3. Phasor Estimation at Off-Nominal Frequency Inputs

Excerpt

Phasors are a steady-state concept. In reality, a power system is never in a steady state. Voltage and current signals have constantly changing fundamental frequency (albeit in a relatively narrow range around the nominal frequency) due to changes in load and generation imbalances and due to the interactions between real power demand on the network, inertias of large generators, and the operation of automatic speed controls with which most generators are equipped. In addition, when faults and other switching events take place, there are very rapid changes in voltage and current waveforms, and depending upon the definition of frequency one would have to accept that power system waveforms under these conditions contain a very wide band of frequencies ranging from DC to hundreds of kilohertz. The consideration of various interpretations of frequency which are of interest in power system engineering will be considered in Chapters 4 and 6. …