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  1. bacon4life

    Power Transformer Rating

    A transformer running at rated temperatures for their entire life may have a lifespan of only 10 years. Sizing slightly larger can dramatically increase lifespan. One consideration is the lifetime cost of losses based on the anticipate generation profile. The ideal design for a generator that...
  2. bacon4life

    Transmission Line Geometry and Impedance/Losses

    Rather than 5 phase, the 5F tower has a double bundle in the center and single conductors at the edges. Seems like basically two separate circuits with the middle phase mounted on the same insulator. Something like this: A------B ---CC--- B------A
  3. bacon4life

    Transmission Line Geometry and Impedance/Losses

    Larger diameter wires, more wires per phase, and tighter phase spacing all reduce impedance. Equilateral triangles will have lower impedance than flat arrangements.
  4. bacon4life

    35kV Line Reactors

    The impedance of 270 ft of bus may be negligible compared to the transformer impedance.
  5. bacon4life

    Inrush current of transformer

    I am used to thinking about a system than has 115/15 kV substation transformer that feeds several circuits that each have dozens of 15 kV/240 V service transformers. Energizing one of the 15 V circuits causes inrush to the 15 kV/240 V service transformers, which is in turn fed by the 115/15 kV...
  6. bacon4life

    Tie Breaker in Series and Bus duct

    Seconding crshears suggestion to ensure you design the tie with adequate isolation points to allow for maintenance of either bus without taking both busses out of service. Beyond that, the second tie breaker adds very little value.
  7. bacon4life

    Electrical Mystery

    Any chance this is part of a multiway switch circuit for a hallway light, where the other switch changed status during your testing?
  8. bacon4life

    Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

    Do you need the load split equally? Or are these located at opposite ends of building crane rail to provide reduce voltage drop?
  9. bacon4life

    UHV/EHV Cables in aerial rack distance to Coke/Blast Furnace Gas

    Is that a gas pipeline feeding the blast furnace? Or exhaust gases from the blast furnace? Would the area be explosive (i.e. classified)?
  10. bacon4life

    Custom ONAF2 Rating

    Utilities often have transformer ratings that take into account the expected duty cycle of a project. A 12 hour duty cycle of 325 MW discharge for 4 hours followed by 200 MW of charging for 8 hours should allow for a somewhat smaller transformer as compared to a constant load. Has the ISO...
  11. bacon4life

    Custom ONAF2 Rating

    Substation transformers are custom built, so there is a little bit more flexibility with the impedance of substation transformers as compared to distribution transformers. A friendly manufacturer's sales person could give you some guidance as to how much it would cost for a slightly higher...
  12. bacon4life

    Custom ONAF2 Rating

    On possible alternative is to ask them for calculated ratings under alternate operating conditions. For example, I have asked vendors to calculate nonstandard conditions such as: an ambient adjusted rating for a zero degrees C ambient a rating assuming the long time overloading parameters in...
  13. bacon4life

    MV Switchgear - Switching multiple sources

    Yes, this quite common.
  14. bacon4life

    Internal Diesel Storage Tank dimensions

    As LittleInch pointed out, consider the refueling logistics when determining the appropriate size for the new tank. If your requirement is for 24 hours of actual run time, it may be helpful to size the the tank to allow for at least 6 months of routine testing loads in addition to the fuel to...
  15. bacon4life

    Probability Distribution of Transformer Inrush

    The typical inrush curves for transformers assume an infinite bus approximation. For an islanded system with a transformer larger than the generator, that will be a rather poor assumption. I am rather confused that the links suggest that 0.5% probability means something will never occur. If...
  16. bacon4life

    Temporary Mobile Substation Grounding and Fencing Considerations

    Oil containment rules vary by state. The requirements in my region are that oil cannot escape into the watershed. For temporary installations far from water, the oil spill prevention plan would typically be to remediate any oil spillage by removing all contaminated soil. There is cost analysis...
  17. bacon4life

    Questions regarding transformer's percent impedance in other than nominal voltages

    Is that a common field test for transformer commissioning?
  18. bacon4life

    120/240V 1P-3W, 100A Service to Very Remote Building

    Some utilities offer 240 V/480 V 1P 3W service for street lights, which is typical used for street lights in my region.
  19. bacon4life

    Offshore power transformer YNd1 vs YNd11

    The 230 kV/66 kV ratio is a bit higher than typical for autotransformers. That being said, it seems weird to have the 66 kV system ungrounded. Many regions are eliminating tertiary windings on 400/230 kV autotransformers.
  20. bacon4life

    HV Power transformer connection type

    The GE publication The-whys-of-wyes provides good info on why to choose each configuration. Your application also matters. Do you have a load, a generation site, or a mix of load and generation? Increased distributed generation is make wye-delta-wye transformers more attractive.

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