随着计算机及各种半导体技术的迅速发展，大量新型敏感设备在工业生产中得到广泛应用，电压暂降已经成为影响工业用户最主要的电能质量问题。当线路发生短路故障时，重合闸动作可能会使电网节点出现多级电压暂降的情况，这会对敏感设备造成多次影响，甚至导致系统瘫痪，带来巨大的经济损失。准确评估多级电压暂降对设备造成的影响对提高供电可靠性、减小经济损失具有重要的理论价值和现实意义，本文以此为目的，考虑设备耐受能力的不确定性，提出了多级电压暂降评估方法。

首先，分析和总结了重合闸动作引起的多级电压暂降波形。将电压暂降幅值和持续时间作为电压暂降的典型特征量，分析了瞬时性故障和永久性故障下重合闸相应动作过程的多级电压暂降波形。同时考虑了电网结构、继电保护类型以及故障位置对多级电压暂降波形的影响，并以PSCAD仿真软件设置不同场景进行波形仿真，所得结果与理论分析结果基本一致，为多级电压暂降的评估提供了基础。

其次，提出了一种考虑设备耐受能力的多级电压暂降权重计算方法。基于仿真所得的多级电压暂降波形，结合敏感设备的过程免疫时间特性(Process Immunity Time, PIT)，合理刻画出敏感设备的多级电压暂降PIT特性曲线，从而分析出各级暂降之间存在关联性的结论。然后运用权值函数法的电压暂降评估方法求出多级电压暂降各级暂降的影响度，利用各级暂降的关联性和影响度指标值对层次分析法进行改进，避免了层次分析法的主观性。并通过改进层次分析法构造多级电压暂降的成对比较矩阵，确定了多级电压暂降各级暂降的权重。

最后，提出了多级电压暂降严重程度评估指标及频次评估方法。基于所得的多级电压暂降各级暂降的权重，实现了多级电压暂降严重程度的量化评估，运用电压损失量的思想对多级电压暂降的幅值进行等效，提出了配电网多级电压暂降频次评估方法。通过改造后的IEEE-30系统进行仿真验证，结果表明：本文提出的多级电压暂降严重程度评估方法合理且有效，减小了评估结果的主观性；频次评估方法能够合理刻画多级电压暂降对敏感设备的扰动程度。同时也验证了本文方法对含分布式电源配电网的适用性，为敏感设备多级电压暂降的评估和治理提供依据。

With the rapid development of computers and various semiconductor technologies, a large number of new sensitive devices are widely used in industrial production, and voltage sag has become the main power quality problem affecting industrial users. When a short circuit fault occurs in the transmission line, the reclosing action may cause multi-stage voltage sag at the grid nodes, which can have multiple impacts on sensitive equipment and even lead to system paralysis, resulting in huge economic losses. Accurately evaluating the impact of multi-stage voltage sag on equipment has important theoretical value and practical significance in improving power supply reliability and reducing economic losses. With this as the purpose, this article considers the uncertainty of equipment tolerance and proposes a multi-stage voltage sag evaluation model.

Firstly, the waveform of multi-stage voltage sag caused by reclosing action was analyzed and summarized. The amplitude and duration of voltage sag were taken as typical characteristic variables of voltage sag, and the multi-stage voltage sag waveforms of the corresponding reclosing action process under instantaneous and permanent faults were analyzed. At the same time, the influence of power grid structure, relay protection type, and fault location on the waveform of multi-stage voltage sag was considered. Different scenarios were set up using PSCAD simulation software for waveform simulation, and the results obtained were basically consistent with the theoretical analysis results, providing a basis for the evaluation of multi-stage voltage sag.

Secondly, a multi-stage voltage sag weight calculation method considering equipment tolerance was proposed. Based on the multi-stage voltage sag waveform obtained from simulation, combined with the process immunity time (PIT) characteristics of sensitive equipment, the PIT characteristic curve of multi-stage voltage sag of sensitive equipment is reasonably characterized, and the conclusion that there is correlation between each stage of sag is analyzed. Then, the voltage sag evaluation method using the weight function method is used to calculate the impact degree of multi-stage voltage sag. The correlation and impact index values of each stage of sag are used to improve the Analytic Hierarchy Process (AHP), avoiding its subjectivity. And by improving the Analytic Hierarchy Process to construct a paired comparison matrix for multi-stage voltage sag, the weights of each stage of voltage sag were determined.

Finally, a multi-stage voltage sag severity evaluation index and frequency evaluation method were proposed. Based on the obtained weights of multi-stage voltage dips, a quantitative evaluation of the severity of multi-stage voltage dips was achieved. The amplitude of multi-stage voltage dips was equivalent using the concept of voltage loss, and a method for evaluating the frequency of multi-stage voltage dips in distribution networks was proposed. Through simulation verification of the modified IEEE-30 system, the results show that the multi-stage voltage sag severity evaluation method proposed in this paper is reasonable and effective, reducing the subjectivity of the evaluation results; The frequency evaluation method can reasonably characterize the degree of disturbance of multi-stage voltage dips to sensitive equipment. At the same time, it also verifies the applicability of the method proposed in this article to distribution networks with distributed power sources, providing a basis for the evaluation and management of multi-stage voltage dips in sensitive equipment.

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