Metal Enclosed Switchgear Vs. Arc Flash

[ThePunisher]

We have specified a metal enclosed switchgear built as per ANSI C37.20.1. An arc flash reduction system (ARMS) was specified (Eaton make) to reduce the arc flash. With ARMS activated at the incomer circuit breaker, the arc flash is substantially reduced at the switchgear bus side. The line side arc flash is still high though.

My concern is that, does the metal enclosed construction have adequate segregation between the switchgear bus side from the line side such that the line side arc flash will not propagate to the bus side?

Are the barriers between the incoming cable compartment and the bus sufficient? I appreciate any experience for this. Thanks.

 

[dpc]

Standard switchgear is not tested for arcing faults, so it cannot be assumed that an arcing fault in one section will not propagate to adjacent sections or that the inter-section barriers will not be blown off. Obviously the section barriers will help, but unless each section is arc-rated, there is no assurance that the protection is complete. You also cannot assume that the doors will stay on, even if latched.

 

[rbulsara]

What you are looking for can be had, to an extent, if you have metal "clad" switchgear not metal enclosed.



Rafiq Bulsara

http://www.srengineersct.com

 

[ThePunisher]

Thank you. I was also having the same thinking as well. The brochures seems to be deceiving and I will send a query to the manufacturer to ensure that this is arc rated or if the construction resembles like of a "metal-clad" construction.

 

[ThePunisher]

I asked design to inquire manufacturer if the line side and bus side are adequately segregated in compartments so as to ensure that the line side arc will not jumper over the bus side. They offered justifications that barriers are in place which for me is not what I considered as "adequate segregation".

Will insulating the bus in addition helps?

 

[dpc]

Unless it has been tested for arcing faults in a test lab and they can produce certified test reports, it is not arc-rated.

Is this ANSI rated switchgear? There are ANSI standards for arc-rated switchgear.

Insulating the bus reduces the risk of arcing faults, but the potential hazard does not change. The worst-case of a three-phase arcing fault is always a possibility.

 

[ScottyUK]

If you are in IEC-land then IEC TR 61641 might be of interest. It is a technical report rather than a standard because there is ongoing squabbling about the test procedures, but there are seven test criteria which might be of use when writing your spec. I would reference the test procedure in the IEC document and call out precisely which criteria you want the board to pass.

Some of the 'squabbling' I mentioned relates to some manufacturers using fully insulated bars are able to claim that their gear is arc-proof by virtue of it being 'impossible' to strike an arc because the IEC test procedure doesn't allow insulation to be damaged in order to initiate the arc. I think certain manufacturers are playing cute games with the wording of the IEC document and as it stands the document essentially allows non-arc-rated boards to masquerade as arc-proof.

Maybe it is 'impossible' to strike an arc; I seem to remember that it was 'impossible' for a very famous liner to sink to the bottom of the North Atlantic too...


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If we learn from our mistakes I'm getting a great education!

 

[ThePunisher]

Can I then say that if this is not a low voltage switchgear whose compartments aren't arc rated, the bus arc flash should be rated similar to the line side arc flash (at the line side of the incoming circuit breaker)due to a possibility that the line side arc flash may tend to jump over to the bus.

In this case, the ARMS will not be that useful except for bus faults only.