DC GeneratorsDC GENERATOR THEORYTo reduce eddy-currents, the armature and field cores are constructed from laminated (layered)steel sheets. The laminated sheets are insulated from one another so that current cannot flowfrom one sheet to the other.HysteresisLossesHysteresis losses occur when the armature rotates in a magnetic field. The magnetic domainsof the armature are held in alignment with the field in varying numbers, dependent upon fieldstrength. The magnetic domains rotate, with respect to the particles not held in alignment, byone complete turn during each rotation of the armature. This rotation of magnetic domains inthe iron causes friction and heat. The heat produced by this friction is called magnetic hysteresisloss.To reduce hysteresis losses, most DC armatures are constructed of heat-treated silicon steel,which has an inherently low hysteresis loss. After the heat-treated silicon steel is formed to thedesired shape, the laminations are heated to a dull red and then allowed to cool. This process,known as annealing, reduces hysteresis losses to a very low value.MechanicalLossesRotational or mechanical losses can be caused by bearing friction, brush friction on thecommutator, or 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 assuring proper brush seating, using proper brushes, and maintainingproper brush tension. A smooth and clean commutator also aids in the reduction of brushfriction.Rev. 0 Page 11 ES-05
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