Oil Circuit Breaker Di-electric Results 3

[lgc]

I'm wondering if anyone can assist. I'm looking for typical di-electric test results for 11KV OCB oil. I am situated in Australia, and have checked the relevant standard, which provides good info for testing technique and equipment but nothing in regard to what breakdown voltage levels would be expected for used OCB oil.

Any help would be much appreciated.

 

[edison123]

BDV for oil for 11 KV should be more than 30 KV with 2.5 mm gap setting.

 

[lgc]

Thanks, thats what I need to know

 

[cuky2000]

Appear that there is a diversity of practices for testing oil dielectric breakdown voltage (DBV) applicable to oil circuit breakers (OCB) that could vary in a wide range from 16 kV to 40 kV.

The IEEE Std C57-106 suggest a DBV> 25 kV for aged oil circuit breaker in service measured using ASTM Std D 877. This standard consisting of disk electrode system of 25 mm diameter square-edged disks separated by 2.5 mm. For reference see column 9 on the enclose table

http://www.nttworldwide.com/docs/nttdiag.pdf.

Similarly the Western Area Power Administration use 25 kV as described on page 6 of the enclose publication

http://www.wapa.gov/rm/psmmCHAP-07.pdf

On the other hand, the standard practice of the US Department of Interior- Bureau of Reclamation use a DBV> 20 kV for oil circuit breaker. They also recognize that some manufacturer's instructions even allow 16 kV. See page 6 in the enclose site

http://www.usbr.gov/power/data/fist/fist3_16/fist3-16.pdf

Beware that oil is not necessarily in good condition even when the dielectric strength is OK because this do not count for carbon, acids, gases and metal particles in the oil.

There are other supplementary tests used to diagnostic OCB conditions such as DISSOLVED GASES IN OIL, PARTICLE COUNT, PARTICLE TYPE AND OIL QUALITY. For additional reference, consult NETA, Doble Test or similar organizations.

 

[ausphil]

You may want to try AS1883:1992. It gives a guide to the maintenance and supervision of insulating oils that are in service. Table 2 at the rear gives quite detailed explainations on all oil test results (ie water content, IFT, acidity, DDF etc) for various equipment types and voltages.

20kV should do you as a good start.

 

[lgc]

Thanks Cuky2000 and ausphil for your replies. All great info. I have checked out AS1883, and that seems to be the best reference for my purposes.

 

[snowytec]

Oil testing of CBs appears to be a dying trend in Aussie. It does depend on the oil quantity of course. Many companies dealing with CB oil quanitities of just 50litres will prefer to just clean the oil tank and change the oil. The reasoning behind this is simply the cost to remove the CB from service, the time to 'get at' the oil, the cost of the oil (yes, increasing from a $1 to $2.50 this year) all have an impact. Some companies that may have up to 4000 of these 50litre jobs may do random sample testing just to keep an eye on trends. Otherwise, all the oil goes back to reconditioning. But, oh yes, the new oil will be tested before use.