b'Engineer Innovation | ElectronicsAvoiding the next major Power Black-Out with Digital TwinsBy Hilary Chisepo, MSc(Eng), PhD(Eng) candidate,University of Cape Town, South AfricaPower transformers in bulk transmissionexperience excessive stray flux that may networks are vulnerable to the adversegenerate hot spots in the windings, tank effects of geomagnetically inducedand core, leading to the onset of currents. Power system instability, majorinsulation degradation, gassing and in blackouts and overheating ofsome cases, immediate failure. transformers are the main concerns for utilities. To understand the mechanismsGIC-related failures in the Southern that bring about the overheating, aAfrican network showed that thermal reliable FEM modeling approach needsdamage can occur in power to be verified with physicaltransformers even at quite low levels of measurement data, but data fromGIC. As a result, South Africas power important large power transformers areutility, Eskom, now includes DC seldom available. Model laboratorywithstand capability in their power transformers can be used to investigatetransformer procurement specifications, the electrical and magnetic reposeand so do utilities in many other under simultaneous 50/60 Hz and GICcountries.(quasi-dc) excitation.Factory verification testing with DC is Geomagnetically induced currentsnot viable from a financial and (GICs) are caused by abnormal spacelaboratory power capacity point of view weather that occurs periodically and isand so very few practical results are known to have adverse effects on poweravailable e.g. single phase transformer systems. These GICs, having frequenciesGIC test performed by Siemens, Austria in the milli-Hertz range that are quasi- [1]. Approximations of the response of DC relative to the power frequency,power transformers can be achieved enter long transmission networksthrough laboratory testing of smaller through grounded power transformertransformers and comparing neutrals. Power transformers exposed tomeasurements with various modeling GICs experience partial half-cycletechniques, but care is needed when saturation due to the DC offset of thefabricating the test transformers to normal AC excitation. This partialachieve representative results and saturation causes the generation ofreliable findings.undesirable even and odd harmonics, significant draw of reactive (non-active)Testing of FEM modeling in Simcenter power, voltage collapse and excessiveMAGNET Softwarestray flux which contributes toLaboratory tests were performed in a overheating inside the transformer.previous study as part of an MSc(Eng) research project at the University of How do GICs cause overheating ofCape Town [2]. This study investigated power transformers? The active andthe response of transformers of different structural metallic parts simultaneouslycore structures with GIC emulated in a 36'