SI fabricated a mock up and developed an inspection procedure utilizing an L-wave technique for detecting liquid inside the brace from the outside. The procedure was simplified to a pass-fail method. After successful laboratory demonstration at a utility facility, field tests were initiated. When liquid was detected, holes were drilled in the braces and samples were drawn and tested. Several braces were determined to contain higher than desired PCB levels.
Oil is used in transformers primarily as an insulating and damping medium.
The transformer that failed was not known to contain high levels of PCB's. Its oil had been tested several times and found to be within acceptable levels. This was done after the unit failed to meet the guaranteed sound level. The utility had not been informed the beams had been PCB filled. During manufacture, a vacuum is pulled on the transformer tank for oil filling.