Investigating the impact of Powerformer on voltage stability by dynamic simulation

This paper provides an overview of a dynamic analysis carried out on a modified Nordic test system to determine the impact of the Powerformer on voltage stability. The unique aspects of the Powerformer are highlighted and the modeling of long-term dynamic elements, especially those pertinent to the study of the Powerformer are discussed. Overexcitation limiter models created for use in the PTI PSS/E analysis program are discussed and utilized. The importance of choosing the right value of overexcitation limiter gain is highlighted and discussed. The impact of the location of the Powerformer and the compensation scheme utilized on the time to collapse following a system contingency is also highlighted and discussed.     

Determination of power system coherent bus groups by novel sensitivity-based method for voltage stability assessment

This paper presents a method that is used to determine the coherent bus groups of a system with similar reactive reserve basins. The differences between this proposed method and another widely accepted voltage stability analysis method are highlighted in this paper and results obtained from the proposed method are discussed. This method is highlighted as being more efficient and requiring comparatively less VQ curve computations. Definitions are proposed for the categorization of buses by the cause of their loading limitation. Results obtained from the test systems support the method's validity and the validity of the bus categories proposed. By determining the reactive reserve margin, it is possible to determine which generators will have an impact on the maximum permissible loading of a bus and which will not. This information is particularly useful for performing voltage stability analysis.