MIL-HDBK-1004/2A
2.4.2
At-Grade Mounting. For at-grade mounting on a concrete base, there
is no kVA limit. Tamper-resistant transformers (classified as pad-mounted
compartmental-type units) should generally not be specified in ratings of over
500 kVA, but in no case larger than 750 kVA. When sheet-metal enclosures are
not tamper-resistant, provide ground-mounted units with a fenced enclosure or
even a concrete or brick structure, where adverse weather conditions make such
an installation advisable. For required clearances between buildings and
insulated transformers, refer to MIL-HDBK-1008.
2.4.3
Indoor Installations.
Indoor installations are covered in Section
5.
Overload Capacity. Consider the accelerated loss of equipment life
2.4.4
if transformers are to be overloaded. Refer to ANSI C57.91 Guide for Loading
Mineral-Oil-Overhead and Pad-Mounted Distribution Transformers Rated 500 kVA
and Less with 65 Degrees C or 55 Degrees C Average Winding, C57.92 Guide for
Loading Mineral-Oil-Immersed Power Transformers up to and Including 100 MVA
with 55 Degree C or 65 Degree C Winding Rise, and C57.96 Guide for Loading
Dry-Type Distribution and Power Transformers and Fink and Beaty, Standard
Handbook for Electrical Engineers.
2.4.5
Transformer Noise Level. Refer to NEMA TR-1, Transformers,
Regulators and Reactors for maximum permissible noise levels for transformers.
2.4.6
Overhead Distribution. Use the criteria in ANSI C57.12.20,
Requirements for Overhead Type Distribution Transformers, 500 kVA and Smaller:
High-Voltage 67,000 Volts and Below; Low-Voltage 15,000 Volts and Below. Do
not use self-protected transformers having an internal secondary breaker,
internal primary fusing, and integrally mounted surge arresters. These
transformer accessories are provided for transformers generally described by
industry as a pole-mounted type. The replacement of fuse links is considered
to require specialized personnel not usually available at naval facilities.
2.5
Circuit Interrupting Devices. Select from fuses, circuit breakers,
and automatic circuit reclosers for protective line considerations. Provide
switches to localize defective portions of aerial and underground circuits and
to accomplish dead-circuit work. Select from nonload-break or load-break type
switches.
Fuses. After consideration of the necessary current-carrying
2.5.1
capacities, interrupting duties, and time-current melting and clearing
characteristics, select fuses from the following types:
a)
open fusible link,
b)
expulsion type,
c)
boric-acid type, and
d)
current-limiting type.
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