Oil to oil bushings

[stevenal]

A bushing on a '74 Westinghouse faulted recently. The transformer is fed from a 69kV underground line. An oil filled compartment attached to the transformer houses the cable terminations and the exterior portions of the oil to oil bushings. I cannot find a record of any pf testing on the bushings, and would not know what's acceptable since I don't see any nameplates. Anyone have experience with these bushings? Are they pf testable? Acceptable values? Failure prone with age?

 

[thermionic1]

If your company has a service agreement with Doble, they would likely have this type of data readily available. You probably need a little more info than '74 Westinghouse. I think type O or O+C might be something similar. I'd check with your maintenance department. We have a special crew we call the Doble crew. If you are leasing a test set, you have the agreement. If you have the agreement and the SW for testing, you can look up from the test computer.

 

[stevenal]

The drawing says Condenser bushing 464C969. It is made up of wraps of copper foil and craft paper with no porcelain (so no shrapnel to take out the porcelain terminations). This is the first time our present crew has opened the termination housing. Our test equipment is Omicron, so no Doble contract. Perhaps someone with such a contract would be willing to share a few key points?

 

[prc]

Please check whether the bushing has a test tap ( a terminal insulated from the flange in a small covered terminal box on the mounting flange). If available you can check. Otherwise not possible. Since there is no porcelain covering, please keep the bushing covered to avoid moisture entry and consequent damage.

 

[stevenal]

No test taps. We'll be replacing all three for good measure, so not too worried about moisture affecting the old ones.

 

[stevenal]

I'm beginning to think moisture was the problem. I can find no records of the termination compartment oil ever being tested. The compartment appears to be a sealed design, but the top access panel is in the gas space. Any leakage past the gasket would go unnoticed, and moisture in the oil would likely make into the bushing paper. The replacement bushings will be cycloaliphatic epoxy, so oil contaminants should not enter them. Regardless, we will begin oil testing once repairs are complete.