Multiple VFD Installation

[ControlThis]

I am designing two .75kw VFD's into an industrial control system. It will be used in the US but the design may also be shared with a sister company in England. My question is regarding the thermal magnetic breaker and EMC filter that will be in the supply lines to the inverters. Can both inverters share the same breaker and EMC filter if rated appropriately? Or, should they both have thier own breaker and filter? I've shared these components before, but would like to know what others think. Are there any code issues with this? In the US or Europe? Is it common to go this route or is it frowned upon.
Any insight greatly appreciated!!

 

[dpc]

How would you work on one drive without shutting both down?

 

[ControlThis]

This is a fairly small system controling only these two motors. I don't foresee a situation where I would be working on one drive and have a requirement that the other be powered up. Nor would I recomend that the maintenance guys do this either.

 

[jraef]

First you need to resolve your own feelings about protecting VFDs with fuses or circuit breakers. The main issue is, circuit breakers cannot act fast enough to protect a VFD. The counter issue is, if something goes bad in the VFD that would require the SCPD to protect the circuit, the VFD (in that size range)is toast anyway; fast acting fuses just serve to limit the collateral damage. If you want fuses, then separate the circuits because the cost of a second set of fuses is not worth worrying about. If not, then the smallest CB you can put in there (15A in this case) is more than adequate for the wire feeding both VFDs.

 

[Marke]

I would definitely use separate filters, one per drive.
If you combine the two inputs, and then try to filter, you will have twice as much noise power to get rid of and will need more attenuation in the filter.

Note, input filters are only of value if you cable between the drive and the motor in screened cable with the screen properly terminated at each end. If you run an earth wire to the motor (in addition to the screen)run it back to the drive earth, not the mains earth. The drive is the generator or source of power (and noise) for the motor. A separate earth back to the supply will greatly increase the noise level and reduce the effectiveness of the filter.
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[controlsdude]

make sure you have an overload device per motor on the output of the vfd.

if multiple motors on one vfd
motor hp = vfd hp x 1.33
but some say
motor hp = vfd hp x 1.1

I have no problem with breakers use them all the time with vfds, use ul489 approved with an inductive trip curve. I do not see why you would want to use fuses.

one Filter can be used for both motors for the one drive, just watch the overall length of field wire to the motors. The vfd manu should point this out to you in their specs.


If your exporting to the US I would make sure all components are UL listed and the panel UL/CSA stickered if possible there before you ship. That way there is no question in any part of the country when it comes for an electrical inspection locally.

 

[DickDV]

No overload device on the output of any drive feeding just one motor. Let the drive software to the overload protection as it is designed to do. Only use overload devices on drive outputs when multiple motors are fed by a single drive.

 

[ozmosis]

Regarding the installation in the UK and with respect to the EMC filter. You must go with the recommendation provided by the VFD manufacturer to ensure correct compliance with the EMC Directive, that is the law.

 

[ScottyUK]

Well strictly the law says (paraphrased) "Thou shalt meet the EMC Directive" but like most laws it doesn't say how to meet it. Ozmosis has by far the easiest and most cost-effective means of doing it.


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If we learn from our mistakes I'm getting a great education!

 

[bklauba]

Ozmosis, gotta look that one up. Maybe it's something to do with the Wizard of . . . , or perhaps Mr. Osbourne?

(maybe osmosis?) Try English, wait, you are English!

(I know I am going to pay for this, but I could not resist!)

BK

 

[jraef]

Tangent alert!

I think it probably came from his moving (a form of osmosis) from England last year to Australia, commonly referred to as "Oz" (probably phonetically from "OZ-tralia"). Moved to Oz, Oz-mosis. Am I right Patrick?

 

[ozmosis]

Yes, a move from blighty down under (again) caused the sudden name change, as well as a new company that made my original handle rather inapropriate.

scotty, not sure what you mean by me having the easiest and cost effective way? but I'm currently in India working away at 1.48am and the ol' brain is going a bit fuzzy at the moment.

Don't forget, a VFD/VSD is not actually covered by itself in the EMC Directive, it is only a component of a system (the system requires a VSD,cable and motor and possibly filters) so this is why the onus is on the installer to ensure they follow the installation guidelines correctly to ensure they meet the EMC Directive.