MIL-HDBK-1004/5
b) Output disconnect. Use a vacuum contactor to disconnect the
output of the unit rather than a circuit breaker, because the contactor is
both smaller and less costly. In addition to overload and short-circuit
protection, a contactor can provide overvoltage, undervoltage, underfrequency,
and reverse-power control features, which are not available from a fused
switch.
3.3.5
Feeder Distribution Center. The feeder distribution center serves
as the 400-Hz medium-voltage system control point. Feed the output of all the
frequency conversion assemblies into a common bus which supplies all the
400-Hz medium-voltage feeders. It serves as a point to measure 400-Hz usage
and to correct the system's no-load power factor to almost unity by balancing
the capacitance of each feeder cable. Figure 6 shows a typical feeder
distribution center.
3.3.5.1
Metering. Normally, do not install recording type meters in an
unmanned facility. If records are required, transmit them to a point where
personnel are available to maintain orderly record keeping and storage.
Shunt Reactors.
An example of shunt reactors sizing is shown in
3.3.5.2
paragraph 3.2.3.2.
3.3.6
Central Plant Buildings and Other Equipment Shelters. The same
reliability standards cited for equipment shall also apply to structures
sheltering any part of the 400-Hz system or its environmental support systems.
Provide spaces around equipment for ease and convenience of testing,
maintenance, serving, and equipment removal. Provide a minimum 5-foot
(1.5-meter) aisle space around each frequency conversion assembly. Larger
aisles may be required to allow for replacement of defective equipment. Design
buildings with knockout panels for future expansion. Control mechanical
systems automatically by thermostats which maintain correct temperatures under
all operating conditions. Provide roof exhaust fans as required. Provide
louvers and air handling units for air supply which have filters which prevent
entrance of dusty air into the operating parts of the motor-generator sets
(see MIL-HDBK-1003/7, Steam Power Plants - Fossil Fueled). Include other
considerations normally provided for diesel-engine generators and switchgear
rooms.
3.4
Low-Voltage Utilization System Design. A low-voltage utilization
system extends from the utilization service assembly as shown in Figure 1 or
from the solid state frequency conversion assembly as shown in Figures 1a and
1b to the parked aircraft. The layout of aircraft parking defines the
location of the parked aircraft units (see MIL-HDBK-1021/2, General Concepts
for Pavement Design) which will define the locations and number of utilization
service assemblies or solid state frequency conversion assemblies and
determine if a single, low or medium-voltage feeder is capable of supplying
only one hangar, several hangars, or aprons. Integrated design with the
aircraft fixed point utility systems (see MIL-HDBK-1028/6, Aircraft Fixed
Point Utility Systems).
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