Voltage Stability Assessment of the Polish Power Transmission System

PSE S.A. is the sole Transmission System Operator in Poland and, as such, responsible for the provision of reactive power resources for maintaining the voltage within predefined limits. This paper describes the problems associated with the investigation of voltage stability of transmission power grid. Voltage problems are the result of heavy loading of transmission lines and transformers. Voltage instability has been responsible for voltage damage in some parts of Polish Power Transmission System (PPTS) on 26 June 2006. The voltage criteria used for voltage security assessment should require, that the worst bus voltage at post-contingency N-1 and sometimes N-2, must be approximately greater than 0.95 p.u. for generator buses and 0.9 p.u. for others. At the stage of planning, the active power transfer margin may be used as a proximity measure of voltage collapse.