Effect of ADLash optical fibre cable on corona inception gradient and electric fields around the earth wire of the Apollo-Cahora Bassa HVDC transmission line

A high voltage direct current power line consisting of a shield wire above a square bundle of conductors is modelled using the boundary element method. This is done to plot the electric field surrounding the shield wire outer strands and the surface electric field strength. It is demonstrated that the surface gradient of the bare shield wire is close to corona inception at the rated voltage. The model is then modified to include the representation of a fibre optic cable (ADLashreg) directly in contact with the shield wire. The electric field surrounding the shield wire and its surface electric field strength its again plotted. The relative permittivity of the ADLash is higher than the surrounding air and it is seen that the electric field at the air/dielectric/earth wire interfaces is enhanced. This is likely to increase the incidence of corona on the shield wire that could cause damage to the ADLash