Michael Kempf M.Sc.

Behavior of water droplets under the influence of electric fields


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The impurity of an insulator surface significantly influences its insulation properties and can lead to a failure of the insulator. To reduce the impurity more and more insulators are made out of silicone instead of porcelain. One of the main benefits of such insulators is the hydrophobicity of the insulator surface as well as the flexibility in the manufacturing process. Due to the hydrophobicity the development of a liquid layer, which would increase the conductivity of the surface, is inhibited. The surface properties of the insulator are mainly influenced by the aging process of the material. Therefore, the aging of the material and the influencing factors have to be investigated.

Water droplets on an insulator surface.
Experimental setup for the investigation of water droplets under the influence of electric fields.

Both, the hydrophobicity and sessile droplets on the surface, influence the aging of the insulator material. The sessile drop on the surface leads to an enhancement of the electric field near the triple line between water, air and the insulator. This enhancement can cause partial discharges, which can provoke a damage of the insulator surface and finally can result in the loss of the hydrophobicity.

In the scope of the Collaborative Research Center Transregio 75 (SFB-TRR 75) “Droplet Dynamics Under Extreme Ambient Conditions” the properties and the behavior of water droplets under the influence of high electric fields is investigated to improve the understanding of the mechanisms and the influencing factors as well as the forecast of the aging process.

In addition, the nucleation of water droplets under the influence of high electrical fields is investigated. The icing of high-voltage transmission lines or insulators are critical, especially in cold regions. Accreted ice on the transmission lines can lead to an unbalanced load of the pylons or can initiate an oscillation of the transmission line. Due to the additional load the maximum load of the pylon can be exceeded, which would result in a pylon collapse. Furthermore, the icing of insulators can cause a functional failure of the insulator. Consequently, the icing of transmission lines and insulators influences the reliability of the energy supply.

To improve the understanding of the main mechanisms of the icing under the influence of electric fields, several experiments are performed in the scope of the SFB-TRR 75 project in collaboration with the Institute of Fluid Mechanics and Aerodynamics.

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