VFD Volt Drop Question

andyb · Oct 15, 2015

Thanks for all the input guys, I'm just going to concern my self with the cable installation side of things as instructed.

That still leaves me with the problem of suitability. I defiantly will not be going down the SY route. If using swa does the armour need earthing at both ends? I mean in terms of for screening properties. If not then at the wet end I could terminate into a plastic enclosure using IP68 plastic glands.

Besoeker what do you mean by excessive dv/dt ? and what does the us in 3kV/us stand for?

I've heard back from the people doing the install to inform me that 6mm is required, which brings me back to my original question regarding VFDs and volt drop.
These are 5.2Kw 10.4a pumps so I'm assuming that the variable frequency has an efect on vd.

andyb · Oct 15, 2015

Just re read the email from the company doing the work and they inform me that they will be supplying some screened Belden cable to be run from the pump back to the control panel. No problem with that, but they then go on to ask me how long the run is so they can supply the right amount.

If they do not know the length of the run how could they calculate the volt drop of the pump cable?

Also, if I'm using armoured for the pump and the Belden is screened, would there be an issue with emc?

Darkwood · Oct 15, 2015

You require an effective screening from drive to pump, usual methods are a screened cable grounded to the motor case and usually a specified ground on the drive... your situe differs somewhat though so you may need to look into alternatives here.... like the link mentions I posted e expresses in that the seawater itself provides a screening effect.

Like besoeke mentions in a reply to me you really don't need to worry about fitting in line filters, chokes or reactors for your length but always check with the drive install instruction to confirm this and to see what screening, earthing arrangements are required etc.

If all your doing is running cable from A to B then most of the design issues don't fall in your court.

You say they have supplied a cable for the submersible, now in my experience the pumps are pre-flexed and sealed pumps so not something you would be able to replace yourself unless it has a user IP68 terminal block?