Three-winding transformers equipped with on-load tap changers are widely used in power systems. The impact of tap-changer control across the entire range of regulation from the maximum tap to the minimum tap needs to be taken into account in some power system analyses. This article demonstrates that described in literature and applied in some computer packages certain modeling assumptions for three-winding transformers operating on the off-nominal taps, are incorrect. Consequently these assumptions can lead to significant errors. The new method for the calculation of tap-dependent values of transformer equivalent impedances is proposed. The calculations for sample transformers are provided.

中文翻译：

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利用拉格朗日插值法估计三绕组变压器的非标称参数


配备有载分接开关的三绕组变压器在电力系统中得到广泛应用。在某些电力系统分析中，需要考虑从最大抽头到最小抽头的整个调节范围内分接开关控制的影响。本文证明，文献中描述的以及在某些计算机软件包中应用的针对在非标称抽头上运行的三绕组变压器的某些建模假设是不正确的。因此，这些假设可能会导致重大错误。提出了计算变压器等效阻抗的抽头相关值的新方法。提供了示例变压器的计算。