criticality of a bus for a specific contingency whereas the FVSI method identifies the weak bus but does not provide the information about the criticality of a bus with respect to selected contingency. Further, additional voltage support devices can be installed at critical buses to improve system stability. 

## Conclusion

A fuzzy based Criticality Index is developed in this paper to rank critical or weak buses in a power system under normal and line outage contingencies. 

Line Flow index and voltage profiles at load buses are evaluated using fuzzy rules to compute the Criticality Index, which is further used to rank the critical buses. The identification of a critical bus in a power system is useful in determining the location of additional voltage support devices to prevent possible voltage instability. The proposed method is tested on Five Bus Test System. 

## References

1. R. A. Alammari, "Fuzzy System Applications for Identification of Weak Buses in Power Systems", The Arabian Journal for Science and Engineering, Vol. 27, No. 

2B, Oct. 2002. 

2. Y.Y. Hong and C.H. Gau, "Voltage Stability Indicator for Identification of the Weakest Bus /Area in Power Systems", IEE Proceedings Generation Transmission Distribution, Vol. 144, No. 4, July 1994. 

3. I. Musirin and T.K. Abdul Rahman, "Estimating maximum loadability of weak bus identification using FVSI", IEEE Power Engineering Review, Nov. 2002. 

4. Y.L. Chen, "Weak Bus-Oriented Optimal Multi-objective VAR Planning", IEEE 
Transactions on Power Systems, Vol.11, No.4, Nov. 1996. 

5. Y.H. Song H.B. Wan, A.T. Johns, "Kohonen neural network based approach to voltage weak buses/areas identification", IEE Proceedings Generation Transmission Distribution, Vol. 144, No. 3, May 1997. 

6. Tao He, Sharma Kolluri, Sujit Mandal, Floyd Galvan, Rastgoufard, "Identification of Weak Locations in Bulk Transmission Systems Using Voltage Stability margin Index", IEEE Power Engineering Society General Meeting, 2004. 

7. R. B. Prada, E.G.C. Palomino, L.A.S. Pilotto, A. Bianco, "weakest bus, most loaded transmission path and critical branch identification for voltage security reinforcement", Electrical Power Systems Research, No. 73, pp.217-226, 2005. 

8. A.O. Ekwue, H.B. Wan, D.T.Y Cheng and Y.H. Song, "Singular Value Decomposition method for voltage stability analysis on the National Grid System(NGC)", Electrical Power and Energy Systems, No, 21, pp. 425-532, 1999. 

9. A. M. Chebbo, M.R. Irving and M J H Sterling, "Voltage Collapse Proximity Indicator: Behaviour and Implications", IEE Proceedings-C, Vol. 139, May 1992. 