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摘要
After maintenance and switching operation mode, when converter transformer of ultra high voltage direct current (UHVDC) system is recharged and put into operation, its residual flux and magnetic bias can transform the working condition of iron core, which is easy to produce inrush current, and greatly increases the risk of commutation failure of receiving end converter. This paper studies the generation mechanism of inrush current and the influence of series closing resistance on inrush current. Meanwhile, according to the influence characteristics of closing resistance on the amplitude and phase of flux during closing, the magnetic bias function is constructed; for star and delta connection converter transformers, the corresponding phase selection closing strategies based on magnetic bias simulation are proposed, respectively; the ideal closing time of mutual cancellation between residual flux and magnetic bias during closing is calculated, and phase selection closing is carried out. The no-load closing model of UHVDC converter transformer is established using PSCAD/EMTDC for simulation analysis, and the real-time test verification is carried out based on RTDS experimental platform. For 20 different residual flux conditions, 60 inrush current results of Y-bridge converter transformer are all less than 0.14 kA, 51 inrush currents of D-bridge converter transformer are less than 0.3 kA, and the other results are less than 0.43 kA. The experimental results show that the proposed phase selection closing strategy can effectively suppress inrush current caused by the operation of converter transformer. ? 2022 Science Press.
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