MIL-STD-704F
equipment requirements of MIL-STD-704." The equipment specification should also specify the type of electric power to be utilized and the detailed performance required during normal, abnormal, emergency, starting, transfer and power failure operation of the electric system. The electric power characteristics specified herein are minimum requirements for utilization equipment. Therefore, specifications for utilization equipment that require greater operating margins should include specific electric power characteristic operating ranges that exceed those stated herein. Utilization equipment specifications should never specify operating ranges that are narrower than those specified herein nor waive compatibility with the electric power characteristics specified herein, since that could result in failure of the equipment to perform as required. Utilization equipment specifications should also include requirements that reduce the likelihood of the equipment having an adverse effect on the electric power characteristics provided by the electric system. High inrush current, low lagging power factor, high peak power to average power ratio, high current ripple amplitude, and current distortion are some characteristics of utilization equipment that can adversely affect the electric system by degrading electric power characteristics or increasing capacity requirements. Minimizing these undesirable utilization equipment characteristics involves tradeoffs with weight, cost and reliability that are specific to each type of equipment and should be addressed in the utilization equipment specification.
6.7 Pulsed load design issues. Pulsed loads are a potential cause of unacceptable voltage modulation. Hence large pulsed loads may require excess power source capacity or dedicated power sources to protect other aircraft equipment. The utilization equipment designer should strive to minimize the current modulation produced by pulsed loads.
6.8 Non-linear loads and effects. Attention must be given to non-linear loads and their effect on the AC power bus. All loads should not introduce excessive current distortion such that other equipment is affected.
6.9 Precedence. Tables and equations included in the figures take precedence over the graphical representation of the figure itself. Continuous reproduction of the figures may result in the distortion of the curves.
6.10 Guidance and lessons learned.
6.10.1 Compatibility and testing. Historically users of MIL-STD-704 interpret or view the electrical power quality characteristics limits in this document as they would those of a typical power source/generator. This interpretation is incorrect. An aircraft electrical system is composed of a variety of power components (generation, conversion, inversion, control, power
distribution, power management devices, etc.) that provide power to aircraft buses and utilization equipment terminals. Each component and subsystem is designed and tested to its individual equipment specification, which often requires tighter performance than does MIL-STD-704 to compensate for the effects of loads as well as the associated feeder/line voltage drops therein. Therefore, the limits specified herein are minimum requirements for specifying that utilization equipment is compatible with aircraft electrical power. To ensure utilization equipment is compatible with the aircraft power, system testing as outlined in MIL-HDBK-704-1 through -8
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