MIL-HDBK-1004/5
2.3.2
Medium-Voltage System. The development of a medium-voltage system
which distributes three-phase, 400-Hz electric power at 4,160 volts can
provide a more economical system. A typical, 400-Hz medium-voltage system is
shown on Figure 1. Detailed requirements are provided in Appendix A.
2.3.3
Flight-line Electrical Distribution Set (FLEDS). A FLEDS system may
be used in conjunction with the low-voltage or medium-voltage system. The
components of an individual FLED set are shown in Figure 1c. A FLED system
consists of a number of FLED sets which distribute 200Y/115 volts at 400 Hz to
a maximum of two aircraft per FLED set. Normally the FLED system is procured
and installed by NAVAIR, therefore, certain design characteristics to support
the FLED system must be obtained from NAVAIR. Examples of a typical FLED
system are shown in Figure 1d.
2.4
Surveys. Before replacing existing local low-voltage systems with a
central medium-voltage system, make preliminary surveys to ensure the cost
effectiveness of the replacement. Generally, consider only naval and Marine
Corps facilities having existing 400-Hz requirements of 500 kilovoltamperes
(kVA) or more for replacement with central medium-voltage systems.
2.4.1
Energy Conservation. Full load efficiency of the motor-generator
set portion of frequency conversion assemblies ranges from 73 to 88 percent,
depending on the size of the sets and the type of motor drive (induction or
synchronous). The use of many sets, operating underloaded, lowers
efficiencies, increases energy usage and cost, and probably increases
maintenance and shortens operating life.
2.4.2
Economic Studies. When preliminary surveys and studies indicate
that a central system may be economically feasible, a complete life-cycle cost
analysis may be necessary. Make field measurements of the actual demand loads
on each existing low-voltage 400-Hz system. Determine power requirements,
characteristics, and locations of all existing utilization equipment and
service points. The using agency shall advise of any changes in load
requirements contemplated to serve anticipated mission changes so that this
information may be included in determining the capacity required for a central
system.
2.5
Types of Loads. Various types of loads on naval stations and Marine
Corps bases require 400-Hz electric-power input. The power factor of these
loads varies from 0.8 to 1.0.
2.5.1
Aircraft. The number of each type of aircraft serviced at naval
stations and Marine Corps bases determine the total demand. For computation
of 400-Hz aircraft loads, use the maximum load in Table 1 with a demand factor
applied to the total load as given in Table 2.
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