According to the Electric Power Research Institute (EPRI) Power Electronics Applications Center, “A sag or dip, as defined by IEEE (Institute of Electrical and Electronics Engineers) Standard 1159-1995, ‘IEEE Recommended Practice for Monitoring Electric Power Quality,’ is a decrease in rms (root-mean-square) voltage or current at the power frequency for durations from 0.5 cycles to 1 minute, reported as the remaining voltage . . .
“用来描述电压跌落(或短时电压下降)幅度的术语是令人困惑的。推荐的用法是“下降到20%”，这意味着线路电压降低到正常值的20%，而不是降低20%…IEC(国际电工委员会)对这种现象的定义是倾斜。这两个词被认为是可以互换的，美国人更喜欢用sag…
“在某些出版物中定义的典型下垂持续时间范围为两毫秒（循环约为八分之一）到几分钟。下垂持续时间被细分为三类 - 瞬间，瞬间和临时恰到恰逢三类中断和膨胀。“
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