Type Test on Complete Underground Power Cables

Here in this article, we would like to present a sample type test report on complete underground power cable:

Bending test in accordance with IEC 60840, clause 12.3.3

A cable sample of approximately 40 m was bent six times around a test cylinder with a maximum diameter of (25 x (d+D) +5%) at ambient temperature.

The results are stated in annex A. For a picture of the bending test, a reference is made to Annex G.

 Result: The test was completed successfully.

Partial discharge test at ambient temperature in accordance with IEC 60840, clause 12.3.4.

After the bending test and short duration test, the cable samples were examined for partial discharges in accordance with IEC 60885-3 at ambient temperature. The sensitivity of the measuring circuit was checked with a calibrator, and the noise level was < 2 PC. The voltage was first raised to and held to 133 kV (1, 75 Uo) for 10 s and then lowered to 114 kV (1, 5 Uo). At this voltage, the partial discharges were measured. For the results, reference is made to Annex A.

Result: No visual internal partial discharges were established.

Measurement of the dielectric loss angle in accordance with IEC 60840, clause 12.3.5

After the partial discharge measurement as mentioned under 2.1, the dielectric losses of the test installation were measured at Uo and a conductor temperature of at least 95 °C.  The results are stated in annex A. 

 Result: The test results met the requirements.

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Heating cycle voltage test in accordance with IEC 60840, clause 12.3.6

The test installation was subjected to a power frequency test of 152 kV (2 Uo), 60 Hz for at least 480 h. During this test, the test set-up was subjected to at least 20 heating cycles. Each heating cycle consisted of 8 h heating and 16 h of natural cooling. During the last 2 h of each heating period, the conductor reached a temperature of at least  95 C (5 C above the maximum rated temperature). For the data of the test, a reference is made to Annex A.
Result: The test installation passed the test successfully. 

Partial discharge test in the hot condition in accordance with IEC 60840, clause 12.3.4

After the heating cycle voltage test, the test the set-up was examined for partial discharges in accordance with IEC 60885-3 at a conductor temperature of at least 95 °C The test was carried out as described in 2.1. The results are stated in annex A.
 Result: The test results met the requirements.

Short duration power frequency withstand voltage test in accordance with Tranco specification

After the above-mentioned tests the test installation was subjected to a power frequency test of 275 kV (3,6 Uo), 60 Hz for at least 1 minute. The test was carried out while the test installation was at ambient temperature.
Result: No breakdown occurred.

Impulse withstand voltage test in accordance with IEC 60840,  clause 12.3.7

After the above-mentioned tests, the test set-up was tested with an impulse voltage while the conductor was heated to a temperature of at least 95 C (5 C above the maximum rated temperature). The test was carried out in accordance with IEC 60230 and IEC 60060. The sample was tested with ten positive and ten negative voltage impulses of 650 kV. The oscillograms of these tests are stated in annex B.
Result: No breakdown occurred. 

Power frequency voltage test for 15 minutes in accordance with  IEC 60840, clause 12.3.7

Upon completion of the impulse withstand voltage test, a voltage test was executed with an alternating voltage of 50 Hz. The test installation was tested with a voltage of at least 190 kV  (2,5 Uo) for 15 minutes in accordance with the specification. The test was carried out while the test installation was at ambient temperature.
  Result: No breakdown occurred.

Examination of the cable and the accessories after the tests in accordance with IEC 60840, clause 12.3.8

After completion of the electrical tests as mentioned above the cable and the accessories were dismantled and inspected for electrical degradation of the insulation. For pictures of the dismantling, a reference is made to Annex I.

 Result: No signs of electrical degradation were detected. The construction of the accessories complied with the construction drawing

Tests on semi-conducting layers

Electrical resistivity before and after aging in accordance with IEC 60840, clause 12.3.9

The resistivity of the extruded semi-conducting layers was measured and calculated according to annex B of the IEC 60840. The aging treatments were carried out in accordance with IEC 60811-1-2, clause 8 at a temperature of 100 C for 7 x 24 h. The measurement was carried out at a temperature of 90 C. The test results are stated in annex F.

Result: The test results met the requirements as stated in the specification