05-10-2010, 12:47 PM
[attachment=5042]
prepared by:
Hatem Al-Ghannam
Introduction
-The stator of the dc motor has poles, which are excited by dc current to produce magnetic fields.
-In the neutral zone, in the middle between the poles, commutating poles are placed to reduce sparking of the commutator. The commutating poles are supplied by dc current.
-Compensating windings are mounted on the main poles. These short-circuited windings damp rotor oscillations
-The poles are mounted on an iron core that provides a closed magnetic circuit.
-The motor housing supports the iron core, the brushes and the bearings.
-The rotor has a ring-shaped laminated iron core with slots.
-Coils with several turns are placed in the slots. The distance between the two legs of the coil is about 180 electric degrees.
-The coils are connected in series through the commutator segments.
The ends of each coil are connected to a commutator segment.
-The commutator consists of insulated copper segments mounted on an insulated tube.
-Two brushes are pressed to the commutator to permit current flow.
-The brushes are placed in the neutral zone, where the magnetic field is close to zero, to reduce arcing.
-The rotor has a ring-shaped laminated iron core with slots.
-The commutator consists of insulated copper segments mounted on an insulated tube.
-Two brushes are pressed to the commutator to permit current flow.
-The brushes are placed in the neutral zone, where the magnetic field is close to zero, to reduce arcing.
-The commutator switches the current from one rotor coil to the adjacent coil,
-The switching requires the interruption of the coil current.
-The sudden interruption of an inductive current generates high voltages .
-The high voltage produces flashover and arcing between the commutator segment and the brush.
