Articles techniques et présentations

A suspension composite insulator has been designed for the HVDC energization of an overhead line supported by the L7 tower of Scottish and Southern Energy (SSE). It has been chosen to apply a pole to ground voltage of 216 kV for a triple symmetrical bipolar scheme. To verify the feasibility of the design, it has been necessary to study the possible corona effect and pollution accumulation areas on the insulator. Thus, with the use of COMSOL Multiphysics^®, a voltage gradient investigation has been conducted along the object profile.

To achieve the results in a reasonable time, the model has been simplified by representing the tower core as a smooth full metallic element. A simulation has proven that the same type of simplification could not be applied to the metallic cross arms of the tower without losing a good level of results accuracy. For this reason, these have not been simplified.

The available computational power has allowed to compute only a portion of energized line. To do so, the AC/DC and CAD Import Modules have been used balancing the trade-off between time and accuracy of the simulation. In fact, the described techniques are addressed to those approaching this trade-off for overhead line insulation simulations.

The results suggest the corona effect would occur at the insulator ends, because the electric field is locally higher than the dielectric strength of air. Also, the recursive pattern of electric field magnitude along the insulator creepage path has allowed to identify the regions where the risk of pollution accumulation is higher.

Thus, the deployment of corona rings or alternative solutions are needed to alleviate the insulators present electric stress which would otherwise significantly reduce their lifetime. Therefore, this work demonstrated the need to verify the voltage gradient along a newly designed insulator surface.