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VLT Low Harmonic drives – preserve the net quality21 September 2009Frequency converters do not draw current in a linear fashion from the feeder network. As they switch, the rectifier bridges load peaks of energy into the storage devices of the converter such as dc link capacitors. This leads to non-linear peak loads instead of a sinusoidal current flow.
These non-linear currents, reacting with the supply network impedance, result in harmonic distortions of the mains network voltage. To reduce these undesirable effects, Danfoss provides a range of VLT Low Harmonic Drives. They combine, in an ideal manner, all the advantages of active filters with those of the variable speed drive.
The integrated active filter is optimally adapted and eliminates the network effects caused by the drive.
Discrete structure increases availability
An important feature of the new VLT Low Harmonic Drives is, that since the filter function is totally separated from the drive, the motor voltage is identical to the output voltage of the drive. This is an important point especially in retrofit installations. This feature has the advantage that a any failure of the filter section will not prevent the frequency converter from continuing in operation.
While the performance of other technologies for reducing harmonics or instability depends on the regulated motor effect, the new VLT Low Harmonic Drives permanently regulate network and load conditions without affecting the connected motor.
Optimal utilization of transformers
In addition, it optimises transformer and cable usage, since the Low Harmonic Drives absorb and minimise the reactive power. The integrated graphical user interface allows for easy setup, quick configuration and status display.
Cooling via rear duct
A unique cooling concept passes air through a cooling duct on the back on the heat sink and reduces the air circulation around the electronic components. This IP54 duct removes up to 85% of the excess heat. The reliability and durability of the drives is improved by this dramatic reduction of the temperature and reduced contamination of electronic components.
VLT Low Harmonic Drives are perfect solutions for
• Meeting IEEE519 recommendations
• Generator powered installation
• Installations with Generator Backup
• Soft power grids
• Installation of HPdrives in grids with
limited excessive power capacity
Voltage range
• 380 – 480 V AC 50 – 60 Hz
Power Range
160 - 710 kW
(Matching drive frames D, E and F)
Enclosure degree
• IP 21, IP 54
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