| Modern power electronics gave rise to many new applications, offering to the customers comfort, flexibility and good efficiency. But its increasing proliferation during the last decade has caused many power quality problems. The latter appear in the form of various disturbances affecting one or more following parameters: The frequency of the system, the amplitude of the three voltages at point of common coupling, the waveform which must be nearest possible to a sinusoid and finally the symmetry of the three-phase system, characterized by the equality of the modules of the three voltages and their relative dephasing.; The perturb voltages in an electrical distribution network are mainly the voltage swell, the voltage sag, the harmonic voltages and the unbalanced voltages. The last two are generally caused by the flow of the harmonic and/or unbalanced currents thus being able to cause severe effects. The passage of these harmonic currents in the impedances of the electric feeder system may generate harmonic voltages at points of common coupling and then pollute the consumers connected to the same electrical distribution network. Among the effects which can cause the harmonic voltages, we quote: the heating, the interference with the telecommunications networks, the malfunctions of certain electric components as well as sub synchronous resonance. As for the voltage sags, they are caused by two types of phenomena: first is known as random, like the lightning or the accidental short-circuits, second is known as intrinsic and it is due to the operation of apparatus with fluctuating load or to the start up of apparatus needing a high starting current. The voltage sags are likely to disturb and degrade the operation of certain installations and thus being able to damage certain equipments. This research project suggests a simple and easy approach to avoid at the same time all the effects mentioned before through the use and the installation of an active compensator between the point of common coupling (PCC) and the load to be protected. The technique used in this project is easy to use, very flexible and very effective. It shows a good efficiency and it gives good results to correct all the disturbances generated by arc furnaces. It is self-adapting as it could be used to correct the defects of harmonics and voltage sags/swells generated by many types of unbalance three-phase loads. |
