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|  MIL-C-18312F
6.4 Prevention of corona. All metal parts, fittings, conductors, and attachments which operate at higher potential
than other adjacent parts of the housing, should be carefully finished in order to insure that all sharp corners and
edges are removed to minimize the possibility of corona discharge under the service conditions specified herein.
Parts, such as conductors, from which the removal of sharp corners and edges would be impractical, should be
spaced in such a manner as to prevent harmful corona discharges under the service conditions specified herein.
6.5 Mounting. Tubular style capacitors with dimension L or D of 1.250 or 0.670 inches, respectively, and greater,
should not be supported by their leads. These capacitors should be provided with a supplementary means for
mounting, such as a tangential bracket for uninsulated cases and a wrap-around band for insulated cases.
6.5 Definitions.
6.6.1 Liquid-filled capacitors (see 3.3.1). A liquid-filled capacitor is a capacitor in which a liquid impregnant
occupies substantially all of the case volume not required by the capacitor element and its connections. Space may
be allowed for expansion of the liquid under temperature variation.
6.6 2 Momentary breakdown (see 3.6). Momentary breakdown is defined as a single or a series of rapidly
succeeding capacitor discharges evidenced by abrupt decreases in insulation resistance of values below the limit
specified in 3.9 and followed by restoration of the resistance to a value above this limit.
6.6.3 Flashpoint of impregnant (see 3.20). Flashpoint of a material (liquid or solid) which emits combustible vapor
may be defined as the temperature to which the material must be heated in order to emit sufficient vapor to form a
flammable mixture with air.
6.7 Standard capacitor types. Equipment designers should refer to MIL-HDBK-198, "Capacitors, Selection and
Use of" for standard capacitor types and selected values. MIL-HDBK-198 provides a selection of standard
capacitors for new equipment design.
6.8 Supersession data. Specification sheet MIL-C-18312/1 has been canceled. Recommended substitute item
may be selected from style CH09 covered by MIL-C-18312/2.
6.9 Recommended voltage derating. The recommended maximum dc working voltage permitted in the applicable
temperature range shall be no greater than the value specified in table IV, less the peak value of the ac voltage. The
peak ac component of voltage should not exceed 20 percent of the dc voltage rating shown in table IV, or the value
calculated from the following formula, whichever is smaller:
(Tdc - T)Ae
=
VP AC
ΠfCD
Where: VpAC
= peak value of ac component.
2
e = convection coefficient in watts per cm per C. The value of "e" is approximately
equal to 0.0006.
f = frequency in cycles per second of ac component.
2
A = exposed capacitor case surface area in square centimeter (cm );
exclusive of portions occupied by terminal mountings.
C = nominal capacitance in farads.
D = maximum dissipation factor shown in 3.8, at the applicable high
test temperature (see 3.1).
T = maximum ambient operating temperature expected within equipment
containing capacitor.
Tdc = high ambient test temperature in degrees centigrade (see 3.1).
Notwithstanding this requirement for operation in the interval of 84C to 85C for characteristic R units and 124C, to
125C for characteristic N units the value of 84C and 124C, respectively, should be applied for "T" in the formula
with the value of ac component not to exceed 1 percent of the rated dc voltage.
18
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