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  1. lyla1711

    Primary and Backup Relay Timing

    In this case, we will have two SEL-351s, and we don't have to deal with reclosing, so that will make it pretty easy. I've come across similar arrangements in existing subs, but I did not fully understand why they were set that way - thanks for the detailed reply.
  2. lyla1711

    Primary and Backup Relay Timing

    I've been asked to create settings for an MV switchyard with primary and backup relays. So regular MV feeder breakers will have two relays connected to them. The trip outputs will be in parallel in the control circuit (on a single trip coil). Should I have a time delay between them, or should...
  3. lyla1711

    Fiberglass Conduit

    Has anyone ever used fiberglass conduit? I'm working on a site with heavily loaded below grade conduit runs with high load factor, and the fiberglass is supposed to help the cable ampacity derating (it does a better job of radiating heat than hdpe or PVC). I've used the 90s, and they were...
  4. lyla1711

    35kV Line Reactors

    We're working on a 35kV ring bus constructed out of GIS (four buses) and underground conductors. So it will be M-T-M-T-M-T-M-T (back to the first M), with each bus served by a substation transformer running the Delta Var 2 paralleling scheme. The loading on each bus is nearly identical...
  5. lyla1711

    70:250.30(A)(1) Exception 2

    Hello, forum. I've learned a lot reading here over the years - thanks to all the contributors. I have a question on grounding and bonding of a customer-owned primary service in the US, falling under the 2017 NEC. It's semantics, but I'm curious to hear how other interpret it. Article...
  6. lyla1711

    Ductbank Derating

    Oh man, I just read it as soon as I posed this... Thank you, 7anoter4. 310.60 Conductors Rated 2001 to 35,000 Volts. (A) Ampacities of Conductors Rated 2001 to 35,000 Volts. Ampacities for solid dielectric-insulated conductors shall be permitted to be determined by tables or under engineering...
  7. lyla1711

    Ductbank Derating

    I see that in the 0-2000V section, but I do not see a similar paragraph in the 2001-35kV section.
  8. lyla1711

    Ductbank Derating

    I know this topic has been discussed a lot here, but I have a situation with a twist that I haven't seen discussed elsewhere. For the overwhelming majority of the run I'm concerned with, it's a textbook three-conduit system directly out of the examples in NFPA 70. For about ten feet before it...
  9. lyla1711

    Opening LV vs MV Breakers

    Looking to get consensus here. I have an application where we can either open a 13.2kV vac breaker (feeding a 2000kVA transformer) or a 3000A 480V unit substation breaker (fed by said transformer). There are about 1200A worth of load on the 480V side. Both breakers can be opened remotely...
  10. lyla1711

    Parallel 15kV Feeders

    The sources are fed from different circuits in the same upstream sub, and they always float between the same two taps when the load is split. Additionally, there are other feeder breakers on the upstream bus (the one with T1). The feeder breakers we're discussing represent about half the total...
  11. lyla1711

    Parallel 15kV Feeders

    I probably do have enough information to perform those calcs. I do struggle with the idea of circulating current - what is physically happening. Are you aware of any good explanations of this?
  12. lyla1711

    Parallel 15kV Feeders

    The transformers have tapchanger controllers (beckwith m-2001d) which use the circulating current method. They're always within one tap position of each other, and we do have an off-tap alarms being monitored. The feeder length on one side is about 1000' and it's 750' on the other side. The...
  13. lyla1711

    Parallel 15kV Feeders

    This is an NESC application. The load on either feeder is fine for the cable size and 51/50 relay settings. The system is redundant so that either feeder can handle the entire present day load of the plant should one side have an outage.
  14. lyla1711

    Parallel 15kV Feeders

    Right - so we will see the majority of the current flow through the (2) sets of 750s, but we won't see any objectionable circulating current or reverse power flow or anything strange like that..... Right?
  15. lyla1711

    Parallel 15kV Feeders

    We have a situation where we are planning to parallel conductors of different length and characteristics. We have a 15kV M-T-M switchgear with paralleled transformers (automatic tap changer controls fully commissioned for paralleling), but the gear is run with the tie normally open. This gear...
  16. lyla1711

    GSU, Small Industrial Application

    That's correct, Kiribanda. The gens are standby - they will only operate when there is a utility outage. The transfer switch that the owner would like to buy is closed transition type. I'm thinking the correct configuration is to ground the gen neutral, run 3-wire to delta 480 side of...
  17. lyla1711

    GSU, Small Industrial Application

    One line is attached. I know it lists the transformer on there at grounded wye to grounded wye, but that will be updated. I'm thinking it's wye configured gens with the neutrals grounded, and that feeds a step up transformer which is delta on the gen side and wye on the utility side. I'm just...
  18. lyla1711

    GSU, Small Industrial Application

    I'm hoping to get some advice for integrating some parallel generators and a step-up transformer at an industrial plant. We have (4) 1MW generators which will be paralleled and backfeed a single 480-13.2 step-up transformer. This will feed a service rated MV ATS and pick up the entire plant...

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