ABSTRACT

With the ongoing expansions and growth of the electric utility industry, including deregulation in Nigeria, numerous changes characterized by additional generating stations, increase in transmission lines and loads, outages, blackouts, natural disturbance and system faults are experienced thereby pushing the transmission systems closer to their stability and thermal limits and hence, causing the  transfer of reactive power, power swings and oscillations during steady state operating conditions to constitute a major problem of voltage instability. This dissertation uses four FACTS (Flexible Alternating Current Transmission System) devices; Static Synchronous Series Compensator (SSSC), Thyristor Controlled Series Compensator (TCSC), Static Var Compensator (SVC) and Static Synchronous Compensator STATCOM) to investigate the voltage magnitude profile, active and reactive power losses of the Nigerian 48-bus power system network for steady state stability enhancement as well as the responses of the synchronous machine rotor angle, speed, quadrature and direct axis voltage component behind transient reactance, real and reactive power for transient stability enhancement (TSE) during fault and line outages contingences. Power system analysis toolbox (PSAT) is employed in this dissertation to model the Nigerian 48-bus system and optimally placed the FACTS devices at the weakest bus that was found out through the computation for voltage stability sensitivity factor (VSSF) after continuation power flow (CPF) simulation was completed. From the CPF, it was observed that buses 3(Kaduna), 4(Kano), 6(Makurdi), 9(Jos), 13(Osogbo), 22(Ugwuaji) and 28(Ayede) were found to be very weak buses with the following voltage magnitude: 0.45045 p.u., 0.36128 p.u., 0.4527 p.u., 0.45069 p.u., 0.76656 p.u., 0.79321 p.u. and 0.78631 p.u. respectively. Bus 4(Kano) was noticed to be the weakest bus with voltage magnitude of 0.36128 p.u. which was confirmed with the computation of VSSF with the bus having the highest factor of 0.57724 and therefore, the weakest bus and most suitable for the installation of the FACTS devices. Likewise for transient stability analysis, it was observed that buses 11(Kaduna TS), 12(Katampe TS), 13(Gwagwalada TS), 21(Jos TS), 22(Lokoja TS), 25(Ajaokuta TS), 28(Makurdi TS), 30(New Heaven TS) and 35(Ugwuaji TS) were found to be very weak buses with voltages well below 0.800 p.u. as follows: 0.69135 p.u., 0.73763 p.u., 0.74688 p.u., 0.54149 p.u., 0.76864 p.u., 0.79118 p.u., 0.61286 p.u., 0.74694 p.u. and 0.73874 p.u. respectively. Bus 21 (Jos TS) was noticed to be the weakest bus with voltage magnitude of 0.54149 p.u. and the highest VSSF of 0.45519 hence most suitable for the installation of the FACTS devices. For steady-state analysis, the FACTS devices enhance stability through restoring the voltages at those weak buses back to an acceptable value of ±5% of the normal 330 kV voltage magnitude profile (1.0pu). and also mitigating against both real and reactive power losses in the system while in the case of transient stability analysis, the devices exhibited appreciable damping capabilities of power system oscillations illustrated in the reduction of post fault and post outages' settling time of the power system and the enhancement of voltage profile for power system dynamic stability. Eigenvalue method of stability analysis also showed that SVC was the best compensator during both contingencies of fault and line outages. Comparing the four FACTS devices, the generation of more negative eigens as in the case of SVC, indicate the capability of the device to effectively return the system to its marginal stability state faster than other FACTS devices.