A new technique for voltage stability analysis in a power system and improved loadflow algorithm for distribution network

Voltage collapse may occur in a power system due to loss in voltage stability in the system. Therefore voltage stability analysis is important in order to identify critical buses in a power system, i.e. buses which are closed to their voltage stability limits and thus enable certain measures to be taken by the control engineer in order to avoid any incidence of voltage collapse. This paper presents a new technique to determine the static voltage stability of load buses in a power system for a certain operating condition and hence identifies load buses which are close to voltage collapse. A voltage stability index with respect to a load bus is formulated from the voltage equation derived from a two bus network and it is computed using a Thevenin equivalent circuit of the power system referred to a load bus. This index indicates how far the load buses are from their voltage stability limits and hence identifies the critical buses. The performance of this index is tested using a 9 bus radial network and the 24 bus IEEE Reliability Test System for its validity. A comparison is also made between this index and the impedance ratio used by Sterling et al. as the voltage collapse indicator. This paper also presents a new loadflow technique to compute the power flow solution for a radial network which is found to be more superior than the Second Order Newton Raphson and Distflow since it takes less iterations to give a loadflow solution.