Mechanical LossesRotational or mechanical losses can be caused by bearing friction, brush friction on thecommutator, and air friction (called windage), which is caused by the air turbulence due toarmature rotation. Careful maintenance can be instrumental in keeping bearing friction to aminimum. Clean bearings and proper lubrication are essential to the reduction of bearing friction.Brush friction is reduced by ensuring: proper brush seating, proper brush use, and maintenanceof proper brush tension. A smooth and clean commutator also aids in the reduction of brushfriction. In very large generators, hydrogen is used within the generator for cooling; hydrogen,being less dense than air, causes less windage losses than air