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  • Users: VxA
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  1. VxA

    Volatge level Selection

    If you are in the US or Canada, I would have been tempted to recommend 4.16kV. Waross has an excellent point about it being a good idea to use voltage levels that are in common use in your area. I'm guessing you are not in the US or Canada as you stated the motor ratings in kW not hp (which is...
  2. VxA

    Async vd Sync Motor Evaulation`

    7carisfast, I'm guessing you've got your row labels mixed up in your last post. Otherwise, the Eff seems quite low, and in conflict with your first post. I didn't notice the motor voltage stated anywhere. What voltage is the motor going to run at? For every % more efficient one motor is...
  3. VxA

    VFD reactors

    You can order AB MCCs with line & load reactors right in the MCC bucket from the factory (for less motors 75hp and less). For larger VFDs you will need an additional vertical section or enclosure...
  4. VxA

    Motor current imbalance

    I'm not so sure a 15% current imbalance is all that severe (though I'd be interested in hearing why it might be considered a major issue and what detrimental affects it would cause). I have read that current imbalance is typicallu between 6 & 10 times greater than the voltage imbalance. So if...
  5. VxA

    Motor starter coil voltage vs. motor voltage

    Just going to echo what jraef and dpc are saying. The guy either doesn't know what he's talking about (in regards to this) or you misunderstood what he was telling you. I suspect the former.
  6. VxA

    VFD Voltages

    Where are you at? In the US and Canada, the company I work for has installed several VFDs on large ID fans in the range of 600hp-1500hp (450kW-1100kW) on 4160V. I'm guessing you're not in the US, as you stated the power requirements in kW rather than hp. We have also installed boiler feed...
  7. VxA

    CABLE VS. CONDUIT TO CONNECT MOTOR

    I think the thing to remember here is that someone lost their life. It's ok to discuss the shortcomings in design, implementation, operations, etc. that may have lead to this accident, but ridiculing the victim is something we as engineers should avoid.
  8. VxA

    CABLE VS. CONDUIT TO CONNECT MOTOR

    I don't think it's a code issue so much as a best practice issue. I know lots of facilities that would use an armoured cable (type MC or Teck) and route it in some sort of channel to about 3 feet from the motor and then let the cable loop into the motor connection box. If you're using tray...
  9. VxA

    Calculating Electricity Usage/Cost for a 3 phase motor

    waross, True enough. I guess the real question is how accurate are you trying to get, and how much of a pain in the *** are you willing to put up with to get there. With most facilities I would typically do any work in, it would be nearly impossible to use the utility meter method, as it...
  10. VxA

    Calculating Electricity Usage/Cost for a 3 phase motor

    1) take the average amps 2) multiply by square root of 3, 3) multiply by the voltage (460; or whatever -- from the motor's nameplate). 4) multiply by the power factor (from the motor's nameplate). Assume 0.85 if you don't have that data available (or better yet consult the manufacturer's data)...
  11. VxA

    Short Circuit MVA

    I guessing you left out the sqrt 3 factor, but seems like you've got it tracked down now.
  12. VxA

    Watts Losses from insulated cable

    Even if you have a 100 feet of each conductor (15 carrying around 500A each at 110 degrees C) inside the room, I still can't get my I^2*R calculations to yield more than approx. 15kW of heating from the cables. Just out of curiousity, what kW value are you thinking you have based on your...
  13. VxA

    NEC 2005, Article 409

    Hi, Ok, first let me say that these are my first impressions, and I am no expert on this subject (so hopefully some of the guys/gals that are will add their $0.02 to this one). I'm not totally familiar with Article 409, so I can't comment on your power transformer question, though it would...
  14. VxA

    Worst Electrical Fault

    Typically, as the others are saying, the three phase 'bolted' fault will be the fault with the largest magnituude. Now "worst" fault can depend. If we are talking Arc Flash, an arcing fault of a significantly lower magnitude could be worse than one with a high magnitude. This is because the...
  15. VxA

    1800 RPM otors versus 3600 RPM

    You may want to consider the duty of the motor. An Allen-Bradley PowerFlex 700 Drive rated for 200hp "Normal Duty", is only rated for 150hp "Heavy Duty." You may want to make sure that the original drive was not oversized on purpose due to the harsh life the motor and drive will be exposed to...
  16. VxA

    Arc Flash Calculation

    Electricpete is right on. The information required to do an arc flash analysis will come from the end user (and the utility). I'd say trying to pin that requirement on the OEM wouldn't be the way to go.
  17. VxA

    Arc Flash Calculation

    I agree with Scott, If you need this done soon, then you're best off to call in a consultant that does these on a regular basis. If you have a couple / few months, then perhaps you could buy the codes and go to some seminars. Arc Flash analysis can be quite involved. A proper Arc Flash...
  18. VxA

    conductor sizing for electric motor

    If the FLA you are stating of 360A comes from the nameplate, then you can use that, otherwise you need to consult 430-150 which says to use 382A. You must size the conductors to have a rated ampacity of at least 125% of the motors FLA. Thus, if we assume your FLA is 360, the conductors must be...
  19. VxA

    Twisted-shielded wire lengths

    If that's the case, I think the formula would reduce to: NewL = OldL * [TwistL / (TwistL + 4*pi^2*Dwire^2)] using the example of 200m of cable, 1mm wire diameter, an a twist length of 50mm, this yields a length of 198.43m. Looking at it closer, I think this is probably the correct approach...
  20. VxA

    3 motors common duct

    My impulse would be to say that running one motor at full speed would be cheaper than running three at a lower speed. It probably depends on the characteristics of the VFD though. Don't have any proof though, just a gut feel. Thanks, VxA

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