Increase of Diagnostic Capabilities of Voltage Fluctuation Indicies

Voltage fluctuation indices are parameters describing the power quality in the power grid. These indices consist of two quantities, the amplitude $\delta U$ and the rate f of voltage changes. These indices are determined from changes in the rms values of voltage at time U(t). Voltage fluctuation indices allow statistical evaluation of voltage variation, also considering flicker assession. In addition, voltage fluctuation indices allow recreation of voltage changes caused by disturbing loads that changes its operating state with a frequency of up to 20 Hz. The recreation of voltage changes allows recalculation of voltage fluctuation indices to other parameters describing voltage variations, and allows determination of parameters associated with sources of voltage fluctuations. The paper has been proposed a new method for determining voltage fluctuation indices that allows for the recreation of voltage changes, considering disturbing loads that change their operating state with a frequency greater than 20 Hz. The need to change the method of determining voltage fluctuation indices is justified by the increasing number of power electronics devices, which are the source of this type of disturbances. The quality of the proposed solution was verified by simulation and experimental studies with the use of the short-time flicker indicator Pst.