A brief on Transformer Oil Filtration.
Working in the Indian transformer service industry I have observed that transformer oil and it's maintenance is undervalued in the industry and overlooked by many professionals. I wanted to shed some light on the same and want to bring to the attention of curious engineers, a very well written thesis by B.Sc students I found online while trying to educate myself on the topic.
The thesis not only explains as to how transformer failure relates to degradation and non maintenance of transformer oil but also urges us to be responsible with the same as it is non biodegradable. The only way to be efficient with transformer oil is by getting it filtered properly and periodical.
I have attached the thesis at the end and below is the conclusion :-
Following the fact that all the heating procedures results in the production of a toxic gas, we conclude that there was the actual loss of chemical structure and significant breakage of chemical bonds. The resulting chemical composition of the oil does not produce the same effect as the initial oil sample. There is, in effect, a reasonable point to conclude that; viewing the interesting trends we got from our graphs, and considering the already‐proven scientific statements on transformer oil properties, we came out with the following conclusions:
1. Aged (acidified) transformer oil has a lower breakdown voltage. It can ruin the transformer‘s smooth functioning.
2. Moisturized transformer oil has a lower breakdown voltage. Heat increases moisture solubility and soaking of the paper on the transformer windings.
3. Contaminated transformer oil can also reduce breakdown voltage by decreasing its dielectric insulation properties. We see that in the decreasing trend in the experiments with NaOH(aq).
4. Also we would not leave out commenting on the beautiful trendy graph we got from the experiment with moisturized and overheated transformer and vegetable oil. There was a remarkable decrease in the transformer oil insulation properties. This was definitely because of the breaking of bonds and formation of smaller molar mass compounds which do not have good insulation and dielectric properties. As we can see from Fig(6.2.1), we observed the formation of many bubbles when we reached high temperatures. Bubbles, which considerably decrease surface tension, are a veracious indication of the presence of impurities; in this case, moisture.
5. Arcing horn gaps can be used to prevent over‐voltages and other impulse voltage surges. 
6. Corona rings could also be used to distribute the electrical fields, preventing the protected hardware and the corona ring itself from corona. This can be used on 138Kv voltage lines or higher.
7. Most importantly, acknowledging the fact that transformer oil, despite its fantastic insulation and cooling properties, it has a major disadvantage of being highly toxic to 40 the environment, and very low biodegradability