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  1. MKFPE

    T-Model Values for Zero Sequence Network for YNyn0d1 Transformer

    Sorry for the delayed reply and I hope this is of use. I'm retired and do not look at the forum often these days. I have uploaded an old worksheet for LibreOffice Calc, Excel, etc. I created to transform the impedances to the "T" format. Some actual transformer data is entered from an old...
  2. MKFPE

    Solar Farm Interconnection Voltage Selection

    It can be done, Practical? Depends. You need to do a power flow study to determine if voltage drops and power losses are acceptable. It comes down to economics and that is different in every situation. I doubt a rule of thumb is of much value. You need to do the math, comparing options of...
  3. MKFPE

    Ampacity of Multiple Paralleled Conduits in Air

    Hi, I believe both Okonite and Kerite engineering/catalog publications provide guidance for multiple conduits in air. These come to mind since I specified EPR cable exclusively for several decades with excellent reliability, in fact I know of no failures with many thousands or perhaps tens of...
  4. MKFPE

    Adding conduit holes on side of Switchgear in the field

    Can you meet the cable minimum bending radius specification using LBs? As I recall for MV cable with tape shield it is typically 12 x OD, probably about 12 inches for 1/0 cable. I was not involved with work covered by the NEC very much since the majority of my career was spent doing utility...
  5. MKFPE

    86 relay current draw?

    eeprom, 3 more things: 1) Your lockout relay has been abused. I would be concerned about its future reliability. 2) I would get some training for your operator, understanding of protective device function appears to be needed. LOR tripping is a "call in the experts" situation, not something...
  6. MKFPE

    86 relay current draw?

    eeprom, Relax and use Ohm's law, pretty basic stuff. If you know the applied voltage and the resistance in the circuit the current equals the voltage divided by the resistance. Again, if the coil resistance is about 24 ohms as you said in your original post the current is 125/24 = 5.2 Amps. If...
  7. MKFPE

    86 relay current draw?

    eeprom, I think thermionic1 is on to something, but it is still a bit puzzling. Older lockout relays can become "sticky" after sitting unoperated for years and if the fault was intermittent the initiating relay might have dropped out before the 86 could operate. I have seen this, but the...
  8. MKFPE

    Vacuum fill or not?

    Thanks prc & OffTap100. Our Substation Supervisor told me your answers are a "confidence builder." He has has developed his plan for this work and will be following the advice to use the filter press in and out. We will allow plenty of time between this work and energizing. Further inquiry to...
  9. MKFPE

    Vacuum fill or not?

    We have a 24 year old 69kV-12.47kV 10MVA power transformer with nuisance oil leaks at the sidewall mounted LV bushings. It was recently removed from service for replacement by a larger unit. The transformer is currently in storage awaiting installation in its new home at a different substation...
  10. MKFPE

    Estimating Split Factor using Annex C in IEEE 80

    Here is something you might want to try as a sanity check for your calculations: I use WinIGS software for grounding analysis. It is quite powerful. A very limited (compared to WinIGS, not to other short circuit programs) but free related program which is kind of a mini-version is available...
  11. MKFPE

    Transformer Switching with Air Switches

    Well, this one has gotten a bit off track from the original question but I'll go ahead and add an automatic grounding switch related comment to this excellent discussion: In the one case I am familiar with wherein one of these things actually operated in response to a transformer differential...
  12. MKFPE

    Transformer Switching with Air Switches

    Google "Current interruption using high voltage air-break disconnectors" You will find a Phd thesis (David Peelo) with lots of information regarding the issues. I once watched a fellow at a steel plant drop a 75MVA 138kV transformer using an ancient gang operated vertical break switch with the...
  13. MKFPE

    Electromechanical relays - asymmetrical fault current

    In industrial settings I have seen recommendations for the high side instantaneous unit to be set at 1.25 times the symmetrical let-through for a 3-Ph bolted secondary fault. Industrial installations usually don't experience a lot of faults compared to a utility substation feeding overhead...
  14. MKFPE

    soil resistivity measurement and interpertation

    I think jghrist has it right. The photo indicates this is some sort of rural area. Are any water well records available for wells in the area? Where I am our State Dept. of Natural Resources has put all well records, dating back decades, on line. (They were always available the old-fashioned...
  15. MKFPE

    Grounding of utility poles equipped with radio equipment

    Hi, Depends on the lightning activity at your location and how important the radio is. An excellent reference for grounding design is the Motorola "Standards and Guidelines for Communications Sites" Publication R56. Recommendations are given depending on how you classify the installation in...
  16. MKFPE

    Phantom fault currents

    Hi muniengineer, If I understand your description these two circuits are completely separate geographically. The only common feature is perhaps the construction of the overhead spans. I am curious regarding your faults being above what your modeling shows. These levels are similar to what we...
  17. MKFPE

    I have a problem where I need to calculate the induced voltage of a pipeline running parallel

    Gunner is right on all counts, the electric field shouldn't be much of an issue considering the voltage and distance. Magnetic induction becomes an issue if the parallel section is of considerable length and the conductors are close and the currents are high. There are no precise definitions...
  18. MKFPE

    System loss calculations due to voltage imbalance

    I note that you work for a municipal system. I do as well, and in my case this means a limited budget available for engineering tools. If you are in the US, APPA DEED has an inexpensive book covering manual calculations as well as inexpensive software. I have used their TRANSPAC program for...
  19. MKFPE

    Protection relays

    I have adopted SEL only for our system. Their customer support is absolutely the best of any company I have dealt with and I have been in this field since 1975. You should seriously consider their high-interrupting capacity output contacts for your trip outputs. On our system we had several...
  20. MKFPE

    Rigid Aluminum Conduit (RAC)

    This may help: http://steeltubeinstitute.org/steel-conduit/resources/gemi-analysis-research/

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