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  • Users: qman5
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  1. qman5

    Riser sizing for ungrounded systems or neutral grounded systems

    Hello all, In the case of ungrounded system, where the SLG fault current is sensibly 0, or in the case of a NGR, limited by the NGR current, do you typically size the grounding pigtail risers for this limited current, or the maximum fault current (e.g. LLL, LLL)? Consider an ungrounded delta...
  2. qman5

    When do you call it quits for grounding of metallic items inside substations.

    The code isn't very practically helpful (NEC and CEC). Are there better comprehensive references? So I bond a permanently installed platform in a basement that is nowhere near energized conductors? Some clients are concerned about induced voltages for absurb reasons. Do I go through the efforts...
  3. qman5

    1/6 (16.6%) Concentric Neutral and other fractions

    The neutral is there to carry unbalance current and also capacitive charging current. I would assume that if we are confident that our loads are balanced, and ideally have no neutral, bu code dictates that we need one. Practically speaking, we would like to minimize the extra cost of the...
  4. qman5

    1/6 (16.6%) Concentric Neutral and other fractions

    The loads are connected Delta(HV)-WyeGnd(LV). The cables are on the LV side. (I edited my second reply, I'm interested in the theory).
  5. qman5

    1/6 (16.6%) Concentric Neutral and other fractions

    Specifically, this is at the 25 kV level. This was a utility substation application for outgoing feeders and also switchgear-to-switchgear connections in the same station. The loads are unknown -- only the feeder ampacities are known. However, this is more of a general questions. I am in the...
  6. qman5

    1/6 (16.6%) Concentric Neutral and other fractions

    Can someone shed some light on why we would use a 1/6th (or other fractions) than 1/3rd (33%) or 1 (100%)? I understand that 1/3 (33%) concentric neutrals are used for 3 phase loads and 1 (100%) concentric neutrals for single phase applications. I'm not immediately aware of any applications...
  7. qman5

    HV Insulator Discharge

    Silicon insulators will not explode causing fragments. Just an observation: Are the shed profiles not reversed? Looks like this would cause water to accumulate and possibly contribute to the tracking.
  8. qman5

    GIS high speed earthing switch

    It's possible to discharge loaded cables or overhead lines via a fast acting ground switch (the acronym has always made me laugh) or high speed earthing switch (HSES). Protection-wise, this is something that I cannot comment on. At this point, I understand that is a merger is what the switch is...
  9. qman5

    100% redundancy question for HVAC system

    Hello all, If there is a specification requirement for a "100% HVAC redundancy requirement", what would you consider in terms of redundancy? Let me explain further. For our particular situation for a small building that contains 2 rooms, each with AHUs capable of handling 100% of the load for...
  10. qman5

    The responsibility of spare HV cable definition

    Generally speaking, who is responsible for the allocation of spare HV cable lengths? By spare I mean that would be generally discarded during the installation process. The designer or the purchaser or installer? (in our case, we are the purchaser + installer!) My customer gave me lengths of x...
  11. qman5

    Recommendations for in-class courses for learning P&C

    As part of my yearly training, I have been tasked to select something that will in aid my development. I'd like to learn more about the fundamentals of P&C. I would like to get your recommendations on courses that you think are worth taking. In classroom is preferred. If it was up to me, I'd...
  12. qman5

    At what MVA does transformer differential become commonly used?

    I'm working with a 10, 7.5 and 5 MVA transformer and am wondering if I need to specify CTs for transformer differential? The configuration is actually: Recloser --> 10/7.5/5 MVA --> MV switchgear with 1 incomer and 3 outfeeds. I'm not familiar with protection nor with the customer's...
  13. qman5

    Underhung 220 kV surge arrestors

    Agreed with the above in terms of the possibilities of failure and the ease of replacement. We recently installed underhung arresters due to a limitation of space. The preference is to go with composite housings, but some utilities do not accept these. The risk of catastrophic failure is higher...
  14. qman5

    Proper use/dimensioning of extractor fans for GIS building

    crshears, I'll be straightforward: I appreciate your input, but this is what I find one of the biggest problems in today's older engineer demographic (and what sometimes translates to non-sense specs). You raise some good points about SF6 leakage and climate, but that's about it. You should...
  15. qman5

    How I handle a blown bid and its associated takeover?

    I've taken over as the lead engineer for a project, where I have been assigned to lead the technical success of a turn key project. It's a smaller project for what my company usually handles, but I've already started to find huge mistakes, mostly on the technical side. For example, a UPS system...
  16. qman5

    Proper use/dimensioning of extractor fans for GIS building

    I would reach out to the manufacturer to get their recommendations. You might need to pay more for a larger humidity range, but you could cut down on HVAC costs. GIS normally has a high operating temperature range (-25C to +40 (or higher!)). There is a lot of heat generated per bay (on the order...
  17. qman5

    220 kV GIS Cable Termination

    Thank you for those slides -- very interesting! On one of my current projects, I have a cable compartment about 4 meters deep and 5 meters long that we will be pulling cable into. (230 kV cable @ 1200 mm2). For our case, the manufacturer has cleared the use of installing the terminations above...
  18. qman5

    HV Connectiors for Substations

    Just ask the supplier to recommend you a clamp for the maximum ampacity you foresee. You can always go and calculate this rating, but calculating hole diameter and the effect on ampacity... don't worry about this for now. Trust your supplier (until he's wrong)
  19. qman5

    Control and Power Conductors in Same Conduit

    What bothers me about the CEC or NEC is that it is not always practical. What about cases where you have the same (e.g. 1000V) insulation rating with foil shielding? In this case, I see no objection to running power and control cables in the same trench/conduit/tray.
  20. qman5

    Termination of coaxial bonding cables for link boxes

    Thanks, this makes more sense to me now. My confusion stems from the fact that the standard doesn't seem to distinguish between a single run or minor sections. I then question if single core cables can be used for 3 phase link boxes when the distances between terminations is greater than 3...

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