System impedance As an example, a 400 kW FC 202 drive on a 1000 kVA transformer with 5% impedance results in ~5% THDv (total harmonic voltage distortion) at ideal grid conditions, whereas the same drive on a 1000 kVA, 8% imp. transformer leads to 50% higher THDv, namely 7.5%. Harmonic performance Each harmonic mitigation technology has its own THDi characteristic which is load dependent. These characteristics are set at ideal grid conditions without pre-distortion and with balanced phases. Variations hereof will result in higher THDi values. Fulfilling the standards To determine whether or not the harmonic pollution of a given application/grid exceeds a specific standard, many complex calculations must be done. With the help from free Danfoss MCT 31 harmonic calculation software, this is made easy and less time consuming. Width (mm) THDi (%) 50 40 30 20 10 0 5.5 30 90 315 630 1000 (kW) Drive power rating Total Harmonic distortion Each drive generates its own total harmonic current distortion (THDi) which depends on the grid conditions. The bigger the drive is in relation to the transformer the smaller the THDi. 3500 3000 2500 2000 1500 1000 500 160 355 710 VLT® 12-pulse w/o autotransformer AHF LHD/AAF VLT® 12-pulse w/o autotransformer AHF LHD/AAF (kW) Wall space In many applications the amount of available wall space is limited and must be utilized to the greatest extent possible. Based on different technologies, the various harmonic solutions each have their optimum size and power relationship. System efficiency The running cost is mainly determined by the overall system efficiency. This depends on the individual products, true power-factors and efficiencies. Active solutions tend to keep the true power-factor independent of load and grid variations. On the other hand, active solutions are less efficient than passive solutions. | Content | Danfoss Drives · DKDD.PB.202.A8.02 21
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