Voltage sag mitigation in distribution networks

Abstract

Power quality is one of the major concerns and worries in the present era. It has become vital especially with the introduction of sophisticated and sensitive 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 Devices (Dynamic voltage restorer and the Distribution Static compensator) used to mitigate voltage sags in distribution networks. Dynamic voltage restorer injects required voltage in series with the supply voltage for correcting the voltage dip. The D-STATCOM injects a current into the system to mitigate the voltage sags. This project presents the performance of 30Mvar STATCOM installed by Umeme at roofing rolling mills. The Dynamic Voltage Restorer and the Distribution Static Compensator were modelled and simulated in MATLAB/SIMULINK and their performance under different faults causing voltage sags were studied and analyzed. A PI controller was used to control the devices. The performance of the DVR and the D-STATCOM were compared still using the same software. 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. The voltage dip is a serious problem and UMEME should install more FACT devices like the DVR and the STATCOM to mitigate the problem of the voltage dips and reduce on the economic losses experienced by factories.