VFD for Other Than Motor Load?

[Laplacian]

In V/Hz mode with a transformer coupled load, can say a bank of resistive heaters be fed? If so, what type of load imbalance could it handle?

The VFD is "free" and a new SCR controller will cost as much, or more than a simple VFD.

 

[DickDV]

I've seen VFD's operating resistive loads successfully but why the transformer?

Also, set the drive for constant volts per hertz so the speed input translates directly into voltage change which translates by voltage squared into heat.

 

[Laplacian]

Transformer is existing step-down. Ancient SCR controller failed and out of service V/Hz VFD is available. We will try on Friday, but just seeking input on feasibility here first. My concern is load imbalance across the three phases. Transformer is delta primary, wye secondary with solidly grounded neutral.

Imbalance can be as high as 35% before heater probe replacement can be scheduled.

 

[CJCPE]

The imbalance will not necessarily cause the VFD a problem as long as you don't overload any individual phase but the VFD may have some protection circuit that could trip it. The transformer won't tolerate voltage boost at low frquency. Be sure to set the boost to zero. You might want to set the output V/Hz a little lower than the transformer rating just to be sure you don't saturate the transformer.

 

[jraef]

You may find trouble with the transformer on the load side of a VFD. Most are not designed to handle low frequencies and/or high harmonics. It takes a really good steel lamination to avoid having the eddy current and stray losses cause a meltdown of the transformer core. Most off-the-shelf transformers use the cheapest materials available.

 

[ScottyUK]

Low frequencies shouldn't hurt the transformer if the drive is a linear V/Hz type because the flux density will be maintained. Make sure the low frequency voltage boost is disabled: 0Hz = 0V. Could be noisy though if any laminations are loose. Completely agree that high frequencies will cause higher losses though.


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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Be sure Voltage Boost is disabled.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

There is a discussion about using a transformer after a VFD in thread237-189759 .

It is also about other things, but the risk of heating the transformer core is stressed. I will do some measurements on a small drive and a small transformer to find out how severe the problem is.

It may take a while before I can do that. Will probably have results beginning of next week. Can you wait that long?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Gunnar; aren't you going to warn about disabling the Voltage Boost too?!?!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

I was planning to do that. But couldn't find a new twist to it. Most words have been taken :-(

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jraef]

Be sure the EMF potential enhancement system is made to be non-functional.

 

[Skogsgurra]

Yes! By all means. Yes!

Hmm... Why didn't I think of that? :-(

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Hahah.

Of course this was all a "dig" to Scotty but I doubt he's even noticed.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Laplacian]

Thank you for so much input. I spoke with an applications engineer with the manufacturer today and he said that the drive wouldn't care as long as the highest phase current was below the continuous nameplate rating. The output phase loss protection parameter can be disabled. He did mention a disclaimer about the transformer being rated for the VFD output and recommended a sine filter.

I will update after Friday's testing.

I will also be sure to select the null option for the potential enhancement variant .

 

[itsmoked]

LOL

Thanks for the feedback.
We await your Friday report!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Maybe you should leave some boost (aka VES or APE) in.

After all, the transformer has some R in its windings. And it doesn't hurt compensating for it. BUT NOT MUCH!!!



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

You lot think you are just _so_ funny don't you??

Glad you got sorted out Laplacian. Remember to disable the voltage boost!


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Sometimes I only open my mouth to swap feet...

 

[Skogsgurra]

Yess! aren't we?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ozmosis]

Laplacian
What voltages are you talking about from VFD-transformer?
Also, when you talk about output phase imbalance, do you really want to disable the output phase loss detection in the VFD, would it not be preferable to keep it in?

 

[Laplacian]

480V VFD output, 90V(l-l, 52V(l-g) transformer output. I don't necessarily want to disable phase loss protection; but I don't want the VFD to trip on low current on a single phase. Load imbalance can be as high as 40%, but the system will still provide enough KW to heat the process.