Estimation of Maximum Loadability in Power Systems by Using Fast Voltage Stability Index

Abstract

The occurrence of voltage collapse is very much dependent upon the maximum load that can be supported at a particular load bus. Any attempt to increase the load beyond this point could force the entire system into instability, leading to voltage collapse. This would indicate that the power system physically could not support the amount of the connected load. This article demonstrates the use of line-based voltage stability index, called Fast Voltage Stability Index (FVSI), in order to estimate maximum loadability of a particular load bus in the system. The process involves an evaluation of voltage stability condition of a system by computing the FVSI for each line. The point at which FVSI closed to a predetermined FVSI limit indicates the maximum possible connected load to a bus termed as maximum loadability. The operating margin in a system can also be estimated by taking the difference between the load at the base case and the maximum load. The estimated maximum loadability on several load buses allows the identification of a weak bus in the system. The load buses were ranked according to their maximum loadability, where the load bus having the smallest maximum loadability was ranked highest. Hence this bus was identified as the weakest bus because it can withstand only a small amount of load increase before causing voltage collapse. This technique was tested on the IEEE Reliability Test System (RTS), and results proved that the proposed technique is able to estimate the maximum loadability in a system. This information is useful to planning or operation engineers in ensuring that any increment in the system will not exceed the maximum loadability, hence violating the voltage stability limit.