Enhancement of power quality using unified power quality conditioner in distribution systems: a case of Mufindi paper mills, Iringa, Tanzania

With the increase of non-linear loads in electric power systems, power quality distortion has become a serious issue in recent years. In the paper industry, the main production line needs high quality electric power because it consists of several coupled motors working simultaneously together with precise speed. Mufindi Paper Mills experiences voltage variations problems caused by system faults, switching of power lines and capacitor banks, and large motor start-ups that result in undesired speed and stoppage of motors. These power quality disturbances cause paper rolls to break, poor paper quality, process downtime, revenue losses, idle work forces, wasted energy during process restart and failure of equipment. Power quality problems have received a great attention nowadays because of their economical impacts on both utilities and customers. In this research, a unified power quality conditioner (UPQC) was designed, modeled and simulated by synchronous reference frame theory. The proposed system is comprised of series and shunt inverters, which can compensate the Voltage sags and swells. PI controller was used to stabilize the DC link voltage and balance the active power between the shunt and series inverters and the Phase-Locked Loop generated reference signals. The proposed UPQC system was analyzed using MATLAB/SIMULINK software. The simulation results confirmed the correct operation of the proposed system. Also, from the analysis, the losses incurred by Mufindi Paper Mills was estimated as USD 10,066,761, and the revenue losses incurred by TANESCO was USD 3,644,734 for three years under study. TANESCO and customers have to install UPQC, which has the capability of improving different power disturbances like voltage sags/swells, voltage unbalance and flicker.