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Arc Flash Curtain around switchgear

Discussion in 'Equipment to Reduce Arc Flash Dangers' started by tweason, Apr 13, 2012.

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  1. tweason Junior Level

    I am looking for input for placing arc flash curtains around my 4160 switchgear. The arc flash boundary is upwards of 460' (according to the calcs) in some of my 4160 areas. My thought is placing a curtain around the area would reduce that boundary. Has anyone implemented this type of modification successfully?
  2. PaulEngr Sparks Level

    There are shock protection blankets but no "arc flash curtains" as such.

    There is arc resistant (medium voltage) switch gear that is constructed by having a substantial front face and "blast doors" on the top or back to redieect the arc blast. These work as long as the front doors are closed and all latches attached properly. However, the design for this is a performance test...it reveals nothing about how to do it without lab testing.

    In a similar way any sort of substantial wall is going to limit or eliminate an arc flash hazard. The tricky part is that there is no test data or calculation to indicate what would be an acceptable wall. Most folks use a little judgement and assume that a substantial (block/concrete) load bearing wall will do the trick.

    By far the best approach is reducing the arc flash itself. This means either modifying the trip units or breakers directly, or moving employees farther away with the use of mimic panels, handle extensions, and the like. Lots of folks like to talk about remote rack out devices but experience has not been so good with a lot of these. It seems that if the switchgear was intentionally designed then the device is more likely to actually work when needed.
  3. SCGEng1 Sparks Level

    Just out of curiosity are you putting the 460’ distance on your equipment labels?
  4. Walt Mendenhall Junior Level

    Yes, to protect a large DC heater terminal array we used an arcflash blanket customized by Estex Manufacturing for a unique DC application. However this was AFTER other mitigation techniques were employed first. The dc voltage was reduced physically separating the + and - terminals from each other, then installing a non-conducting barrier between them. This reduced the voltage from 600Vdc + to - to only 300Vdc + to gnd or - to gnd. Cutting the voltage in half reduced the AF by a factor of 4. Next was to keep the protective curtain far enough away that the combined Kevlar/glass layers weren't compromised by the arc heat or blast pressure. The curtain had to be supported top and bottom as well as easily removed, so a mockup was sent to Estex to make sure we got it right the first time. The blanket material had been tested at Kinectrics with actual arcs and test dummies by Hugh Hoagland, but at specific distances and for various exposures expressed in kA and cycles. We had to convert this data to our metrics of cal/cm2 and psf with enough margin to validate the blanket would withstand the energy of not only one, but a cascaded event fed by multiple rectifiers in this installation. The engineers who designed the heater hadn't really thought about the arc hazard before we got involved, and would have been measuring the DC terminations to adjust the rectifiers (really dc drives) in shirt sleeves with multimeters with a (cascaded) exposure of 357cal/cm2 at 18 inches!!!
  5. elihuiv Sparks Level

    ASTM F2676 is for arc flash blankets/curtains. These blankets are now mentioned in NFPA 70E (my proposal).

    Testing on, and use of the blankets for many years in the utility networks has shown excellent protection for workers.

    We do most of the blanket testing and the blanket manufacturers can assist in how to install properly.
    Zog likes this.
  6. Matchstick Junior Level

    I do not know anything about arc-flash curtains but would like to gather more information from you on the arc-flash calcs. What is the fault current, fault-clearing time, and is there an upstream PD? The reason I ask is we had a situation at our station where our FPB was >100' and this was due to a low fault current being seen by the PD. The low current resulted in an extremely long FCT and subsequently a high incident energy. We adjusted the PD's instantaneous setting to fix the issue. Hope this helps some.
  7. Flash Junior Level

    Tweason:
    Use either 2 or 3 seconds as your manual time and rerun the calcualtions and see what you get.

    Elihuiv:
    On the topic of blankets, if possible please provide answers the following:

    1. Aren't most blankets merely dielectric protection and that is where the testing/retesting is required.

    2. Has ASTM actually tested blankets that are protection from incident heat energy.

    3. Has anyone tested blankets with the IEEE box as the heat source. The IEEE box subjects material to a different type of heat energy than much of the ASTM arcs produced by two rods.

    4. Is there an actual reference in the new 70E that discusses blankets as protection from incident energy?
  8. tweason Junior Level

    I am posting the labels with the flash boundary. I am at a nuclear power plant, so there is a nuclear safety aspect that I must adhere by. Changing the setpoints would be my preference and the obvious solution, but changing setpoints or gear is a very long term and expensive solution. I would like to come up with a solution that I can implement in the near term. There are concrete walls on at least 2 sides in the switchgear areas.
  9. Zog Sparks Level

    Are the HK breakers in question 1E? What types of interactions are you concerned about?
  10. PaulEngr Sparks Level

    That's what I thought too but after looking, no, there is actually a thing called an arc flash blanket. It's a barrier to an arc flash. They have a rather interesting rating system.

  11. elihuiv Sparks Level

    The standard is cited but using them as protection has yet to be defined. We know what they will do but an installation standard has yet to be written and it is up to the user to decide at this point. Some improper installations will provide significant protection but we have yet to reach consensus on how to approach this. NEVER use blankets and put workers in NO protection. They will likely reduce energy reaching the worker and MAY prevent all energy from reaching the worker but the installation and matching to the hazard is the key. The manufacturers who have tested have good guidance. Keep the discussion up. This will be a good viable protection strategy in the coming years. My 2012 IEEE-ESW paper gives a few new ideas if you got it.
  12. KevinAF Junior Level

    Hello,

    I am evaluating options to mitigate against high arc flash incident levels within a ships' switchboard compartment which houses both the switchboards and the control equipment for operating the switchboards.

