Predicting Generator Coupling Using Power System Impedance Matrices

Abstract

The combination of power flows on multiple lines constitutes a flowgate. Transmission flowgates are one tool being used to deal with wide-area stability issues because experience with dynamic simulation suggests that proximity to a stability limit may be approximated using a transmission flowgate. An inconvenience associated with flowgates, however, is the absence of a defined procedure by which to identify where they need to be implemented in the power system. Knowing which machines swing together as a result of a disturbance somewhere in the system is helpful when considering possible flowgate locations. The concept of how the system impedance matrix can be used to determine which generators in the power system move together for a given contingency is discussed in this thesis. Once a mathematical model of a multi-machine power system is formed, the system impedance matrix can be extracted from this model and used to suggest groups of machines which are likely to be electrically coupled together when the system is perturbed. The term “influence” will be used to refer to the degree to which impedances affect the total dynamic coupling because several factors affect the coupling between machines under dynamic conditions. This electrical coupling is validated by the in-phase behavior of generator rotor angles in the system. The generator rotor angle plots are obtained through time domain simulations and compared via visual inspection to the groups of machines as identified by the system impedance matrix values.