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Essentially, a bushing is like an insulating plug for your transformer. They allow electrical current to travel safely from the cable into the transformer’s tank, preventing the outer metal structure from becoming energized. Bushings are typically constructed of molded, glazed porcelain and can use mineral oil or synthetic resin bonded paper to increase dielectric strength.


Failure modes

  • Extreme temperatures (can cause structural cracks)

  • Flashover (high temperatures, damage to porcelain)

  • Glazing defects (threatens insulation integrity)

  • Pollution (contamination on the bushing surface can reduce the dielectric strength which can lead to deterioration and eventual failure). 

  • Oil leaks

  • Partial Discharge breakdown 

Reliability considerations

  • Power factor and capacitance electrical tests

  • Partial discharge (PD) monitoring

  • IR scanning

  • Visual checks for damage

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Power factor for bushings

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