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 Post subject: SKM vs EasyPower Results
PostPosted: Sat Dec 07, 2013 12:41 pm 
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I am replicating a project that was originally done in SKM about 4 yrs ago and I am using EasyPower Ver 9.5. There are some differences in conductor impedances but nothing major. I have found one item that is curious. For this particular panel:
SKM: HRC 0, 1.2 cal/cm^2, Ibf 16.06kA, Iarc 8.35 kA, Trip time 0.044 sec

EasyPower: HRC 1, 2.4 cal/cm^2, Ibf 16.4 kA, Iarc 8.515 k, Trip Time 0.086 sec

The protective device is a Siemens Sentron NXD6 1200A breaker with a 1200A trip and Inst at 5000A. Now what is interesting is when the TCC is plotted, SKM's Iarc current would result in a trip time of ~0.091 sec. When I cross a trip time of 0.044 on the curve, the corresponding current is ~12.4 kA.
This is at 480V, 60hz system
Any thoughts or comments?

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PostPosted: Mon Dec 09, 2013 5:49 am 
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Location: Cincinnati, OH
Did you obtain the published TCC from Siemens? The next step would be to compare the Siemens TCC with the Easypower and SKM TCCs to see if either software package matches the vendor's TCC.

I examined the breaker TCC in both SKM and Easypower and the curves are different in my libraries as well. Based upon a quick visual check with the arcing currents you indicated above, your clearing times match what I'm seeing as well. Looks like one or both libraries are suspect - we need the TCC from Siemens to investigate further.


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PostPosted: Mon Dec 09, 2013 6:21 am 

Joined: Mon Nov 25, 2013 8:03 am
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wbd wrote:
I am replicating a project that was originally done in SKM about 4 yrs ago and I am using EasyPower Ver 9.5. There are some differences in conductor impedances but nothing major. I have found one item that is curious. For this particular panel:
SKM: HRC 0, 1.2 cal/cm^2, Ibf 16.06kA, Iarc 8.35 kA, Trip time 0.044 sec

EasyPower: HRC 1, 2.4 cal/cm^2, Ibf 16.4 kA, Iarc 8.515 k, Trip Time 0.086 sec

The protective device is a Siemens Sentron NXD6 1200A breaker with a 1200A trip and Inst at 5000A. Now what is interesting is when the TCC is plotted, SKM's Iarc current would result in a trip time of ~0.091 sec. When I cross a trip time of 0.044 on the curve, the corresponding current is ~12.4 kA.
This is at 480V, 60hz system
Any thoughts or comments?

Did you check for upstream miss-coordination? It sounds like SKM sees a protective device upstream that is tripping faster that the immediately upstream device, or SKM is looking farther upstream than EasyPower. In SKM, look at the arc report to identify the devices that cut off arc energy accumulation.


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PostPosted: Mon Dec 09, 2013 6:34 am 
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No that is the correct device and it is listed as the tripping device. That breaker feeds a panel by a 500 mcm copper conductor (3 single phase) in a steel conduit and is 335 ft long.

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PostPosted: Mon Dec 09, 2013 7:41 am 
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Did you check with SKM and Easy Power's tech support people? If you do, can you post what happened so the rest of us can see how they responded? I use Easy Power and have found their tech support pretty good. I don't use SKM, however a few years ago, I got a chance to compare the results produced by another vendor who used SKM against the results with Easy Power. My experience was the results were very very close. I did not have access to the other vendor's survey data, so it's possible his data was slightly different, which could explain the slight variations.


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PostPosted: Mon Dec 09, 2013 7:48 am 
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I have not checked with either company on this issue. I do not have SKM and I am replicating the study by using the report which has all the data input as well as the afh results table.
A while ago, I did ask EasyPower if they had ever compared results from some samples with SKM to see what the results were. I had asked that question since I had noticed differences in conductor data on a previous study.
They said they had not done any comparisons between SKM and EasyPower.
I do agree on EasyPower's technical support. They are very responsive and excellent to work with!

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PostPosted: Mon Dec 09, 2013 4:01 pm 
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I noticed that you had listed "SKM: HRC 0, 1.2 cal/cm^2...." I believe that this may be an area where it is using the IEEE 1584 Exemption page 6. I states, "
Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low impedance transformer in its immediate power supply.
There is an option in SKM that you can select that will force these locations to be 1.2 Cal/cm^2 and Category 0.

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PostPosted: Mon Dec 09, 2013 5:09 pm 
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Yes but please read carefully and you will notice that this is at 480V, therefore the exemption does not apply. Further, I would err on the conservative side and say that at 1.2 cal/cm^2 the PPE should be HRC 1. It seems that SKM is non-conservative in this area. I had hoped that someone from SKM or with extensive SKM experience was on this website and would provide some valuable insight.

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