Voltage Stability and Reactive Power Issues in the National Grid System

Abstract The reactive power requirement on the National Grid system have risen as a result of increased power flows and the shorter timescale on which power stations are commissioned and withdrawn from services. Power transfers across internal system boundaries are found in some cases to be determined by voltage limits and the need to avoid voltage collapse, rather than thermal capability of the transmission plant. In addition, a separate reactive powermarket is also running by the National Grid Transco. This paper reports on the voltage stability andreactive power issues in the UK National Grid System. A brief introduction to the National Grid System is given first. Thenthe paper presents voltage stability analysis methods developed for the system withdetailed descriptions of animproved Singular Value Decomposition method for identifying weak busbars in terms of voltagestability. Numerical results are included on the power system with over 2600 busbars.