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  • Users: swn1
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  1. swn1

    How would you approach this customer complaint?

    You'll just embarrass your customer, he's wrong, so don't push it. Instead, run a simulation using some decent EE software and give him a generous interpretation of the result. The "garbage in, gospell out" effect will dispell most doubt, and it wasn't his error.
  2. swn1

    Circuit breakers withstand S.C current & no. of operations?

    Experience in a breaker shop, we had a number of older power plants and pipeline stations as customers. The ones who had modernized old lineups, replacing old breaker-as-starter units with new vacuum-breaker-as-starter units had much sorrow and woe. The mechs are made of stamped sheet metal...
  3. swn1

    Synchronization of an isolated generator with load to grid

    You can run coupled to the grid with droop controls on both power and voltage, but unless the grid is very stable at the point of interconnection you wouldn't want to do it unattended. A far better setup is to use feedback control of both real and reactive power. Meanwhile, the protective...
  4. swn1

    Voltage Collapse

    Just because there are three PTs doesn't mean they are all being read. Make sure the relay knows there are three! Yes, it happens.
  5. swn1

    Circuit breakers withstand S.C current & no. of operations?

    Modern breakers are not built like the old ones. The vacuum bottles will take many operations but the mechanisms will wear out. For this kind of duty choose a contactor, not a breaker, and back it up with fuses if necessary.
  6. swn1

    Data Center Battery Ground Bus

    Last time I saw AC on the DC bus it was in a lineup of medium voltage switchgear with 48VDC floating control power. Somebody had modified one of the units to be a motor starter. In the process they re-wired about half of the control panel to run from the local control power transformer...
  7. swn1

    programming language functionality

    Mathematica, perhaps?
  8. swn1

    Breaker Not Tripping

    ...The instantaneous unit is operated by secondary current and, depending on how it is adjusted, it is possible to have it drop a target without quite closing the trip circuit. Is the "closed" indicator light on? This is *usually* wired to indicate continuity in the trip circuit, but not always.
  9. swn1

    kW Meter hook-up (2 element)

    When you hook up a two element meter to a three-phase circuit with the typical open-delta PT arangement the voltage triangle is offset because the B corner is grounded. This is irrelevant when computing energy in a three-wire load circuit, in principle. In practice, the effect is that the...
  10. swn1

    LV air circuit breaker in motor service

    The older AKR breakers hold up to rebuilds well. There are a lot of them in the junk yards so you'll be able to keep it going for years. For 480V service there is room for both a vacuum contactor and a set of fuses on the frame, but you have to modify the platform some. You can have the shop...
  11. swn1

    Async vd Sync Motor Evaulation`

    No, I'm just suspicious. Why are they selling those motors at that price to this customer at this time? Probably trying to get the design-in, might be dumping, who knows? But the engineering decision is being biased toward the induction motor because of the below-market price offered for...
  12. swn1

    Using hydrogen for cooling armature

    Because hydrogen is less dense than air it is not centrifuged out of the rotor as much as air. Helium also has good thermal properties and is inert, but it is twice as dense as hydrogen. Is density the determining factor?
  13. swn1

    Vacuum CB's potentially dangerous?

    We never see BF in industrial systems. We'd like to, but the systems are usually pure radial and the breakers are more reliable than the never-exercised transfer trip circuits would be in practice. The single-failed-bottle scenario won't clear a ground fault on the bad phase. That means that...
  14. swn1

    kW Meter hook-up (2 element)

    When checking the calibration of a two-element meter with a single-phase source, you need to energize both potential coils. There is an adjustable shading coil on the potential coil cores that is used to generate torque to cancel the friction in the shaft bearings and register. Your low-power...
  15. swn1

    Synchronous Motors out of step relay

    Most vendors call this function "pull out" when it is applied to a motor, the "out of step" terminology is usually seen when it is applied to generators. The settings are seldom critical. The relay's job is to trip out the field and/or the main supply when the motor "pulls out of sync". This...
  16. swn1

    Async vd Sync Motor Evaulation`

    The usual justification for a sync motor is based on their stiffness with respect to cyclic torque variations. Reciprocating compressors and certain kinds of mills are the usual applications we see. Back in the day they used sync motors as something akin to a virtual gear train to maintain...
  17. swn1

    clamp meter load

    The ideal CT is impervious to nearby magnetic fields. Real ones aren't. When clamped on near a transformer or motor you will get some influence. I've had "fluctuations" in measured current that weren't really there twice in the recent past. Once due to the influence of a contactor coil and...
  18. swn1

    Full Voltage non Reverse 2300v induction Motor Starter

    The selection of the GFCT depends on how your system is grounded. You need to know minimum and maximum GF currents. I second the recommendation for a Multilin 239.
  19. swn1

    Excitation System Mathematical model

    OK, I'll bite. BSEE, MS Applied Math, working with a lot of sync machines these days. Do you just need the math or do you need it programmed into some particular simulation environment?
  20. swn1

    state of outputs when computer hangs

    Best piece of advice I've seen on watchdogs is to split the "set" and "reset" operations between separate sections of the code. Make the hardware timer require transitions so the process has to execute in both sections to keep it reset. One system I built had numerous communicating processes...

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