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Regeneration is a phenomenon that
occurs on curtain types of loads
where the load has the ability to
overdrive the power source supplying
it or raise the DC bus voltage due
to load electrical parameters.
Diode and SCR power rectifiers
cannot absorb the extra energy generated
when inertial type loads are mechanically
overdriven. When a DC motor is overdriven
the motor, in effect, becomes a
generator. The rectifier being a
one way system, due to the reverse
voltage blocking of the semi-conductor,
when a motor regenerates onto the
DC bus, the bus voltage rises. If
this energy is not managed, the
bus voltage can rise to a dangerously
destructive level. A regenerative
absorption circuit, normally designated
as an "RGA", is used to
provide a dissipating path for regenerative
energy and keep the DC voltage at
a safe level for both the rectifier
and load. The principle is similar
to a dynamic braking circuit on
a DC motor control.
The Kinetics model RGA consists
of a bank of mill duty resistors,
voltage sensitive circuitry and
a mill duty DC contactor to apply
the resistor bank across the DC
bus to absorb regenerative energy
when it is present.
As a generally established practice,
regeneration absorption circuits
are sized at 10% of the kilowatt
rating of the rectifier or 25% of
the largest motor horsepower. The
DC pickup voltage to apply the RGA
is typically set at 15% above the
nominal DC bus voltage rating. A
250 VDC bus would have an RGA set
for pickup at 290 VDC.
Common applications requiring
a RGA: cranes, elevators, lathes,
boring mills and fans.
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