MIL-HDBK-1004/5
2.5.2
Avionics. In addition to aircraft, other loads such as repair shops
for electronic equipment, require 400-Hz electric power for maintenance and
testing. Load requirement shall be provided by the using agency in such
cases.
2.5.3
Other Facilities. Research, development, training,and other types
of facilities may require 400-Hz distribution systems. If the using agency
cannot provide load requirements, compute such loads on a watts per square
foot (square meter) basis when firm loads are not available (see MIL-HDBK-
1004/1, Electrical Engineering, Preliminary Design Considerations).
2.5.4
Special Requirements. Facilities indicated in paragraphs 2.5.2 and
2.5.3 have more stringent 600-Hz power requirements than the Fixed Point
Utility System (FPUS) provides.
Prior to supplying these facilities from
FPUS, verify that equipment installed will not be damaged by FPUS power
tolerances. Use local converters for these systems.
2.6
Consideration of System Voltage Parameters. The inductive
contribution to the reactance voltage drop of 400-Hz systems is roughly seven
times greater than that of 60-Hz systems, which necessitates certain
modifications to conventional distribution and utilization system design to
compensate for the increased voltage drop. Specifications for limiting
voltage drop are covered in later sections, but the following requirements
apply generally to 400-Hz systems.
2.6.1
Development of Guidelines for Parameters. Voltage drop is always a
concern in the design of 60-Hz systems. Give even closer attention to voltage
parameters in the design of 400-Hz systems because the voltage drop is much
larger. When designing 400 Hz systems, take into account the effects of
varying cable lengths and connected loads.
Items Affecting Design. The designer must consider maximum loads
2.6.2
and applicable cable-length limitations. Based on acceptable end-voltage
requirements, determine maximum allowable cable and equipment impedances.
Methods to be used for compensation or elimination of impedance are important
also. Overcompensation of voltage drop can be as bad as under compensation.
The voltage range which provides satisfactory aircraft power is the key
element to an acceptable 400-Hz distribution system.
2.6.2.1
Acceptable End-Voltage Requirements. The voltage range of 108 volts
minimum to 118 volts maximum specified in MIL-STD-704, Aircraft Electric Power
Characteristics, is the operating voltage range of the equipment inside the
aircraft. This operating voltage range takes into account a 0- to 5-volt drop
in the electrical distribution system inside the aircraft. Accordingly, the
full-load and no-load voltage at the interface (aircraft connection input
point) should never drop below 113 volts nor rise higher than 118 volts.
These parameters also apply to the input to the FLEDS system.
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