Low voltage model for the study of slow disturbances in medium voltage grids

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The proliferation of both, sensitive and pollutant loads at the users equipment has placed the power quality issue as an important challenge for facilities and utilities. Power system simulation programmes are powerful tools to study the generation and propagation of disturbances in order to establish a feed back with the measuring plans.The main difficulty with power system simulation programmes applied to power quality studies in medium voltage networks is the accuracy of the model of the network itself, in particular that of the loads. Numerous load models of individual LV components are reported in the literature. If the composition of these loads at different sites is adequately known, the aggregation method adapted with field measurements may be used to obtain a global load model for higher voltage network levels. These methods present a weakness since the measurements are carried out in the steady state or, in the best case, in the pre and post steady states for the long time disturbances leading, therefore, to non-accurate results.This paper presents a technique to obtain a LV load model adapted for the study of the long duration disturbances, also called slow disturbances, which goes beyond the classical methods and also exploits the measurements ‘during’ a long time disturbance. This model combines a static and a dynamic components which take into account the power consumption of the passive and active loads of an industrial plant. The process for obtaining the model will be explained and the results of the proposed models in ATP-EMTP environment are verified against the measured voltage and current waveforms.