Medium Voltage Power Conversion Equipment Standards

[johnnyw]

Has anyone seen a copy of the Underwriter's Laboratory (UL) standard 347A Medium Voltage Power Conversion Equipment, and if so can you comment on its' usefulness? Most of the medium voltage drive manufacturers list conformance to this standard in their drive specifications, but I have not had any success with UL in trying to obtain a copy. From what I gather, this standard may be in a preliminary status, and thus is not available for purchase.

 

[LionelHutz]

I can access all UL standards online and there is nothing for UL347A there. Usually, if there is something under development there are documents such as bulletins and outlines on-line so with nothing listed I'd say there is no such thing as UL347A.

Who's listing conformance to a standard that does not exist?

 

[jraef]

You are correct, that standard does not yet officially exist AFAIK, but several manufacturers are already referencing it. Technically, it is still under development so there is nothing to purchase, but essentially it is a marriage of UL508 for the control aspects, which doesn't cover medium voltage, and UL347 for the medium voltage switchgear aspects, which doesn't cover controls.

I didn't think this was being applied to drives however, I was under the impression that it was for soft starters. It started off when Benshaw went to get the first UL listing on their MVRVSS starters a few years ago, but ran into the fact that UL had no standards for MV soft starter testing, so they made one up as described above. Then other manufacturers complained to UL that they cannot give one manufacturer an exclusive listing, so UL started a project to develop the standards.

The problem was, there are only a few manufacturers of that equipment, most of which approach it in very different ways. So for UL to arbitrarily create a standard based on one of them would be devastating to all the others. The result is, UL came to those few manufacturers and asked them for input and expertise, including reviewing the input of the others. As you might imagine, that is going to be a long bloddy battle. Last I heard, the project was not complete and accepted. So for your case, if you are one of the existing manufacturers working with UL to make an acceptable standard, you know what it is. If you are someone attempting to get in on the action, you are probably going to have to wait it out.

 

[LionelHutz]

Hmm, there is a UL347B available in the Outline stage with no actual standard being available yet. maybe this is what you're looking for.

By reading the first few paragraphs in the scope of the standards I read that UL347 is for motor starter applications up to 7.2kV and UL347B is for motor starter applications from 7.2kV to 15kV. UL347B is also for applications involving static switching elements for use from 1.5kV up to 15kV. I believe this means using SCR switches aka soft-starters.

The UL347B Outline document reads like a standard but I'd guess it's an Outline because it's still not a completed accepted standard. Online I can even download other documents related to the standards. For example, UL508 has around 30 documents on-line.

Jraef is quite correct that UL347B would have been started by Benshaw looking for UL approval on their 15kV class of soft-starters. The Benshaw 5kV starters have been UL listed for many years now (I'd think at least 10 years now).

 

[johnnyw]

Thanks for the responses. There is a reference on the UL site to 347A (see link), but I was not successful in getting additional information from UL.

http://www.ul.com/controlequipment/standards.html

I have seen reference to this standard from at least four manufacturers of medium voltage drives (only two indicate the standard is in some preliminary state). I would have thought if it is being referenced for compliance, then it should be available for review. Oh well.

 

[johnnyw]

PS, I also found reference to UL 347A (draft) in NEMA ICS 61800-4-2004 (Adjustable Speed Electrical Power Drive Systems
Part 4: General Requirements—Rating Specifications for a.c. Power Drive Systems above 1000 V a.c. and Not Exceeding 35 kV).

It is referenced in the test section under short circuit withstand capability.

 

[LionelHutz]

Interesting. Anyone can get involved in the standard development process so if some document exists you can access it. If it is being referenced it should exist in some uncompleted form.

Go here;

http://www.comm-2000.com

Click on the UL Standards tab at the top and then click on the big UL that appears in the window. This page lets you look at the list of available Standards, Outlines and CSDS proposals amoung other stuff. Read the more info descriptions of what the outlines and CSDS's are. There should be either a proposal or outline for 347A if it's being worked on.

UL347A would be driven by some of the medium voltage drive manufacturers.

UL347B was driven by Benshaw wanting UL approval on their 15kV starters. Benshaw doesn't manufacture any VFDs.