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To understand the operation of the commutator, consider the
simplified diagram of Figure 3.4. In the figure, the brushes are
fixed, and the rotor revolves at an angular velocity ω m; - the
instantaneous position of the rotor is given by the expression: θ =
ω mt − γ.
The commutator is fixed to the rotor and is made up in this
example of six segments that are made of electrically conducting
material but are insulated from one another. Further, the rotor
windings are configured so that they form six coils, connected to
the commutator segments as shown in Figure 3.4.
Figure 3.4 - Rotor winding and commutator
As the commutator rotates counterclockwise, the rotor magnetic
◦
field rotates with it up to θ = 30 . At that point, the direction of
the current changes in coils L3 and L6 as the brushes make contact
with the next segment.
◦
Now the direction of the magnetic field is −30 . As the
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