Voltage Sags In Power System

The voltage sag, one of the most important dynamic power quality disturbances, may cause the misoperation of an electric power system's sensitive loads and cost a lot of money. Voltage sag has been given great interests all over the world, especially in the industrialized countries.This thesis presents the basic concepts, the characterization of voltage sag, which includes magnitude, duration, and phase-angle jumps. The basic voltage sag analytical techniques based on circuit theory and reliability theory is followed. Methods of their measurements and calculations are also been discussed. Stochastic assessment and harmfulness of voltage sags are given out, too. A new method based on fault analysis (short circuit) theory is given out to estimate voltage sag levels and the number of voltages sags at a particular customer location in a distribution system. As an example, the IEEE 30 nodes system has been calculated and the results been analyzed. In the end some countermeasures against voltage sags are given out.