The corona discharge of transmission lines is one of the main reasons causing electromagnetic environmental issues. We selected practical operated lines from Shandong province of China to explore the effect of pollution grade and service year on the corona discharge of practical operated lines. Experimental results show that corona discharge becomes more serious as the service year lengthens. When the operated years are close, the general environment along the transmission lines plays an important role in electromagnetic environment degradation. Comparation of the photon number of operated lines with data obtained using corona cage improve that corona cage test can be
equivalent to the transmission line.

corona discharges;pollution grade;service year