Are shielding electrodes necessary for HVDC line insulators?

Summary

Shielding electrodes may be essential in AC to mitigate the voltage drops/electric field on the insulators, especially on the insulator section line side. Grading electrodes are important in AC to limit radio interference for cap and pin insulator strings and are even more important for composite insulators to avoid localized critical electric field strength condition . The situation is different in DC where the voltage distribution is generally dominated by resistive currents both in clean and contaminated conditions. Electric field calculation are reported of the electric field distribution along composite insulators showing that in practical service conditions shielding electrodes would not have any capacity to control the voltage distribution. On the basis of the study the need of shielding electrodes for DC lines is discussed, taking into account all the functions shielding electrodes have to cover (local corona prevention, grading function, power arc protection function).

Additional informations

Authors

NEMETH, LAFLAMME

Keywords

HVDC, line insulators, shielding electrodes, electric field