A model for calculating thickness and surface conductivity of water film on an inclined insulator string

It is well known that the presence of a highly conductive water film over ice-covered insulator is a prerequisite to form local violet arcs across air gaps. This paper develops a model for calculation the thickness and surface conductivity of the water film formed over ice-covered insulators due to Joule heating effect. Different conductivities for water film layers are considered in the model mainly due to the rejection of impurities to the ice surface during the solidification process. The continuity equation and the Navier-Stokes equations of motion for the water film flowing down an inclined insulator string due to gravity are used to obtain the velocity distribution. Water film thickness of and ice layer melting time are determined by taking into account the heat flux at the inclined plane due to the viscous dissipation and Joule heating and by assuming a quasi-steady-state model. As well, the influence of angle of inclination on thickness and surface conductivity of water film was studied. The model is integrated with a static arc model for flashover voltage prediction to improve its capability to be used for inclined insulator strings and its accuracy compared to present models.