Harmonic current distortion is caused by the 6-pulse diode rectifier of the variable speed drive. The harmonic currents are affecting the installed serial

equipment identical to reactive currents. Consequently harmonic current distortion can result in overheating of the supply transformer, cables etc. De-

pending on the impedance of the power grid, harmonic current distortion can lead to voltage distortion also affecting other equipment powered by the

same transformer. Voltage distortion is increasing losses, causes premature aging and worst of all erratic operation. The majority of harmonics are reduced

by the built-in DC coil but if additional reduction is needed, Danfoss offers two types of passive filters.

The Danfoss AHF 005 and AHF 010 are advanced harmonic filters, not to be compared with traditional harmonic trap filters. The Danfoss harmonic filters

have been specially designed to match the Danfoss frequency converters.

AHF 010 is reducing the harmonic currents to less than 10% and the AHF 005 is reducing harmonic currents to less than 5% at 2% background distortion

and 2% imbalance.

3.6.17 Output Filters

The high speed switching of the frequency converter produces some secondary effects, which influence the motor and the enclosed environment. These

side effects are addressed by two different filter types, -the du/dt and the Sine-wave filter.

du/dt filters

Motor insulation stresses are often caused by the combination of rapid voltage and current increase. The rapid energy changes can also be reflected back

to the DC-line in the inverter and cause shut down. The du/dt filter is designed to reduce the voltage rise time/the rapid energy change in the motor and

by that intervention avoid premature aging and flashover in the motor insulation. du/dt filters have a positive influence on the radiation of magnetic noise

in the cable that connects the drive to the motor. The voltage wave form is still pulse shaped but the du/dt ratio is reduced in comparison with the

installation without filter.

Sine-wave filters

Sine-wave filters are designed to let only low frequencies pass. High frequencies are consequently shunted away which results in a sinusoidal phase to

phase voltage waveform and sinusoidal current waveforms.

With the sinusoidal waveforms the use of special frequency converter motors with reinforced insulation is no longer needed. The acoustic noise from the

motor is also damped as a consequence of the wave condition.

Besides the features of the du/dt filter, the sine-wave filter also reduces insulation stress and bearing currents in the motor thus leading to prolonged

motor lifetime and longer periods between services. Sine-wave filters enable use of longer motor cables in applications where the motor is installed far

from the drive. The length is unfortunately limited because the filter does not reduce leakage currents in the cables.

MG.20.X1.22 - VLT

Remote Site Products - 1-888-532-2706 - www.remotesiteproducts.com

http://www.remotesiteproducts.com/p-20783-Danfoss-131X8145-VLT-Automation-VT-Drive-VFD-FC322-460V-.5-HP.aspx

Automation VT Drive FC322 Design Guide

is a registered Danfoss trademark

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