Due to Danfoss’ efficient power modules the VLT drives are extremely energy efficient.

Ninety-eight percent of the power supplied is utilised in the application and only 2percent is lost through the drive system.

Despite the small percentage of losses, 2percent of for example 450kW is still 9000W – corresponding to the heat from 150 classic light bulbs. With a series of drives mounted in a control room, there still is an issue to handle.

But Danfoss has expanded its range of VLT drives with power capabilities all the way up to 1.2MW. Drive voltage ratings range from 380VAC through 690VAC. A back-channel cooling method solves the heat loss problem by exhausting the majority of the cooling air and 85percent of the heat loss to the outside of the control room. Furthermore, this cooling air only passes over heat sink surfaces and is not seen by the internal electronics components of the drive resulting in extended life and reliability of the drive. Heat gain inside the control room is therefore only 0.30percent of the drive power rating, and excess heat from a 450kW drive will be only 1350W – corresponding to the heat from only 23 light bulbs – or one heavy-duty vacuum cleaner.

The overall electronic design of VLT Drives together with the use of high quality electronic components is the basis for unsurpassed energy efficiency. Once heat losses in the electronics are limited, so the energy used to operate the fans can also be limited. This way VLT high power drives end up losing only 2percent of the provided energy as heat. The rest is utilised in the application.

The VLT high power drives all have their energy efficient power transistors mounted up against the effective aluminium or copper heat sinks, which at the same time effectively separates cooling air and heat gain from the electronics. With this principle, it is possible to force cold air through the cooling duct without polluting the electronics with dust and other residues from the ambient air. Once controlled, the cooling air stream can be ducted directly outside the cabinet – or outside the building.

Dust, steam and other residues will be carried with the cooling air and deposit on the inside of the ducts. Smooth surfaces and clever designs of the cooling ribs reduce this problem as the cooling ribs are easily cleaned.

As an option, the back channel cooling duct work and heat sinks can be ordered with corrosion protection for installations in harsh environments – salt-air environments near the ocean, for example.

The cooling concept and now provides IP00 chassis mount drives and dedicated duct kits, fitted for mounting the high power drives in standard industrial cabinets such as the Rittal TS8 Series, which makes commissioning extremely easy. With the kit, the built in fans of the drive take in cooling air from outside the cabinet, through the heat sink, and out from the top of the cabinet.Mounted inside the cabinet, the drive is well protected. A remote mounting kit is provided to place the local control panel of the drive on the front of the cabinet, so the drive can be operated without opening the cabinet.

The design of the VLT drives makes them easy to fit in even small installation spaces. Built-in filters, fused dis-connects, enclosure options – including IP54 – and accessories facilitate this compact installation. The need for external ac coils is eliminated by the built-in dc coils for harmonic suppression.

The VLT feature Automatic Energy Optimisation vector technology ensures maximum magnetisation of the motor, minimising passive, damaging currents and flux in the motor.

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Peter Kartanos is with Danfoss Drives A/S, Graasten, Denmark. www.danfoss.com