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  1. b_gibb

    Sizing Cables for a Xfmr

    I believe we are saying the same thing. The cable size depends on the transformer's primary current — my point is that it is indirectly dependent. It is directly dependant on the protection size. The cable size changes if the protection size is selected at 125%, 150%, 175%, 200%, etc... ben...
  2. b_gibb

    Sizing Cables for a Xfmr

    The cable is sized for the protection, not the transformer full load rating. For example, if your fuse is 30A, you need to size the cables for this value. In other words, calculate the protection first, then the cable size. ben bengibb.ca powerdesignerpro.com
  3. b_gibb

    Hello , Can I use CT accuracy clas

    I've been down the rabbit hole on this sizing. It was good for my understanding but I'd recommend not doing that. Just stick to the recommendations of the relay manual. It's not so much saturation that is the concern but rather mismatched CTs (saturating at different times, etc.). ben...
  4. b_gibb

    Rope Busbar - Design

    I assume you mean flex bus? If so, follow the manufacturer's specifications for ampacity. I've used Nvent Eri Flex Bus before and it's been good. Expensive, but easy to install and a good product. https://www.nvent.com/en-ar/eriflex/products/nvent-eriflex-flexbus-conductor-0 ben bengibb.ca...
  5. b_gibb

    Locating Oil type transsformers inside building

    I wouldn't recommend oil-filled inside. The fire suppression due diligence and insurance paperwork would be a nightmare. I'd look at two 3-4 MVA dry-types. The manufacturers may be able to do a 7.5MVA dry-type too. Better lead time with dry-type as well I believe. ben bengibb.ca...
  6. b_gibb

    Device that Data Logs Generator Output?

    I can't imagine a generator that operates less than 45Hz. Variations in speed are typically 2-3 Hz from the fundamental frequency (50 or 60Hz, depending on where you are). But maybe I'm misunderstanding the application. Regardless, I've found the Phoenix Contact power meters (EEM series) were...
  7. b_gibb

    Rigid bus simplified short-circuit calculation

    I'm trying to follow the IEEE 605 example for calculating the cantilever force on a rigid bus insulator due to short-circuit. I understand the example with the exception of how they determined the equivalent forces (F1, F2, F3 in Figure F.2) from the Fsc. Example: F3 = 3 x Fsc_corrected * L /...
  8. b_gibb

    low voltage main-tie-main

    Are you already planning to have the SEL-751s for protection purposes? If so, then they could do the ATS logic with no problem. If not, an SEL-751 for just logic purposes is an expensive solution. Typically those low-voltage DS breakers come with integrated LSIG protection, no? Just confused...
  9. b_gibb

    Solar Transformer

    I'll build on a couple of points that have been mentioned. My First step would be to the utility, as they may dictate what is required and then you are over halfway there. The other half is what the inverters require. Depending on the manufacturer, you may get lucky in talking to an engineer...
  10. b_gibb

    CT saturation — I'm missing something

    I find the PSRC Excel sheet is a great visual, but doesn't actually tell you "does the CT saturate" or give Vs=?? for a given fault current. As such, I'm looking to confirm the right formulas myself (going back to the original question in this thread).
  11. b_gibb

    CT saturation — I'm missing something

    Hi Kiribanda. My intuition is the same as yours. But I would like to show through math/formulas, which brings me back to the root question. I'll need to prove that moving to 800:5 or 1200:5 will work.
  12. b_gibb

    CT saturation — I'm missing something

    Assuming we can figure out the saturation formula, we are considering a C200, 600:5, such as the Amran 103-601.
  13. b_gibb

    CT saturation — I'm missing something

    Agreed, but not sure how to factor in the DC offset / asymmetrical current without the x/r factor in there somewhere...
  14. b_gibb

    CT saturation — I'm missing something

    Hi! I want to determine if my 600:5 CT will saturate. I have all the information but I feel like my formula is not correct. I understand it to be: Vs = ( Ifault / CTratio ) * ( Burden of CT and leads and relay ) * ( 1 + X/R ) Where, Vs = is the voltage developed on the secondary of the CT...

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