This thesis deals with problems related to voltage stability in the highvoltage transmission system, specially from the aspect of new transitions of utilities. Two main cours will be highlited, first one is the demand for the bigger generations and transmissions capacities, and second one is the permanent process of deregulations and privatizing process. The causes of voltage instability were analyzing. These causes can have a very strong influence at each part and device in the power system, also during the process of planning and operating the system preventive and corrective actions have to be taking. This special measurement must be implementing because of alleviation the negative consequence of voltage instability. Three main factors are dominant in the time frame of dynamics of voltage stability, dynamics, and static reserve of reactive power, voltage automatic regulation and the load characteristics. Steady state approach in the thesis attention has focused on the voltage regulation and load characteristics. In the very beginning of each analysis has made an initial calculation. First step is analysis of result of load flow calculation, considering the wide spread conditions of the power system, during the normal and contingency state. Here have analysis of these terms on northwest part of Croatian power system. Special conditions for the initial voltage instability states have calculated. These particular model of power system have used to perform and analysis influence of automatic voltage regulator and load characteristics. In the very beginning of the voltage instability, voltage regulator action like blocking and tap reversing together with load characteristics who are dominantly have constant impedance characteristic, have very positive influence to decelerating the speed of degradation system characteristics. In the other words, these actions are not enough to stop voltage collapse; they are only giving some time for the corrective actions have been taking. In the whole system must be reconsidered the conditions. On the system level must be realize central or automatics blocking voltage regulation, together with possibilities of tap reversing. Future work has to take investigation of load modeling with new load characteristics definitions in our power system. This is not enough for complete alleviation of voltage instability problems. In the system has to be implemented the undervoltage shedding and upgrade exist wide area monitoring and wide area protection. Today load flow calculations have to been perform on the classical way with Gauss-Seidel and Newton-Raphson technique, together with many variation and modifications of these technique. To avoid the problem of singularity of Jacobian matrix other methods has developing like a continuation power flow. Special attention has to be give to Jacobian matrix, the result of the analysis can give to us very useful criteria for the voltage sensitivity index.