Although Danfoss VLT drives now offer 98% internal efficiency, that 2% loss still represents a fair amount of heat in larger drives. At 450kW, for instance, there is still 9kW of heat to be dissipated from within the drive and when there are a series of drives in a control room, heat is an issue that must be taken into consideration when planning the installation.
With advanced air-cooling techniques Danfoss has managed to expand its air-cooled VLT range to 1,200kW (380-690V), thanks to a novel cooling channel at the rear of the drive, which extracts 85% of the heat created, and ensuring its exhaust to the outside of the control room. This heat is effectively isolated from the drive control circuitry resulting in extended drive life and higher reliability.
Innovative heat management techniques have been adopted to direct most of the heat away from the control section of the drive. High-efficiency power transistors are mounted on thermally efficient heat sinks (copper in some instances) with the heat sink fins mounted into a cooling duct at the rear of the drive. Cool air can be drawn from, and exhausted to the outside of the control room or even from outside of the building while intelligent design of the heat sink ribs ensures minimum retention of ambient pollutants.
Corrosion protection of the cooling circuits is available as an option to cope with harsh environmental conditions. And where the customer requires conformity with standard industrial enclosures, Danfoss has developed the concept into an IP00 format that enables the drives to be mounted into standard industrial cabinets such as the Rittal TS8 series.