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  1. Robert789

    Sawmill Motor - LRA, Softstart, etc.

    The system (Bandit 3680) is separate from the rest of the mill. An operator is using a front end loader to deliver the material that will be chipped. The unit presently is set up to retract the infeed conveyor when the speed of the unit drops by 300 rpm. Upon conversion from diesel to...
  2. Robert789

    Sawmill Motor - LRA, Softstart, etc.

    I have received further information about the planned installation and it is indeed a chipper, not a debarker, that has the 400 HP motor proposed for it. The chipper is a standalone unit that has previously been powered by diesel. The owner is considering converting the unit to electric...
  3. Robert789

    Sawmill Motor - LRA, Softstart, etc.

    I'm evaluating a customer's request to install a 400 HP motor for de-barking trees at a sawmill on our distribution system. I've calculated the voltage dip due to locked rotor amps of the motor and determined that it would not be appropriate to allow it to start at full voltage (about 5.6% dip...
  4. Robert789

    residential stray voltage - investigation procedures

    Sorry about that, the applicable code is the NEC (rules for bonding of pools are in section 680.26), not NESC. I think that this issue was first addressed in the 2005 version and bonding requirements were again strengthend in the 2008 version. Robert
  5. Robert789

    residential stray voltage - investigation procedures

    A large percentage (maybe over 50%) of the instances I've seen involving someone being shocked in a shower ended up being due to a shorted element in an electric hot water heater. Often in the same residence where the problem was reported, but frequently several houses away. When we receive...
  6. Robert789

    Parallelling transformers during switching

    If no load is dropped during the switching operation, I think that matching voltage prior to switching will not result in high circulating current (nor will the transformers share load equally after they are paralleled). With the voltage matching method, I think that the each transformer will...
  7. Robert789

    Power Transformer Inrush Calculation

    prc, For a line to ground fault on the secondary side of a delta-wye transformer bank, the fault current will be split between two phases on the primary side of the transformer. Fault current seen by each fuse will be {1/sqrt(3) = 0.58} times the fault current in a wye-wye connection. Robert
  8. Robert789

    Power Transformer Inrush Calculation

    I'm looking at the existing protection for a bank of three single-phase, 2500 KVA, 44 KV to 13.2/7.62 KV transformers, connected delta-wye, at a rural substation. Protection for this transformer bank was originally supplied by 125 Amp Southern States Type PF fuses. About 2 years ago (before I...
  9. Robert789

    OVERVOLTAGE DURING SINGLE LINE FAULT

    My understanding of it is that it is caused by a shift in the voltage of the neutral with respect to remote earth. If a bolted fault occurs on one phase of a distribution feeder, the voltage across the fault is essentially zero, but the voltage at the substation is still pretty close to the...
  10. Robert789

    Grounding at light pole base

    Several posts refer to tripping an overcurrent device for a short in a metal light pole. Utilities that I have worked for don't typically have a protective device between their light poles and the distribution transformer serving them. A hot leg contacting the light pole would energize the...
  11. Robert789

    High temperature compsite core transmission wire

    I am somewhat curious about these conductors as well. I have a radial line, 115 KV, 15 miles of 795 ACSR on concrete poles, that will likely need to be upgraded in the next 5 years. The line was not designed for future bundling or addition of a second circuit. My dilema in evaluating the...
  12. Robert789

    Use of Reclosers for Capacitor Bank Switching

    I don't believe that we have reactors on the 600 KVAR banks. We do have them on some multiple sets of 1800 and 2400 KVAR banks at other stations.
  13. Robert789

    Southern California Outages - Utility Perspective

    Typically, we would place up to 5 or 6 houses on a 50 KVA transformer. I'm figuring on around 10 KVA per house during peak times. When it gets hot enough, I think you have to expect that everyone's air conditioning will be running at the same time. It was in the mid 90's in North Carolina...
  14. Robert789

    Load

    Lets go back to %Z and %Voltage Regulation for a minute (or at least to my understanding of it). %Z is numerically equal to the percent of primary voltage that you would have to apply to a transformer to get its full rated current to flow when the secondary terminals are shorted together...
  15. Robert789

    Use of Reclosers for Capacitor Bank Switching

    I'm thinking that a call to the manufacturer of the recloser you intend to use may be in order. 330 Amps or so at 90 degrees leading may not be exactly what they designed the unit for. Make sure you look at the source impedance when considering switching a bank this large. We tried switching...
  16. Robert789

    Lead Power factor

    Assuming that we are dealing only with a distribution circuit and not generators, I would mainly be concerned with voltage rise. If I have the equation correct, the voltage rise can be calculated from the source impedance as follows: {((KVAR per Phase)/(KVln))/Ibase} * X1 = %VR The utility...
  17. Robert789

    Utility refuses to provide X/R ratio

    I think the utility's response is appropriate. When approached with similar requests, I provide available fault current at the transformer secondary assuming infinite bus on the primary side. I also let them know that this is based on the existing transformer which could be replaced with a...
  18. Robert789

    Westinghouse T&D Book

    I bought my copy a couple of years ago through www.bookfinder.com . I think that I paid about $75 for it at the time. Five copies are listed on the site now in the $120 range. Just type in "transmission distribution reference" in the search field. Robert
  19. Robert789

    The Physics of Elecrtrical Failure: Ungrounded Systems

    How many times did Jennifer Lopez marry last year? If she was married twice, and each of her husbands married once, then that would be three persons married during the year (an odd number).
  20. Robert789

    Underground dist. and trans. cable books

    Southwire publishes a Power Cable Manual that is approximately 100 pages or so. I have a copy and it appears to be pretty good. You can request a complimentary copy from Southwire's web site (www.southwire.com). I bought a copy of the Westinghouse T&D book a year or so ago (everybody needs...

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