As we have seen in section 5 of Chapter 8, most converter-fed drives causedistortion of the mains voltage which can upset other sensitive equipment,particularly in the immediate vicinity of the installation. We have also discussedsome of the options available to mitigate such effects. This is, however, a complexsubject area and one which, in most cases, requires a systems overview rather thanconsideration of a single drive or even group of drives. It requires an intimateknowledge of the supply system, particularly its impedances.With more and larger drives being installed, the problem of mains distortion isincreasing, and supply authorities therefore react by imposing increasingly stringentstatutory limits governing what is allowable.The usual pattern is for the supply authority to specify the maximum amplitudeand spectrum of the harmonic currents at the point of supply to a particularcustomer. If the proposed installation exceeds these limits, appropriate filter circuitsmust be connected in parallel with the installation. These can be costly, and theirdesign is far from simple because the electrical characteristics of the supply systemneed to be known in advance in order to avoid unwanted resonance phenomena.Users need to be alert to the potential problem and, where appropriate, ensure thatthe drive supplier takes responsibility for handling it.Measurement of harmonic currents is not straightforward and here the standardsgiúp với IEC 61000-4-7:2002 cung cấp có giá trị hướng dẫn.
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