Research on corona characteristics and type selection of fittings in extra high voltage alternating current substation

In order to eliminate the energy loss and electromagnetic interference caused by corona discharge, the size selection and design of fittings under different voltage levels and different altitudes are studied in this paper. The corona discharge phenomena of several extra high voltage (EHV) alternating current (AC) substations are observed by ultraviolet (UV) imager. It is found that the areas with serious corona discharge in EHV AC substations are mainly concentrated on the shielding ring of terminal insulator string and shielding ball of conductor. The electric field calculation model is established for two typical fittings with serious corona discharge in COMSOL multiphysics software, and the distribution of electric field intensity on the surface of different sizes of fittings under the voltage level of 500 kV and 750 kV is calculated based on the finite element method. The results show that the maximum electric field intensity (MEFI) on the surface of the shielding ring of the terminal insulator string appears at the connection between the arc and the straight line of the shielding ring; the MEFI on the surface of the shielding ball appears in the ball head. Compare the numerical values of the corona onset field intensity (COFI) of the fittings at different sizes and altitudes calculated by using the physical calculation model of the COFI, so as to determine the size selection of the fittings at different altitudes and different voltage levels. The corona onset tests of fittings carried out in low altitude areas and high altitude areas verify the applicability of the size selection design of fittings at different altitudes and different voltage levels. The results show that the size selection design of fittings for 500 kV high altitude substation shall refer to the size selection of fittings for 750 kV plain substation.