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 Post subject: PTW32 V7.0 vs. V6.5
PostPosted: Tue Oct 30, 2012 12:20 pm 
Sparks Level

Joined: Mon Apr 14, 2008 7:10 am
Posts: 142
I was told by SKM that there is 1% chance that you could get different result of Arc flash study by using new PTW32 V7.0 comparing to V6.5. Have anyone encountered this issue yet? How do you deal with that if you have a high HRC where the original HRC is very low?


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PostPosted: Wed Oct 31, 2012 6:04 am 
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Joined: Thu Jul 07, 2011 6:03 am
Posts: 67
Location: Netherlands
Did SKM say why? I sometimes encounter very small differences in calculated short-circuit currents within a project when making changes, but I've always assumed these to be rounding differences due to the iterative calculation process. These slight differences could theoretically lead to a different arc flash hazard (i.e. the arcing current sits right on the edge of a device magnetic trip pickup) but I've never seen it.


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PostPosted: Wed Oct 31, 2012 8:07 am 
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Joined: Mon Apr 14, 2008 7:10 am
Posts: 142
I received a readme.txt from SKM talking about various changes that they have added/made in new version of PTW32 program. These changes will result in slightly differency in your result if you had an old project. However, what I want to know is if anyone has seen big changes to the result yet. I will be very nervous if it was HRC #0 but now HRC#3 and I really don't know how to explain this to the client. We all know that a little change to the clearing time could affect the IE significantlly.


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PostPosted: Tue Nov 06, 2012 5:22 pm 

Joined: Fri Mar 16, 2012 7:14 pm
Posts: 7
Maybe I am into the 1%. On build 7020b1 and below I was obtaining a huge error. Upstream the bus had 3.89 cal/cm2. After the bus I have a dummy wire 0.1m long 7000A ampacity. Downstream the wire the IE is now 151.4cal/cm2. On build 7021b1 upstream the bus had 3.91cal/cm2 and downsatream the wire, 5.3cal/cm2. A little bit better than before but wrong anyway. On next build, 7022b1 that bug was fixed. Actual build is 7025b1. When I began to have such errors I switched back to 6.5 and I am still using it. I prefer wait until middle of 2013 to make the jump. I do not want to loose again two weeks job. BTW, the fix appeared after almost two months, from June 22nd to Aug 10th.


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PostPosted: Thu Nov 22, 2012 4:31 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
I realize this is an old thread but...

You can do "partial runs" in SKM for studies. Under normal circumstances this may not be an issue. But if you have significant "backfeeds" of current upstream, you could get some wild and crazy results that would then contaminate other parts of the study only after you do a full, complete run. That's the theory anyways.

In practice I've seen strange things like this happen even with full runs and on version 6.5. Usually I can eventually figure out a way to correct it but it drives me crazy. Watch out especially for your upstream/downstream settings. I was hoping that 7.0 would correct a lot of the bugs in 6.5. SKM may have been the first out there and certainly the most popular power system analysis software but it is by no means reasonably bug free. I still love the one where I can't click DIRECTLY on the "settings" tab or it shows up blank and I have to click something else, then back to the settings tab. If I had a choice in the software selection I probably would have gone to someone else but we've owned and used SKM since all the way back over 15 years ago when it was DOS based.


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