Voltage sag in electric power system

As one of the most important part of power quality, voltage sag has been paid great attention all over the world, especially in the industrialized countries. The basic concept, the characteristics of voltage sag which include magnitude, duration and phaseangle jumps of voltage sag, methods of measurement and calculation were fully discussed. Stochastic assessment and tremendous harmfulness of voltage sag to electric power system and customers were followed. A sag analysis program is of great significance for utilities to enhance their system. In the end some countermeasures to limit and reduce voltage sags were given.