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  1. MD88

    Transformer cost vs primary voltage..?

    Hi there, does anybody know roughly what the cost differential (in percent) would be for a transformer of a given size, but with alternate primary voltages? For example, take a 2MVA 600V secondary transformer.. if we take 13.8kV primary as the base, what would be a rough %-adder be for 24.94kV...
  2. MD88

    Delta-Delta vs Wye-Delta Step Up

    @waross right I did include the grounded wye primary option by mistake, definitely do not want that. If all switching is 3 pole, is there a real risk of switching transients on the wye delta option? For what it’s worth, the distance between the existing step down and this step up will be max...
  3. MD88

    Delta-Delta vs Wye-Delta Step Up

    Hello, I have a situation where we have a 4.16kV/480V delta/wye w/ 5A NGR, and we want to step it up to 25kV. If we had the money and time, I would order a 480/25kV delta/wye (or a 4.16/25kV delta/wye actually)… but all we can find is 480/25kV delta-delta and wye/delta (ie: a step down...
  4. MD88

    5 conductors per phase parallel run

    Yeah, I don’t want to trefoil, just because I’d need to up the cabling. I’m thinking ABCCBA ABCCBA ABC for the 15 conductors, using maple blocks to maintain 100% space.. any comments on that?
  5. MD88

    5 conductors per phase parallel run

    No, not in conduits - specifically for the thermal reasons you mentioned. The intent would be to use cable tray and/or maple spacer blocks to maintain 100%+ spacing around the cables in order to use the free air rating of the single conductors.
  6. MD88

    5 conductors per phase parallel run

    Hello, I've got a 2500A, 600V run to put in, and I'd like to use 15x1c-350MCM 100% spaced as per CEC Table 1 (Canadian project). My question is what would be the optimal conductor and phasing arrangement to minimize the inductive reactance differences. Any tips or references would be much...
  7. MD88

    Transferred GPR to underground mine

    Very good point! Sorry I should have done that right off the bat... I hope this clears up my question, and what my understanding of the situation is. Red is fault path on the isolation sub primary, and blue is the fault path for isolation sub secondary. Thanks very much!
  8. MD88

    Transferred GPR to underground mine

    Hello, As per CSA M421, and I think several other mining electrical codes around the world, the ground potential rise (GPR) is limited to 100V for underground and open pit mines. Since the GPR at the main utility tie sub is usually much higher than this, the UG mine substation power grounding...
  9. MD88

    Transmission Engineering Resources?

    Hi all, I've somewhat recently started my own engineering firm, and while I've designed many substations while working at larger companies, I now am basically on my own and don't have access to their vast technical resources (ie: senior staff with specializations on many issues). I was...

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