说明：  the objective is to check the real time security By two kinds of performance indices, i.e., active power index (PIP) and reactive power index (PIV) the contingency selection is performed. Using Newton Raphson (NR) iterative method the MATLAB programming code is written for obtaining the solution of load flow equation. Using the algorithm of singular transformation method the MATLAB code for YBUS is written as the elements of the bus admittance matrix (YBUS) used here..