ptonsparky
Tom
- Occupation
- EC - retired
I suspect the load side of both drives are bundled together and that is where the problem arises. My SEWAG.
VFD Noise Problem
- Thread starter andrewc23
- Start date
- Status
Aleman
Senior Member
- Location
- Southern Ca, USA
Looking at the pic it looks to me that that both motors are bonded to the box. Each motor ground should go back to the VFD separately. But I have seen them
done with a single ground on multiple drives and motors without problems. And I have also seen the same scheme cause bad noise problems. In any case, look over the
grounding on the drives and motors carefully because if not done correctly there will be noise issues.
done with a single ground on multiple drives and motors without problems. And I have also seen the same scheme cause bad noise problems. In any case, look over the
grounding on the drives and motors carefully because if not done correctly there will be noise issues.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Why is that a problem? Motors don't care about any "noise" on the lines, drive's probably don't care - I have never had such trouble with the power leads anyway when multiple circuits from multiple drives are in the same space. I could understand other equipment not playing well if it had supply leads bundled with these drive outputs. I also understand it may not be the greatest or recommended practice, but still have a hard time seeing bundling the output leads of the two drives in this application effecting the associated drives. I've seen a lot of drives thrown in place of an existing motor starter and never have had this kind of trouble when output leads were left in raceways with other conductors to other motors or drives - even some in non metallic raceways. Have seen them cause interference with other equipment though whether a single drive or not.
ptonsparky
Tom
- Occupation
- EC - retired
I suspect the drive does care. So much information is going back and forth that wires bundled as they are would cause some problems. My guess.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I have never been in an accident when I used to drive drunk, ergo, it must be OK to do so...
When you have multiple motor leads bundles but no VFDs, the risk of induced voltages on adjacent wires is mitigated by the fact that they are all operating at the same frequency, so mutual induction is cancelled out by adjacent opposing magnetic fields from the other phases. But with VFDs involved, the outputs from each VFD are no longer in phase with each other, so no cancelation. What happens then is that there become higher voltages on the output leads, which can interact with the transistor firing scheme to create a high dv/dt (delta voltage over delta time) situation which can in turn cause the transistors to misfire and ultimately fail. That "noise" being made by the VFD that only happens when both are running is a likely symptom of this. It may not have failed yet, but it's only a matter of time. I have seen it happen in almost every situation like this, eventually.
It can also exacerbate the formation of reflected waves in the motor leads, which causes the motor winding insulation to break down. If the leads are under 50' circuit length that would not be an issue if in separate conduits, but I just witnessed a Baldor 250HP motor that failed on insulation breakdown because the installer routed the output leads back into the same open cable tray as the input leads. There was only about 30' of circuit length and the motor was inverter dourly with 2000V insulation, but the spikes we recorded were 2400V. Changed the motor leads to shielded cable, everything went back to normal.
When you have multiple motor leads bundles but no VFDs, the risk of induced voltages on adjacent wires is mitigated by the fact that they are all operating at the same frequency, so mutual induction is cancelled out by adjacent opposing magnetic fields from the other phases. But with VFDs involved, the outputs from each VFD are no longer in phase with each other, so no cancelation. What happens then is that there become higher voltages on the output leads, which can interact with the transistor firing scheme to create a high dv/dt (delta voltage over delta time) situation which can in turn cause the transistors to misfire and ultimately fail. That "noise" being made by the VFD that only happens when both are running is a likely symptom of this. It may not have failed yet, but it's only a matter of time. I have seen it happen in almost every situation like this, eventually.
It can also exacerbate the formation of reflected waves in the motor leads, which causes the motor winding insulation to break down. If the leads are under 50' circuit length that would not be an issue if in separate conduits, but I just witnessed a Baldor 250HP motor that failed on insulation breakdown because the installer routed the output leads back into the same open cable tray as the input leads. There was only about 30' of circuit length and the motor was inverter dourly with 2000V insulation, but the spikes we recorded were 2400V. Changed the motor leads to shielded cable, everything went back to normal.
- Status