Why are underground transformers and their bushings hermetically sealed?

Underground transformers and their bushings are hermetically sealed primarily to guard against moisture damage. Moisture can cause corrosion and deterioration of the internal components, which can lead to insulation breakdown and ultimately result in transformer failure. By sealing these transformers, manufacturers prevent water ingress and maintain the integrity of the insulating materials. This is especially important in underground installations where access for maintenance is more limited and environmental conditions can be more challenging.

Although electrical leakage insulation and enhancing thermal conductivity are important factors in transformer design, the primary reason for hermetically sealing the units is to protect them from moisture. Noise pollution reduction is not relevant to the sealing of underground transformers, as their operation is typically designed to minimize noise in residential and urban environments regardless of hermetic sealing. Thus, sealing is essential for ensuring reliability and longevity in their operational environment.