Bus Overvoltage Faults: How to Resist
So, you’re beginning to size a new servo motor and drive for an application. How do you go about doing this? What helps you look closely at the loads, mechanism type, move and motion profiles, voltage available to power the system, and the many other factors that need to be considered for an optimized motion solution? Sizing tools can be highly beneficial for achieving optimized products. However, one needs to pay attention to the warnings and information provided in sizing systems.
Using Kollmorgen’s sizing tool, Motioneering, enables you to select the correct motor and drive, yet also presents a frequently overlooked requirement: REGENERATION RESISTORS. Depending on the application and the deceleration profile, the motor may be generating power that must be dissipated when the motor is slowing down. This will manifest itself as a bus over-voltage fault in the drive. When this occurs, the motor literally becomes a generator. Motioneering will indicate the wattage (power) needing to be displaced based on the system data entered.
An example is shown below:
The sizing tool is indicating that this power causes high voltage levels to be generated. You’ll need to add a “regen resistor” to the drive to dissipate this energy as heat. The drive’s Installation Manual will advise both the necessary resistance as well as what fuses are also required within the regen circuit. If a machine has multiple drives, you MAY BE able to “share” a regen resistor, where the bus voltage is regulated by a common resistor. This too will be covered in the Installation Manual.
Regen. Yet another way to “Dot your I’s and cross your T’s” when quoting a job or designing your machine…. Doing it right, prior to product selection, protects the motor, drive, and keeps you from getting called out to see what is causing this “bus over-voltage fault”.
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