EVALUATION OF POWER SYSTEM STABILITY RESERVE FOR THE NIGERIAN TRANSMISSION GRID

Abstract

In this study, the stability reserve of the Nigeria transmission network during probabilistic steady state stability and transient stability disturbances was investigated. This research is justified by the frequent occurrence of system collapse over the past decade. The Nigerian transmission grid at the base year (2014) was modelled for power flow and stability evaluations using power system analysis software (Neplan). In order to obtain normal power flow on the base network, convectional FACTs devices (SVCs) and additional circuits to existing lines were added. A continuous power flow algorithm for the evaluation of steady state stability and transient stability reserves is proposed. In this study, the stability reserve of the base transmission grid under random steady state disturbances was evaluated using 64 slack bus and load centre simulation scenarios. Transient stability reserve was evaluated for 280 slack bus and load centre scenarios, under which 3 phase short circuit fault was simulated on selected lines respectively. The lines are Egbin - Ikeja West, Benin – Onitsha, Egbin – Benin, Ikeja West – Oshogbo and Jos – Gombe. In order to improve the stability reserve of the base grid, reinforcement with additional transmission lines, installation of FACTs devices (SVCs) and transmission voltage upgrade of specific buses to 500kV on the existing grid were simulated respectively. Also, an alternative long term transmission grid expansion model with combined transmission lines and SVCs reinforcements only was evaluated for sufficient steady state and transient stability reserve. The obtained power flow for the base network indicates critical voltages at New Haven (East), Sakete (West), Jos (North), Gombe (North), Yola (North) and Damaturu (North). A total of 16 out of 64 steady state stability simulations scenarios were observed to be below the standard stability reserve (20%). A steady state stability reserve of 10% was obtainable for the worst case slack bus/load centre scenario for the base transmission network. Also, there is practically no transient stability reserve for most slack bus/load centre scenarios (i.e 94%). Power flow from respective grid reinforcements simulations shows that: with transmission line reinforcement the steady state stability and transient stability reserves for the worst case slack bus/load centre scenario would improve to 20.3% and 17.2% respectively; the installation of SVCs at Damaturu (North), Gombe (North), Kaduna (North), Katampe (West), Benin (West), Sakete (West), Akangba (West), Oke-aro (West), New Haven (East) and Aja (West) would increase the steady state stability and transient stability reserves for the worst case slack bus/load centre scenario to 22.3% and 9.2% respectively; and upgrading the transmission voltage, steady state stability and transient stability reserves of 21.3% and 12% respectively. Power flow of the alternative long term transmission network with forecasted MW loading up to year 2029 will provide sufficient steady state stability reserve of 35.7% and transient stability reserve of 3%. Standard transient stability reserve will require additional reinforcements with FACTs devices and transmission line. The results obtained from this work are useful for decision making by network operators on location of generation stations and transmission network reinforcements