Oct.2023 24
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What is a voltage sag? Solutions?

It is the “temporary reduction of the rated voltage below a specific threshold at one point of the electricity supply line” (Standard CEI EN 50160).

A voltage sag occurs when the residual voltage is reduced to values ranging between 90 and 10 per cent of the rated voltage. The length of the voltage sag is considered between 10 ms up to 1 minute. The majority of voltage sags lasts less than 1 second and has a residual voltage greater than 40% of the rated voltage.  60% of costs due to low power quality are attributable to voltage sags.

If the quality of the electricity supplied to plants goes below a certain level, the equipment no longer operates correctly and issues will probably occur. The total incidence of these costs can be quantified up to 4% of the company’s annual turnover, with peaks around 60% caused by voltage sags (SAG) and short interruptions (source: Leonardo Energy).

The impact of a voltage sag on the production process is definitely lower than that of an interruption, but it should be considered that voltage sags are much more frequent. The interruption hits all the equipment not protected by UPS, while a voltage sag, depending on its depth and duration, may have the same effect or only affect the most sensitive appliances.


In many companies, the production process can be optimized with voltage stabilization and AVC-DVR voltage sag compensation.

In these cases, especially if the power in play is significant, the equipment provided with energy backup, typically UPS, is pointlessly large and costly, both in terms of battery maintenance costs and the low yield due to dissipated energy.

Recommended products: ZSBW series non-contact voltage regulator; AVC-DVR dynamic voltage restorer

Objective: To stabilize voltage and solve the problem of grid falling

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