    In addition to other mitigation options i am very interested in the kevlar curtain solution. Unfortunately this product is not very well marketed or common in the UK and there is no product standards relating to protection ratings, testing or applications etc, can you possibly provide me with more details on this product, or point me in the right direction?

    Also you mentioned NFPA 70E which I understand is an equivalent for the UK Electricity at Work Act Regulations, can you possibly provide me some details in which context arc flash curtain is mentioned in this document?

    Many thanks,
    Kevin
  13. wbd Sparks Level

    I worked a nuke plants for a number of years so I am sensitive to the constraints you must abide by. I would interested to know what relays and breakers are used in the 4160V switchgear. There may be a way to mitigate the arc flash hazard.
    For example, I assume you are looking to mitigate when the breakers need to be raked out/in. For breaker operation (open/close), this is very easily accomplished remotely. Depending on the style of breaker, there are remote operators available.
    Without more info, my concern is that you are trying to protect against a event such as someone walking thru the switchgear room and a spontaneous arc flash event occurs. This is something that the standards are not trying to protect against.
    The other option to consider is installing a arc flash relay such as ABB REA 101 (note: I do not represent ABB but have used that relay in the past to mitigate arc flash hazards).
  14. Boergler Junior Level

    Sorry to bring up an old topic. But you're right, the standard is not state that it is trying to prevent this. The standard says little about when a worker should be protected, therefore all we have is consensus. The consensus, at least for low voltage, is the worker should be protected during live work, racking operations, and switching..etc. Switching is the sticking point because in a plant, this takes place in the control room and personnel may or may not be present near the switchgear.

    Per NEC, switchgear rooms should be locked and only accessible by trained operators. It's easier to maintain a standard of safety if all gear is in a seperate room. I am interested in such blankets as some of our switchgear is in the plant and therefore within the working area by design. Arc flash curtains could be an inexpensive way to isolate the gear from say control room door or passers-by on their way to the turbine.
  15. PaulEngr Sparks Level

    Up to this point, the standard only vaguely referring to "interacting in such a way as to cause an arc flash". That's where it begins and ends, in the definition. The new 2015 standard is being updated to comply with current safety codes which is changing this and several other places where the new requirement is to estimate both the magnitude of the hazard and the likelihood of occurring. You can get a taste of it by looking at the current 2012 edition and looking at the arc flash tables. In several entries they decreased the H/RC value from the maximum in that section by consideirng the likelihood. Of course this is outright invalid because the hazard itself is not decreased, only the likelihood. So the correct approach would be to assign "H/RC 0" whenever the likelihood is below a threshold value, and otherwise not decrease the values at all. This is exactly what is reflected in the 2015 draft.

    One of the sticking points here of course is...what is the standard, especially for those who are doing their own calculations. When looking at hazards generically and categorizing the injury as a fatality, major injury, etc., there are industry standards for acceptable risk. AIChE's CCPS LOPA Analysis book gives a great summary table in the back. Suffice to say that single fatalities generally require a likelihood of less than 1 in 100,000 per year, major injuries about 1 in 10,000, and so forth. Reported arc flash injuries have been calculated at an average rate in the US at 0.1/10,000 workers (as per ESFI's latest statistical study). Arc flash fatalities account for less than 10% of those. So electrical equipment even today already meets these thresholds. All that we need to be concerned with is "high risk" equipment or activities. We can numerically estimate these using data in the IEEE Gold book (formerly IEEE Standard 493, not sure where they are renumbering it to). Breakers easily meet this standard if they are properly maintained, and those are among the lowest reliability of any equipment. That leaves any activity in which the likelihood of an arc flash is caused by personnel directly. Some (but not all) "live work" definitely meets this threshold requirement. Once the activity becomes something like landing a wire under energized though, most human performance literature estimates a 90% relaibility rate for human activities. This is several orders of magnitude worse than the required 1 in 10,000 or better.

    Blankets/curtains are a great product idea but since we don't have actual standards yet to predict when and where to use them, the only way that you can use them would be to do testing on your equipment and with specific blankets. Even the blanket manufacturers are saying that you still have to wear some arc rated clothing while using the blankets so for the scenario that you are suggesting, they won't work. Where they are best served today is in areas such as while working inside of manholes where the current industrial practice (IEEE 1584+NFPA 70E) falls way short of providing a solution.
  16. PaulEngr Sparks Level

    Forgot to mention...there are always dozens of people who have written public inputs to the NFPA 70E Committee referring to the problem of "just walking by". Every time, the committee has responded that "just walking by" does not in itself pose an arc flash hazard. However they recognize that this is situation dependent...if work is going on, equipment is in clearly poor shape, etc. So most of the proposed changes have been rejected due to this issue of the best way to properly phrase the "just walking by" issue. However given the number of comments that you can find in the published reports, you can easily strike "just walking by" off the list of conditions where an arc flash hazard could exist in terms of interacting with equipment, and use the ROPS (or whatever the new version is called) as support for this position because as a consensus safety opinion, it has been repeated many times by many committee members.

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