Voltage Sag Mitigation in Distribution Networks

Abstract

Power quality is one of the major concerns in the present era. It has become important especially with the introduction of sophisticated devices whose performance is dependent on the quality of the power supply. Power quality is an occurrence manifested as nonstandard voltage, current or frequency. One of the major problems dealt with here is the voltage sag. To solve this problem, custom power devices are used. This project presents Flexible Alternating Current Transmission System (FACTS) devices i.e. Dynamic voltage restorer (DVR) and Static synchronous compensator (STATCOM) used to mitigate voltage sags in distribution networks. A DVR injects required voltage in series with the supply voltage to compensate the voltage sag while a STATCOM injects current into the system to compensate the voltage sags. This project presents the performance of 30MVAr STATCOM installed by Umeme at roofing rolling mills. The DVR and the STATCOM were modelled and simulated in MATLAB/SIMULINK and their performance under different faults causing voltage sags were studied and compared. A PI controller was used to control the devices. The results showed that the STATCOM injected more voltage noise and transients into the system than the DVR. On the other hand, the DVR injected more harmonics and caused more voltage unbalance than the STATCOM. Voltage sags is a frequent costly problem and Umeme should install more FACTS devices like the DVR and the STATCOM to mitigate the problem of the voltage dips and reduce on the economic losses experienced by industries.