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12.
The Differences between a 3-Phase Motor Generator
and a DC Motor Generator
The wind turbine used in the following experiments uses a 3-phase motor generator, also called
an alternator that is much more efficient at producing electrical power as compared with a
conventional DC motor. The following will point out these differences.
The main difference between a DC motor and a 3-phase motor is the number of coil windings
inside the motor. A DC motor has 1 coil winding whereas a 3-phase motor has 3 coil windings.
The rotor of a DC motor consists of a coil wound around it, but not touching it. This coil is
connected to the motor terminals with a brush type commutator. The function of the commutator
The rectified output of a DC motor generator outputs 2 half cycle positive waveforms as shown
here. Notice that the power drops to zero on every half cycle, which makes DC motors (like the
ones Thomas Edison developed) very inefficient and unreliable.
In contrast to a simple DC motor, there are 3 coils wound on the
stator of the 3-phase motor and they are spaced 120 degrees apart.
There is no commutator in the motor. The three rectified phases and
rectified DC output waveforms are shown below:
is to switch the polarity of the coil as the rotor rotates every half cycle.
Since the brushes are in contact with the rotating rotor, they will
eventually wear out.
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