Use of V-I characteristic as a tool to assess the static voltage stability limit of a power system

P-V or Q-V curves are very commonly used to determine the maximum permissible load or static voltage stability limit of a power system. Voltage versus current curve or V-I characteristic is presented as a tool to assess the voltage stability limit. It requires only bus voltage and current data at present and some immediate past operating points. The above data are processed through the least squares method to establish the V-I characteristic. The extrapolated part of the characteristic is then used to estimate the critical load at the verge of voltage collapse. The proposed method does not require the knowledge of other system parameters or system-wide information. Any change in system condition usually modifies the V-I characteristic and thus the effect of the change is indirectly incorporated in finding the critical load through the V-I characteristic. The effectiveness of the proposed method is vigorously tested on the IEEE 30-bus system. Some of the results obtained by the proposed method are also compared with the corresponding actual values found through repetitive power flow simulations and are observed to be in excellent agreement.