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.

The voltage is lowered while the partial discharge level in picocolombs is recorded. Corona testing is extremely sensitive to defects in the cable as well as external electrical interference. Shielded rooms are provided to minimize this external noise.

Related post

No comments: