PD measurements during commissioning (SOAK) 72,5-420 kV kabelanlegg
When it comes to commissioning of cable systems at higher voltages, IEC 62067 and IEC 60840 are often used as a basis. According to these, one can either perform an AC Hipot test (20-300 Hz) or a so-called SOAK test.
During the SOAK test the system is energized for 24 hours without load. The test is passed if the system does not fail during these 24 hours. Weaknesses that need time to develop will thus not be detected by a SOAK test. For an error to occur within the first 24 hours, the error must be of a critical nature in the first place.
SOAK test combined with PD monitoring of joints and end terminations
An alternative is to combine the SOAK test with PD monitoring. This is done by temporary installing PD sensors at joints and terminations. The sensors can either be mounted in Link boxes where applicable, or directly on the cable at the joint. The PD sensors can be left behind so that they can be used for testing at a later occasion.
During the SOAK test itself, the cable system is monitored. Whether a joint or an termination has PD activity at this voltage, it will only be a matter of time before an accident occurs. By combining the SOAK test with PD measurements, it is known that the system is PD free at operating voltage. The disadvantage is, of course, that one does not detect weaknesses that are ignited by an overvoltage.
Nevertheless, this is a good alternative where one can not perform AC Hipot testing. The costs will be a fraction of what an AC test will be while making sure that the joints, end terminations and cable are PD free before taking over.
Picture; PD monitoring system from Prysmian Electronics