Braking Resistances - Eaton PowerXL DC1 20 Series Installation Manual

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
will be increased as a result. If the voltage value is too high, the DA1 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
braking energy fed back into the variable frequency drive can be dissipated in
order to limit the DC link voltage.
DC1-...B-A... variable frequency drives (frame sizes FS2, FS3, and FS4)
feature an integrated braking chopper. The brake resistors are connected to
the internal braking transistor with terminals DC+ and BR so that they will be
connected in parallel to the DC link. In addition to this, the braking chopper
must be enabled using parameter P-34 (= 1 or = 2).
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.
Device series Mains
connection
DC1-12... Single-phase
DC1-32... Three-phase
DC1-34... Three-phase
For example, in the case of DC1-34... variable frequency drives, the braking
chopper will be switched on at a DC link voltage of approximately 780 V DC
and then back off at 756 V DC. During this stage, the braking transistor and
the brake resistor will be active continuously.
DC1...20... and DC1...OE1 Variable Frequency Drives 02/20 MN040059EN www.eaton.com
Voltage class Braking chopper
on
230 V 390 V
230 V 390 V
400 V 780 V
2 Engineering
2.7 Braking resistances
DC
, the
B
Braking chopper
off
378 V
378 V
756 V
45