Magnetizing Inrush Current Elimination Strategy Based on a Parallel Type Asynchronous Closing Hybrid Transformer

Abstract

When the power transformer is connected to power grids, due to the existing remanent magnetism (RM) and the voltage transient component, the transformer will generate a large magnetizing inrush current (MIC). The MIC not only seriously threatens the safe operation of the transformer, but also causes the misoperation in the differential protections. To solve the aforementioned problems, a novel MIC elimination strategy of the hybrid transformer (HT) based on an asynchronous closing technology is proposed in this article. First, through the rational design of the HT topology, the parallel auxiliary winding (PAW) of the HT is established and the magnetic coupling mechanism is realized, which lay the magnetic circuit foundation for the MIC management. Second, a step-type synchronous magnetic field is established through PAW without considering RM. After the action of step-type magnetic field, the core flux increases sinusoidal linearly and enters into the rated steady stable. Finally, by controlling the stabilization time of the oblique wave and the primary voltage signal of the power grid, when the core flux is stabilized, the nonsynchronous closing of the HT can effectively alleviate the generation of the MIC. The validity and feasibility of the proposed scheme are verified by building an HT prototype platform, which provides some reference for the difficulty of measuring RM and avoiding MIC in the power system.