Not all transformer oil contains PCB's. In fact, NONE do now thanks to Congress, the EPA, and TSCA Act. (See 40 CFR Part 761. At one time, I had most of it memorized) Most electrical equipment, until the 60's were filled with plain mineral oil. Inexpensive distillate of coal oil, easy to get, however, quite flammable. PCB's were developed for fire prevention measures because PCB's are self extinguishing, meaning someone finally came up with a transformer that wasn't full of flammable liquid (mineral oil). It was the best thing since shirt pockets because transformers could now be installed indoors closer to where lower voltage power was needed, and less expensive cabling and bus requirements were called for, meaning reduced installation cost. Unfortunately, while burning at normal temperatures and putting itself out, PCB fluid also releases difurins and dioxins, the same stuff in the defoliant used in Vietnam, Agent Orange. That was the bad part. Otherwise, the worst effect on humans by actual PCBs is chloracne (zits caused by the PCBs). The benzene solvent was far worse than the PCBs. Benzene will give you chemical burns worse than gasoline, especially while it's hot. Just the vapors from benzene are very irritating to skin. I used do the insulating oil sampling and testing in a paper mill that had 159 transformers, most of which were PCB filled, some that were contaminated, and very few that were clean mineral oil. Some of the samples I drew I can remember being at 80 degrees Celsius. I had one sample explode in my hands because the oil was too hot and stressed the glass sample bottle. Luckily, I had on safety glasses and gloves. I've been up to my elbows in Pyranol while working on transformers, and suffer NONE of the symptoms attributed to PCB exposures. Look up Pyranol and Inerteen and Wecosol. Wonderful stuff. But the effects stated are greatly exaggerated.
PCB's are the ONLY substance ever declared toxic by Congress. EVER. That sort of declaration is normally the jurisdiction of the FDA or EPA. The EPA set up rules for getting rid of it because Congress made it impossible for them not to. Strangely enough, railroads were exempt from most of the rules for a very long time. The Railroads had lobbyists just as good as the ones that worked for major electrical manufacturers of the time, and the economy was also suffering in the mid-80's. I won't say that transformer manufacturers had any influence over the decisions of Congress, but they sure as heck made a lot of money on those decisions. The Railroads survived the slump because the didn't have to reinvest in their prime movers (locomotives) and distribution equipment. They did, however, immediately change the treatment process for wood products used in rail construction to eliminate PCBs. I helped GE make a bunch of money on the decommissioning, disposal, and recommissioning of new equipment, and my final reward for my efforts was being sold like a piece of used farm equipment after 27 years of service. That's a whole other story though. BILLIONS of dollars were made for getting rid of transformers, and GE got a big head start on all the competition. Some of the equipment that was decommissioned was sold by GE less than 20 years before. A lot of customers wound up with one transformer for the price of three. The price to get rid of one was nearly twice the cost of a new one. there was a demand, and GE had the answers. Customers had no choice other than to close the site, and they'd STILL have to pay for the mitigation. GE got paid a lot of money thanks to one ruling by Congress, and industry footed the bill for it. However, GE spent most of what they made cleaning the Hudson River, Pittsfield, Massachusetts, and Rome, Georgia, as well as nearly every service shop that ever did any service work on liquid filled equipment. The dredging operation on the Hudson is STILL going on. I'll give you three guesses how industry recouped their money, and the first two don't count. There was another exclusion from the rules. Manufacturers of carbonless forms (the type the Government uses more than anyone else) were still allowed to produce it and use it in their process. Every sheet of paper except the top copy of carbonless forms is PCB contaminated.
There have been a lot of experiments with transformer insulation liquid since the PCB debacle. The most promising, while not the most cost efficient, is silicone based fluids which are fire retardant as well, making them very good indoor units. That fluid is a variant of the stuff used in fake boobies. However, it is expensive to produce, ergo, more expensive to buy, and harder to get with the breast enhancement craze. You can make a lot of very expensive breast implants with the amount of silicone fluid it takes to fill a transformer of any significant size. Freon has also been used because it's electrical properties and fire resistant properties are good for indoor units. One of the features of Freon filled units is they are quite a bit smaller because of the heat transfer characteristics of liquid Freon. This is quite a cost saving in copper and iron requirements, but the fluid costs offset any savings by quite a bit. Well, the transformer is relatively small, but the radiators are ENORMOUS compared those used for other insulation liquids. The largest problem is that transformers get hot and cold and eventually start leaking. Leaking Freon is probably a much greater problem than PCB's, if you ask Climate Change proponents. The stuff produced when a failure does occur isn't very nice either. Then someone decided to try SF6, sulfur hexaflouride gas. That was very short lived, also for very good reason. The trend now is that industries are trying to design their facilities so that the transformers are all outside, thus eliminating the fire risks associated with flammable mineral oil because it's so much less expensive than alternative insulation liquids. We have come full circle.
Then, along comes the NFPA. Don't get me started on Arc Flash mitigation. However, the PCB business in the 80's and Arc Flash Mitigation in the last 20 years paid a lot of my salary. I much preferred automation and controls work, though.
