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#168010 - 08/25/07 09:01 AM Isolation Transformer and VFD's
windmiller Offline
Junior Member

Registered: 12/05/06
Posts: 43
Loc: Alaska
Hi,
I have several VFD's that have fried SCR's. Allen bradley says this is from a power surge or Lightning strike. We have a 138 kV line coming in that is stepped down to 13.8 then 4160 then 480 etc. etc.

Is the best solution a Isolation transformer to protect the VFD's or is there another solution?

Thanks

Windmiller
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#168015 - 08/25/07 12:21 PM Re: Isolation Transformer and VFD's [Re: windmiller]
gibbonsseabee80 Offline
Member

Registered: 10/10/05
Posts: 40
Loc: Chesapeake, VA
Hello Windmiller,
I recommend you install a sqare D surgelogic TVSS EMA series on the 480volt side of you service. They are very expensive depending on the level of protection and if you want an integral diconnect. Intermatic makes great TVSS units also. I have installed 6 3500 series TVSS and just installed a square D surgelogic EMA series. They also have surge counter and dry contacts on the from for remote monitoring. Just a suggestion and worth checking out the links below

http://ecatalog.squared.com/pubs/Electri.../1300BR0201.pdf


http://www.intermatic.com/Default.asp?action=subcat&sid=124&cid=63&did=6
_________________________
Brian Gibbons

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#168020 - 08/25/07 01:08 PM Re: Isolation Transformer and VFD's [Re: gibbonsseabee80]
windmiller Offline
Junior Member

Registered: 12/05/06
Posts: 43
Loc: Alaska
Thanks i will look into this.

windmiller
_________________________
We all live under one King

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#168064 - 08/26/07 09:31 AM Re: Isolation Transformer and VFD's [Re: windmiller]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
 Originally Posted By: windmiller
Hi,
I have several VFD's that have fried SCR's. Allen bradley says this is from a power surge or Lightning strike. We have a 138 kV line coming in that is stepped down to 13.8 then 4160 then 480 etc. etc.

Is the best solution a Isolation transformer to protect the VFD's or is there another solution?


You already have three isolation transformers front of your drive to "protect" it from lightning or surges external to your power grid, why do you think one more will help? You may want to look at your internal power grid and see if your facility is creating the power surges.

In the mean time the TVSS suggestion is probably your best solution.

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#168066 - 08/26/07 10:14 AM Re: Isolation Transformer and VFD's [Re: JBD]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
VFD's do not have SCR's in them. If the fried section of the drive is on the input side, you have a bad rectifier bridge . If it is on the output side it will be the IGBT's.

Isolation transformers are used primarily on DC drives, as DC drives care little regarding what is feeding them, provided the voltage is in the correct range and all three phases are present. You already have three general purpose XFMR's in front of the drive. Or are they isolation XFMR's?

Input surges can be tamed to a certain degree with the use of a line reactor. If your drives do not have line reactors built in, then you must install them yourself.

Also make sure that the fuses that supply the drive are of the SCR type. Same type used on DC. If it's a breaker you will have to live with it.

There is nothing you can do if it is a direct lightning strike. You can purchase surge protectors, but lightning will blow them out too. However, there are some products available that say they can protect from lightning strikes. I don't believe it.

CHECK ON THE LINE REACTORS.

GET POCO INVOLVED. IT VERY WELL MAY BE THEIR PROBLEM NOT YOURS.

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#168072 - 08/26/07 12:32 PM Re: Isolation Transformer and VFD's [Re: JValdes]
windmiller Offline
Junior Member

Registered: 12/05/06
Posts: 43
Loc: Alaska
Hi,
Thanks for the reply. I will pass on your comments to Allen Bradley who has inspected the drives and responded that the SCR's were undoubtedly fried by lightning.

On the rest of your comments I have forwarded them on to our engineer for review.

I will check the fuses.

thanks

Windmiller
_________________________
We all live under one King

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#168073 - 08/26/07 12:35 PM Re: Isolation Transformer and VFD's [Re: windmiller]
windmiller Offline
Junior Member

Registered: 12/05/06
Posts: 43
Loc: Alaska
Hi,
I found this post:

Bipolar Transistor technology began superceding SCRs in drives in the mid-1970s. In the early 1990s, those gave way to using Insulated Gate Bipolar Transistor (IGBT) technology, which will form the basis for our discussion.

Thanks

Windmiller


Edited by windmiller (08/26/07 12:38 PM)
Edit Reason: correction
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#168086 - 08/26/07 06:52 PM Re: Isolation Transformer and VFD's [Re: windmiller]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
 Originally Posted By: windmiller
Hi,
I found this post:

Bipolar Transistor technology began superceding SCRs in drives in the mid-1970s. In the early 1990s, those gave way to using Insulated Gate Bipolar Transistor (IGBT) technology, which will form the basis for our discussion.

Thanks

Windmiller


You are confusing the output of the drive with the input. IGBTs are used on the output only.

Most VFDs use diode bridge input sections, however I believe the A-B still offers SCRs as an option.

If lightning was causing your drives to fail, then you should have other components in your facility also affected. It is unlikely that the A_B factory could differentiate between a lightning induced over voltage and one caused internally to your facility.

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#168119 - 08/27/07 11:31 AM Re: Isolation Transformer and VFD's [Re: JBD]
windmiller Offline
Junior Member

Registered: 12/05/06
Posts: 43
Loc: Alaska
Hi,
ok thanks. I apprecitate your comments.

It sounds like you know a thing or two about it.

Windmiller
_________________________
We all live under one King

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#168164 - 08/28/07 09:34 AM Re: Isolation Transformer and VFD's [Re: windmiller]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
JBD,
Good point regarding other equipment failure resulting from lightning. If other equipment did not see catastrophic failure I doubt that it was lightning.
I once had several inverters that had defective input bridges when we received them. Of course they did not fail until the drives had run for several days or weeks. The warranty covered the repairs.

Not to knock Allen Bradley, but my drive repair guy hates the control. Just the drives, not the PLC's ect....

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