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  1. wcaseyharman

    black start using aeroderivative turbine

    As long as you can power up the auxiliaries and the starting motor any type of unit can be blackstarted. We have a 40 year old 75MW heavy frame turbine that’s black start capable, but it takes a 2MW caterpillar genset to get it started. You just need to make sure your power source is large...
  2. wcaseyharman

    Phase-earth fault in YNd11 step-up transformer while operating at no load

    To confirm, does the main power feed the wye side of the transformer? Is the main power feed derived from a grounded Y transformer? I ask because it’s more typical in my experience for the source to be grounded, and the loads, such as this transformer, run ungrounded. This prevents the load...
  3. wcaseyharman

    Woodward Easygen vs PLC control system

    In 2023 we had a contractor install an Easy Gen and we installed a 700G and a Basler DECS 400 on a 2.5 MW MP45 that powers a microgrid. We are pretty happy with it. We have a site with old Caterpillar controls, it seems very confusing to troubleshoot. Granted, we were heavily involved in the...
  4. wcaseyharman

    Adaptive Setting LV Circuit Breakers for IBR Microgrids

    I had to use multiple setting groups in multifunction relays and reclosers in order to make it work. Used communications to switch groups when the generator islanded. I attempted to use some directional elements, but had trouble with them misoperating with low power high var situations.
  5. wcaseyharman

    Adaptive Setting LV Circuit Breakers for IBR Microgrids

    The major challenge I had was differentiating load current from fault current when trying to achieve selectivity. With synchronous generators the minimum fault current can be less than load current, and in order to trip for all faults the overcurrent set point had to be less than the maximum...
  6. wcaseyharman

    Adaptive Setting LV Circuit Breakers for IBR Microgrids

    How much selectivity do you need in island mode? You could use standard overcurrent elements in grid tied scenarios where there is sufficient fault current, then use time coordinated under voltage relaying during islanded situations. Alternatively, I recently used microprocessor relays to...
  7. wcaseyharman

    Inverters for solely Syncing / Sourcing VARS

    Yes, at least one brand is called a Static VAR compensator (STATCOM). S&C made the one my company has, but I don’t think they manufacturer them anymore.
  8. wcaseyharman

    L-G Fault Zero Sequence Current in un-faulted phases

    I think the answer is yes, the other two phases technically have I0 current, but you can’t measure it as it’s canceled by the positive and negative sequence currents in the phases without the fault, so the current is zero in the unfaulted phases. The only exception is that you can absolutely...
  9. wcaseyharman

    Delta Winding with grounding transformer on utility sub-transmission & distribution

    How old are these installations? I only ask because in my company a very similar situation is present, but it’s due to a change of system grounding philosophy over the last 100 years. The 55kV transmission system, which was the original system transmission voltage, was originally ungrounded...
  10. wcaseyharman

    Earthing of neutral on single phase transformer

    Well, if the 230V side has no ground reference then presumably the neutral voltage could be anywhere depending on the leakage impedance to ground. I’ve seen similar issues with ungrounded DC systems - typically they float with positive and negative sides equal between ground unless one side has...
  11. wcaseyharman

    VFD(VSD) on sluice gates

    I could see adding VFDs on single phase systems to allow for 3 phase motors would be a good practice. The max torque on a gate would be closed with the full force of water behind it, and single phase motors don’t have great starting torque. I have a feeling a smaller VFD and 3 phase motor would...
  12. wcaseyharman

    Short circuit fault condition KA

    1000000/(440*sqrt(3))=1,312.16 If the transformer is a 5% impedance: 1312.16/.05=26,243.2 1000000/(6600*sqrt(3))=87.477 87.477/.05=1,749.54
  13. wcaseyharman

    Upgrading Utility Distribution Transformer with an NGR

    My utility often installs neutral reactors in distribution substations, 0.5 ohms typically. I remember hearing it was to limit the LG fault current to prevent damage to concentric neutrals on cables during LG faults, but I need to verify that.
  14. wcaseyharman

    Struggling to understand how Back EMF works in AC Motors

    Same thing waross is saying, but from a theory perspective. The fundamental theory is: V= d_phi/dt, where phi is the magnetic field. In an AC motor or generator the stator magnetic field is generally sinusoidal. The derivative (slope) of a sine wave is proportional to the magnitude of the wave...
  15. wcaseyharman

    To replace obsolete Mark VIe steam turbine control system

    We’ve been talking with GE about obsolescence, so far all of our cards and controllers from 2008 are still supported. We still have UCSA controllers, first generation MarkVIe equipment. At some point they are supposed to provide us with an upgrade plan for each plant, although I think they are...
  16. wcaseyharman

    Generator Protection - Selection of Fuse based on Sustained Current

    Simplest protection is to use undervoltage along with overcurrent/overload protection - low fault currents, unless your fault is very far away, result in low voltage. With more sophisticated relaying a voltage restrained or controlled overcurrent relay, 51V, can be used instead for better...
  17. wcaseyharman

    Generator Protection - Selection of Fuse based on Sustained Current

    Yes, the current away from the generator will be lower. The curve referenced earlier is a bit tricky because it appears to include the dynamic response of the exciter. What this means is the fault voltage driving the fault current is varying. Depending on what you trying to do this may or may...
  18. wcaseyharman

    Generator Protection - Selection of Fuse based on Sustained Current

    It depends. On a close in bolted 3PH fault an instantaneous breaker would likely trip. A single phase fault away from the generator might not generate enough current to trip the instantaneous element, and if it’s tripping on the breaker thermal curve then I would expect it to be in the sustained...
  19. wcaseyharman

    To replace faulty power alternator with a smaller unit

    Depending on interconnection requirements you may need to keep in mind VAR capability and may need to run the turbine at an even lower load to provide VAR headroom - our transmission providers require 33% VAR capability at full load. Some generators have curves available to increase output on...
  20. wcaseyharman

    2MVA generator

    A couple of thoughts: 1. Since V = d_phi/dt, voltage should be linear with speed with a fixed magnetic field. What voltage do you need? 2. That sounds complicated since you’d generally need to rotate the machine - shiv and belt drive with a pony motor? Is this a bust fed excitation system...

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