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  • Users: JMatt
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  1. JMatt

    No Arc Flash Analysis for <75HP Motors

    They didn't apply a "safety" factor to conservatively apply the standard. Their method is actually less stringent than the standard. If you have to model a system including motors 50HP and less, you'll consider more arcing fault current than if you raise the limit to 75HP. Using those...
  2. JMatt

    Industrial plant incoming voltage regulation and voltage drop

    Are you checking the voltages at the two switchgear simultaneously by looking at a real-time SCADA system? It's not impossible for you to check the voltage at one switchgear, then have your load profile change during the time that it takes you to get to the next switchgear. 4035V to 4130V is...
  3. JMatt

    No Arc Flash Analysis for <75HP Motors

    Usually motor circuit contribution (even for larger low-voltage motors) is extremely small and won't significantly increase your arc energy. tem1234 is correct about IEEE 1584.
  4. JMatt

    Arc flash study using ETAP

    How in the world do you have 50 buses between the fault and the protective device? Are you modeling every pole on a long distribution line as a bus?
  5. JMatt

    Using a 351 relay for LTC control

    I've never done it myself, but one of my subcontractors is doing it for me. It should be easy. Just make sure the timers are set up to keep from accidentally chattering the outputs. Also, make sure you don't have latches or SER points that chatter. Each time they toggle, the position is...
  6. JMatt

    Single phase tripping

    Use negative-sequence overcurrent tripping. May I suggest reading "Negative-Sequence Overcurrent Element Application and Coordination in Distribution Protection" by Ed Schweitzer. This is freely downloadable at selinc.com/literature
  7. JMatt

    PDC

    I agree with davidbeach. One additional comment: Your core-balance CT's are likely much more sensitive than your residually connected phase CT's. You may want to check the amount of ground fault current available to ensure that the residually connected phase CT's respond properly. For...
  8. JMatt

    transformer

    It's likely that your 415V nominal system is actually operating around 432V.
  9. JMatt

    Breaker Failure Question

    I vaguely remember a scheme like this implemented in a SEL relay. The breaker failure timer would start the instant that an overcurrent trip condition was detected. Then, a breaker failure would be declared if that overcurrent pickup did not dropout within a specified amount of time AND a...
  10. JMatt

    Arc Flash Study with No Protective Devices?

    That sounds bogus. If they don't analyze realistic expected fault-clearing times, the study is no good. They may as well draw a 1000 ft. circle around every piece of elec. equip and say, "Do not enter." I'm a bit less forgiving than dpc. If I were you, I'd get a different consultant. That...
  11. JMatt

    Low voltage circuit breaker arc flash

    Is 26kA the "bolted fault" current at the piece of equipment in question or is that just a number to tell the spreadsheet what your source Z is? I'm guessing that you input 26kA as the source (1.5MVA transformer with Z=7%), but there's a large impedance between the LV breaker and the equipment...
  12. JMatt

    50N vs 50G Currents

    That is the kind of insightful affirmation that I was looking for! That makes perfect sense. Cheers, rbulsara.
  13. JMatt

    Differential Relay On A NEMA E2 Starter?

    You can simply set up your trip equation to block on phase currents that exceed the contactor rating. I don't recall how the logic in a Multilin would read, but a SEL would be: TR = 87P AND NOT 50P1T # where 87P is asserted for a differential trip but if phase current exceeds 50P1P, the TR...
  14. JMatt

    Advantages of a Protective Relay Network

    I am sure your local Multilin, Schweitzer or ABB vendor rep will be happy to share their respective propoganda with you. Here's a link to the GE powerpoint on Enervista... http://www.docstoc.com/docs/2634730/Welcome-to-the-new-GE--PowerPoint-template! SEL also makes a nice system sold as...
  15. JMatt

    50N vs 50G Currents

    Parameter clarification: I meant to say that this is a low resistance grounded system. cranky108 says: "If I understand the question, it is possible to have zero sequence current on the X0 bushing, but not the sum of the three X1, X2, X3 bushings. It's simple, it's called a transformer...
  16. JMatt

    50N vs 50G Currents

    antigfk: True SEL does exactly the opposite of IEEE 242. A 50N element is asserted sensing current from the "In" input. 50G is a mathematical summation. all: My hope is that both the 50N element AND the 50G will pickup for faults on the SWGR bus, but only the 50N element will pickup for...
  17. JMatt

    Low Inst. Recloser

    A recloser should certainly be disabled during any hotline work. I also recommend a temporary low-set instantaneous that can be armed/disarmed using a selector switch or pushbutton. As for your other feeder where a time delay may allow the line to be damaged on temp. faults, this just isn't...
  18. JMatt

    50N vs 50G Currents

    In most SEL relays, there are two different ways to measure ground fault current. One way (SEL relay word 50N) uses the current as measured by a core-balance CT physically wired to the In terminals. The other (50G) uses the mathematical summation of the three phase CT's. My question is this...
  19. JMatt

    69kV Line protection

    Sometimes 51 relays can miscoordinate with distance relaying. Be sure to do a coordination study with the protective devices feeding this 69kV line.
  20. JMatt

    CCTV

    CCTV...Closed Circuit Television? Did you possibly mean CCVT...Coupled Capacitor Voltage Transformer?

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