MIL-STD-1399-300 Electric Power, Alternating CurrentThis military standard section establishes electrical interface characteristics for shipboard equipment utilizing AC electric power to ensure compatibility between user equipment and the electric power system. Characteristics of the electric power system are defined and tolerances are established, as well as requirements and test methods for ensuring compatibility of shipboard user equipment with the power system. The policies and procedures established by MIL-STD-1399 are mandatory. This section and the basic standard are to be viewed as an integral single document for use in the design and testing of electric power systems and user equipment.

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MIL-STD-1399-3008

5.1.4.1 Phase angular relations. The ungrounded three-phase source shall have an angular relationship of 120 degrees between phases under balanced load conditions. If the source is a grounded, 4-wire system (with neutral), the angular displacement between phases shall not exceed 120 degrees ±1 degree under balanced load conditions.

5.1.5 Electric power system protection. Protection is provided for the electric power system but not for user equipment.

5.1.5.1 Type I, 60 Hz electric power system. The electric power system protection shall be a circuit breaker and/or fuse that are sized to provide overcurrent and fault current protection.

5.1.5.2 Type II, 400 Hz electric power system protection. For the 400 Hz electric power system, protective devices (separate from protection devices that may be provided to integral conversion equipment) are provided to interrupt the Type II electric power system within 100 to 170 msec if the voltage or frequency excursions exceed the limits set forth below:

a. Overvoltage: 120 to 130 percent of nominal voltage in any phase measured line-to-line. b. Undervoltage: 70 to 80 percent of nominal voltage in any phase measured line-to-line. c. Overfrequency: 425 to 435 Hz.

d. Underfrequency: 365 to 375 Hz.

5.1.5.3 Type III, 400 Hz electric power system protection. For the 400 Hz electric power system, protective devices (separate from protection devices that may be provided to integral conversion equipment) are provided to interrupt the Type III electric power system within 100 to 170 msec if the voltage or frequency excursions exceed the limits set forth below:

a. Overvoltage: 110 to 120 percent of nominal voltage in any phase measured line-to-line on delta-connected systems and line-to-neutral on 115 to 200 Vrms wye-connected systems.

b. Undervoltage: 84 to 90 percent of nominal voltage in any phase measured line-to-line on delta-connected systems and line-to-neutral on 115 to 200 Vrms wye-connected systems.

c. Overfrequency: Above 415 to 425 Hz.

d. Underfrequency: 8elow 375 to 385 Hz (surface ships).

5.1.5.4 Conditions not protected against. The electric power system protection shall not interrupt the electric power to the user equipment under the following conditions:

a. High voltage excursions of very short duration (voltage spike) (see Figures 5 and 6). b. The momentary interruption and restoration of power of less than 100 ms.

c. 500 VDC insulation resistance tests performed using megohmmeters. (Surface ships)

d. Active ground detector tests (submarines) where 150 VDC is added to the 440 Vrms waveform and 50

VDC is added to the 115 Vrms waveform. NOTE: Legacy systems may utilize 500 VDC added to the 440 Vrms waveform and 150 VDC added to the 115 Vrms waveform.

5.1.6 Electric power system parameters. Ensure power system parameters shall be as specified in 5.1.6.1 through 5.1.6.3.

5.1.6.1 System frequency. System frequency is 60 Hz. Where there are overriding design features demanding a different frequency, deviations from this requirement are subject to the requirements of 4.4 and 6.5.