1. Under normal or selected contingency, for a chosen load bus, the reactive power loading is increased until the load flow solution fails to converge. The load prior to divergence is maximum load for that bus. 

2. At maximum load, bus voltage profiles and line flow index are determined. 

3. Bus voltage profiles and line flow index are expressed in fuzzy set notation. 

4. Severity index of line flow index and bus voltage profiles are also represented in fuzzy set notation. 

5. Using Fuzzy-If-Then rules severity index for bus voltage profiles and LF 
index are determined. The FIS is tested in MATLAB 7 Fuzzy Toolbox. 

Criticality index for each load bus is computed using equation, CI = Σ SILF + Σ SIVP
6. The above procedure is repeated for all the load buses and for all critical contingencies. 

8. Buses are ranked in decreasing order of Criticality Index. 

![0_image_0.png](0_image_0.png)

## 4 Test Results

The proposed approach is tested on Five Bus Test System. It consists of 2 generators, 3 load buses and 7 transmission lines. 

A) Without Line Outage Contingencies Table 2 shows the voltage profile of load buses at base load and critical load at respective load buses. Critical load of a bus is determined by increasing reactive load at that bus until load flow fails to converge. The load prior to convergence is the critical load of that bus. Table 3 shows line flow index at base load and critical load at load buses without line outage contingency. Table 4 and 5 shows severity index for voltage profiles and line flow index calculated using fuzzy rules shown in Table 1. Table 6 provides the criticality index along with rank obtained from fuzzy approach without line outage contingency. 