2 Engineering
2.6 Brake resistors
58
DA1 Variable Frequency Drives
08/18 MN04020005Z-EN
www.eaton.com
2.6 Brake resistors
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. TheDC link voltage
U
DC
will be increased as a result. If the voltage value is too high, the DA1
variable frequency drive will disable its inverter, If the voltage value is too
high, the DA1 variable frequency drive will disable its inverter, after which
the motor will coast uncontrolled.
DA1-…B-… variable frequency drives 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
P1-05 (= 2 or = 3). 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.
For example, in the case of DA1-34… variable frequency drives, the brake
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. To protect against thermal
overload, under parameter P6-19, the resistance value R
B
and under
parameter P6-20 rated output P
DB
of the braking resistance can be set.
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.
Device series
Power supply
Voltage class
Brake chopper on
Brake chopper off
DA1-12…
Single-phase
230 V
390 V
378 V
DA1-32…
3-phase
230 V
390 V
378 V
DA1-34…
3-phase
400 V
780 V
756 V
DA1-35…
3-phase
575 V
975 V
945 V
