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In search of a fuse that limits arc flash incident energy

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  • paulengr
    replied
    Originally posted by pv_n00b View Post

    Since arc currents are typically much lower than the available fault current and not in the current limiting range of current limiting fuses, the fuses won't clear in the required 0.07 seconds.
    That’s a lot of assumptions. Arcing currents are around 50-100% of available fault current. The current limiting range is a separate issue. It is linked to the fuse rating but neither one is related to the available fault current. It’s not uncommon to see both high enough that the fuse easily current limits and trips on both arcing and bolted faults, particularly when they are fairly small.


    Sent from my iPhone using Tapatalk

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  • pv_n00b
    replied
    Originally posted by jtinge View Post
    We had a Mersen engineer make a presentation on arc flash reducing strategies using fuses. Check out the link for more info.

    https://ep-us.mersen.com/services-do...energies-fuses
    Since arc currents are typically much lower than the available fault current and not in the current limiting range of current limiting fuses, the fuses won't clear in the required 0.07 seconds.

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  • jtinge
    replied
    We had a Mersen engineer make a presentation on arc flash reducing strategies using fuses. Check out the link for more info.

    https://ep-us.mersen.com/services-do...energies-fuses

    Leave a comment:


  • paulengr
    replied
    This is strictly for higher voltages but if I remember correctly Mersen has a “bring your own relay” system and S&C has their own relays where they supply a medium voltage fuse and a capacitor mechanism that stores enough energy to blow the fuse (high current low voltage). When the relay triggers it the fuse blows. This gives you breaker/relay control at fuse speeds.

    Also ABB has two versions of their arc flash relays. The first version uses “point” light sensors. The idea is Mount one sensor per cubicle. The other version uses a single unclad fiber to collect light that can be quite long. So busway light detection is certainly not impractical.

    Realistically though when the fault current approaches operating current there is just not enough headroom for fuses to discriminate effectively. Then again neither does anything else. Breakers do better up to a point.

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  • Hv&Lv
    replied
    Originally posted by pv_n00b View Post
    This is more than an academic exercise. Starting on 1/1/2020 NEC 240.67 kicks in and we need arc energy reduction in circuits with fuses 1,200A and above. Right now there is no fuse that can provide this, but I am hoping that an electronic fuse shows up that can do it. Otherwise it's going to require expensive arc flash detection circuits and additional relays.
    I don’t think these arc flash relays are too high in cost at all. We aren’t talking about a lot of money for what they can do and the multi functionality of them.

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  • pv_n00b
    replied
    This is more than an academic exercise. Starting on 1/1/2020 NEC 240.67 kicks in and we need arc energy reduction in circuits with fuses 1,200A and above. Right now there is no fuse that can provide this, but I am hoping that an electronic fuse shows up that can do it. Otherwise it's going to require expensive arc flash detection circuits and additional relays.

    Leave a comment:


  • engineerintraining12
    replied
    Originally posted by Jraef View Post
    just saw this on an ad today, it looks interesting. I am not endorsing it, have never used it etc. But G&W are a reputable company.

    https://solutions.gwelec.com/cliplv/...fault-risk-now
    very interesting, I'll have to check that out

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  • engineerintraining12
    replied
    Originally posted by paulengr View Post
    If you just take a blown fuse and plug it in, the incident energy is reduced to zero. Works every time, no calculations needed.
    haha, point well taken! No need to keep things running, we aren't dealing with a hospital

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  • Jraef
    replied
    just saw this on an ad today, it looks interesting. I am not endorsing it, have never used it etc. But G&W are a reputable company.

    https://solutions.gwelec.com/cliplv/...fault-risk-now

    Leave a comment:


  • paulengr
    replied
    If you just take a blown fuse and plug it in, the incident energy is reduced to zero. Works every time, no calculations needed.

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  • beanland
    replied
    I agree that a fuse cannot do both. Switch to a MCB with electronic trip unit with an arc flash reducing option.

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  • ron
    replied
    Unfortunetly if you are outside of the fuse current limiting capabilities, you are likely out of luck.
    Littlefuse makes a protective relay to reduce arc flash incident energy, but it requires both current detection and light (flash) detection, and you will not be able to do that light detection for the entire length of the busway. FYI https://www.littelfuse.com/products/.../pgr-8800.aspx

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  • Hv&Lv
    replied
    Originally posted by engineerintraining12 View Post

    That’s what I did, I looked at the worst case arcing fault current (around 2000A at the beginning bus and 1000A at the end) and the fuses that are there don’t clear the fault current fast enough to get a low incident energy. I think that the issue is I’m needing two different things at this location, time delay, and fast fault clearing which I can’t have both. I don’t even want them working on this busway live to be honest.
    That was why I was asking my question about personal or equipment protection. I don’t think you can do both effectively.
    For our HLT all delays are taken off and we use a 50 element with a very minimum value for pickup. I don’t care about what’s downline, I want personnel protection over anything else.
    The relays I see with a HLT function do little more than block reclosing and use the fastest curve available.
    With the experiments I have done with a relay tester, not using the factory logic and using the 50 element, I can reduce the maximum amps by ~600-800 amps. That’s a lot to the guy doing the work. Sometimes it’s actually me on a hot bus, so I prefer these changes.

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  • engineerintraining12
    replied
    Originally posted by ron View Post
    Even though there is 6000A available bolted fault current at the beginning of the busway, you need to determine the available arcing fault current, then plot that on the 400A fuse curve and you want it to clear way down on the Y axis (time).
    That’s what I did, I looked at the worst case arcing fault current (around 2000A at the beginning bus and 1000A at the end) and the fuses that are there don’t clear the fault current fast enough to get a low incident energy. I think that the issue is I’m needing two different things at this location, time delay, and fast fault clearing which I can’t have both. I don’t even want them working on this busway live to be honest.
    Last edited by engineerintraining12; 09-16-19, 07:56 PM.

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  • ron
    replied
    Even though there is 6000A available bolted fault current at the beginning of the busway, you need to determine the available arcing fault current, then plot that on the 400A fuse curve and you want it to clear way down on the Y axis (time).

    Leave a comment:

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