| Popis: |
Present distribution networks are undergoing a rapid increase in the level of harmonic pollution, because of the installation of an increasing number of distorting receivers, with increasing unit powers. The compensation of the reactive power in such a network, usually carried out to increase the average power factor of the consumers, can cause phenomena of amplification of the deforming regime, with negative effects on the efficiency and operational safety of the installations belonging to both the distribution operator and consumers. To avoid or mitigate these negative effects, the installation of high-power shunt capacitor banks will usually be done by associating them with or including in-absorbing passive filters or detuned filters. For a correct choice of compensation solutions, it is necessary to perform an analysis of the network in the frequency domain, to identify the parallel resonant frequencies, produced because of the presence of capacitor banks. This analysis is based on the determination of the harmonic impedances “seen” in the nodes of the network, of which the most important is the node to which the compensation installation will be connected. The harmonic impedance depends on both the characteristics of the distribution network and those of the consumers, including the compensation-filtering installations, the correctness of its determination depending on the correctness of the modeling of the circuit elements. The article presents a case study of an area of MV distribution network, carried out by modeling in the MATLAB - Simulink program environment which has in its own library a “measuring instrument” that allows the rapid determination of harmonic impedance. It is considered a stationary regime of high active and reactive load, over which an accentuated harmonic pollution is superimposed, modelled by high rms harmonic currents. Several solutions of passive current compensation on the fundamental frequency and on the most important harmonic frequencies are compared, using as main criterion the value of the total harmonic voltage distortion in the network nodes. |
