Comparison of integration of Phase Shift Transformer (PST) and Flexible Alternative Current Transmission Systems (FACTS) devices in the power system network. Case study: Rwanda power transmission network

Abstract

FACTS devices are used to compensate reactive power on a transmission line, distribution, and generation; this study presents the comparison of the integration of PST, UPFC, and STATCOM in Rwanda‘s 110 kV north hub transmission line for reactive power compensation. The study utilizes MATLAB/SIMULINK (2013a) to mode the Rwanda 110 kV north hub transmission line without compensation, with PST, UPFC, and STATCOM that consists of two-generation NTARUKA and MUKUNGWA, and four buses: NTARUKA bus, MUKUNGWA bus, GIFURWE bus, and RULINDO bus. A power flow study was carried out without compensation to determine weak buses and the problem of instability; it showed that the GIFURWE bus has higher reactive power than other buses. Mathematical modeling was done and this study indicated power flow analysis for each model design. After compensation using PST, STATCOM, and UPFC, the operating per unit voltage at buses was found to be within the minimum limit of 0. 9 P.U. the design without compensation showed the voltage magnitude of buses at 0. 8 P. U; with PST, the voltage per unit of buses varies between 0.988 P.U and 0.997 P.U; with STATCOM, the voltage per unit of buses varies between 0.9 P. U and 1.1P. U; with UPFC, the voltage per unit of buses varies between 0.9 P. U and 1.1 P. U. The findings of real and reactive power showed that the real power of the model with PST and STATCOM was reduced at all buses. This means that the operation of PST and STATCOM causes the losses of real power. The real power of UPFC increased at all buses. This means that UPFC can adjust the transmission of power flow and decrease the real power losses. The result of this study after comparison indicated that UPFC performs better and controls the real and reactive power more than STATCOM and PST, and STATCOM compensates reactive power more than PST. Finally, UPFC improves the voltage stability more than PST and STATCOM.