Evaluation of temperature rise in continuously loaded distribution earthing electrodes

This paper examines the relationship of current densities and temperature rise in continuously loaded earth electrodes as may be applied in Single Wire Earth Return (SWER) systems. The existing design practice for electrodes has been based on some fundamental calculations related to resistance and voltage rise and industrial experience. There is no comprehensive design method that relates the intensity of the electrode loading and the service life. An analytical model of a hemispherical electrode is established. The temperature rise is proportional to the soil thermal resistivity and electrical resistivity and the square of the electrode current. The final temperature will largely determine the loss of soil moisture which is a major factor in the failure of electrodes. The analytical model provides guidance as to current densities that are likely to result in long electrode lifetimes.