Corrected Estimation of the Transformer Winding Eddy Losses for Utility-Scale Solar Photovoltaic Plant Application

As South Africa continues its quest for a diverse en-ergy mix aimed at reducing its dependence on coal energy generation, the deployment of renewable energy power generation is being accelerated. The Integrated Resource Plan (IRP 2019) driven by the Independent Power Producers (IPPs) has committed to gen-erate, in excess, 18 GW capacity solely based on renew ables by 2030. To this end, the era of renewable energy technologies brings about a knowledge gap related to harmonics and distortion intro-duced by inverters and the use of non-linear loads. The design as-pects of the power infrastructure intended to operate in renewable energy technologies should incorporate special technical require-ments. A conventional distribution transformer does not meet this requirement. The step-up transformer is common in wind, concen-trated solar power and solar photovoltaic energy generation, in which, the significant generated harmonic losses on the trans-former result in hotspot temperature rise, thermal ageing and con-sequently, untimely failures. The basic assumption made by the IEEE Std C57.110-2018 that the winding Eddy losses in conduc-tors with dimensions less than 3 millimeters is progressive along with the square of the harmonic frequency is not consistent with conductors of larger dimensions, especially above the 5th harmonic order due to the skin effect. In this study, a corrected harmonic factor to accurately estimate the winding Eddy losses is proposed. The study is based on a hermetically oil-filled step-up transformer intended for service in a utility-scale solar photovoltaic plant.