MIL-STD-704 establishes requirements
for electrical power characteristics on aircraft at the
the electrical power system and the user equipment.
The standard AC power is a 400 Hz, II
5/200 VAC, 4-wire, 3 -phase, Wye-connected system with the neutral of the Wye
grounded. Loads greater than 0.5 kVA must use 3-phase power.
Singlephase loads must be connected line-to-neutral.
The only alternative, when specifically authorized, is 230/400 VAC with the
requirements proportional to the II 5/200 VAC limits.
The standard DC power is 28 VDC. An
alternate is 270 VDC. This is the nominal DC voltage obtained when the
standard 200 VAC, 3-phase, line-to-line aircraft voltage is bridge
rectified. Studies have shown major overall advantages for aircraft
using 270 VDC as the primary aircraft power. For this reason, a large
share of the Navy exploratory and advanced development funds for aircraft
electrical power system development in recent years has been spent in
developing the components necessary for a 270 VDC system.
Fortunately, power supplies can be developed for 3-phase, 115/200 VAC input
power that can be directly used on 270 VDC with no modification. If
initially considered, these dual-input power supplies have minimal impact on
the size, weight, cost and other attributes when compared to power supplies
that are only designed for 3 -phase, II 5/200 VAC