MIL-STD-704 Aircraft Electric Power CharacteristicsThis standard establishes the requirements and characteristics of aircraft electric power provided at the input terminals of electric utilization equipment. MIL-HDBK-704-1 through-8 defines test methods and procedures for determining airborne utilization equipment compliance with the electric power characteristics requirements defined herein. Electromagnetic interference and voltage spikes are not covered by this standard.

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MIL-STD-704F

f.  NATO                              North Atlantic Treaty Organization g.  POR                                Point of Regulation

h.  RMS                                Root Mean Square

i.  STANAG                         Standardization Agreement j.  VA                                   Volt-ampere

3.2  Abnormal operation.  Abnormal operation occurs when a malfunction or failure in the electric system has taken place and the protective devices of the system are operating to remove the malfunction or failure from the remainder of the system before the limits for abnormal operation are exceeded.  The power source may operate in a degraded mode on a continuous basis where the power characteristics supplied to the utilization equipment exceed normal operation limits but remain within the limits for abnormal operation.

3.3  AC voltage.  AC voltage is the root mean square (RMS) phase to neutral value for each half cycle.

a.  Steady state AC voltage is the time average of the RMS voltage over a period not to exceed one second.

b.  Peak AC voltage is the maximum absolute value of the instantaneous voltage.

c.  The direct current (DC) component of the AC voltage is the average value of the voltage.

3.4  Aircraft electric power systems.  An aircraft electric power system consists of a main power source, emergency power source, power conversion equipment, control and protection devices, and an interconnection network (wires, cables, connectors, etc.).  The main power is derived from aircraft generators driven by the aircraft propulsion engines.  Emergency power is derived from batteries, engine bleed air, independent auxiliary power units, ram air driven generators, or hydraulically driven generators.

3.5  Crest factor.  The crest factor is the absolute value of the ratio of the peak to the

RMS value for each half cycle of the voltage waveform.

3.6  Current.  Alternating Current (AC) current is the RMS value for one half cycle measured between consecutive zero crossings of the fundamental frequency component.   Direct Current (DC) current is the instantaneous value.

3.7  Current modulation.  Current modulation is the difference between maximum current and minimum current.  Percent current modulation is the ratio of the current modulation to the average (mean for DC, RMS of the fundamental for AC) current multiplied by 100 over a one second period.

3.8  DC voltage.  Steady state DC voltage is the time average of the instantaneous DC

voltage over a period not to exceed one second.

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