For perfect status survey of transformers, one method is absolutely recommendable: The monitoring of dielectric loss factor tan δ in the insulating oil.

With ongoing aging of the transformer, the dielectric features of the insulating oil deteriorate gradually. The dielectric loss factor tan δ, which describes the amount of dielectric losses, increases slowly and steadily.

Influences on tan δ

  • Increase of moisture in the insulating oil
  • Polar acting particles as aging products:
    • Solved insulation varnishes
    • Decomposition residuals of paper and cardboard (cellulose)
  • Temperature of oil (viscosity)

Detection of Malfunctions

However, a rapid increase indicates malfunctions that can lead to dielectric breakdown. Continuous survey of tan δ during normal transformer operation (online monitoring) helps you, the operator, recognise malfunctions early and prevent accidents.

The continuous monitoring of tan δ is the reliable and simple tool for increasing the operational safety of your transformers. 

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