A comparative study of voltage stability indices used for power system operation

With the gradual increase in population and increased use of modern machinery, the power demand is always on the rise. Any power network has the ability to cater to a specific maximum volume of load. Increase in load demand makes the system weaker and thus, the power system tends to work under stressed conditions. Increase in system load above a certain threshold may result in cascaded voltage collapse which in turn leads to the system becoming unstable and finally blackout. It thus becomes quite essential to find out the stress conditions of the network during planning stage. Various indices are present in literature to study the health of the system to study how close the system is towards the instability region. In this article, some of the indices have been tried on two conventional electrical systems, viz., WSCC 9 bus system and IEEE 118 bus system and a study has been done to find out the maximum system load that the systems are able to withstand before collapsing. A comparison among all the indices considered is done and a conclusion is drawn as to which of the indices gives a better result.