I. INTRODUCTION
Power companies are facing a major challenge in the maintaining of quality and security of power supply due to ever-increasing interconnections and loading in large power system networks. Economic constraint has forced the utilities to operate generators and transmission systems very near to maximum loadability point. One of the major problems that may be associated with such a stressed system is voltage instability or collapse and that causes a steady-state security problem. To operate a power system with an adequate security margin, it is essential to estimate the maximum permissible loading of the system using information about the current operating point. The maximum loading of a system is not a fixed quantity but depends on various factors, such as network topology,availability of reactive power reserves and their locations etc. this paper deals with maximum permissible loading of a power system using some locally measurable quantities. When the loading of a power system approaches the maximum power or voltage collapse point, the voltage magnitude of a particular bus (or area) decreases rapidly. However