Tan Delta versus Partial Discharge testing on cables

[TaifaEngineering]

Thoughts on this? What is the preferred test for all of you, and why?






www.taifaengineering.com

[Nick1234]

Thoughts on this? What is the preferred test for all of you, and why?






www.taifaengineering.com

It all depends on the application. In general I feel that the Tan Delta is the better test but it is more invasive the cable must be de-energized and made safe. The Partial Discharge testing if they have the hardware installed can be done live.

In general for a site that has infrequent shutdowns Partial Discharge would be the way to go and it can provide information on problem cables that you can then check with Tan Delta during a shutdown.

[Kalbi_Rob]

It all depends on the application. In general I feel that the Tan Delta is the better test but it is more invasive the cable must be de-energized and made safe. The Partial Discharge testing if they have the hardware installed can be done live.

In general for a site that has infrequent shutdowns Partial Discharge would be the way to go and it can provide information on problem cables that you can then check with Tan Delta during a shutdown.

My last company recommended performing Online PD annually, and every 5 years performing Tan-Delta or Offline Partial Discharge since OLPD doesn't detect minor electrical treeing, while the offline test can.

I believe the overall difference lies in the cost and safety placed on the customer to work around. Tan-delta is cheaper (I have determined failure in a cable within 3 months with TD), but Offline Partial Discharge is much more accurate, and Online Partial Discharge is more convenient to continued operations.

[SecondGen]

Thoughts on this? What is the preferred test for all of you, and why?
www.taifaengineering.com

Offline PD is the most accurate if you are going to take the cable down but is really specialized and expensive. Tan Delta combined with VLF will give you a good baseline for comparison in the future and is much cheaper. Online PD is a good non-distructive test, but like an infrared scan its only useful for monitoring, not a replacement for offline maintenance.

From NETA World Spring 2017: Tan delta tests the health of the insulation as an average value of the length of the cable, and therefore, small sections with significant defects cannot be detected. Partial discharge detects these small defects but cannot detect aging effects (like water trees) until they result in discharge. Thus, these two tests are complementary, and it is advisable to do both at the commissioning of any cable.

https://www.eatechnology.com/america...17_FlowONE.pdf

[Billhig]

Offline PD is the most accurate if you are going to take the cable down but is really specialized and expensive. Tan Delta combined with VLF will give you a good baseline for comparison in the future and is much cheaper. Online PD is a good non-distructive test, but like an infrared scan its only useful for monitoring, not a replacement for offline maintenance.

From NETA World Spring 2017: Tan delta tests the health of the insulation as an average value of the length of the cable, and therefore, small sections with significant defects cannot be detected. Partial discharge detects these small defects but cannot detect aging effects (like water trees) until they result in discharge. Thus, these two tests are complementary, and it is advisable to do both at the commissioning of any cable.

https://www.eatechnology.com/america...17_FlowONE.pdf

Thanks for the reference, I wrote that article. Online PD is the way to go to test large populations or to test frequently. If you aren't seeing during normal operating conditions, do you really care that you get PD inception at 1.5 nominal? If you permanently install RFCT/HFCT, then you can test any time in a safe, shirt sleeve environment.

Once you start seeing PD online, then think about running offline tests. I feel that once you go to the pain of getting an outage and bringing in a test company, you might as well to Tan Delta and PD.

[SecondGen]

Thanks for the reference, I wrote that article. Online PD is the way to go to test large populations or to test frequently. If you aren't seeing during normal operating conditions, do you really care that you get PD inception at 1.5 nominal? If you permanently install RFCT/HFCT, then you can test any time in a safe, shirt sleeve environment.

Once you start seeing PD online, then think about running offline tests. I feel that once you go to the pain of getting an outage and bringing in a test company, you might as well to Tan Delta and PD.

Great article and important points to remember, thanks for stopping by!