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  • Users: Hertz
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  1. Hertz

    IEEE-518

    IEEE-518, dealing with the separtion between power and control cable trays was withdrawn in 1997. Does anybody know if is replaced by another standard or another standard covers the material?
  2. Hertz

    Motor Insulation Class

    Has anybody heard of Class C insulation for canned (sealless motors)?
  3. Hertz

    Unit-Substation Transformers Efficiency

    Thanks all for your excellant comments. I remember from my college days in the last century that the maximum efficiency of the transformer is at a point where the no-load(iron), and load (copper) losses are equal. I want to know where that point is? Is it at 100%, 90%, 50% or what?
  4. Hertz

    Unit-Substation Transformers Efficiency

    Does anyone has a graph showing the efficiency vs. loading for unit-substation transformers rated 1500-2500 kVA? In double-ended unit-substations these trafnsformers are usually loaded at 50%, and I am interested in seeing what penalty one pays for this. Thanks
  5. Hertz

    Induction vs Synchoronous Motors

    Thanks all for your good comments. I am going to be more specific. We are trying to buy two reciprocating compressors, one rated at 10,000 hP, and the other at 1,500 hP., both 360 RPM, 6.6 kV, 60 Hz. How do we decide on induction/synchoronous. I remember seeing a graph as I described in my...
  6. Hertz

    Induction vs Synchoronous Motors

    I am looking for a graph of hP/rpm, showing the suitability of induction/synchoronous motors. Any Ideas?
  7. Hertz

    HAZARDOUS AREA QUESTION

    Gas detectors could be installed outside fence, and on both sides of the temprary road. These will operate gates in order to stop the traffic in case of a gas detection. Check with AHJ to see if this meets the local codes.
  8. Hertz

    480V 3-Phase Help - Unbalanced

    I do not understand your concern about unbalancy. In any industrial facility there is always some degree of unbalancy. Also the 480 volt transformers are usually rated at 225 kVA and up, so a single 15 kW unbalanced load will not be a big problem . If you are planning to install many of these...
  9. Hertz

    160A 3 phase plug for China

    You need to make sure that the combination of the plug and receptacle is of the "Dead Front Interlocked" type. This combination will permit the user to safely unplug the portable equipment.
  10. Hertz

    Reliability of an existing stand-by power Generator

    Contact the generator manufacturer. They have peocedures for inspecting and testing the generator utilizing load banks.
  11. Hertz

    Ratings on double-ended switchgear

    It mostly depends on the application. In most cases the non-essential load can be shed from the substation, and the remaining transformer is required to supply the essential load on both buses. Also it is customary to use the fan-cooled rating of the transformer to supply the total essential...
  12. Hertz

    Cable sizes

    Don't forget the rules for derating cables for ambient temperature, and also for the number of current carrying conductors in raceways.

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