Seals are important element to prevent transformer oil leakage in oil-immersed transformers. The performance of the sealing rubber will change in the transformer oil

which may lead to leakage. In order to study the swelling characteristics of the sealing materials in transformer oil

the nitrile rubber and fluorinerubber

which are commonly used in transformers

are selected for swelling experiment and de-swelling test. The weight

volume

hardness and mechanical properties of the sealing material after swelling and de-swelling are tested and analyzed. The thermal analyzer and scanning electron microscope are used to analyze the sealing material before and after swelling and after de-swelling. The conclusion is drawn through the experiment: the nitrile butadiene rubber is more invaded by the transformer oil

and the transformer oil has a strong extraction effect on the fillers

additives

and small molecular groups in the nitrile butadiene rubber

resulting in irreversible reduction of weight

volume and hardness. The mechanical properties are also significantly reduced. The invasion of oil contents has a great impact on the properties and chemical structure of nitrile rubber. The weight and volume of fluorine rubber in transformer oil increase slightly

but generally remains unchanged

and the increased weight and volume can be recovered through de-swelling test. Its mechanical properties

chemical structure and composition remain basically unchanged

which show a good oil resistance performance.