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Safest ways to protect permanent magnetic

What’s a permanent magnet (PM) motor?

A PM motor is an ac motor that uses magnets embedded into or attached to the surface of the motor’s rotor. The magnets are used to generate a constant motor flux instead of requiring the stator field to generate one by linking to the rotor, as is the case with an induction motor.

atlas copco bolaite oil cooled pm motor

Atlas Copco Bolaite oil cooled PM motor

 The archenemy – demagnetization

Although the material is called Permanent Magnet, the magnet is not standing forever. It has its own capabilities and limitations. If the material is exposed to high temperatures or impacted by large electrical disturbance, this could cause PM to demagnetize. if this situation happens, the working life of PM will be shortened forever.

Measures are taken to protect PM

To ensure the PM motor has a long working life, Atlas Copco has taken ways to protect and remove this risk.

1.  Adopt high-quality permanent material – SmCo5

SmCo5 has a much higher temperature resistance (250~350℃ ) than commonly used material-NdFeB (60~200℃), this most stably material ensures Atlas Copco’s PM motor could work in high temperature areas.

      • SmCo5 Magnetic stability is higher ( Flux weakening 0.03%/ ℃ )
      • NdFeB Magnetic stability is lower ( Flux weakening 0.19%/ ℃ )

SmCo5 also has a much lower iron content which is 14-17%, whereas NdFeB has a 63.95-68.65%. Higher iron content will cause rust for the motor. This could bring down motor efficiency and increase power consumption.

 2. Use oil to cool down the motor

atlas copco bolaite oil cooled pm motor

Oil cooled pm motor

Cooling oil from the cooler first fully in contact with PM motor shell then send to rotor housing to cool the rotors. With Thermal control system, the PM motor could work safely in low temperatures. This could protect permanent material from demagnetization.

Cooling oil flow chart

Atlas Copco PM motor cooling oil flow chart

Atlas Copco PM motor cooling oil flow chart

  • Low temp. cooling oil adsorb heat from the motor shell, no cooling fan needed for motor
  • Oil then pass through airend, adsorb heat from airend, then go through after cooler


When today’s focusing is on saving energy, Permanent magnet motors are now the most energy-efficient motors for air compressors. Atlas Copco Bolaite has taken measures to ensure that your motor is fully protected in high temperature working conditions. Now it’s the best way to approach energy efficiency with Atlas Copco Bolaite oil cooled PM motor air compressors.


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