I spent more than 10 years as a power company's
FPE and have been involved in dozens of
substation schemes.
The determining factor on protection of a large
power Tx is a complex matrix of:
Type of fluid in the Tx and any coolers
Volume of fluid
Normal termperature of fluid
Indoor/Outdoor
Location of substation with regards to other properties
Fire separation between tranformer cells and other parts of the substation
Criticality of the power supply to the building or site
In the case of transformers using mineral oil
then anything containing more that 2000 litres
(say >520 US galls) working at above 85°c/185°F
which is critical to the operational needs of the
building should be protected.
Normal approach is a deluge system providing at
least .2 US gpm/ft2/minute. Most European
insurers and reinsurers are now of the opinion
that this application rate which is = to
10l/m2/min is too low and some are asking for 2x
this rate on key transformers in power generating
stations.
The two transformers should really be separated
by a blast wall which is as high as the highest
part of the transformer (ie the busbar/bushings
or the oil conservator. (NB not fire wall as NFPA
850 - but a wall which will resist the
significant impact of an exploding bushing.)
Best advice on location etc is in NFPA 850 - this
has a table/diagram showing the trade off between
separation by distance and compartmentation.
Incidentally there is little problem with
applying deluge rate pressures on live busbars -
the divided nature of the spray is not
electrically conductive and quite frankly if the
fire results from an explosion in the transformer
tank/tapchanger ( 75% of all Tx fires) then the
supply will already have isolated itself on a
protection relay (Buchholz trip).
I guess you are stuck with the location - in
which case make sure that there is a sump beneath
the two Tx's to retain the oil and water - this
should lead to an interceptor and separator.
European practice is to gravel fill the sump
after installation of cabling.
Let me know if you need any more help.
Regards
Stewart
We have been asked to provide a quote for fire protection of a room (80'
x 25' x 50' high) that contains 2 very large oil-cooled transformers.
This room is located inside an unheated steel manufacturing building.
The entire building right now is unsprinklered. The insurer for the
business has requested fire protection for the room containing the
transformers only. I read an article that suggested using NFPA 15 and
provide exposure
protection but it also stated that oil-filled transformers should be
located outside the building. What is the best way to protect this
room? Is fire protection now
required thought the building?
Thanks,
Dewayne
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