Behavior of water droplets on polymeric insulation surfaces under hybrid field stress

Corona discharges caused by water droplets on the surface of polymeric insulators can affect the long-term reliability of the component by lowering the surface hydrophobicity encouraging surface discharges. It is well-known that droplet-initiated discharges behave differently under AC and DC field stress affecting the hydrophobicity of polymeric outdoor insulation materials. The presented investigations study the effect of hybrid field stress on partial discharges at singular water droplets. The behavior differs depending on the direction of the electric field as also known for uniform AC or DC fields. Tangential oriented field stress is more critical to aging phenomena due to a significantly lower pd inception level. By high speed analysis of the droplet deformation the oscillation frequency is linked to the acting electrostatic forces depending on the AC and DC component of the excitatory electric field. Thus, the mechanical oscillation model is extended for hybrid field stress.