High Voltage Bushing Failure Cause Analysis

For high-voltage bushings, particularly oil-paper capacitor bushings, due to their complex structure, long maintenance cycles, and high maintenance difficulty, it is crucial to promptly inspect and maintain oil-paper capacitor bushings to minimize and eliminate bushing-related incidents.

By analyzing past bushing failures, the following primary causes of failure have been identified:

1. When dirt on the bushing surface absorbs moisture, it reduces insulation resistance, leading to flashover and tripping. Flashover can also damage the bushing surface. When dirt absorbs moisture, its conductivity increases, not only causing surface flashover but also potentially increasing leakage current, causing the insulating bushing to overheat and damaging the porcelain material, or even causing breakdown.

2. Due to failed sealant gasket sealing, poor sealing at the top of oil-paper capacitor-type insulators may allow water ingress, causing insulation breakdown. Poor sealing at the bottom may cause oil leakage, leading to a drop in oil level. The primary causes of sealant gasket failure are twofold: first, insufficient tightening force due to inexperienced maintenance personnel; second, prolonged operation beyond the recommended cycle or defects in the sealant gasket quality. Other issues, such as faults in the grounding small bushings, can cause the end screen of the bushing to develop a floating potential, leading to partial discharge.

3. The bushing itself has an unreasonable structure and defects.

4. Additionally, contamination of the bushing oil level window makes it difficult to see the oil level, leading to oil deficiency after annual pretest sampling.

5. Human factors. For example, during major repairs of the bushing, incomplete vacuuming leaves residual air between the screens. Under the influence of a high electric field during operation, this can cause partial discharge, and even insulation breakdown, leading to accidents.

6. The structure of the bushing head is improperly installed. For example, the wire terminals do not make tight contact with the rain cap; the rain cap does not make tight contact with the terminal lugs; or the terminal lugs do not make good contact with the terminal board, resulting in increased contact resistance and overheating of the wire terminals.