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

Hz systems. These systems have a nominal voltage of 115 volts with a nominal frequency of 60

Hz and are used in support of COTS equipment only.

All power types may not be available on all aircraft platforms. The selection of the input power type for utilization equipment shall take into consideration the aircraft power types available on the intended platform and the capacity of the electrical system of that aircraft platform.

5.2.2 Phase sequence. The phase sequence shall be A-B-C and aircraft wiring and equipment terminals shall be marked accordingly. Generator terminals shall be marked T1-T2- T3 corresponding to A-B-C, respectively. The phase sequence shall be counterclockwise (positive) as shown on figure 2.

5.2.3 Normal operation. Normal operation characteristics shall be in accordance with figures 3, 5, and 7, table I for 400 Hz systems and table II for variable frequency systems; and figures 8, 10 and 12, and table III for 60 Hz systems.

For variable frequency systems the rate of change of frequency from onset of a normal frequency transient measured for over a period of time of greater than 25 milliseconds shall not exceed 250

Hz per second.

5.2.4 Abnormal operation. The overvoltage and undervoltage values shall be within the limits of figure 4 for 400 Hz and variable frequency systems and figure 9 for 60 Hz systems. The overfrequency and underfrequency values shall be within the limits of figure 6 for 400 Hz systems, and figure 11 for 60 Hz systems. The overfrequency and underfrequency for variable frequency systems shall not exceed the 360 - 800 Hz steady state values.

For variable frequency systems the rate of change of frequency from onset of an abnormal frequency transient measured for over a period of time of greater than 25 milliseconds shall not exceed 500 Hz per second.

5.2.5 Emergency operation. All power characteristics in emergency operation shall be the same as normal operation.

5.3 DC power characteristics.

5.3.1 Type system. DC systems shall provide power using direct current, two-wire or negative ground return system having a nominal voltage of 28 Volts or 270 Volts. These systems shall conform to figures 13, 14, 15, 16, 17, 18 and table IV.

5.3.2 28 volts DC system.

5.3.2.1 Normal operation. Normal operation characteristics shall be in accordance with figures 13, 15 and table IV.

5.3.2.2 Abnormal operation. Overvoltage and undervoltage values shall be within the limits of figure 14.