Electrical Testa for 100% Inspection
The
Insulated Cable Engineers Association (ICEA) recognizes three alternative test
methods for electrical testing of secondary cables (up to 1,000 volts phase to-
phase).
AC Spark Test. The cable conductor is
grounded. The covered / insulated cable surface is passed through a close
network of metallic bead chains or similar contact electrode. The electrodes
are at an ac voltage potential selected on the basis of the type and thickness
of the covering.
In the event
of a pinhole, skip, or other sufficiently weak spot (electrically speaking), a
fault to the grounded conductor occurs. The fault triggers an alarm such that
the operator can mark the fault for removal or repair.
DC Spark Test. This is similar to the
ac spark test except direct current, higher potential values, and continuous
circular electrodes are used.
Alternating Current Water Tank Test.
The entire reel of finished cable is immersed in a water tank with only the
cable ends protruding above the water. After a soak period to insure that water
has permeated the entire reel of cable, the cable conductors are energized at
an ac voltage level that is dependent on
material
type and thickness.
The test voltage is applied for five minutes.
The water acts as a ground and during the soak period it is hoped that water infiltrates
in to any damage, pinhole, or electrically weak areas.
Insulation Resistance Test. For most modern
insulations, this test is meaningless, but persists in industry standards. In
connection with the water tank test above and while still immersed, a bridge is
used to read the insulation resistance.
For modern
insulations, the readings are so high that “apparent” differences, even though
possibly huge, are meaningless and dependent on numerous factors unrelated to
the insulation resistance.
Testing Medium Voltage Cables
The tests
described under Section 6.1 are also applicable to medium voltage cables. These
tests are generally conducted in a dry environment on finished cables.
Unique to
medium and higher voltage cables is the partial discharge test. AEIC requires
that such cables be subjected to a partial discharge while on the shipping
reel. The cable must be allowed to “rest” after manufacturing to allow any
pressures that were developed during manufacturing to escape.
It must be
performed prior to the ac voltage test. Alternating current voltage is raised
to an established level that is approximately four times operatq voltage.
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