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 Post subject: SKM - Short Circuit Calculation Problem
PostPosted: Tue May 29, 2012 1:32 pm 

Joined: Tue Jan 17, 2012 5:00 pm
Posts: 39
Well, after using the SKM and ETAP I would suggest that ETAP is the best software for Power System Studies because I have had significant trouble using SKM except printing arc flash labels. Enough !! Right now I am in trouble with SKM again, I am performing short circuit analysis "A_Fault Analysis" which is based on ANSI standard.

From the data block attributes I 'm displaying the short circuit values on my single line diagram but the SKM is not calculating the short circuit values on the downstream secondary side of the transformer. However, it is calculating the short circuit values on the up-stream buses.

Any expert suggestion to this problem will be highly appreciated!!

Thanks
MD


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PostPosted: Tue May 29, 2012 3:26 pm 

Joined: Mon Apr 18, 2011 1:43 pm
Posts: 11
Location: Denver, CO
I'm sure you checked this but it could be something as simple as a disconnected wire (are the lower buses grayed out?) or an "out of service" flag on the lower buses or gear.


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PostPosted: Wed May 30, 2012 8:04 am 

Joined: Tue Jan 17, 2012 5:00 pm
Posts: 39
Thank you for your comment. I think the problem I'm getting is due to ANSI calculation methodology. "If there are two or more transformer between the generator and the fault bus then generator is assumed as remote contribution". In my case since there are two transformer between the utility and fault bus it might be assuming utility as a remote contribution.


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PostPosted: Wed May 30, 2012 9:52 am 
Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 550
Location: Wisconsin
What you are describing is not an inherent problem with SKM's offering. I regularly have multiple transformers between my sources and some busses.

Are you sure the SC value is not being calculated, or is it simply not being shown?
It could be as simple as having the datablock hidden on that bus.


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PostPosted: Wed May 30, 2012 12:47 pm 

Joined: Mon Apr 18, 2011 1:43 pm
Posts: 11
Location: Denver, CO
You might try SKM support as well. I've found them to be very responsive - [email protected] .


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PostPosted: Wed May 30, 2012 1:41 pm 

Joined: Tue Jan 17, 2012 5:00 pm
Posts: 39
Nops!! Data blocks are not hidden. Data blocks are showing momentary RMS value as 0 kA.

When I run on comprehensive short circuit method the short circuit current levels are displayed. But When I try to run ANSI and change the data blocks according to ANSI attributes it shows 0 kA on the secondary side of those transformer who are at the second level away from the utility.


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PostPosted: Mon Jun 04, 2012 10:59 am 

Joined: Mon Jan 26, 2009 5:00 pm
Posts: 46
Location: Midwest
Pay close attention to datablocks and also the study settings. The ANSI study won't automatically calculate momentary and interrupting duty. These options must be selected to calculate these parameters.


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PostPosted: Tue Jun 05, 2012 8:37 am 

Joined: Wed Feb 01, 2012 10:44 am
Posts: 23
Location: Atlanta, GA
Do you have a bus at the secondary side? Does it show up in the SC report? Under the SC setup, did you select "all buses"?


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PostPosted: Wed Jun 06, 2012 9:12 am 

Joined: Tue Jan 17, 2012 5:00 pm
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Yes!! I think the problem is with "momentary RMS current " datablock. I want to display this datablock but this only works for high voltage or medium voltage nor for low voltage.


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PostPosted: Wed Jun 06, 2012 9:13 am 

Joined: Tue Jan 17, 2012 5:00 pm
Posts: 39
If you want to know further about this check this conversation:

http://www.eng-tips.com/viewthread.cfm?qid=322885


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PostPosted: Wed Jun 06, 2012 10:12 am 

Joined: Wed Feb 01, 2012 10:44 am
Posts: 23
Location: Atlanta, GA
Moeen ud Din wrote:
Yes!! I think the problem is with "momentary RMS current " datablock. I want to display this datablock but this only works for high voltage or medium voltage nor for low voltage.


The SKM short circuit module you are using is for ANSI calculations. ANSI calculations would not generate "momentary" results for a low voltage bus, since the LV breakers do not have a "momentary" rating. Use the SKM datablock results that have the prefix "LV" for the calculated ANSI results for LV buses. If you don't see what you want, you might try the Dapper short circuit module for your calculations, which is not based on ANSI methods.

ANSI Standard C37.13 is the critical standard used for calculating the fault duty at low voltage buses, whereas ANSI Standards C37.5 and C37.010 are the critical standards used for calculating the fault duty on medium and high voltage buses. For medium and high voltage buses, both closing and latching (withstand and momentary, respectively) duties, and an interrupting (contact separating or breaking) duty are calculated.


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PostPosted: Wed Jun 06, 2012 1:56 pm 
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Joined: Fri Apr 27, 2012 6:49 am
Posts: 40
CSC has a great answer.

I use "ANSI Sym 3P LV" for my datablock.


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PostPosted: Tue Jun 12, 2012 9:00 am 
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Joined: Mon Jun 07, 2010 9:40 am
Posts: 119
As CSC says, your issue is in what data you are displaying in the data block. Not the module or the calculations itself.
SKM however has to take some of the blame here. Their documentation on the datablock elements is POOR.


CSC wrote:
The SKM short circuit module you are using is for ANSI calculations. ANSI calculations would not generate "momentary" results for a low voltage bus, since the LV breakers do not have a "momentary" rating. Use the SKM datablock results that have the prefix "LV" for the calculated ANSI results for LV buses. If you don't see what you want, you might try the Dapper short circuit module for your calculations, which is not based on ANSI methods.

ANSI Standard C37.13 is the critical standard used for calculating the fault duty at low voltage buses, whereas ANSI Standards C37.5 and C37.010 are the critical standards used for calculating the fault duty on medium and high voltage buses. For medium and high voltage buses, both closing and latching (withstand and momentary, respectively) duties, and an interrupting (contact separating or breaking) duty are calculated.


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PostPosted: Thu Jun 14, 2012 1:26 pm 

Joined: Tue Jan 17, 2012 5:00 pm
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Agree!! very poor documentation of SKM for datablocks. The datablock information for my projects are very vital piece of information. Any how I have run the system based on "comprehensive short circuit method " as I needed asymmetrical fault levels at low voltage.

I had a tough time with SKM!! but some of the features of SKM are very good, for example arc flash curves on TCCs, they are helpful when you want change the settings of protection devices for reducing arc flash.


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PostPosted: Mon Jun 18, 2012 6:05 am 
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Superman Engineer wrote:
...but some of the features of SKM are very good, for example arc flash curves on TCCs, they are helpful when you want change the settings of protection devices for reducing arc flash.


What do you mean by "arc flash curves on TCCs"?


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PostPosted: Mon Jun 18, 2012 2:46 pm 

Joined: Tue Jan 17, 2012 5:00 pm
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"C-Lines or Energy Lines", These lines can be drawn on TCC's. By looking at C-Lines and Protection device TCC, you can easily judge what parameters of protection devices are needed to be changed in order to reduce arc flash. I normally use this feature it's quick and fast.

This feature is also available on ETAP 11.1.


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