Voltage Dip Immunity of Equipment and Installations

Voltage dips (also known as “voltage sags”) are short-duration reductions in voltage magnitude. Their duration is typically between a few cycles of the power-system frequency and a few seconds. The interest in voltage dips is mainly due to their impact on end-user equipment. Industrial processes may malfunction or shut down due to a voltage dip resulting in significant financial losses.

Voltage dips are due to short-duration increases in current magnitude, whereas voltage dips due to short circuits and earth faults are of most concern for customers.

This report presents the results from an international working group sponsored by CIGRE, CIRED and UIE aimed at improving the understanding of the compatibility between installations and the electricity supply. The working group was founded in 2006 and its work stretched through the first months of 2009. The working group has addressed a number of aspects of the immunity of equipment and installations against voltage dips and also identified areas were additional work is required. Compatibility between equipment or installations and the power supply can be improved in a number of ways: through alterations to the power grid; by installating mitigation equipment at the interface between the sensitive equipment and the grid; and by improving the equipment or the installation. This report only addresses the latter way of compatibility improvement, without expressing any opinion about whether this is the preferred way.

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