Influence of climatic conditions in China on reliability of power earthing system

The paper is addressed to studies of earth electrodes´ corrosion occurring in different climatic conditions based on comparative results from Poland and Jiangxi province in south of China. The Polish company Galmar-manufacturer of copper coated earth electrodes and conductors started in Poland in 2003 the long-term project of field corrosion tests of earth rods made from different materials. The results of field corrosion tests of steel earth rods with zinc galvanized and copper protective coatings are analysed after exposure in two different sites in Poland after removal from soil in 2 years intervals (after 2,4 and 6 years). In year 2009 Galmar representatives visited few sites in Ghanzou (Jiangxi province) in China where was observed corrosion of earthing system 110 kV substation and 220 kV transmission line after relatively short time of service (app. 7-10 years). The examples of earth electrodes corrosion in China have been analysed and compared with the results from field test in Poland. The prediction of service life time of any kind of earthing systems, which should be usually not shorter than 20-30 or more years is difficult and usually not taken into account as the design factor. The results of long term field corrosion tests of different types of earth rods in Poland and examples of unexpected fast corrosion damages in earthing system installed in Ghanzou in China show the increasing role of corrosion aspects when designing the earthing system especially for power system installation with the aim to assure their stable parameters in expected service time.