Both electric utilities and end users are becoming more and more concerned about the quality of electric power. There are three major reasons behind this increased concern: the new generation load equipment are more sensitive to power quality, the raising harmonic level of power systems and the increased end user awareness.
Poor power quality has a number of consequences including high energy usage, higher maintence costs and equipment instability. When entire processes are automated, the efficent operation of machines and their controls becames increasingly dependent on the quality of power. Signs of poor quality can be electrical harmonics or voltage instability.
This dissertation examines the phenomenon of voltage instability and the phenomenon of voltage sags. A voltage sag is a short-duration reduction in the voltage caused by fault or the starting of large loads, for example motors. They are way more common than interruptions but they can cause the sensitive equpments to trip or fail thus they can cause a loss of profit.
This dissertation presents the definition and the caracteristics of the voltage sags, then presents the fundamental principles of protecting our devices from voltage sags. Then I present the international statistics about voltage sags and in the end of the first half I present how can we use some of our protective devices (UPS or flywheel) to control voltage, reactive power and frequency in the power system.
In second half of this presentation I present a working Matlab Simulink model of a DVR or Dynamic Voltage Restorer. I present the steps of making the model and then I present with a simulation how it’s working.