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Recent content by rockman7892

  1. rockman7892

    Breaker vs Motor Operated Switch for Substation Bus Tie

    I've got an application in a distribution substation where there are manual switches serving as bus ties between several different 13.2kV distribution buses. These bus ties are intended to be used when a transformer on a given bus is out of service in order to supply the bus through tie from...
  2. rockman7892

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

    I've come across a few small municipal distribution systems recently that had either their sub-transmission or distribution systems served from and interconnection substation to local transmission system owned by others (larger IOU) and noticed that the low voltage side of these transformers for...
  3. rockman7892

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

    I know that for a single L-G fault the ground fault current If on the faulted phase is represented as 3I0 and it is this 3I0 that can be measured and represented as ground fault current. I also understand that this 3I0 value comes from the contribution of both the pos sequence, neg sequence and...
  4. rockman7892

    Upgrading Utility Distribution Transformer with an NGR

    My understanding has always been that L-N loads are prohibited due to the fact that normal neutral current will flow through resistor and cause voltage drop across resistor thus creating a dangerous voltage potential between neutral and ground. That was always my understanding in the industrial...
  5. rockman7892

    Upgrading Utility Distribution Transformer with an NGR

    The distribution circuits in this application are fed from a sub what has a 138kV wye - 13.8kV delta transformer with a grounding transformer connected to delta side of transformer. So not a conventional wye grounded substation but rather a 13.8kV delta with grounding transformer. NGR was...
  6. rockman7892

    Upgrading Utility Distribution Transformer with an NGR

    Is there an advantage to having a neutral reactor as opposed to a neutral resistor on a distribution circuit? From what I've seen this is commonly done with generators where the Z0 is much less than Z1 causing zero sequence current to be much higher than positive sequence current and this the...
  7. rockman7892

    Upgrading Utility Distribution Transformer with an NGR

    A utility customer is considering installing an neutral ground reactor on one of their distribution transformers (12.47kV). I'm familiar with NGR in several other applications but have not seen many of these installed on distribution transformers. Is it common for utility's to have NGR's on...
  8. rockman7892

    Temporary Mobile Substation Grounding and Fencing Considerations

    I'm looking into a temporary mobile substation to temporarily restore power to a site with 60kV utility incoming stepped down to 12.47kV for distribution to facility. Mobile sub would consist of 60kV breaker, 5MVA transformer and 12.47kV secondary breaker. The only option for temporary...
  9. rockman7892

    Equipment Ground Conductor (EGC) on delta system with a grounding transformer

    Good points on shield. I'll have to look into concentric neutral as use as 2 conductor assembly but I do recall seeing recently that NEC permitted its use as an EGC. If that is the case is it still cheaper to run a separate EGC than use a concentric neutral cable just for the purpose of...
  10. rockman7892

    Neutral Grounding Practice for Utility Pad Mount Transformers

    Thanks. In my application I have a 4-wire distribution service coming into site and assuming distribution is a Mult grounded system. This incoming line hits a pole mounted disconnect, then padmounted recloser before it finally hits wye side of interconnection transformer. From reading the NEC...
  11. rockman7892

    Equipment Ground Conductor (EGC) on delta system with a grounding transformer

    Thanks Waross I'm trying to determine if the shield of an MV cable can be used to satisfy that EGC or if I must add a separate EGC cable or change cable to concentric neutral type. From what I understand the NEC doesn't allow shield to be used as an EGC to carry GF current of significant...
  12. rockman7892

    Equipment Ground Conductor (EGC) on delta system with a grounding transformer

    On an industrial or renewable site that is served from the Delta side of an interconnection transformer and has a grounding transformer (wye -delta) for sourcing ground fault current and limiting overvoltage, is an equipment ground conductor (EGC) as required by NEC still appliable to this...
  13. rockman7892

    Fault current capability of DFIG generators

    I've been looking at several wind projects that use Type 3 (DFIG) and Type 4 (Inverter) generator types. From what I've read both of these types of generators have limited fault current contribution capabilities due to the presence of the inverters. I've been familiar with limited fault...
  14. rockman7892

    Neutral Grounding Practice for Utility Pad Mount Transformers

    Thanks for responses. Even is this wasn't a utility pad mount transformer but rather a pad mount transformer within the customer premises I'm assuming the answers would be the same in that the concentric neutral could be used to carry neural current and fault current in system? Or would a...
  15. rockman7892

    Analysis for determining location of arrestors on overhead distribution lines

    I'm curious at a high level what this analysis would involve. Would you have to look at voltage transient at each pole and evaluate along with pole grounding and arrestor rating?
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