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  1. MAGTiger

    bearing currents vs. common mode current

    Good info, thanks all. Neil
  2. MAGTiger

    bearing currents vs. common mode current

    Electricpete I would agree that the the majority of the common mode current entering the motor terms gets to ground in the stator. The larger question remains, how to identify or separate bearing current from the stator ground current. I would expect the signature of the bearing current to be...
  3. MAGTiger

    bearing currents vs. common mode current

    Is anyone aware of documented research which relates bearing life to the magnitude of rms or peak(pulsing) current? I can measure and reduce common mode current near the motor terminals and must assume that most of the common mode current in this location particularly the peaks (current...
  4. MAGTiger

    Antoher Wind Turbine Question

    my understanding is that large wind turbines are expected to develop about 33% of nameplate power on a continuous basis converted to KWH. If that assumption holds true you may be able to deliver 200 watts on average. Neil
  5. MAGTiger

    Antoher Wind Turbine Question

    Keep us informed of your progress, I'd be intrested to know when it's all done how much it costs to set up a 600w wind supply. Neil
  6. MAGTiger

    12 or 24 pulse drive

    This is a cost/benefit analysis. "Using multipulse rectification is usually the least expensive way to mitigate harmonics". Come on, line reactors are the least expensive way to mitigate harmonics. This analysis can't be made without costs, target THD and realistically you need to know the...
  7. MAGTiger

    SCCR rating - engineering supervision

    EEPROM, I can't speak to breaker use as we don;t use them in this capacity. We build 508A panels all the time and we have a letter written by a UL Engineer that clarifys our requirement. We use 2 current limiting fuses in series, per phase. Both fuses are class T. The source side fuse is...
  8. MAGTiger

    SCCR rating - engineering supervision

    Take caution using current limiting fuses. Ul does not recognize the current limiting capability if the fuse is located in a branch. Neil
  9. MAGTiger

    Single Phase to Three Phase Converters

    A 15hp 3 phase VFD can be supplied from a single phase source then provide a 3 phase output to the motor at 7.5hp. This is a fairly common application. Should work well as long as you don;t need to change voltage. Neil
  10. MAGTiger

    Problem with motor chokes for VSD

    there is another possibility. If this is a 3 phase choke with a 3 leg core, then if the leads are grossly over sized by cross section, you can have a high amount of common mode current. Such a reactor will saturate in the yokes from this condition. Need to reduce the common mode current. This...
  11. MAGTiger

    Variable speed drive cable

    I'll qualify my statement by saying that the VFD cable we have test experience with was purchased around 10 years ago and frankly I don't know if it has individually shelded strands. But we did ground the shield and our results were that the overvoltage ringup was not as bad as the armored cable...
  12. MAGTiger

    Variable speed drive cable

    I think you will find a properly sized dv/dt filter with armored cable (again properly sized) to be a more cost effective solution. The problem with the VFD cable is that it is basically jus protecting itself. You will still get ring-up at the motor terminals. One of the really big problems I...
  13. MAGTiger

    How much load can a single phase 75KVA OH TX really handle?

    These transformer commonly see 250% of rated current for relatively short periods say 1.5 hours, mainly in the morning when everyone wakes up. Then in the afternoon again a high overload maybe 150-200% but lasting a few hours, then 10-20% for about 8 hours,... The oil provides a significant...
  14. MAGTiger

    Reducing VFD Power output without reducing speed?

    It's kinda like putting a 60w light bulb in a socket where previously there had been a 100watt bulb. The new bulb only draws 60watt regardless of the circuit and socket's ability to deliver 100w or more. Neil
  15. MAGTiger

    filter inductor and DC

    With regards to residual flux. This gets to my point about the likelihood of a transformer saturating much more quickly than an inductor. Inductors typically have much lower permeabilit, made so by air gaps. The air gap allows the residual flux to seek a very low level. Unlike transformers...
  16. MAGTiger

    industrial control panel wire ampacity

    I believe, UL508A table 28.1 is going to assume the temperature of the air in the enclosure to be 40 to 50C. I've heard arguments both ways but believe it's customary for UL to allow 50C in the ICP enclosure. Neil
  17. MAGTiger

    filter inductor and DC

    Well, like I said, it probably isn't saturating but keep in mind that the inductance changes (drops) as the core nears saturation. This is because the permeability of the steal drops with flux density. So effectively as the inductor reaches saturation, the inductance is falling and the effect is...
  18. MAGTiger

    filter inductor and DC

    It probably would not saturate an inductor, maybe a transformer. But the air gap in the inductor covers a lot of sins. However, even if it had saturated the inductor, that shouldn't prevent the motor from running. When the core saturates, the inductance goes to the air core inductance of the...
  19. MAGTiger

    DC Electrical Distribution Systems for Buildings?

    jghrist! you've written the magic words, "renewable energy". If it's in the name of renewable energy, they it shall be done and cost will not be an obstacle. Politicians will be falling over themselves to throw money at such a project. Neil
  20. MAGTiger

    4hp single phase motor problem

    Sorry, I just scanned the thread so excuse if this has been suggested but why not use a 3 phase motor and VFD but supply the VFD with single phase. This is a fairly common solution. Just upsize the VFD 175 to 200%. so a 7.5hp VFD would drive the 4hp 3ph motor. Plenty starting torque and speed...

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