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#126890 - 03/02/01 08:18 PM Electric Arc Heat Flux Calculator
Bill Addiss Offline
Member

Registered: 10/07/00
Posts: 4196
Loc: NY, USA
Recently, Duke Power created a piece of software called Electric Arc Heat Flux Calculator (developed by Alan Privette) to give the consumer a approximate estimate of the hazard involved in his application. Inputting variables such as Supply Voltage, Amps, Arc Gap and Cycles of Arc. The result is a measure of heat produced in cal/cm2 (calories per square centimeter).

Free Download
http://www.oberoncompany.com/OBEnglsh/FAQElect.html


Submitted by Joe Tedesco, http://www.joetedesco.com

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#126891 - 03/03/01 01:38 PM Re: Electric Arc Heat Flux Calculator
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
This is great!
One Q....the first entry " enter arc current in amps" , would this need to be the Short Circuit calc?


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#126892 - 03/10/01 04:16 AM Re: Electric Arc Heat Flux Calculator
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Steve,

You are most likely correct. It should reflect the available amount of current at that point, so what ever the fault calcs would show at that point - at the voltage involved [either L-G or L-L / L-L-L if the two are different], would be the thing used.

I'm not familiar with this person's calculator, just checked out the download page but did not download the calculator.
I have seen - and used - calculations like this from other sources [manuals and engineering books]. The typical use is, of course, a fault energy measurement, but there is another use - to calculate HID lamp arc power and other discharge lamps.

Did notice that this person does limit the values between 1KA and 10KA, which is quite useful in a majority of applications. This is not too bad for a freeware program [public domain].

Let me know how it looks [spreadsheet or VBasic application] and how it works out [easy to use, etc.].
Also, if it's a Macro, or VBA script[if you don't know what this means, don't worry!].

Scott SET
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#126893 - 03/10/01 04:28 AM Re: Electric Arc Heat Flux Calculator
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
I'tll be a time saver, the short circ calc will need to be done. the distance from the serving transformer constitutes an R factor that seems to play a make or break figure in this calc ( the Short cir. cal).

The end calc is good for only one point, and as you stated L-L, or whatever. To complicate this would be to introduce the concept of "series" rating, or whatever could happen L-L, or otherwise down through the components.

I suppose i'm just confusing the issue here...


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#126894 - 03/10/01 05:38 AM Re: Electric Arc Heat Flux Calculator
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Quite the opposite, your thinking of valid items that are so various per location is crucial and quite on point! I myself, can turn an Anthill into Mount Everest by thinking of more and more possibilities , but in this case, you are not confusing the matter at all.

A series rated system should yield an amount determined at the load, through a device rated at that determined level at that point, but what happens if that device is exceeded! Now we're looking towards the next device.
Then there's the way the fault makes contact. Small - fragile conductors that have a relatively poor contacting surface produce low level faults. They usually trip the OCPD by means of a timed overload, rather than overcurrent.
Medium size faults can come from any number of situations and can be so unstable that they could keep from tripping an OCPD for more than 10 seconds! They could also become larger with locally generated contributions, or with better contacting areas. This is one of the problems with 4 wire Wye systems that are 1000 amps and larger, with higher than 150 VAC to ground [480Y/277 VAC 3 phase 4 wire Wye].
High level faults will almost always exceed capacity of frames sized 225 amps and lower, rated for 240 VAC [typical 10KAIC @ 240VAC frames]. If they don't blowup, they just have their contacts welded closed.
One bad thing [plus something to consider] is that most multi pole devices [2 and 3 pole breaker frames] have their capacity rated as L-L-L, making the per pole [single pole, or L-G] level extremely low. A good solid ground fault of medium size can exceed the capacity of one pole, causing failure to trip [or explosion - hopefully!!].

Another contributor to fault levels is, of course, Induction Motors - there's a local source of fault current that flows from the motor, to the transformer, then in most cases, back again through the system!
Nevertheless, motor contribution would be an almost impossible level to give an absolute sum to. The general way is to use the LRA, which comes close enough to what a typical medium to heavy loaded induction motor will develope when the system voltage drops to near zero and the current density becomes limited during a fault situation.
Completely different stuff happens to lightly loaded or no-loaded induction motors.
Not too sure what Commutator motors will do [DC motors], but they should contribute some level of DC back into the system.

I see that you stated in your message using a value of R from transformer to some point. That looks like the Ohmic method of fault calculations [as opposed to point-to-point].
Is that what is used in the mentioned calculator program, or is this your preferred method of fault calcs?

Keep me up-to-date!

Scott SET
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#126895 - 03/10/01 03:33 PM Re: Electric Arc Heat Flux Calculator
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Scott,
it is my prefered method . E , I and R are somewhat easily conveyed in the field.
( until you get ahold of 'em in a thread!)

Most inspectors usually are satisfied with a service installation SSC given the calc starting with the local utilities numbers at the transformer terminals.

Unless, as you said , bigger motors are included on the load side.

A major player in the calc is the R factor, which is considered the distance / wire R. So it's just as visually relavant too...

I use Stallcup's method ( R method)

the Bussman link has negligable distances, or i think one example does 25', but can be ammended.

I often wonder, having spent phone time with milbank , anchor, etc, people on the horn, how some of these pad mounted x-formers can have a residential meter mounted right on them where the R is next to 0....




[This message has been edited by sparky (edited 03-10-2001).]

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