Electrical Power Systems Technology

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362 Electrical Power Systems Technology


where the power source is connected to the motor. Four terminals are ordi-
narily used for interconnection purposes. They may be labeled A1 and A2
for the armature connections, and F1 and F2 for the field connections. If
either the armature connections or the field connections are reversed, the
rotation of the motor will reverse. However, if both are reversed, the mo-
tor shaft will rotate in its original direction, since the relationship between
the armature and field windings will be the same.


SPECIALIZED DC MOTORS

There are several specialized types of motors that operate on direct
current. Among these are dynamotors, brushless DC motors, and DC step-
ping motors.


Dynamotors
One specialized type of DC motor is called a dynamotor. This motor,
depicted in Figure 14-9, converts DC voltage of one value to DC voltage
of another value. It is actually a motor-generator housed in one unit. The
armature has two separate windings. One winding is connected to the
commutator of the motor section, and the other winding is connected to
the commutator of a generator unit. A magnetic field, developed by either


Figure 14-8. Torque and speed characteristics of DC motors: (A) Armature cur-
rent versus torque, (B) Armature current versus speed

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