Selection of pilot buses for VAR support and voltage stability risk analysis

The primary objective of this thesis is to develop an index for the placement of reactive power support devices to ensure reliable operation of power systems. It is especially aimed at improving the load voltage profile and system security when loading is increased. Maintaining a good system voltage profile and security is an important aspect in voltage stability studies, especially with the ever increasing power consumption and system disturbances or contingencies. A new VAR support placement algorithm is developed using a standard continuation power flow and N-1 contingency criterion to pinpoint the best locations for the placement of VAR devices. The objective formulation takes into account the worst case voltage deviations at all load buses and at the same time maximizes the loading margin under different contingencies and loading levels. The algorithm has been tested on three standard benchmark test systems and demonstrates that the proposed algorithm improves considerably when compared to an existing method, for locating a suitable site for VAR support.;The secondary objective of this research focuses on the important aspect of estimating and quantifying the voltage collapse risk with and without the VAR support. It is motivated by the perception that VAR support guarantees additional security for the current system and is economically justifiable. A decision tree based model is designed for estimating the risk, which accounts for both the future system uncertainties and the consequences associated with violation of limits and voltage collapse. A case study on the standard IEEE 24 bus reliability test system investigates the different scenarios and evaluates the risk. The results prove that in spite of high installation costs, an SVC can make the system more reliable and ensure cost savings