Oil Monitoring in High Voltage Transformers

Transformer oil has several functions

  • Insulates against voltage breaks
  • Prevents corrosion
  • Dissipates heat
  • Protects insulation
  • Reduces noise

Therefore, we need:

  • Aging resistance
  • Low coefficient tan δ
  • Suitable viscosity at low temperatures
  • Good corrosion prevention properties

It is necessary to monitor four important parameters:

  • Breakdown voltage
  • Tan δ
  • Water content in insulating oil
  • Temperature
The course of the transformer oil degradation process can be measured by available devices only in the advanced state of aging. The OilSens® instrument enables reliable measurement of changes in the properties of transformer oil throughout its use. The measurement is provided by three circular electrodes which are immersed in oil. Electrodes are used to measure electrical conductivity, relative permittivity and temperature. The conductivity is characterized by a breakdown voltage and, together with the permittivity, allows the calculation of the water content.
The sensor is equipped with a self-learning adaptive interpretation algorithm due to the correlation of the conductivity and permittivity with the oil temperature.
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The model allows calculation of temperature compensated permittivity and also the calculation of breakdown voltage. The most important application is the process of oil regeneration in large transformers, which can take several weeks. The state of regeneration can be monitored remotely, e.g. via mobile phone. The use of the OilSens® device allows to increase the efficiency of the regeneration process and thus the reliability.