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 Post subject: ETAP/SKM Modeling of Allen-Bradley 140G Series MCCBs
PostPosted: Wed Apr 22, 2020 2:07 pm 

Joined: Wed Apr 22, 2020 12:24 pm
Posts: 4
I am having issues with the modeling of Allen-Bradley 140G Series molded case circuit breakers (MCCBs) with electronic trip units (ETUs) in SKM and ETAP software. The issues are with the maximum clearing times of these devices in the fault current region, which is extremely important since it affects arc flash calculations and protective relay coordination.

The Allen-Bradley documentation is unclear and contains contradictions. Also SKM and ETAP disagree on the maximum clearing times of this equipment in the instantaneous and hardware override regions. Here are some facts.

  1. For a 140G-M with LSI trip unit, ETAP assumes the maximum clearing time is 60ms in the instantaneous region, but only 10ms in the hardware override region.
  2. For the same device with same settings, SKM assumes the maximum clearing time is 60ms in both the instantaneous region and in the hardware override region.
  3. Rockwell (Allen-Bradley) publication 140G-SG001E-EN-P contains a TCC that shows a maximum clearing time of 30ms in the instantaneous region. The clearing time in the hardware override region is not clear. I sent a clarification request to them about this.
  4. Rockwell (Allen-Bradley) Support Knowledgebase Center Post QA26552 published on 2/14/2020 states that "all 140G/140MG Circuit Breaker frames will clear a fault in 30ms (2 cycles) or less". 30ms and 2-cycles are not the same thing, especially if you are at 50Hz. I've sent a clarification request to them about this.
  5. The same issues exist with Allen-Bradley 140G-K and 140G-N devices. However Allen-Bradley documentation is inconsistent for these, showing different instantaneous region maximum clearing times of 20ms and 40ms instead of 30ms, which contradicts their QA26552. I've sent a clarification request to them about this.

I have been in communications with Rockwell (Allen-Bradley) about this, and I'm having difficulty getting the answers I need. I've been in communications with ETAP, and they insist that their modeling is correct, even though it contradicts Allen-Bradley documentation. I am awaiting a response from SKM about this.

Most users of SKM/ETAP software will automatically assume that modeling of protective relay devices is done correctly by the software. I've been guilty of that myself in the past. I noticed the issues described in this post while working on a project to convert a large and complex SKM model to ETAP and noticing that arc flash calculations were very different between SKM and ETAP.

Has anyone else had to model Allen-Bradley 140G Series devices in ETAP/SKM software and run into this issue?


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 Post subject: Re: ETAP/SKM Modeling of Allen-Bradley 140G Series MCCBs
PostPosted: Thu Apr 23, 2020 6:32 am 

Joined: Wed Apr 22, 2020 12:24 pm
Posts: 4
See these attachments for items #1 and #2 of the original post. They show the modeling differences between ETAP and SKM for the exact same device with the exact same settings.


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 Post subject: Re: ETAP/SKM Modeling of Allen-Bradley 140G Series MCCBs
PostPosted: Mon Apr 27, 2020 12:02 pm 

Joined: Tue Apr 17, 2012 9:17 am
Posts: 10
I've seen this same issue. I'm sorry I don't have a solution for you, but I was wondering if you got anymore information from Allen Bradley or a response from SKM?


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 Post subject: Re: ETAP/SKM Modeling of Allen-Bradley 140G Series MCCBs
PostPosted: Tue Apr 28, 2020 4:15 pm 

Joined: Wed Apr 22, 2020 12:24 pm
Posts: 4
I finally received a ruling from Rockwell Allen-Bradley product engineering in Milwaukee, WI. The correct clearing times of the 140G-K, 140G-M and 140G-N with LSI trip units are:

Instantaneous Region:
All 3 have a 60ms clearing time.

Over-Ride Region:
The 140G-K & 140G-M have a 11ms clearing time.
The 140G-N has a 5.5ms clearing time.

In the over-ride region, SKM was considerably off, using 60ms instead of 11ms. ETAP was only marginally off, using 10ms instead of 11ms (or 5.5ms). Also, for unknown reasons, SKM erroneously used a different clearing time of 30ms when instantaneous tripping is disabled.

This information has been passed on to SKM, ETAP and EasyPower technical support, so that they can update their library files.

I edited the ETAP library myself for my project since I can't wait for ETAP to do it. See the attachments for new annotated TCCs I created in ETAP that show the correct clearing times, per the new information received from Rockwell Allen-Bradley.


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 Post subject: Re: ETAP/SKM Modeling of Allen-Bradley 140G Series MCCBs
PostPosted: Mon May 18, 2020 9:46 pm 

Joined: Mon Jan 20, 2014 9:59 pm
Posts: 1
Thank you for pointing error in OEM libraries. So, it is always better to cross verify libraries with OEM published curves for equipment used in project. Your information is very helpful.


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 Post subject: Re: ETAP/SKM Modeling of Allen-Bradley 140G Series MCCBs
PostPosted: Tue May 19, 2020 5:02 am 

Joined: Wed Apr 22, 2020 12:24 pm
Posts: 4
The problem in this case is that the published OEM (Allen-Bradley) information was confusing and contradictory. This caused different interpretations of the same information by ETAP, EasyPower and SKM.

In today's engineering world, we trust & rely on software more than ever before, and this can be dangerous. Young engineers without experience will take for granted that all software generated results are correct. An experienced engineer however should be able to recognize when software generated results look suspicious, but this unfortunately doesn't always happen due to tight project budgets and schedules.


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