Commissioning on 2,2 km subsea cable

The importance of conducting commissioning with partial discharge testing of new important cable circuits

At both ends the subsea cable were jointed over to top-side cables. During the installation deviations with the stress control over the conductor had been made in joints at far-end.

This resulted in critical partial discharges already at operating voltage.

The transition joints passed both the withstand-test and the TanDelta test but were clearly rejected due to the partial discharge test. This shows once again the important` s of combining the withstand test with sensitive partial discharge measurements. Many installation faults will not result in a complete breakdown during withstand test, hence it will be undetected during test. When it comes to TanDelta testing, this is generally a test for revealing aging in "bigger" parts of the insulation not detecting losses originating from PD`s.