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  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

    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...
  5. 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...
  6. 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...
  7. 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...
  8. rockman7892

    Neutral Grounding Practice for Utility Pad Mount Transformers

    I was wondering what standard practice was for grounding of neutral connections on utility pad mount transformers served from and overhead distribution line that contains a neutral. Question applies 1-phase pad mount fed from OH lateral feeder but similar question also applies to 3-phase with...
  9. rockman7892

    Analysis for determining location of arrestors on overhead distribution lines

    Is anyone aware of an analytical or modeling approach for evaluating location of arrestors on overhead distribution lines? Most approaches I've seen have been ones that utilities have adopted over years or more general "rules of thumb" but was curious if there was an analytical approach using...
  10. rockman7892

    Sizing a diesel generator based on metering data

    I'm in the process of determining size of 480V diesel genset for an industrial site to replace existing temporary units. I'm evaluating size based on both metering data captured via a portable power meter for site at service entrance as well through load calculation in order to evaluate both...
  11. rockman7892

    Wye neutral connection on a Delta-Wye Distributed Generation Transformer

    Looking at an application where a new 24.9kV - 12.47kV transformer is being added for interconnection of wind farm to utility 24.9kV distribution line. Transformer is 15MVA and will have delta side facing generation (with grounding transformer on that side) and the wye side facing 24.9kV...
  12. rockman7892

    How is power sold directly between generator and remote user across different utility entities?

    This is a question which I've wondered about for quite some time and although I think the answer comes down to commercial agreements as opposed to flow of electrons I was curious to hear from some of the experts here. As an example I've heard of scenarios where a new generation plant or...
  13. rockman7892

    Supply Side and Equipment Grounding Conductors in HV Substation

    I know that the NEC requires additional Equipment Ground Conductors (ECG's) to be run with any feeders between equipment and Supply Side Bonding Conductors (SSBJ) to be run between transformers of separately derived system and downstream equipment. My question is in a HV substation environment...
  14. rockman7892

    138kv Cable in Tray

    I’m looking at a project where customer is looking to install temp 138kv-34.5kv transformer in existing substation in order to repair existing transformer. Plan is to locate tramp transformer in separate location in yard and reconnect HV and MV bushings to existing buses work to minimize...
  15. rockman7892

    PT ratings on impedance grounded systems

    I know that for applying a PT on a 4.16kV impedance grounded system (non-rigidly grounded)the PT needs to be a 2400/4160Y PT as opposed to a 2400/4160GY PT due to the fact that the neutral bushing needs to be a fully rated bushing for when neutral floats to line voltage during certain fault...
  16. rockman7892

    Grounding Transformer In distributed wind generation

    In relation to my other recent post I'm looking at an application where there are (3) 3MW wind turbines connected to a 12.47kV collector feeder before interconnecting to a 12.47kV distribution line (there is actually a voltage regular between turbines and utility line to bring 12kV turbine...
  17. rockman7892

    Transformer Differential with Reclosers

    Is it possible to implement transformer differential protection using (2) reclosers on high and low side of transformer? Looking at application where existing 15kV recloser would be on low voltage side of new 15MVA transform and consideration adding new 25MVA recloser on 25kV high side for...
  18. rockman7892

    Use of voltage regulators with step-up transformer on distributed generation

    I'm looking at an application for a distributed generation wind site that currently has about 12MW of wind generation at 12kV that goes through collector system and step voltage regulator before interconnection point of 12.47kV utility distribution line (recloser and metering at interconnection...
  19. rockman7892

    HV GIS Substation Considerations

    I’m in the preliminary stages of concept design for new 345KV GIS substation and was hoping to hear any experiences or best practices others have had with GIS layout. Substation topology will be incoming 345kV lines to GIS which will then feed (4) distribution transformers. Proposed method...
  20. rockman7892

    NESC conduit burial depth requirements?

    Does the NESC have any specific requirements for 34.5kv pvc conduits encased in concrete ductbank beyond what is required by NEC? NEC allows for 24” min burial depth for MV pvc conduits that are encased in 2” of concrete. Does the NESC require any greater burial depths?

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