MIL-DTL-24643C
Yd =
Measured decay time from signal channel number two, in microseconds
L
=
Measured specimen length, in feet; measurement accuracy shall be within ±1 percent
In an identical manner, the remaining selected transmission lines shall also be tested.
4.9.7.4 Observation. Specimen failure shall be construed if any transmission line exhibits either a rise time or a
decay time which is greater than that specified (see 3.1).
4.9.8 Voltage withstand. This test shall determine the ability of completed cable to withstand overvoltages
without exhibiting electrical discharge through insulation or jacketing material, either between conductors, or
between these conductors and any conducting material which may be in contact with the surface of the cable during
in service use.
4.9.8.1 Specimen. The specimen shall consist of a unit of product as specified in 6.7.1.
4.9.8.2 Special apparatus. Apparatus shall include the following:
a.
An adjustable voltage source, which shall be in accordance with either of the following, as appropriate (see
(1) An AC voltage source which shall produce a single-phase, approximately sinusoidal voltage under all
test conditions, which shall have a frequency of not more than 100 Hz, and which can be adjusted to the specified
rms magnitude (see 3.1). This source shall have the capacity to provide an effective power of not less than 5 kVA,
and shall incorporate an overload relay which shall reduce the source voltage to zero whenever an applied load (that
is, the specimen, see 4.9.8.3) attempts to draw electrical current to exceed this effective power capacity.
(2) A source of DC voltage which can be adjusted to the specified magnitude (see 3.1), and which shall
have the capacity to provide an electrical current of not less than ¼ A. This source shall incorporate an overload
relay which shall reduce the source voltage to zero whenever an applied load (that is, the specimen, see 4.9.8.3)
attempts to draw electrical current to exceed this current capacity.
b. When required, a water tank, which shall be filled with water and shall be of sufficient size to contain the
specimen, shall be used as specified in 4.9.8.3.f and 4.9.8.3.g (may not be required, see 4.9.8.3.f and 4.9.8.3.g).
4.9.8.3 Procedure. The voltage source shall be electrically connected to the specimen as specified (see a, b, c,
d, e, f, and g). For each connection, the test voltage from the voltage source shall be increased, in a uniform manner,
from 0 v to the specified voltage (see 3.1) during a period of not more than 60 seconds nor less than 10 seconds,
except that specified voltages of less than 600 v may be applied instantaneously. (This gradual voltage application
is generally necessary to prevent a current in rush, and the consequent tripping of the voltage source overload relay
caused by specimen capacitance.) This specified voltage shall then be maintained for a period of 1+½, -0 minute
(unless the voltage source overload relay trips, see 4.9.8.4), following which the test voltage shall be reduced to zero
at approximately the same rate as which it was applied.
a. Conductor to conductor (components): Specimens incorporating one or more insulated conductor
transmission lines (as pairs or triples) with overall shield within each transmission line: One transmission line shall
be selected for measurement. One insulated conductor shall be selected and electrically connected to one terminal of
the voltage source. All other conductors within that transmission line shall be electrically connected to the other
voltage source terminal. The transmission line shield is to be left unconnected. The voltage withstand test shall then
be performed as specified. In a similar manner, the voltage withstand test shall be performed between each
remaining conductor within the selected transmission line and the short circuited combination of all other conductors
within that transmission line. Following this, and in an identical manner, the voltage withstand test shall be
performed on all remaining transmission lines within the specimen. (Additional measurements may be required, see
b, c, d, e, and f.)
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