VFD shielded motor cable

[sndbodkin]

We are replacing VFD on a submersable pump because two of the phase buses melted together. The well is app. 80 ft. deep. Could the busses have melted because the motor leads not shielded?

 

[Jraef]

What do you mean by "phase busses"? On the line side of the VFD? Then no, not a chance that the unshielded cables had anything to do with that.

If you mean the bus bar looking arrangements inside the VFD, then they would be the DC bus, not "phase busses" and yes, that is a possibility. But you would have to have damaged the transistors first, then forced the VFD to keep operating since most will trip off-line if that happens.

If you had bus bars on the load side (why; I can't imagine), then maybe, but not likely.

Not having shielded cable on the output is usually damaging to the motor, not the equipment. But the reflected waves can bounce back and take out the transistors on the drive as well if all the conditions are right. A load reactor would have helped.

 

[sndbodkin]

Yes I am talking about the DC bus. We are in the process of installing a load reactor. The VFD has been temporarily bypassed and the motor is running fine. How important is it to pull the well and install the shielded motor cable?

 

[ptonsparky]

IMO, not very important. The load reactor is for the protection of the motor windings, as I understand it. I believe the line reactors are more for the protection of the drive under fault coinditons.

 

[Jraef]

Rather than pull new wires, I would look at a complete load filter package from someone like MTE or TCI. Load filters incorporate the reactor with tuned RC networks to increase the effectiveness. They can protect the motor windings as well if not batter than shielded wire. In a lot of cases there is no alternative for shielded cable and this is the work around.
http://www.mtecorp.com/motor.html
http://www.transcoil.com/#klc

Reactors on the load side of a VFD will slow down the rise time of any current spikes, whether they are the result of a shorted load or he reflected wave phenomenon. It usually makes the rise time slow enough to prevent di/dt damage to the transistors and/or for the VFD protection circuits to shut it down and prevent collateral damage (in the case of a fault).

 

[coulter]

... We are in the process of installing a load reactor. ... How important is it to pull the well and install the shielded motor cable?

Have you discussed this with the VFD mfg? Before installing an load reactor, or shielded cables, I would think a call to the MFG to see exactly what their installation specs are would tell you more than any guesses we might make - especially since we have no knowledge of the type or model of VFD.

carl

 

[BAHTAH]

Vfd & Wells

Vfd & Wells

I have been involved in many well installations over the years and only used one drive manufacture. I don't know who's drive you are using or the HP of your pump but a good way to tell the quality of a drive is by the standard length you can run to the pump without any external equipment. I know Danfoss is 1000ft and Allen Bradley may be in that range but I am not sure. We have done some installations where the pumps were at 700ft with no problems. In our case it takes one pump to get the water out of the well and a booster to help pump it to storage tanks for a gravity system. If the cable is shielded the length will be reduced. I would contact the mfg of the drive if you don't have the spec's to verify the length you can run.

 

[sndbodkin]

The drive is an ABB. I have contacted the drive manufacture and the individual I spoke with suggests that the cable should be shielded but he was unsure that the cable would eliminate this specific problem.

I was probing here to get feed back from others that may have suggestions on the matter.

You all have been very helpful.
Thank you,

Stuart Bodkin