Articles
Active Filters Simplify Harmonic Mitigation
December 13, 2006
•Article: Active Filters Simplify Harmonic Mitigation
By Reza Tajali, P.E.
Square D/Schneider Electric Power Systems Engineering
Awareness of the environmental impact of high power consumption and the necessity of reducing the cost of energy have made variable frequency drives (VFD) uniformly present in modern water treatment plants. VFDs and the associated control equipment modify the frequency of the power that is delivered to the motor, changing the pump speed. Therefore, the pump can be run at the optimum speed for the level of flow that is needed, minimizing the energy consumption.
From the viewpoint of the 60 HZ power system, the VFD is a non-linear load, which draws a distorted current such as the waveform. This waveform is very rich in 5th and 7th harmonics and contains lesser amounts of the 11th and 13th harmonics. [this spectrum is true for 6-pulse PWM's, but do we know that 6-p is the predominant VFD in w/ww? Many folks, us included, have been supplying 12&18-p drives, but do we know what the mix in installed base is?] Higher order harmonics are present in smaller quantities and only cause problems in rare cases where high order resonant conditions exist in the system.
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•Article: Active Filters Simplify Harmonic Mitigation
SOURCE: Schneider Electric
