I am currently working a project that uses a 40HP 460VAC motor to drive a reciprocating pump. I have done several of these in the past without issue, however my boss decided to through me a curve ball and add a VFD to the mix. The motor SF is 1.15 so I selected a 50HP VFD (GS4-4050). The issue I am having is once the motor gets moving (over 50hz) I get a DC Bus Overvolt alarm. I believe I have traced this to the fact it is a reciprocating pump and the motor regeneration is causing the over volt. Now from what I have read is that there is 3 ways to solve this 1. Add mass (not sure I could sell this one) 2. Using a breaking resistor 3. Buying a drive that monitors shaft load and can back of on excitation to avoid over generation. Option 2 being the most economical I would love to be able to go that route but the Brakes for the drive I currently have are only rated to 10% duty cycle and I am not sure how to determine if my current load would exceed that. Anyone know how to calculate this? Alternatively anyone know of a good VFD that monitors shaft load?
Thanks for the help,
Paul
How long does it take before the over volt alarm 4 sec, 10 sec or 20 sec.?
A VFD over voltage fault can occur during power up. If this is sporadic anomaly, check the incoming voltage. If the voltage is within specs. . . look for a jumper that connect the common capacitors to ground. You may have to look at the circuit board where a standoff screw terminal where this jumper is located. This is usually removable.
Check your manual.
Your environment could be rife in ground noise. This ground noise would come through these capacitors that could cause the voltage rise in the DC bus.
Yes, there are three ways to solve a deceleration bus over voltage problem, and any of those you've mentioned could work. But you only cited your perceived deceleration over voltage which [rightfully] elicited assumptions and speculations in the hope that a suggested solution could serve your purpose.
There are four causes of VFD Over voltage Fault.
1. Acceleration during ramp up which is caused as I mentioned unstable power source and ground noise.
2. VFD over voltage fault at deceleration.
This fault is common if the braking torque requirement exceeds drive braking capacity. This situation is noticeable when you hit stop during ramp down. . . while the load is still spinning faster than the set frequency. When this happens the regenerated power is pumped back and stored in the the DC bus. . . another cause of over voltage. In this instance the motor is acting like a generator.
One solution is to increase deceleration time.
3. Over voltage fault during normal operating mode.
This usually occur if the driven machine has a clutch disconnect. The sudden drop in load in the event the drive shaft is de-coupled would cause the motor to over speed and regenerate power to cause rise in the DC bus. This is when resistors come to the rescue.
4. Over voltage when VFD is not active [sitting idle]
In an industrial environment where all kinds of loads are present and there are large inductive loads could cause fluctuation/spikes in the power distribution. This needs to be investigated. . . improper transformer taps could also cause over voltage.
Using a generic pocket sized meter (those cheap ones) LOL cannot capture this fast occurring event.
An oscilloscope could easily capture the history of anomalous voltage rise.
All the best