Moisture-proof is an important measure to ensure the safety of outdoor electrical equipment. In addition to the advanced humidity control measures such as temperature and humidity control device and moisture-proof monitoring system, a new type of environmental friendly moisture-proof sealing material -- moisture-proof and fire-proof sealant, is increasingly used for outdoor padmount transformer, cable box, outdoor terminal of substation and other common outdoor electrical equipment.

This paste-like sealing material, which is composed of basic glue, filler, curing agent and other auxiliaries, can be quickly solidified into elastic rubber material by using polymer mixing technology. It can fully seal the bottom gap of electrical equipment and play the role of moisture-proof, fire-proof and dust-proof. Its good moisture resistance can effectively reduce the water vapor permeation into electrical equipment in high humidity outdoor environment, and prevent the internal circuit from short, metal rusting and other safety threats.

However, there is still no relevant in-depth study on its moisture-proof effect, and lack of industrial standards. Researchers and developers have no effective method to quantitatively analyze its moisture-proof effect beside long-term observation and comparison. In this paper, referring to the water vapor permeability test method of plastic film and thin film, we demonstrate a test and verification method of moisture resistance of moisture-proof sealant.

The test object is a sample provided by an enterprise. The testing equipment is Labthink W3/060 water vapor permeability test system. The test is based on GB/T1037 "Water vapor permeability test method for plastic film and sheet". Cup method, also known as gravimetric method, is based on the principle of calculating the water vapor permeability of the sample by measuring the change of the mass of the test cup with the permeation time. The water vapor permeability of sealant with different formulations is different. Therefore, the moisture barrier properties of the sealant can be objectively evaluated through the test and analysis, so as to make the moisture-proof performance of outdoor electrical equipment more predictable.

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