Home » Industry News » Compressors & Plant Equipment » “Energy saving” PM (permanent magnet) rotary screw compressors up to 75 kw output

Manufacturers of Rotary screw compressors with Permanent Magnet (PM) drive have all experienced problems in the past with air cooled Permanent Magnet motors, although the technology is considered the most advanced new driver for Air compressors.

The main cause of failure was due to overheating, a Permanent Magnet motor fails when the motor temperature exceeds 130°C the properties of the material incorporated in the magnets lose strength and the magnet can be permanently damaged.

The first generation PM motors had insufficient cooling which caused them to overheat when the motor stopped and started too often or the speed went outside the Screw elements designed speed envelope, this can occur when utilizing first generation variable speed drive technology.

The second generation of PM motors were thus designed with greater air cooling capacity to cater for this anomaly, by fitting a separate motor and fan, but it meant you required a bigger footprint to accommodate the cooling fan assembly, besides that the larger cooling fan also drew more power which reduced actual power savings!

This defeated the objective of obtaining optimum efficiency and energy savings were consequently unverified on these first generation VSD compressors.

The third generation of Italian designed PM motors used by Airstream compressors incorporates a special magnetic material called Rare earth Neodymium (NdFeB) which can withstand temperature rises of up to 180 °C the motor thus exceeds IE3 International standards of efficiency, under variable load conditions as well as with limitless stop and starts, the running speed can go down to 25% compared to the limitation of 40% prevalent on most other VSD compressors available in the market today.

The Airstream PM compressor motor is oil cooled using the same lubricant supply cooling down the compressor, which guarantees that the motor temperature will not exceed the compressors operating temperature, as it is controlled by a thermal cut out sensor triggered when the compressor lubricant Exceeds 110°C far below the temperature parameter of the PM motor, efficiency and energy savings quoted on Airstream PM Compressors are thus totally plausible.

There is also a window at the back of the PM not found on previous versions, which makes it easy to verify rotational direction. The unit also does not have conventional roller bearings as the shaft is Morse tapered and magnetically suspended and simultaneously balances the screw air ends bearing load, bolting directly on to the elements flange, it thus does not require a drive coupling arrangement.

Proverbially this makes the motor maintenance free, besides the fact that it will never overheat while the compressor is running and will thus offer optimum efficiency at all times as long as the compressor station is well maintained.

Contact Electroair the official distributors of Airstream PM Compressors in the Western Cape for PM solutions or if you require any further technical information.