ETAP/SKM Modeling of Allen-Bradley 140G Series Circuit Breakers with ETUs 1

[Henri_EE]

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.
[ol 1]
[li]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. See this ETAP TCC.[/li]
[li]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. See this SKM TCC.[/li]
[li]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.[/li]
[li]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.[/li]
[li]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.[/li]
[li]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. I am awaiting a response from SKM about this.[/li]
[/ol]

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

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.

 

[dpc]

Well, A-B will have the final word. Curious if this is an IEC version or US version?

I plotted this device in EasyPower. It shows the "Instantaneous" band as slower (0.04 sec) than the override (0.005) This is the IEC version. I don't know if the TCCs are any different between IEC and US.

 

[Henri_EE]

Thanks very much DPC for giving it a try in EasyPower. I would expect the override to be faster, but I don't think a 0.005 second (5ms) clearing time is possible. Also the Allen-Bradley documentation doesn't show that.

So EasyPower has yet a different interpretation than ETAP and SKM. It seems that ETAP, SKM and EasyPower are all incorrect.

I agree that Allen-Bradley should have the final word on defining the clearing times, and then the software companies need to implement it. I've been trying since 3/9 to get this word from Allen-Bradley.

 

[dpc]

Yes, the 5 ms does seem fast, but I just checked an ABB TMax breaker TCC and its clearing time on instantaneous was also 5 ms. These modern MCCBs have "blow apart" contacts that actually open under high current before the trip mechanism even operates. Half cycle operation is certainly possible and that is 0.008 at 60 Hz. FWIW, I confirmed that in EasyPower, the TCC for the A-B US version and IEC versions are the same.

Let us know what you hear from A-B. Where are you located?

 

[Henri_EE]

I'm in the New Orleans area.

I agree that the 140G-M TCCs are the same for US and IEC. Allen-Bradley uses the same TCC for both in their documentation. The difference is in the ratings of the IEC version.

I'm not familiar with the ABB Tmax, and my ETAP library doesn't have the ABB Tmax. The ABB SACE in ETAP PR212 shows an instantaneous clearing time of 0.07sec.

 

[Henri_EE]

[tt]
I finally got 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.
[/tt]