2 Engineering
2.7 Braking resistances
36
DC1-S…20…, DC1-S…OE1 Variable Frequency Drives
05/21 MN040058EN
www.eaton.com
2.7 Braking resistances
In certain operating states, the motor may run as a generator in certain
applications (regenerative braking operation).
Examples include:
•
Lowering in hoisting gear and conveyor applications
•
Controlled speed reduction in the case of large load inertias
(flywheels)
•
A fast speed reduction in dynamic travel drives
When the motor operates as a generator, its braking energy will be fed into
the variable frequency drive’s DC link via the inverter. DC link voltage U
DC
will be increased as a result. If the voltage value is too high, the DC1-S…
variable frequency drive will disable its inverter, after which the motor will
coast uncontrolled.
If there is a braking chopper and a connected braking resistance R
B
, the
braking energy fed back into the variable frequency drive can be dissipated in
order to limit the DC link voltage.
DC1-S…
B
-A… variable frequency drives with a frame size of FS2 feature an
integrated braking chopper. The braking resistor is connected to the internal
braking transistor using terminals DC+ and BR so that the resistor will be
connected in parallel to the DC link. In addition to this, the braking chopper
must be enabled using parameter P-34. The braking chopper will be switched
on automatically if the braking energy being fed back causes the DC link
voltage to increase to the switch-on voltage’s magnitude.
It is often difficult to specify a suitable brake resistor for specific applications.
This is due to the fact that not all of the application conditions required for
sizing will be available when the engineering stage starts. Because of this,
and as a simplification, brake resistors are instead usually classified for two
load groups:
•
Low duty
: Low load with short braking duration and low duty factor
(up to about 25 %), e.g., for horizontal conveyors and handling
equipment for bulk cargo and general cargo, sliding doors, and
turbomachinery (centrifugal pumps, fans).
•
High duty
: High load with long braking duration and high duty factor
(at least 30 %), e.g., for chain conveyors, winders, and centrifuges.
Device series
Mains
connection
Voltage class
Braking chopper
on
Braking chopper
off
DC1-S1…
single-phase
115 V
195 V
189 V
DC1-S2…
single-phase
230 V
390 V
378 V
Summary of Contents for PowerXL
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