These losses result from a the “resistance” (not electrical resistance) the magnetic material has to being magnetized. The magnetic domains in the material must align to be magnetized and pass flux. These rotating these domains to align takes some energy. Where AC magnetic fields are present, each zero to (+) magnetizing to zero to (-) magnetizing cycle takes some energy to align the domains and this is the hysteresis loss. Different magnetic materials with different crystal structures have very different hysteresis loss characteristics. Hysteresis losses vary proportionally to flux density and frequency.
– These losses appear in the stator in a synchronous machine.
Windage losses –
These are losses from moving air around inside the machine. The rotor “whips” air around and the air resistance causes losses. The rotor fans move air as well. Sometimes the rotor fan losses are included in windage and sometimes they are calculated separately; however, the physics of both are the same. Windage losses vary with the airspeed relative to the motor surfaces squared. In low speed machines these are often trivial, but in large high speed machines (like flywheels and some 400Hz generators) windage losses are a dominant loss. To reduce windage losses and improve cooling, large power generators are sometimes sealed and cooled with hydrogen rather than air.
These losses are induced into the air itself.
Bearing losses –
These are the losses from friction in the motor bearings. Typically these losses vary proportionally with the speed. In hydrodynamic bearings, bearing losses vary with the speed squared.
– These losses are in the bearing material. In hydrodynamic bearings they are in the lubricating fluid.
There are also a number of other losses that are more subtle in synchronous machines they are –