Arc exhaust chamber/duct (plenum)

[sparkview]

Dear all,

We are currently discussing with a switchgear manufacturer if the arc exhaust chamber (plenum) duct on top of the switchgear should exit the substation if a possibly internal ar-flash may occur.
This may be helpful to prevent arc-flash byproducts into the Substation and causing a harmfull situation for personnel.

According to the manufacturer the switchgear has been tested as per IEC 62271-200:2011 and is considered safe. Our personnel is still having doubts about the byproducts and are mandating the plenum to exit the building. Is there any standard to justify this matter?

Your feedback is highly appreciated.

Thanks in advance.

 

[ScottyUK]

If the option exists to vent externally to the building I would take it. The tested gear will vent very hot poisonous gas and smoke if an internal arcing fault occurs: the equipment is designed to prevent direct injury from the arc fault, but it does little to prevent harm arising from the aftermath of a fault if it vents directly into the space above and/or behind the board. If the arc products are vented outside then you don't contaminate your switch house, and you don't have problems of your workers trying to flee the area in near-zero visbility while breathing in toxic fumes and vapours.

 

[stevenal]

I assume it would take a longer duct to exit the building. Did the IEC testing include this longer duct?

 

[jraef]

In some cases if you don't vent out of the building, the blast heat can set of sprinklers and cause additional damage.

I've attached a little video of an MV Arc Resistant motor controller test for your amusement...
This may help drive home the point that even if the gear survives, take a look at what would be vented into the room.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[cuky2000]

Any overpressure inside the switchgear compartment caused by internal arcing will be released through the pressure relief flaps located on the top side of the switchgear. The hot vapor produced by the arcing event can be vented inside the SWGR room or directed outside by a vented duct.

The byproducts should be considered hazardous to personnel and should not be allowed in the area without a special filtered breathing apparatus, as well as other appropriate personal protective equipment (PPE). In addition, there is a risk to generate overpressure that could damage the structure of the switchgear room.

The standards such as IEC 62271-200, Annex A or the IEEE Std C37.20.7 used in the ANSI marketplaces are recommended guides unless it is approved by enforcing agencies such as the building code or required by the project specifications.

 

[che12345]

Dear Mr. javsparky

Q. " We are ... if the arc exhaust chamber (plenum) duct on top of the switchgear should exit the substation if a possibly internal arc-flash ... This ... to prevent arc-flash byproducts into the Substation and causing a harmful situation for personnel. According ... switchgear has been tested as per IEC 62271-200:2011 and is considered safe. Our personnel... doubts about the byproducts and are mandating the plenum to exit the building. "
A1. Reference to IEC 62271-200:2011: Internal arc classification not only states Criterion 1-5, and the state of the indicators after the test; it does also alerts the danger of the hot gases with potential toxic characteristic.
A2. Check the test report on the [size and length] of the exhaust chamber. Obtained a written certified proposal from the manufacturer the (equivalent size and length) of the exhaust chamber exit the substation.
A3. It would be irresponsible to claim that as the board had been type tested to IEC 62271-200:2011,
therefore it is safe to the personnel by allowing the arc-flash by-products to be discharged into the Substation.
Conclusion: exhaust chamber exit the substation is [highly recommended].
Che Kuan Yau (Singapore)

 

[ppedUK]

You need to consult the switchgear manufacturer, or look in their installation manual. Just because it has been tested in accordance with IEC 62271-200 does not make it inherently safe. The manufacturer should be able to provide you with the minimum room dimensions and room volume that have to be complied with if you do not want to install arc vent ducting. As an example, the minimum ceiling height quoted by most manufacturers is 4.0 Metres (but it depends on the design) and you still have to consider other factors such as room volume for over-pressure. If all the criteria cannot be met, then you have to install arc vent ducting. That said, if your ops guys are not happy to operate the gear without the arc ducting (even if you determine that you don't need it) then you will have a hard time convincing them that it is not needed.