Transformer drying/oil treatment

Any increasing water content in the solid insulation of oil-paper insulation systems speeds up the chemical ageing process. The mechanical strength of this system is low, which means that the transformer is more susceptible to mechanical stresses such as those that occur in the event of network short circuits.

Two methods are currently favoured:

  • Low frequency heating (LFH) vacuum drying technology

This method of drying solid insulation is a combination of vacuum drying and the low-frequency heating of windings. The live part is heated by feeding low current (<1 Hz) into high-voltage windings while short circuiting the low voltage winding.

  • Vapour phase technique

This method includes the currently most effective drying process for the active parts of power transformers. The entire drying process takes place in a special plant design, in a vacuum and using a solvent. In this process,
careful consideration must be given to the relationship between vacuum, steam pressure and temperature.