TEST OF THE OUTER PROTECTION OF THE BURRIED JOINT IN ACCORDANCE WITH IEC 60840

Fig-Typical Medium Voltage Cable Joint

Here in this article we will find a case study of type test report for direct buried type cable joint. Hope these text will help us to understand what kind of test actually required for underground power cable direct buried joints. In another article “TYPE TESTS ON COMPLETE UNDERGROUND POWER CABLE” we discussed detail a case study to make sense on type test of an XLPE cupper core underground power cable.

Dry heating cycle test in accordance with IEC 60840

On the joint three heating cycles without voltage were performed. 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).

Result: The test was performed in a correct way.

Water immersion and heat cycling in accordance with IEC 60840

After the three dry heating cycles, mentioned under 3.1 the joint was immersed in water, at a depth of at least 1 meter at the highest point of the outer protection. Then the joint was subjected to 20 heating cycles. In each heating cycle the water around the joint was heated to a temperature between 70 °C and 75 °C (between 15 °C and 20 °C below the maximum rated temperature of the cable conductor) and kept on this temperature for at least five hours. Hereafter the water was cooled down to a temperature less than the ambient temperature +10 °C.

Result: The water immersion and the heat cycling did not give reason for remarks.

DC voltage test on insulation joint in accordance with IEC 60840

After the water immersion and heat cycling, a voltage of 20 kV DC was applied for 1 minute between the metallic screen and the earthed exterior of the joint outer protection. Hereafter a voltage of 20 kV, DC was applied for 1 minute between the metallic screens on both sides of the joint. The test was carried out while the test installation was at ambient temperature.

Result: No breakdown occurred.

Impulse withstand voltage test on insulation between the screens and water in accordance with IEC 60840

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After the above mentioned tests the test set-up was tested with an impulse voltage of 37.5 kV. The test voltage was applied between the metallic screen and the earthed exterior of the joint outer protection. The test was carried out while the test installation was at ambient temperature.  The test was carried out in accordance with IEC 60230. The joint was tested with ten positive and ten negative voltage impulses.

Result: No breakdown occurred.

Impulse withstand voltage test on sheath sectionalizing insulation in accordance with IEC 60840

After the above mentioned tests the joint was taken out the water and the sheath sectionalizing insulation was tested with an impulse voltage of 75 kV. The test voltage was applied between the metallic screens on both sides of the joint. The test was carried out while the test installation was at ambient temperature.  The test was carried out in accordance with IEC 60230. The joint was tested with ten positive and ten negative voltage impulses.

Result: No breakdown occurred

Examination of the joint in accordance with IEC 60840

The joint was dismantled and inspected for water penetration and cracks.

Result: No signs of cracks or water penetration were detected. The construction of the joint complied with the construction drawing.

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