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Just got a question regarding a scenario where a 4160V switchgear is fed by a Generator.

A generator decrement curve has been provided by the manufacture.

I've typically always used the 1/2 cycle method calculation for Arc Flash calculations, but I'm not sure if this is an adequate number to use in this case.

Looking at my TCC, the protection relay curve doesn't intersect with the current decrement curve until close to steady-state.

If i wanted to be on the safe side of things, would it not be acceptable to assign a fixed FCT based on where the two intersect? I believe at 4160V the bolted fault and arcing current should be similar enough for this assumption?

I only ask this as if I assume the calculation is purely 1/2 cycle method, my IE is significantly lower due to a much faster FCT.

Statistics: Posted by Lokiel — Wed Apr 28, 2021 10:38 am

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Then the tripping by the upstream breaker will not prevent the cable from seeing currents beyond their damage curve.

I think the problem is that there is too much fault current for #12 wire.

Options: increase wire size or decrease Fault Current.

Statistics: Posted by bubba — Mon Apr 26, 2021 7:51 am

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Keeps saying "trip curve crosses" damage curve for a 20A breaker protecting 12awg cable.

thanks

Picture:

https://ibb.co/1656NXk

Statistics: Posted by Designer82 — Wed Apr 21, 2021 2:47 pm

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How can your output current be greater than your maximum input current?

VFD's typically rectify AC to DC, charge large capacitor banks to peak voltage and the use PWM or some version of such to convert back to variable frequency, variable voltage AC thus the output current can be substantially larger if the output voltage to the motor is lower until the charge on the capacitors is drawn down.

Statistics: Posted by DavidChief — Tue Mar 23, 2021 7:08 am

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I’m modeling a 200HP output VFD feeding a 200HP pump motor. The ratings from the cut sheet for the VFD are (output max FLA 250A, 160kw, 200HP and input 211A, 175kva) when I input the ratings the load flow calculator fails the VFD but the manufacturer says that the vfd is properly rated for a 200HP motor. I must be doing something incorrect in my model. Does anyone know what I might be doing wrong or any suggestions? Any help would be greatly appreciated.

How can your output current be greater than your maximum input current?

Statistics: Posted by JBD — Mon Mar 22, 2021 11:14 am

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Marcia Eblen and I have a paper for the 2021 IEEE Electrical Safety Workshop [1] where we argue that the 1584-2018 models can be applied up to 35 kV. This is based on EPRI tests of medium-voltage equipment and the IEEE/NFPA data used to derive the IEEE 1584 models. We show that system voltage is not a key factor. The main factors for incident energy are the current, the duration, the electrode orientation, and the electrode gap. Physically, what's important is the arc voltage, not the system voltage. The arc voltage is mainly a function of arc length (with a modest multiplier based on arcing current). For the lengths of arcs you have in MV equipment, any medium-voltage source is stiff enough to supply that voltage. So, the results don't vary significantly with system voltage.

[1] Short, T and Eblen, M, "Comparison of IEEE 1584-2018 Predictions with Tests on Real-World Equipment," IEEE Electrical Safety Workshop, 2021. To be presented in a focus session on Wednesday, March 10, 2021. https://electricalsafetyworkshop.com/sc ... fe98a-d9dc

The submission version of this paper is now available at: https://distributionhandbook.com/papers ... s_2021.pdf

Statistics: Posted by tshort — Mon Mar 15, 2021 6:45 am

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Hi Guys,

Trying to model batteries on ETAP for a DC Arc Flash study. Unfortunately the library for batteries on ETAP is very limited and does not have the real life models that we find on site. I'm using Maximum Power Transfer method to calculate my DC IE. My question is that what parameters of the real battery should I keep similar to the ETAP model when finding an alternative ?

Initially I thought that I should pick a battery on ETAP that has similar amp hour rating, specific gravity and Vpc. But unfortunately the amp-hour rating and short circuit ratings on ETAP are never similar to the real life batteries simultaneously. One of the either is always off.

Upon more research, my opinion is that I pick batteries on ETAP that have similar short circuit ratings to my real battery since the Maximum Power Transfer method uses steady state fault current to calculate the DC arcing current, so the amp-hour rating does not play any role. But i'm not sure ? Is that a valid assumption ?

thanks !

Hi Shawn, ETAP has a simple interface that is easy to create libraries based on data sheet. You can contact ETAP helpdesk to request libraries as well. Meantime, depending upon the version you are using , the modeling of batteries is different. For maximum power method Arc flash , the program uses bus nominal voltage and the available short circuit current . For further assistance, you can reach out to ETAP helpdesk that can resolve your queries.

Thank you

Statistics: Posted by Raghu — Tue Mar 09, 2021 12:54 pm

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Regarding OSHA - as far I saw it OSHA clearly says it is for OPEN ARC equipment only which you see in utility business however I'm looking for up to 36kV metal enclosed switchgears like from ABB, Siemens, Eaton etc whcih are used in industry or as RMU.

If you read the footnotes for the Appendix E, Table 3, you will see the Y for ArcPro in column for 3 phase in a box has the superscript 4. This refers to footnote 4 which states that OSHA will deem the results of this method reasonable when the employer adjusts them using the conversion factors for 3 phase arcs in open air or in an enclosure, as indicated in the program's instructions.

Note that this was written when the original ArcPro was in use and you hand manually do the conversion and the latest version has a drop down box where you pick the type of arc and the adjustment is done in the program.

So, if you looking for a value that you can use in your safety program and have a basis for the result, you would be in a much better legal position if something happened than if you used a method that may be harder to justify in a legal setting. Just saying.

Statistics: Posted by wbd — Tue Mar 02, 2021 6:25 am

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Marcia Eblen and I have a paper for the 2021 IEEE Electrical Safety Workshop [1] where we argue that the 1584-2018 models can be applied up to 35 kV. This is based on EPRI tests of medium-voltage equipment and the IEEE/NFPA data used to derive the IEEE 1584 models. We show that system voltage is not a key factor. The main factors for incident energy are the current, the duration, the electrode orientation, and the electrode gap. Physically, what's important is the arc voltage, not the system voltage. The arc voltage is mainly a function of arc length (with a modest multiplier based on arcing current). For the lengths of arcs you have in MV equipment, any medium-voltage source is stiff enough to supply that voltage. So, the results don't vary significantly with system voltage.

[1] Short, T and Eblen, M, "Comparison of IEEE 1584-2018 Predictions with Tests on Real-World Equipment," IEEE Electrical Safety Workshop, 2021. To be presented in a focus session on Wednesday, March 10, 2021. https://electricalsafetyworkshop.com/sc ... fe98a-d9dc

tshort - it will be great to red it once it is available. I will keep an eye on it as it is inline what I'm looking for.

Regarding OSHA - as far I saw it OSHA clearly says it is for OPEN ARC equipment only which you see in utility business however I'm looking for up to 36kV metal enclosed switchgears like from ABB, Siemens, Eaton etc whcih are used in industry or as RMU.

> Hugh I actually never had to use Arc Pro as most of my work is not utility type but it comes more often so i need to check pricing of it.

PS. I'm from Poland If I didn't present myself I'm Marcin Ruta to keep it more open (you can find me on LinkedIn).

Statistics: Posted by rutz — Tue Mar 02, 2021 3:33 am

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