Chapter 16 DC Machines

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Chapter 16 DC Machines
Rotating DC Machines. Shunt-Connected and
Separately Excited DC Motors. Series-Connected
DC Motors. Speed Control of DC Motors. DC
Generators.
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Chapter 16 DC Machines

• Select the proper motor type for various
  applications.
• 2. State how torque varies with speed for various
  motors.

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3. Compute electrical and mechanical quantities
using the equivalent circuit for dc motors. 4.
Use motor nameplate data. 5. Understand the
operation and characteristics of shunt-connected
dc motors, series-connected dc motors, and
universal motors.
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The DD(X) class of destroyers currently under
development by the United States Navy will use an
electrical propulsion system. Similarly enhanced
electrical-power systems are being developed to
provide the electrical power needed for
drive-by-wire systems in automobiles.
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Basic Construction of Motors
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Characteristics of AC Electrical Motors
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Characteristics of DC Electrical Motors
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Armature and Field Windings
The purpose of the field winding is to set up the
magnetic field required to produce torque. The
armature windings carry currents that vary with
mechanical load. When the machine is used as a
generator, the output is taken from the armature
windings.
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PRINCIPLES OF DC MACHINES
Study of the idealized linear dc machine
demon-strates how the principles of
electromagnetism apply to dc machines in general.
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ROTATING DC MACHINES
The basic principles of rotating dc machines are
the same as those of the linear dc machine.
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Equivalent Circuit of the DC Motor
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Magnetization Curve
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SHUNT-CONNECTED DC MOTORS
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TorqueSpeed Characteristic
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Separately Excited DC Motors
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Permanent-Magnet Motors
Separately excited and permanent-magnet motors
have similar characteristics to those of
shunt-connected motors.
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SERIES-CONNECTED DC MOTORS
Field windings are designed differently
for series-connected machines than they are
for shunt-connected machines.
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Universal Motors

• For a given weight, universal motors produce more
  power than other types.
• 2. The universal motor produces large starting
  torque without excessive current.

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3. When load torque increases, the universal
motor slows down. Thus, the power produced is
relatively constant, and the current magnitude
remains within reasonable bounds. 4. Universal
motors can be designed to operate at very high
speeds, whereas we will see that other types of
ac motors are limited to 3600 rpm, assuming a
60-Hz source.
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SPEED CONTROL OF DC MOTORS
1. Vary the voltage supplied to the armature
circuit while holding the field constant. 2.
Vary the field current while holding the armature
supply voltage constant. 3. Insert resistance
in series with the armature circuit.
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Separately Excited DC Generator
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Equations for the Separately Excited DC Generator
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