A new approach for estimating voltage collapse point based on quadratic approximation of PV-curves

The MW-distance to voltage collapse is a good indicator of voltage stability at a given operating condition in power systems. This indicator is determined using PV-curves obtained through continuation power flow (CPF) program. The CPF method performs several power flow runs requiring a large amount of computing time. This method is reliable for off-line voltage stability studies, but not very much suitable for real-time operation of today's stressed power systems. Given that, it is essential for system operators to have quick information about voltage stability, a new method is needed for a fast estimation of voltage collapse point. This is the main thrust of the presented paper. It is well known that PV-curves are approximately quadratic functions and become exactly quadratic in close neighborhood of the collapse point. Some authors used this fact and suggested methods that use two to three power flow solutions for a relatively quick, but approximate, calculation of the collapse point. The present paper, also based on quadratic approach, proposes a new method for the determination of voltage collapse that uses only one power flow solution and gives more accurate estimate of the collapse point when compared with other existing methods. Another advantage of the presented method is that the estimation becomes more accurate for stressed power systems. In addition, application of the presented method for performing the top/stable portion of the PV-curves provides an effective step-size that reduces the number of power flow runs. The method is tested using the New England 39-bus and the IEEE 300-bus test systems. The results confirm the effectiveness of the presented method.