Recent content by JMatt

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...

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...

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.

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?

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...

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

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...

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

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...

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...

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...

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

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...

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...

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...