Getting Xfmr Oil Samples

We have two 15KV-480V cabinet xfmrs where the analysis determined the FPB to be 21FT and the IE to be 95Cal/cm2 @ 1-1/2Ft from the xfmr secondary. The oil sample tap is located about 2ft below the transformer secondary bushings. Future plan is to have this tap routed to the outside of the enclosure.

Is there any safe way to get oil samples from the transformer other than shutting the power off?

Thanks

When I was doing these as a NETA tech I found this the hardest thing to deal with when the 2000 70E came out. Shut it down until you get the external tap installed. There are several companies with kits to do the external samples.

Funny how no one ever considered the arc flash hazard of this task the last 100 years.

How does oil sampling qualify as an interaction like to cause an arc at the bushings two feet away?

I would say that this is similar to "Perform infrared thermography and other non-contact inspections outside the Restricted Approach Boundary" for 600V switchboards in Table 130.7(C)(9) which has HRC 1. This implies that it is an interaction that might cause an arc flash hazard.

Oh yes, many times you need to wrestle the cables around to get your sampling equipment hooked up.

Our electricans are trained to wear the proper Arc-flash PPE once the FPB is crossed and there is exposed energized conductors. For these xfmrs it would require them to wear 100Cal/cm2 clothing once the door was opened which is not advisable. If I used the table wouldn't I be ignoring the Hazard?

How are others doing this task?

Thanks for all the comments

Once you have done the calcs, you can't or should not back up and use the tables since you would be ignoring the hazard as you say. Why not schedule the sample when you can get some down time on the unit?

Is the 21 ft and 95 cal a result of available current, or clearing time?

If it is available fault duty, the blast just might move them out of the boundary before anything clears.

This is a result of clearing time. Clearing time is limited at 2.0Sec, Available fault is about 40KA on one of them. One thing I did notice is that the SKM software is using 25mm as the gap. I think the actual gap is closer to 6". I will see what this looks like with a larger gap.

I ran the calc's on this xfmr with different gaps using SKM software. Here is the info:

Gap 25mm, IE 94 Cal/cm2 @ 18", FPB 21'-6"
Gap 153mm (6"), IE 45 Cal/cm2 @ 18", FPB 13'-7"
Gap 229mm (9"), IE 9.1 Cal/cm2 @ 18", FPB 4'-2" (Used Lee Equation)

Would it be safe to use EI and the FPB based on the actual gap or is there some reason why I should leave the gap at 25mm? I think the actual gap is between 6 and 12 inches.

Thanks

6" bushing gap is pretty typical on the secondary side for this size xfmr. I would be more worried about electrocution if the oil tap is 2 feet from the bushing.

2 ft is greater than the restricted approach boundary and less than the limited approach boundary. Worker must be qualified.

I know this guy working for an oil testing firm that was in San Francisco pulling a sample from a 3000KVA unit and the way the cable loop was done by a contractor to the busway that when the tester pushed the cables back it created what people standing away from him said he turn into a large ball of fire. He was glad to be wearing his full suit but still sore. Apprently, the cables had a worn spot due to the way the wiring was installed. I believe this went to ground but not sure of the final analysis. There was some legal stuff involved after that. Long story.

I was like you; normally the hazard risk to taking an oil sample would be not so complicated. But I suppose there are a lot of bad installations.