Dc Synchronous Machines

DC Machines:


Main Parts:
• • • • A stationary stator : carries field poles or field coils Rotor: carries armature or armature windings Commutator: for ac to dc conversion Brushes : slides on commutator and collect or supply dc current

• The field poles, which produce the needed flux, are mounted on the stator and carry windings called field windings or field coils • The armature core, which carries the armature windings, is generally on the rotor and is made of sheet-steel laminations. • The commutator is made of hard-drawn copper segments insulated from one another by mica. • armature windings are connected to the commutator segments over which the carbon brushes slide and serve as leads for electrical connection. The armature winding is the load-carrying winding.

Electromagnetic Energy Conversion:
1. When armature conductors move in a magnetic field (produced by the current in stator field winding), voltage is induced in the armature conductors. When current carrying armature conductors are placed in a magnetic field (produced by the current in stator field winding), the armature conductors experience a mechanical force.


These two effects occur simultaneously in a DC machine whenever energy conversion takes place from electrical to mechanical or vice versa.

Electromagnetic Force, f

f=Bli, where B, f and i are mutually perpendicular.

Motional Voltage, e

e=Blv, where B, v and e are mutually perpendicular.

Wire loop rotating in a magnetic field.


Elementary DC Generator with Commutator and Brushes:



Force on a current-carrying wire in a magnetic field.


Flux compression and resulting force.


Commutator and Brushes on DC Machine
To keep the torque ( or current) on a DC machine from reversing every time the coil moves through the plane perpendicular to the magnetic field, a split-ring device called a commutator is used to reverse the current at that point. The...