What kind of sealing material should be chosen for oil-immersed transformers?

Choosing sealing materials that are compatible with the characteristics of transformers is crucial. Technical conditions related to sealing materials include the working medium, working pressure, and working temperature.

●Working medium

The working medium mainly involves transformer oil, air, and water. The working pressure is primarily determined by the steady-state pressure generated inside the transformer during fault conditions and the pressure applied during the sealing test (usually the test pressure of components is higher than that of the transformer body), typically ranging from 0.3 to 0.5 MPa. The working temperature is not determined by the highest temperature during the normal operation of the transformer but by the lowest ambient temperature when the transformer is stored outdoors in winter and the highest temperature during the vacuum drying process of the transformer body using the oil tank, generally ranging from -45 to 115°C.

●Sample materials

Currently, the main sealing material that meets these requirements is nitrile rubber compound. The rubber material grades include 58-421, 8143-20, B-9, and others. All physical properties of these rubber materials have passed tests, and practical use has proven their excellent sealing performance, as shown in the test data.

The performance indicators of this new rubber material are higher than those of the previously used rubber material. For example, in terms of temperature resistance, the new rubber material is rated from -59 to 120°C, whereas the old rubber material has a brittle temperature range of -24 to -40°C, with a maximum operating temperature of 70 to 85°C. Regarding the permanent deformation under constant pressure in transformer oil, the new rubber material is 50%, while the old rubber material ranges from 66% to 85%. Therefore, the new rubber material is quite suitable as the sealing material for transformers.

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