PCB's were used often in transformer and capacitor oils in the old days ,
now they use an oil product called Michaelangelo which doesnt contain it .
PCBs extended the usefull life of the transformer , but the downside its a persistant polutant if it escapes into the environment ,
Theres a chance that even what looks like a wax potted transformer has some small amount of PCB added , I believe they started to phase out PCB in transformers around the late 70's , so probably most electrical utillity companies have dealt with the problem at this stage .
I worked in transformer and motor rewind place for a little while ,
The owner freely addmitted to me he could never adhere to the safety regulations properly ,
He called the bluff of the authorities , told them fine , shut me down , and see how long it takes before the captains of industry are hollering down the blower to the politicians because factories are on shut down and people are about to loose their jobs .