VFDs with long Cables

[roydm]

I often see this topic come up.
In the early days of VFDs when they were SCR based I saw many installations of several hundred feet and I don't think at that time the motors were "VFD rated"
Are we making progress with the new drives or going backwards?
Just curious thats all.
Regards
Roy

 

[CJCPE]

We made a trade. The faster switching devices made PWM drives a reasonable design option. Going to PWM simplified and reduced the cost of the power circuits. The added complexity in the control circuits was hidden away inside large scale ICs and then microprocessors. The more complex control circuitry is less expensive than the more complex power circuitry.

Faster switching also reduces the losses. Reduced losses means a smaller and less expensive package. Reduced losses also means increased efficiency and lower operating cost for the end user.

When we made the trade, we didn’t really realize that we were going to get motor insulation and bearing problems in the deal. By the time the problems were fully recognized, it was too late to go back. In most installations, we have smaller, more efficient, less expensive drives with few problems. Where there are problems, we have an add-on solution that costs a little more, but probably not more than the old designs.

Perhaps multi-level inverters and matrix converters will prove to be a step forward without a half-step backwards.


CJC

http://www.vfdriveinfo.com

 

[Skogsgurra]

An alternate solution is to build drives with a pure sinewave output. It is being done already with power ratings up to 15 kW and hey are used for HVAC in hospitals and other sensitive environments, like stalker ships for the miltary and such. Install with ordinary cables and no filters. You even get a five year guarantee on the motor bearings when you install them. Plus, you can use GFI (RCD or Fi-Schalter or whatever you call them).

I am not sure about the rules here. So I prefer not to spell out the name of the brand. But you can find them if you google relevant terms. The technique used is sometimes called the 'switch circuit'.

Gunnar Englund

http://www.gke.org

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[LionelHutz]

You must be talking about NFO Drives.

Do you have a commercial interest in the company Gunner?

Do they do more than build 0-15kW, 380/400V drives?

 

[ScottyUK]

I have no reason to doubt that those drives are good, other than the lack of published information on how it is achieved. I spent a while looking on the website and came up with nothing tangible. Maybe I am too cynical and untrusting these days, but I no longer believe in magic.


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

 

[MikiBg]

I wrote an e-mail to them after Gunnar told me for that technology/company several months ago. I asked for additional informations and technical data besides those you can download from website. No one even replied. Strange way to promote distinctive product.

 

[Skogsgurra]

I was on their board of directors once. But I quit when the number of lawyers jumped to three. Have no commercial interest any more (other than losing quite a lot of money on them). But it is an astonishing product and I did a description of the technology once. It is still on their home page. May be difficult to find. But I know it is there.

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]

Gunnar,

Please see if you can find it because I'm quite intrigued by this technology. I spent about 15 mins looking and didn't find it.


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

 

[Skogsgurra]

I found it. But it has been "improved" by someone that doesn't know about the matter. The English is not very good either. Anyhow, go to NFODRIVES.se. Then select English flag. Under "The Company" select NFO Patent & The Switch Circuit

I notice several "improvements". The worst is that "Inverters are everywhere" has been replaced with "Inverters are all over the place". Please disregard those "improvements". Also, pictures that were included in the text have been removed. So, I don't think that it is a good idea to read that text any more.

I think that the best description is in the patent text. Will look for the patent number.

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]

I was hoping to see the switching topology, but it seems it is a secret! I'm beginning to wonder if it is a trio of class B amplifiers operating as a bridge but that seems to simplistic.


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

 

[Skogsgurra]

No. That is not the case. I understand that I have to write someting about it. I did one small thing in Swedish several years ago. Shall try to find it and translate it.

Gunnar Englund

http://www.gke.org

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

 

[Skogsgurra]

There is a short text with some pictures at

http://www.gke.org/rapporter/files/NFO 28 november 1.pdf

(sorry, only in Swedish)

It is a report that I wrote for a Swedish Electric Power Research Institution back in 2002.

It shows how energy is stored in the magnetic field in the output reactor. But it doesn't show very well how the transient-free switching is done.

Gunnar Englund

http://www.gke.org

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