Danfoss VLT drive eliminates harmonic disturbances

Edited by the Engineeringtalk editorial team Oct 1, 2009

Danfoss Drives has introduced the VLT Low Harmonic Drive that actively imposes currents into the grid to eliminate harmonic disturbances, so that the sine wave of the grid current is itself restored.

VLT Low Harmonic Drives don't merely reduce or mask current distortion, they attack it at the source by performing real-time analysis and actively imposing currents, as needed, to restore and ensure the highest possible quality sine waves from the power supply grid.

Additionally, they feature a modular design so that most elements are produced in large scale for cost effective production, and as most VLT drives, including VLT Low Harmonic Drives, are individually configured according to the customer's specific needs, they deliver the value of a customised drive for the price of a mass produced unit.

VLT Low Harmonic Drives share the same modular technology platform as the Danfoss VLT high-power drives.

These drives are available in the power range 132-630kW high overload, 160-710kW normal overload, and in a voltage range of 380-480V AC, 50-60Hz.

They meet the IEEE519 recommendation, are available in an IP21/NEMA1 or IP54 (hybrid) enclosure, are UL, cUL and Ctick listed, and carry the CE mark.

They are suitable for: meeting the toughest of harmonics recommendations/standards; installations that are generator powered, or that have generator back-up power; soft power grids; and grids with limited excess power capacity.

'The filter portion of VLT Low Harmonic Drives has the same working principle as a set of noise-cancelling headphones, where the noise or distortion is measured and a computer phase signal is imposed to compensate for that noise,' said Gregers Geilager, product manager, low harmonic drives.

'As a matter of scale, noise-cancelling headphones can inject 100mW at 50-1,000Hz, where VLT Low Harmonic Drives can inject several hundred watts at 250-2,000Hz,' he added.

VLT Low Harmonic Drives cause no increased winding stress and have no impact on bearing life.

They provide the user with a full readout of the unit performance towards the grid, including a graphical overview of grid behavior.

Where the performance of other low harmonic technologies depend on the stability of the grid and load or affect the controlled motor, VLT Low Harmonic Drives continuously regulate the network and load conditions without affecting the connected motor.

In fact, VLT Low Harmonic Drives are motor friendly, with output impulse and shaft voltages compatible with motors conforming to IEC 60034-17/25 and NEMA-MG1-1998 part 31.4.4.2, as per standard VLT drives.

Their design uses a ducted back channel to pass cooling air over heat sinks with minimal air passing through the electronics area.

This allows 85 per cent of the heat losses to be exhausted directly outside of the enclosure, improving reliability and prolonging life by reducing temperature rise and contamination of the electronic components.

There is an IP54 seal between the back-channel cooling duct and the electronics area of the low harmonic drive.