18 Unidrive SP Low Voltage DC Installation Guide
www.controltechniques.com Issue Number: 1
4.6.4 Preventing over-voltage trips from occurring without the use of a brake
resistor
In the above systems in the case where the load is transferring energy back to the drive
through the motor, the DC bus voltage will rise. If the Low Voltage DC supply is unable
to absorb this energy, the DC bus voltage will continue to rise until the drive trips out on
over-voltage (OU). The drive over-voltage level is dependant on the drive frame size
(See section 3.1.2 Low Voltage DC rating on page 9 for details).
Below are recommendations for preventing this from happening:
1. Lower the setting of the regen current limit (Pr 4.06). This limits how much energy
the drive will absorb from the load.
2. Ensure that the drive is operating in one of the Standard ramp modes (Pr 2.04) and
lower the setting of the Standard ramp voltage (Pr 2.08) to 65.
The changing of the Standard ramp voltage can be automated by the use of the variable
select function, (menu 12) and the programmable logic function, (menu 9).
Reducing the regen current limit can result in the drive losing control of the load under
overhauling load conditions.
WARNING
If the above recommendations are unsuccesfull and the drive still trips OV, then it is likely
that the regen energy is significant enough to require a braking resistor. If this is the case
refer to section 4.6.5 System configuration 2 on page 20.
NOTE
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