6.9kV Overhead Line Insulator Test Methods

[devin07]

Hi,
Looking for test methods to determine integrity of porcelain/ceramic insulators on a 6.9kV overhead line - without de-energizing the line. I've looked at both thermography and ultrasound, but understand their results may vary, especially at 6.9kV. Anyone have experience with either of these tests at 6.9kV? I also didn't see anything in ANSI C29.1-1988 (R2002) Test Methods for Electrical Power Insulators. Other than de-energizing the line and performing a ring test, is there anything more scientific? Last resort would be to perform a visual with binoculars, but again not really the most scientific...
Thanks,
Devin

 

[cuky2000]

Did you considered the cost of the test vs. the cost of using a new insulator already tested by the manufacturer?

 

[devin07]

Actually, we have replacement insulators already, but we're looking to postpone replacement until early next year. Trying to determine if postponing the replacement is an 'acceptable risk'.

 

[jghrist]

Transmission line insulators are sometimes inspected visually, but distribution line insulators are usually just left in service unless they fail. They don't fail very often. What makes you doubt their integrity?

 

[Zogzog]

Have you looked at doing inspections with a Corona camera? We do these for co-ops from a helicopter, or if you only have a few you can do ground based inspections.

 

[devin07]

jghrist: One already failed, the reason we started looking at their replacement. Also, since one has failed, is that valid reason to look at replacing them all? Your thoughts?

Zogzog: I understood corona inspections were ultrasound based and at lower voltages, corona is that much more difficult to detect. Have you experience with corona detection at 6.9kV? I'll certainly look into it if it'll work.

I'm beginning to think that line insulators at 6.9kV give little or no indication of imminent failure.

 

[Marmite]

I wouldn't even think about replacing all of the insulators just because one failed, unless you can reliably put it down to a manufacturing defect common to all. You are right to say that insulators generally give little or no indication of imminent failure. Often lightning damage can cause a pin hole to develop in an insulator which causes the line to trip intermittently when it rains. It can be several weeks or months down the line before the insulator fails completely. At distribution voltages lines are patrolled and inspected from ground level using binoculars. Any insulators showing signs of chips, cracks or flashover would be replaced. Regards Marmite

 

[Zogzog]

Oops, thought I read 69kV, not 6.9kV.

Corona imaging is very effective at higher voltages, how low of a voltage it is effective is debatable for sure. 6.9kV is in that grey area, while we have seen corona in switchgear at 4160V, I can't say it is 100% accurate less than 15kV.

 

[Zogzog]

This is off a 12kV insulator

 

[gattie]

Agree with Marmite - Replacing all properly rated insulators on a 6kV line just because one failed is an overkill.
Wait for shutdown & do a visual inspection if you are still unhappy,
but I do not think you should be concerned.

 

[devin07]

Excellent advice. Thanks!

 

[Zogzog]

I agree, not much to worry about, go out there on humid days and just listen for a "sizzling bacon" sound.

 

[desrod]

This might be what your are looking for. it was developed for Hydro-Quebec.

 

[linehand]

I wouldn't worry too much about the insulators failing on 12kV.
If you have some in question it would be a good job for an apprentice to learn to change them out hot.