Insufficient Insulation Margin in 126 kV Vacuum Interrupters: How Targeted Conditioning Provides Directional Repair - Blog

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How do bottlenecks that constrain a product arise?

The 126 kV vacuum interrupter is a high-voltage product, and the breakdown voltage of its vacuum gap does not increase linearly with gap distance. Once the gap increases beyond a certain point, the breakdown voltage tends to saturate. In addition, microprotrusions on electrode surfaces, metallic particles, and surface charge accumulation on insulating supports often make insulation margin a bottleneck limiting product reliability. Although conventional overall voltage conditioning can eliminate some weak points, its energy is dispersed, and its effect on directional repair of local defects is limited.

Steps for targeted tempering

The idea of targeted conditioning is to locate first and then treat directionally.

The first step is defect localization. Through partial discharge detection, electric field simulation, and breakdown voltage statistics, weak insulation areas inside the interrupter are identified, such as shield edges, ceramic-to-metal seals, or microprotrusions on contact surfaces.

The second step is to apply conditioning stress directionally. For the located weak areas, local high voltage or low-current arcs are used for targeted conditioning, so that microprotrusions are melted flat and particles are removed or oxidized, thereby reducing local electric field distortion.

The third step is re-test verification. After conditioning, the withstand voltage level and partial discharge magnitude of the area are measured again to confirm whether the insulation margin has been restored.

Mutual coordination and complementarity

It should be noted that targeted conditioning is not a one-time permanent solution. During long-term operation of a 126 kV interrupter, contact erosion products and particles generated by mechanism operation may still re-accumulate. Therefore, the conditioning process needs to be coordinated with the electric field optimization design and particle trap structure inside the interrupter. At present, domestic 126 kV vacuum interrupters have entered the stage of engineering application, and the improvement of their insulation performance depends on the coordinated improvement of manufacturing processes and conditioning technologies. Targeted conditioning is one of the targeted technical measures.

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