How to predict 10 yr corona damage to PEEK

[ramjet]

We're considering developing a new connector design using a copper rod with .375-24 UNF thread, screwed into a PEEK insulator. The connector will be 5kv rated and the maximum conductor temp will be 300F. We're concerned about corona between the copper and PEEK in the threaded area, but we don't know how to predict precisely what effect this will have over a 10 year life. We can try things like rounding the thread tips, or using teflon tape or sealant to reduce the air gap, but we still would'nt know if that's good enough to last 10 years at 5kv. Any advice?

 

[busbar]

Unless you can get the insulator vendor to commit, it seems like testing would be the only reasonable approach.

 

[ramjet]

A 10 year life test would certainly answer the question, however, I'd rather not wait that long. I'm looking for information on accelerated testing for corona induced degradation or opinions on what type of damage would occur on the PEEK and/or copper at 5kv after 10 years. Does anyone out there have a story to tell about damage caused by corona at around 5kv?

 

[jbartos]

Suggestion: It would be better to start with the corona principles, theory, mathematical relationships, etc. to see which physical parameters may change over the longer period of time and potentially increase the corona. The corona is dependent on the voltage level, active pole radius, etc. Therefore, the voltage should not increase in time, and the radii of conductive live parts should not become sharper, etc.

 

[electricuwe]

Test for corona (also called partial discharge) a few seconds. The partial discharge extiction voltage has to be 1,2 times higher than the rated voltage. Search appobiate standard for exact description of that test.

An insulation containing any organic material (paper, all kind of plastic) will not last on the long run if there is partial discharge.

Partial discharge will destroy any of these material generating carbon and/or acids.

 

[CarlPugh]

Is connector to be used for AC or DC?

Following is for AC 60 hertz.
At 5kv, usually either you have corona or you don't have corona.
It is unlikely that the connector would be able to withstand corona at 60 hertz for 10 years.
The connector should be tested for corona at the worst case of voltage, temperature and altitude. (Highest voltage + safety factor, highest temperature, and highest altitude)

I have had excellent results testing transformers for corona using:
Corona free high voltage source (0 to 10kv)
Low cost oscilloscope (If test setup is not correct, oscilloscope can be damaged)
Circuit per MIL-PRF-27F(This is fairly simple and low cost)

 

[jbartos]

Comment: Normally, properly designed electrical hardware or electrical equipment/installation should not experience a corona under normal operating conditions.
Reference:
C.L. Wadhwa, "Electrical Power Systems," John Wiley & Sons, 1991,
Chapter 6 Corona, pages 135 ...