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  1. Modula2

    Magnetizing Impedance Measurement

    I would like to obtain the magetizing impedance characteristic, voltage versus current, of motors and transformers, on site, 4160 V system. I don't think it is so easy, as voltage would need to be varied from below 4160 to above, or use of some frequency methods. Does someone know if this can be...
  2. Modula2

    Relay Tolerance and Setting Errors

    I think you are right dpc. I will do that and go into more details. For saturation, I found GET-8501 helpful, although my app is another mfr. Thanks
  3. Modula2

    Relay Tolerance and Setting Errors

    David, the 0.12 sec I presented was only for the "relay tolerance and setting errors" portion of the coordination time interval (CTI). Additional items for the total CTI, such as breaker opening time, are not in that number, as I am not questioning them. In the reference I provided, total for a...
  4. Modula2

    Relay Tolerance and Setting Errors

    In Ieee 242-2001, "Recommended practice for protection and Coordination of Industrial and Commercial Power Systems", Table 15-2, a value of 0.12 sec. is given for relay tolerance and setting errors, static relays, coordination time interval, field calibrated relays. I'm wondering what the true...
  5. Modula2

    Arc Flash Motor Contribution

    AusPowEng, I expect the arc current, generally less than the bolted fault, would then include a reduction in the motor contribution. Stated another way, all contributions are accordingly reduced in going from the bolted to the arc current.
  6. Modula2

    Relay-Fuse coordination CTI/Grading Time

    Yes, dpc, it must be that. I see others suggest fuse-fuse as "daylight", and the same for LVCB-LVCB. That seems to settle the fuse total curve as including all tolernaces. So, it must be about CT and relay error. I also now see that some experienced people have a lower interval for relay Inst...
  7. Modula2

    Relay-Fuse coordination CTI/Grading Time

    IEEE 242-2001, p605, suggest a coordination interval of 0.12 between fuse and upstream static relay. Others, suggest similar values such as 0.10, for example, http://siemens.siprotec.de/download_neu/applications/SIPROTEC/english/Appl_03_Coordination_of_Overcurrent_Relais_with_Fuses_en.pdf I...
  8. Modula2

    Arc Flash Motor Contribution

    WDeanN,when you stated that the S/W used by you, allowed specifying synchronous motor contribution over a time period, did you mean that it produces arc flash results at a number of fixed contributions, probably two. Wouldn't actual incident energy be a summation from initial to final, so that a...
  9. Modula2

    Arc flash on secondary of 480V Transformer

    Eleceng01, if I read this correctly, your switchgear room must be category 4 due to the characteristics of the primary device. This is a problem.
  10. Modula2

    Soil Resistivity - Probe Depth

    That's what I said also: formulae are available. But why choose 1 metre probe depth instead of 100 or 200 mm? If the formulae give the same result, then easier to do 100 mm. And if 1 metre, then why not 2 or 3 m. On what basis would the decision be made as to depth?
  11. Modula2

    Industrial facility ground grid design

    The answers to your questions are in IEEE 80.
  12. Modula2

    Soil Resistivity - Probe Depth

    Has anyone seen references on the effect of probe depth vs probe spacing using the Wenner 4 point method. It is easy to see statements that spacing to probe depth should be 10 or 20 to 1, and formulae are available when spacing is not much greater than probe depth. However, exact backup is not...
  13. Modula2

    Static excitation system performances

    So, when the fault is cleared within 300 ms, the unit comes back to synchronism. It's not too far out at that time that it can't be restored. Is that the objective?
  14. Modula2

    Arc Flash MV Switchgear

    jraef, the box is higher by the physics. In Open, the energy radiates outward, so you mainly get the direct. In the box, you get the direct, but also, reflections off the sides of the box. In IEEE 1584, eqn (4), the constant K1 is the difference in calculating incident energy; higher energy for...
  15. Modula2

    Arc Flash MV Switchgear

    ZogZog, that is what I think also. It's by a Consultant, directed by multi-facility owner. Latest IEEE 1584. I'm an independent reviewer. None of them can form basic sequence networks, but they all have software.
  16. Modula2

    Arc Flash MV Switchgear

    For 5 kV switchgear, main or feeder breakers, I expected enclosure type to be Box. However, I am looking at a study where Open type was used, which gives a lower calculated incident energy. Has anyone seen something on this?
  17. Modula2

    Current Transformers for power analyzers

    Handasee, I am curious, as to whether there is some frequency related accuracy of the CT's. I mean, if we are investigating power quality, maybe there are higher frequencies that we want to measure accurately also. Perhaps to 83rd for harmonics. What about rogowski coils?
  18. Modula2

    Autotransformer Motor Start

    Davva, it's the transient impedance, for the initial voltage dip, not subtransient, not synchronous.
  19. Modula2

    Laplace Transform, Fouier Transform or.... Giorgi Operator?

    Bromwich, Giorgi, Carson, Mikusinski, and others, did work based on Heaviside, who invented operational calculus.
  20. Modula2

    IEC short circuit Calculation

    It appears that IEC does not have a method to decay the unbalanced fault currents, consistent with the way it is done for the three phase fault. Is that correct?

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