Contingency Evaluation of the Nigerian 330kv Transmission Grid

ABSTRACT A single line contingency analysis and generator(s) outages were carried out on 330kV, 27-Bus power network using MATPOWER 4.1 embedded in MATLAB to carry out fast decoupled load flow studies in order to identify the voltage violation at various buses, determine power losses at the transmission lines and to compute the performance indices. The performance indices were further ranked in accordance with their severity index. Voltages less than 0.95pu were assumed to be low voltages and voltages greater than 1.05pu were also assumed to be high voltages. We also assumed that power losses greater than 5% are unacceptable. So a base case comparative analysis of the load flow studies using three conventional methods showed that Gauss Seidel could not converge in 0.93seconds and 1000 iterations, Newton Raphson converged in 0.15seconds and 6 iterations. However, Fast Decoupled Load Flow converged in 0.01second and 28 iterations. Hence, owing to its time for numerical iteration, its capacity to hold as many data as possible and its merit of having a matrix alteration formula that can be incorporated and used to simulate problem of contingencies involving power system equipment outages without involving the inversion of the Jacobian matrix for all iteration, then FDLF is considered extensively in the research work. Thereafter, outages of one and two generators are considered to investigate their effect on the voltage drop and power loss. Further, N-1 secure was also carried out on the transmission lines to investigate the performance indices of the lines which were later ranked in accordance with their severity. The outcome of the simulations showed that at a time when there was an outage of Kainji-GS, low voltages were found at Kano, Jos, Gombe, Kaduna, Katampe, Oshogbo, Ajaokuta, New Haven, Aiyede, Ikeja-West, Onitsha, and Akangba buses. And there were also power losses greater than 5% at Ikeja-West to Egbin, Ikeja-West to Benin, Oshogbo to Benin, Kaduna to Shiroro, Kano to Kaduna, Jos to Kaduna and Jos to Gombe. Moreso, it is pertinent to mention that the outage of Kainji GS and the outage of Calabar and Sapele GS showed low voltages at the same buses. The single line contingency evaluation carried out shows that transmission lines from Kaduna to Shiroro have the highest performance indices and ranked number one. The ranking continued until the line with the least severity index which was found to be Jebba GS to Jebba TS.