MIL-HDBK-1004/2A
5.2.5.4 Noise. If local conditions require less than NEMA TR-1 recommended
audio sound levels, make an economic comparison between the cost of
transformers having lower than standard noise levels, and the cost of sound
and vibration isolation of the transformer room. Avoid locating unit
substation rooms near critical spaces requiring low noise levels, such as
auditoriums, sick bays, or living quarters (refer to NAVFAC DM-1.03,
Architectural Acoustics).
5.2.5.5 Emergency Lighting. Provide emergency lighting, of the battery-
operated type, in unit substation rooms.
5.3
Outdoor Utilization Voltage Substations. Base material and
equipment on NFGS-16335. Generally, transformers are be grade-mounted type
subject to the limitation given in this section. Transformers may be pole-
mounted type only when such transformers comply with the requirements given in
Section 2.
5.3.1
Secondary Unit Substation Types. Secondary unit substations should
generally follow the criteria given previously for indoor unit substations
except that requirements for outdoor installations apply. Because these units
are not tamperproof, protect substations from unauthorized access by chain
link fencing of at least 7 feet (2.1 m) in height as a minimum requirement.
Provide three strands of barbed wire above for additional protection only
where such substations are in housing areas or otherwise exposed to military
dependents or where required by the using agency. Other fence materials to
provide equipment masking, sound absorption, or protection against sabotage
may be necessary in some cases (see Figure 3).
5.3.2
Pad-Mounted Compartmental-Type Transformer Units. Provide units in
accordance with the requirements of NFGS-16462. This specification limits the
primary protective options to group-operated, load-break switches. Since such
units are tamper resistant, they need not be fence-enclosed (see Figure 2).
5.3.2.1 Units 500 Kilovolt-Amperes and Smaller Units are not Provided with
Either Taps or a Minimum Percent Impedance Unless Specified. To prevent
excessive interrupting duty on secondary equipment it may be necessary to
check manufacturers' ranges of available impedances, as there is no industry
standard.
5.3.2.2 Units Larger than 500 kVA. Pad-mounted units in three-phase units
larger than 500 kVA are available up to a capacity of 2,500 kVA. These units
are less expensive than secondary substation units. However, because primary
protective devices available for such larger sizes do not provide dead-front
load-break features within the pad-mount construction, the use of units larger
than 750 kVA is not recommended.
5.4
Outdoor Distribution Voltage Substations. Design these substations
to meet the criteria for acceptable power sources in MIL-HDBK-1004/1 and the
recommendations of the Base Exterior Architecture (BEA) plan.
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