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Dynamic braking is a technique for braking in
which mechanical energy is converted to heat or
electrical energy in order to slow or stop
motion. An all-mechanical dynamic brake consists
of rotating vanes that circulate a viscous fluid
in a manner that generates heat. This is one way
that the power of the wind is harnessed for
space heating. An electric dynamic brake
consists of an electric dynamo in which the
mechanical energy is converted to electric form,
and either converted to heat in a
resistor or returned to the supply lines.
Typically, electric braking is accomplished with
the same machine that serves as the drive motor.
Electric dynamic braking is employed in electric
vehicles, elevators, and other electrically
driven devices that start and stop frequently.
See also
Wind power.
The most common type of dynamic braking will be
explained for a direct-current (dc) motor. To
accomplish braking action, the supply voltage is
removed from the armature of the motor but not
from the field. The armature is then connected
across a resistor. The electromotive force
generated by the machine, now acting as a
generator driven by the mechanical system,
forces current in the reverse direction through
the armature. Thus a
torque is produced to oppose rotation, and
the load decelerates as its energy is
dissipated, mostly in the external resistor, but
to some extent in core and copper losses of the
machine. See also
Direct-current motor.
Electric braking can also be accomplished by
causing the energy of the rotating system to be
converted in the armature to electrical energy
and then returned to the supply lines. This mode
of operation, called
regenerative braking, occurs when the
counter-electromotive
force exceeds the supply voltage. |
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