Transformer blast wall design 2

[ahandle]

Hi,

Does anyone have experience with designing transformer blast walls? All standards I've read say something on the lines of "Install a suitable blast wall", without providing any information on the strength the wall needs to be. I am asking this question in a general sense as I know I will have to deal with this time and time again, however in this particular instance at present, the transformers in question are 2 x 10MVA 33/3.3kV oil filled. i.e. blast wall to go between the two.

I know this is not a simple question as all transformers are built different and will rupture at different internal pressures.

If anyone has any guidelines or ball-park figures for a general case, this would be much appreciated.

 

[Marmite]

Although they are called blast walls they are primarily fire walls designed to prevent the spread of fire from one transformer to another. They must be constructed of non combustible materials and be designed to prevent a failed bushing or surge arrestor from causing damage to the adjacent unit. Generally the wind loading, height of the wall etc determines the structural capability rather than a calculated hypothetical blast pressure.
Regards
Marmite

 

[waross]

Designing to seismic standards may be a good CYA move.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

I agree with Marmite and waross.If the distance between it is more than 5 ft you don't need a wall.See NFPA 850 3-2.4.5

http://www.nfpa.org/assets/files/PDF/ROP/850-F2004-ROP.pdf

 

[ScottyUK]

Hmm, I seem to remember a major event at a UK generating site - Drax, perhaps? - where one transformer of a three phase bank had a violent failure which wrecked the neighbouring transformer, not due to fire but due to physical impact.


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

 

[rterickson]

Check out Oldcastle Precast (concrete pullbox and vault mfg) 'TruFire' prefabricated blast wall product.

I think you basically just have to tell them the relevant dimensions of your site and the seismic zone you're in.

 

[fsck]

I seem to remember a major event at a UK generating site

This one?
<

http://files.engineering.com/getfil...4780-9dd5-8aa40b628bfd&file=OESB_08_2009.pdf>

A retired Special Forces friend pointed out to me the fragmentation range exceeded that of a 105mm shell.

 

[BJC]

There is an IEEE standard on substation fire protection. IEEE Std 979.
There is also a Bureau of Reclamation publication on fire protection. IT's on the web but I don't have the site.

The NEC usually covers smaller transformers. The purpose of the NEC is to prevent the transfore fire from spreading to a building or injuring someone.
LArger transformers are usually owned and operated by utilities, they are not covered by the NEC.
Fire protection systems (deluge systems and oil containment systems have to have Spill Prevention, Control and Countermeasure Plans (SPCC). You have to have a plan to prevent the oil that may be released from poluting the environment- It's the law (EPA).

 

[ScottyUK]

fsck,

No, not that one but great example though! The event I'm thinking of knocked out two phases of 750MVA bank as I recall. Serious mess.


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

 

[ahandle]

Thanks to everyone for your responses. Yes, it certainly appears for an outdoor installation the 'Blast Walls' are are typically designed as more of a 'Fire and Shrapnel Wall'.

For everyones reference, an excellant comprehensive guide for fire protection design for substation is the Australian ENA Doc 18. Its still in draft format so can be accessed for free.

http://www.ena.asn.au/udocs/ENA_DOC_18-2008.pdf

 

[PFG]

I recently installed a 2-hour fire/blast wall as part of a 66kV switchyard refurbishment and upgrade at a coal mine in central queensland (australia).

The concept was staightforward - 4 off 5000 x 2500 x 250mm precast reinforced concrete panels erected against 250UC steel columns which were bolted to rag bolts set into bored piers. The panels had "quicklift" pins recessed into them to facilitate lifting into place with a crane.
The bored pier footings, ground beam and panels were constructed in advance which then allowed the 10m long x 5m high wall to be erected in less than 3 hours during a switchyard outage (and site wide power outage).

Australian Standard AS2067:2008 specifies when a fire/blast wall is required. This stadard is presciptive with regard to the dimensions of the wall with respect to clearances from the transformer and adjacent buildings and also takes into account the size and type of the transformer (potential fire/explosion risk).
However AS2067 specifies a rating for fire resistant barriers of 'FRL 120/120/120' as per AS3700.

The design of the wall and footings needs to take into account seismic and wind loading as well as the manoueverability of the panels. I worked with my mechancial and structural team to get the concept right to allow easy erection in the limited timeframe we had available, however I STRONGLY recommend that the detailed design of the blast wall be left to the appropriate discipline.