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3.5 Braking resistors
Excess energy in the common DC bus must be absorbed by the brak-
ing resistors. Depending on the application, one or more braking resis-
tors can be connected. Consider the internal braking resistors of
LXM32 drives in your calculations.
If drives with a different nominal power are connected via the DC bus,
you must connect braking resistors to the drive with the highest nomi-
nal power. See the manual of the respective product for more informa-
tion.
3.5.1 Rating the braking resistor
An insufficiently rated braking resistor can cause overvoltage on the
DC bus. Overvoltage on the DC bus causes the power stage to be
disabled. The motor is no longer actively decelerated.
WARNING
MOTOR WITHOUT BRAKING EFFECT
• Verify that the braking resistor has a sufficient rating.
• Verify that the parameter settings for the braking resistor are cor-
rect.
• Verify that the I
2
t value for temperature monitoring does not
exceed 100% by performing a test run under maximum load con-
ditions.
• Verify that the calculations and the test run take into account the
fact that the DC bus capacitors can absorb less braking energy at
higher mains voltages.
Failure to follow these instructions can result in death, serious
injury, or equipment damage.
The temperature of the braking resistor may exceed 250 °C (482 °F)
during operation.
WARNING
HOT SURFACES
• Ensure that any contact with a hot braking resistor is avoided.
• Do not allow flammable or heat-sensitive parts in the immediate
vicinity of the braking resistor.
• Verify that the heat dissipation is sufficient by performing a test
run under maximum load conditions.
Failure to follow these instructions can result in death, serious
injury, or equipment damage.
Braking resistors are required for dynamic applications. During decel-
eration, the kinetic energy is transformed into electrical energy in the
motor. The electrical energy increases the DC bus voltage. The brak-
ing resistor is activated when the defined threshold value is exceeded.
The braking resistor transforms electrical energy into heat. If highly
dynamic deceleration is required, the braking resistor must be well
adapted to the system.
3 Engineering
LXM32
32
Common DC bus
MNA01M001EN, V1.01, 08.2014