Coupling (PCC) of a grid-connected D2PGS. To accomplish this objective, the harmonic loss factor to account for additional winding Eddy losses of the transformer while in service owing to harmonic currents is evaluated. In addition, the effect of the skin effect on the winding conductors under harmonic conditions is considered. Finally, an improved harmonic loss Factor for winding Eddy losses is proposed. The investigated case scenario and results are then used to examine the capability of the transformer when supplying distorted load current for the purpose of existing and planned D2PGS development.