Specifications.

To limit the amount of harmonic currents drawn by
the load, the specifications controlling the design of shipboard combat and
other systems have been modified in recent years.

SPECIFICATION MODIFICATION DATE REFERENCE

MIL-F-18870E (OS) Amendment 1
25 Apr 1975 6

MIL-E-16400H 23 May 1986 7

MIL-STD-1399 13 Jul 1987
8

Section 300A 13 Oct 1987

MIL-STD-461C 4 Aug 1986 9

The requirement in MIL-E-16400H is typical of the other specifications.
"Each unit of the equipment which can be powered from the ship's electrical
power distribution system shall be designed to minimize harmonic distortion
effects on the electrical system. The operation of each such unit with ratings
specified hereinafter shall not cause harmonic line currents to be generated
that are greater than 3% of the unit's full-load fundamental current between
the 2nd and 32nd harmonic."

"Additionally, currents with frequencies from the 32nd harmonic through 20
kHz shall not exceed 100/n percent of the unit's rated full-load fundamental
current, where n is the harmonic multiple number. Units with power ratings
less than those specified above shall be current amplitude limited such that
no individual harmonic through 20 kHz exceeds a magnitude of 100/n percent of
the unit's full-load fundamental current where n is the harmonic multiple
number."

The impact of meeting this requirement may be illustrated by considering
the 5th harmonic of 60 Hz (300 Hz). Conventional three-phase bridge
rectification (6- pulse) generates a harmonic that is 20% of the fundamental
if an inductive input filter is used and is usually greater (in some cases
equal to the fundamental) if a capacitive input filter is used. If an attempt
is made to filter this 300 Hz harmonic to the 3% limit, the filter can be
larger than a conventional off- line switching-mode power supply of the same
power rating.

FREQUENCY OF RATING OF UNIT

POWER SOURCE (HZ)

60 1 KVA, or more

400 0.2 KVA, or more, on other than a single-phase
115-volt source

400 2 amperes or more on single-phase 115-volt
source.