MIL-HDBK-1004/2A
5.2.5.3 Ventilation. Provide ventilation adequate to dissipate heat given
off by transformers and associated equipment and to maintain safe operating
temperatures. Gravity ventilation is usually not adequate for indoor
substation rooms; in such cases, mechanical ventilation should be provided.
In air-conditioned buildings, an economical and positive means of ventilating
substation rooms is to exhaust tempered air from conditioned spaces through
the substation room.
Table 6
Comparison of Types of Transformer Insulation
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LIQUID-INSULATEDDRY-TYPE
TRANSFORMER
QUALITIES
OIL
LESS-
CONVENTIONAL
EPOXY-
GAS-
FLAMMABLE
ENCASED
FILLED
______________________________________________________________________________
Relative
100%
100%
Varies(1)
Varies(1)
Varies(1)
Impulse strength
(BIL)
Temperature
55 or 65
55 or 65
80
or 150
80 or 150
120
rating(degree C)
Relative
X
X
X + 10 dB
X + 10 dB
X + 10 dB
audio sound
level in dB (2)
Relative weight
100%
120%
80%
95%
125%
:
Relative
100%
100%
100%
105%
120%
dimensions
Application
outdoor(3)
all
indoor
all (4)
all
Maintenance
routine
routine
routine
routine
low
Relative Cost
237% (100%) 200% (130%)
125% (127%)
200% (200%)
220% (220%)
______________________________________________________________________________
(1) Varies from 33 to 66% depending on voltage level. Higher BIL ratings for
dry-type transformer are available, but an increased cost for conventional
and gas-filled types.
(2) X indicates normal decibel level for liquid-immersed units.
(3) Indoor also in fire-resistant vaults when more economical than other
types.
(4) Not recommended in extreme environment containing excessive dirt or dust
or containing concentration of corrosive elements.
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