Contingency Approach for Static Security Assessment on the Nigerian 330 Kv Electric Power Transmission Grid

Abstract

Static security is the property of power system to maintain steady or stable operating state when contingencies such as line outages or component failures occur to avoid economic and technical losses. This study assessed the static security of the Nigerian 330 kV, 30-bus electric power transmission grid using a contingency approach. The steady state performance of the power system was modelled using Newton-Raphson based load flow equations and simulated in ETAP software environment. Bus voltage and line loading violations were determined by observing the voltage profile and line flows compliance with the voltage statutory limit of 0.95 to 1.05 p.u. and 80% loading of the thermal (MVA) limit respectively. N-1 contingency evaluation was conducted on fifty lines of the considered network. Performance index (PI) of the outage lines was determined and used to rank each of the contingency cases. Load flow analysis revealed that New – Haven, Onitsha, Gombe, Jos, Kano and Calabar with voltage magnitudes of 0.9003, 0.9468, 0.6608, 0.8141, 0.8138 and 0.9319 p.u. respectively violated the voltage statutory limit while Okapi-Calabar and Alaoji-Calabar with loading of 101.6 and 84.19 % respectively exceeded the recommended 80% loading of the MVA limit. The system total active line loss was 218.08 MW. Contingency analysis results ranked Benin-Onitsha and Ikeja West-Aiyede having the PI of 80.73 and 3.56 as the most and least critical lines respectively. This study established the suitability of contingency method for the assessment of security of a large-scale network such as the Nigerian electricity grid.