Ultrasound application on switchgear

[matt77]

We have been performing IR and ultrasound inspection on 22/11 kV switchgears. We would like to talk to people who have experience on ultrasound scanning. How do you determine the criticality of the equipment, say you got dB of 32 at 40kHz. how critical is the equipment? What if you got 0 dB but audible hissing sound. Is there any need to reduce the frequency? Is there any standard on decibel limit on switchgear....?looking forward to your response.....
thank you.

 

[alehman]

I'm not sure if there are any definitive numbers for this. I have no experience with ultrasound, but here are some links that might be helpful as a starting point.

http://www.mt-online.com/current/3-97ultra.html

http://www.corona-technology-course.com/forum/

http://www.tibsgroup.com/press/White Papers/Detection of Partial Discharges....html

The following quote is from the last link -
Although the ability to gauge intensity and view sonic patterns is important, it is equally important to be able to "hear" the ultrasounds produced by various equipment. That is precisely what makes these instruments so popular. They allow inspectors to confirm a diagnosis on the spot by being able to clearly discriminate among various equipment sounds.

This is accomplished in most ultrasonic translators by an electronic process called "heterodyning" that accurately converts the ultrasounds sensed by the instrument into the audible range where users can hear and recognize them through headphones.

 

[jbartos]

Suggestion: The ultrasound hardware manufacturer may contacted for more information since the ultrasound scanning results may somewhat vary from the ultrasound hardware manufacturer to manufacturer. Also, there may be need for the scanning equipment calibration.
Visit

http://www.mt-online.com/current/05-98ml.html

http://www.sdt.be/03applications/acorona.html

http://www.usgweb.com/Power.htm#Ultrasonic

etc. for more info

 

[DanDel]

Any audible hissing sound would be indicative of corona and/or leakage bordering on tracking across insulators or bushings. I am not familiar with ultrasound testing either, but I would schedule a shutdown and attempt to find the source of the sound by inspecting insulators or by hipot testing. I would then repair or replace any defective insulators and clean the entire gear.

 

[alehman]

I think a partial discharge sensor might be more senstive.

 

[UKEng]

I have not used this this method myself but have heard from other Engineers who use this as part of their routine maintenance. Apparently it is no use at lower voltages but is useful at voltages of 3.3kv and above. The benefit is that it is non-intrusive and gives a good indication of partial discharge. I think the readings are relative and once you have a 'bench-mark' then you can see if there is any degradation as time goes on. I am no expert in this and only pass on views I have heard.

regards

 

[jbartos]

Suggestion: Visit

http://www.transinor.no/transinor/products/aia/pdf/cigre.pdf

for: The partial discharge detection at a high AC voltage level is the most effective method.

 

[hy]

The Transinor equipment mentioned above is for HV GIS and MV cable terminal Partial Detection.

Similar to the used for Transformers (different frequency sensors).

These ultrasonic and acoustic methods depends very much in the operators skill and experience, for the noises in a substation.
In GIS and transformers is used for finding the location, once it is detected a PD (by IEC 270 method for example).