MIL-HDBK 1028/6A
3.4
60 Hz Electrical System. The electrical systems shall comply
with the requirements of MIL-HDBK-1004/1, MIL-HDBK-1004/6, and the NAVFAC
DM-4 series, Electrical Engineering. System components shall be fully rated
for the intended application.
3.4.1
Switchgear and Equipment. Obtain switchgear and equipment power
from the existing station distribution system, hangar, or adjacent
buildings. The electrical service shall be designed for the total power
required for building supports and the FPUS equipment. Provide primary,
fused, switch protection; lightning protection; substation-type service
transformer; underground service entrance; low-voltage switchgear;
secondary metering; lighting; small power transformers; and control panel.
Service supplied from the primary distribution system at the site shall
provide a substation-type transformer (if required). Transformers shall
have a delta-connected primary and grounded wye-connected secondary.
3.4.1.1
Switchgear Assembly. Provide a 480 wye, 277 V, three-phase,
four-wire, low-voltage switchgear assembly for power distribution in the
building. Supply motor control center, parking apron service islands,
hangar service points from switchgear. Also provide a 25 percent spare
capacity for future requirements. Provide a unitized 480 wye, 277 V, three-
phase, four-wire, 60 Hz motor control center for compressors and
auxiliaries, ventilating fans, unit heaters and 480-208 wye, 120 V
receptacle, and small power transformer.
3.4.2
Distribution System. 60 Hz power shall be distributed to hangar
and parking apron service points by underground main feeders supplied from
the 480 V, three-phase, low-voltage switchgear. Install underground feeders
in concrete-encased, nonmetallic duct banks in accordance with NFGS-16302,
Underground Transmission and Distribution.
3.4.2.1
Main Feeders. Main feeders shall be 480 V, three-phase, three-
wire with color-coded, insulated, grounding conductor. Conductors shall be
sized according to criteria unit demand with diversity applied for the
number of service points connected (see Figure 2). Main feeders shall
supply subfeeder circuit breakers located in parking apron distribution
boxes. Subfeeder circuit breakers shall be rated 600 V, 225 amperes,
three-pole.
3.4.3
Aircraft Grounding Point Requirements. Provide aircraft
grounding points as required by MIL-HDBK-274, Electrical Grounding for
Aircraft Safety.
3.5
400 Hz Electrical System. The 400 Hz electrical system shall
supply aircraft electrical power requirements from frequency converters and
utilization equipment as described in MIL-HDBK-1004/5. The system design
shall provide for no-load to full-load voltage variations which are within
the requirements of MIL-STD-704, Aircraft Electric Power Characteristics.
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