Power quality is very important issue recently due to the impact on electricity suppliers, equipment manufacture and customers. Power quality is described as the variation of voltage, current and frequency in a power system. Nowadays, there are so many industries using high technology for manufacturing and process unit. This technology requires high quality and high reliability of power supply. Power Quality problems encompass a wide range of disturbances such as voltage sags/swells, flicker, harmonics distortion, impulse transient, and interruptions. Voltage sags is the most common type of power quality disturbance in the distribution system. It can be caused by fault in the electrical network or by the starting of a large induction motor. Voltage sags are a remarkable source of economic losses. The purpose of this book is tried to analyze and identify voltage sags problem in power quality especially in a distribution system. The simulation will be using PSCAD/EMTDC software. The mitigation techniques that will be studied are such as Dynamic Voltage Restorer (DVR), Distribution Static Compensator (DSTATCOM) and Solid State Transfer Switch (SSTS).