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Tripping unit

lyledunn
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  • 0
    The photo shows the busbar tails to anABB PR221DS tripping unit rated at 1000A and set to that. You can see thermal damage to the tri-rated 2x120mm2 tails. The outgoing conductors are 2x400mm2 and there is obvious thermal damage to the CTs on that side. The associate Diris meter was showing 895A normal peaking to 985A for sustained periods. The associated switching device is only 800A. This is a brand new installation! 

    I will forward a technical query to ABB but from a design perspective, given the load was specified at circa 900A fairly constant, would you not have opted for a larger tripping unit or are these electronic units able to run at close to In without de-rating. I also think the tail as are undersized by some margin. Given that the switching device is only 800A, it probably not suitable but I wonder if it is contributing to the considerable buildup of heat. The Flir showed 135C on the supply side.

  • 0
    lyledunn:

    ....I also think the tail as are undersized by some margin.


    Can't argue with that.

    The tripping units should be able to operate at In indefinitely (at least withing reason - a couple of decades non stop might not be good) so I doubt if that is the problem, but it is probably a good move to get confirmation from ABB. You say that the switching device is only rated at 800A which I assume means that while the tripping unit is rated at 1000A, the device it is operating is only rated at 800A (e.g. T6 800). If this is the case then the device itself will be overheating as at 900A it will generate 25% more heat than it can dissipate at its rated temperature (so as a rough guide the temperature rise will increase by 25% which will put extra heat into the undersized tails).


  • Former Community Member
    0 Former Community Member
    Is this inside a piece of switchgear, Lyle - because if so, the whole assembly should be subject to BS EN 61439 and had the appropriate temperature rise test undertaken


    For info, that standard may have assumed a diversity of 0.6, and in most cases, a 1000A Circuit breaker can't carry 1000A without exceeding a stated temperature rise - you may well need to state a 1250A device set at 1000A to keep within temperature.


    If you are putting a sustained 1000A through a 1000A device, it may well be that the manufacturer assumed that load was only a thermally equivalent 60% (which he is entitled to do unless you say differently)


    Regards


    OMS


  • 0
    This is in a refrigeration plant. The device is one of three CBs inside a new main panel  which was constructed by local panel builders under instruction from a consultant. Being a new installation, the client is on the war path. I was only there to investigate why the breaker was occasionally jumping out. One of compressors on start-up was drawing 1600A for 4 seconds through a soft start which was faulty and had to be replaced. That might have been an amp or two too much for a tripping unit that was already thermally primed! In any event, there is a proposal for an extra 800Kw of refrigeration and gas scrubbing plant  if planning permission is granted. There is a 500Kw Bio-plant feed in and I believe the parasitic load to be 130Kw. The DNO have just installed a new 800Kva transformer. That with the bio-digester might have just about satisfied the existing demand so we are a transformer short for the new load. It will be interesting to see the solutions proffered.

  • 0
    OMS:

    ...the whole assembly should be subject to BS EN 61439 and had the appropriate temperature rise test undertaken


    I am happy to be corrected but I thought that BS EN 61439 allowed for verification by calculation (I am not an expert - but I know someone who is, so I can always ask....) so it is not necessary to actually perform the temperature rise test, though I am always suspicious of calculations in the place of real performance tests. You are certainly right that it may well need an over-rated device to meet the temperature rise requirements. When 60439 was replaced by 61439 there was a widespread complaint that customers were being forced to buy larger switchboards.


    The ABB Sace TMax has been around for a while so it potentially could be a board to BS EN 60439, but only if  it is older than about 15 years.


    Edit - just read the latest comment about it being a new board, so ignore the final sentence.


  • 0
    Hmm this is a brand new and slightly undersized installation.

    It also looks from the pic as if the overload is not equal on all 3 phases. Is the meter showing the hottest phase ? a pair of 120mm tri-rated tails is not quite enough for 1kA, you may manage better with 2 lots of 185 or even  240mm2  depending if the load is sharing equally, and how good is airflow. ( some typical rating data)- though the fact they look more cooked near the termination is telling.  I also wonder how sound the crimping is


  • 0
    lyledunn:

    The device is one of three CBs inside a new main panel  which was constructed by local panel builders under instruction from a consultant. 


    So who is the designer? It sounds as if there is a grey area between the panel builders and the consultant as to who is actually the designer.


    The tripping unit is an electronic (which nowadays means computer) one, as far as I am aware, and therefore there would be no thermal priming as there would have been in the old days (showing my age here) so it should not matter what the previous current has been as far as tripping goes.


  • 0
    I think I'd be on the war path too ....
  • 0
    mapj1:

    ....  I also wonder how sound the crimping is


    That came into my mind also, but the other aspect is are the lugs the correct size? If they are undersized it just compounds the problem, whether or not the crimping is sound. I have come across overheating due to 50/70 sq mm lugs being put on 95 sq mm cable.


  • 0
    Alasdair Anderson:
    lyledunn:

    The device is one of three CBs inside a new main panel  which was constructed by local panel builders under instruction from a consultant. 


    So who is the designer? It sounds as if there is a grey area between the panel builders and the consultant as to who is actually the designer.


    The tripping unit is an electronic (which nowadays means computer) one, as far as I am aware, and therefore there would be no thermal priming as there would have been in the old days (showing my age here) so it should not matter what the previous current has been as far as tripping goes.




     I am showing my age Alasdair! I don't know how many times I have been told that and still it doesn't stick! 

    Ah, the designer? Well I wouldn't be one for love nor money! I don't think the industry gives them the credit they deserve. The consultant is a lovely chap who seems to work on his own. It does appear that the correct details were not passed to the panel builders. Whoever is to blame, lets hope they have adequate PI insurance in place!


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