Numerically Investigating Interturn Arcing Faults Inside a UHV Converter Transformer

A succession of ultrahigh-voltage (UHV) converter transformer interturn arcing faults have recently emerged, eventually giving rise to catastrophic fire accidents. For a long time, modeling and analyzing transformer interturn faults have been well-known challenges in both academia and industry, while such a dilemma turns out to be intractable in the face of those in UHV converter transformers. In this study, a coupled field-circuit model is presented for numerically investigating converter transformer interturn faults. In the circuit domain, a black box model is chosen for a quantitative description of the nonlinear conductance of the fault arc. As study cases, representative line-side winding (LSW) interturn arcing fault scenarios within a typical single-phase converter transformer are analyzed. The specific results reveal that an interturn fault causes the internal flux distribution to be seriously distorted and leakage flux lines to concentrate around the faulty turns. The LSW interturn fault witnesses a high-amplitude circulating current flowing in the fault loop, and a certain increase in the LSW current, while no apparent fault features can be observed on the valve side. This investigation sheds light on the complex characteristics of interturn arcing faults inside a converter transformer and is expected to offer an alternative to dangerous and costly short-circuit experiments in the field.