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Cool high-power drives

13 April 2011

Danfoss VLT high-power drives are available up to 1.4MW. Thanks to their power module design, they are extremely energy efficient by as much as 98%. However, a loss of just 2% for a 450kW drive is still 9kW, and this heat must be removed in order to protect the drive and ensure its long service life.

With the increased power density of Danfoss VLT drive power sections and a mounting configuration that allows zero side clearance, up to ten 450kW drives can be installed against a wall of just 6m in length. With such compact installations comes the problem of cooling; ten 450kW drives – even if they offer an efficiency as high as 98% - produce 90kW of ‘waste’ heat that must be removed from the installation.

Initial cooling equipment and energy consumption costs for cooling add significantly to the drive’s lifecycle costs. Danfoss has addressed this problem by developing a novel cooling configuration that is both cost effective and highly efficient in terms of heat transfer. This ‘back-channel’ cooling system draws cool air from outside the control room and through the drive, subsequently exhausting it back outside. In this way, the majority of the cooling air and 85% of the heat losses are passed to the outside of the control room.

VLT high-power drives achieve their impressive energy efficiency thanks to the use of highly energy efficient power transistors, which are mounted on aluminium or copper heat sinks. These heat sinks effectively separate the heat dissipation side of the power modules from the interior parts of the drive. Cooling air passes only over the heat sink surfaces and does not enter that part of the drive containing the sensitive control electronics.

This separation therefore ensures that the electronic components do not come into contact with dust or any harmful residues that may be present in the cooling air, extending the life of the drive and improving the overall reliability of the drive installation. Thus ambient air can be forced through the cooling duct without risk of contamination and subsequently passed out of the enclosure or the building altogether.

Heat gain inside the control room is only 0.3% of the drive power rating and excess heat from a 450kW drive will be just 1.35kW.

The back-channel cooling system is standard on Danfoss high-power drives, regardless of the enclosure IP rating (IP00, IP21 or IP54). Optional duct kits can be supplied enabling back-channel cooling to be utilised in standard MCC industrial enclosures. These thermally tested kits ensure efficient drive cooling without any compromise to the ingress protection rating of the enclosure. As an option, the back-channel cooling ductwork and heat sinks can be ordered with corrosion protection for installations installed close to aggressive industrial processes.

Compact design
Built-in RFI filters, fuses and disconnects across the range of enclosure options facilitate compact installation of multiple drives with zero clearance between them. Built-in dc coils for harmonic suppression avoid the need for external ac coils, and access to all of the drive’s components is from the front for easy servicing and maintenance.

VLT drives feature Automatic Energy Optimisation vector technology, which minimises passive, damaging motor currents and magnetic flux – maximising the available electrical power from the drive to the application.


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