Optimizing characteristics in mineral insulating oil used in high power transformers

The most commonly used insulating liquid in transformers is mineral oil. Special synthetic applications such as silicone, ester, perchloroethylene, etc. are used today in special applications, with different characteristics, very low or nonexistent toxicity to mineral oils used in transformers. On the other hand, they have a much better biodegradability than mineral oils in both aerobic and anaerobic conditions. But they cannot directly replace the mineral oil in operation or in repaired units. They have dielectric properties and good heat transfer but have limited their use to special transformers due to the relatively high cost and availability.