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PV analysis is widely used in the industry for investigating voltage stability problems. However, PV analysis doesn't provide any information about weak facilities with potential voltage problems in the system. This work presents a new method of finding the weak locations in a large scale power system. The new method is based on the relationship between voltage stability and the angle difference between sending and receiving end buses. This relationship is derived for a simplified two-bus system and later applied to a large system. For any given operating point, this new approach calculates the voltage stability margin index (VSMI) of every line in the system. The VSMI provides information about the weak locations and also estimates voltage stability margin from the collapse point - lower VSMI value indicates lower margin and vice versa. The proposed method was applied to one of the critical regions in the Entergy System and was successful in identifying weak facilities. Because of simplified approach and ability to calculate indices quickly, the new approach has a potential of being used in a real time environment.