An Approach to the Assessment of Voltage Quality Based on a Modified Power Acceptability Curve

Starting with the Computer Business Equipment Manufacturers´ Association acceptability curves, a procedure for quantifying the voltage quality is proposed. It is based on using the reciprocal of the permissible time duration for each value of the customer voltage. Since the magnitude of the voltage at any network bus changes with time depending on the load curve, the daily average value of the above suggested voltage quality index will provide a suitable figure of merit for the quality assessment. The analysis starts with the derivation of an analytical expression of the voltage quality index, denoted as voltage penalty function, in terms of the voltage. Then, relations are presented for the dependence of this index on the network as well as of the load parameters. Special interest is given to the load factor, the load power factor, its peak value, and the short-circuit level of the power network. The impact of eventual shunt compensation (and its level) on the voltage quality is discussed for both permanently connected capacitors, and for those which are switched only for a certain duration. In the latter case, the effect of the capacitor switching time point is demonstrated. The compensation level, the time point of application, and its duration are the three parameters for which a detailed sensitivity analysis and optimization for the least voltage daily average penalty are conducted. The applicability of the suggested procedure to nonrepeated events in distribution networks is also addressed