Optimal reactive power dispatch algorithm for voltage stability improvement

This paper presents an algorithm for monitoring and improving voltage stability in power systems for a base case and credible contfigency conditions. The monitoring methodology proposed here is based on the L-index of load buses. This index uses information on a normal load flow and is in the range of O (no load of system) to 1 (voltage collapse). The control clgainst voltage collapse is based on minimizing the sum of the squares of L-indices for a given system operating condition. The proposed algorithm gives an optimal setting of various control devices like generator excitation, switchable VAR compensators and OLTC transformers. The algorithm also identifies critical OLTCs that should be made manual to avoid possible voltage instability due to their operation based on voltage improvement criteria under peak load conditions. The proposed algorithm has been tested under simulated conditions on a number of real Indian power systems and the results obtained for a 24-node EHV Indian power network and for a modified IEEE 30-bus system are included for illustration purposes