China's UHV power grid includes UHV AC transmission and DC transmission, with AC of 1000 kV and DC of ± 800 kV. According to the characteristics of China's future power flow direction and load center distribution, as well as the characteristics of UHV AC transmission and UHV DC transmission, in China's UHV power grid construction, 1000 kV AC UHV transmission will be the main form of national UHV backbone grid, so as to realize the synchronous strong interconnection of major regional power grids; The ± 800 kV HVDC transmission is mainly used for long-distance high-power transmission projects with no impact point in the middle and no voltage support. When the voltage on the wire and fittings is very high, the potential gradient on the surface exceeds the critical value, and the visible corona will occur.

　　The air on its surface is ionized under the high potential gradient, giving off blue light and sound, which is the phenomenon of corona discharge. The harm of corona, first of all, is the consumption of energy, resulting in power loss. Secondly, corona will produce radio interference, which is strong at 0.51.5mhz. In order to control the corona and reduce its harm, it is particularly important to install this kind of protective hardware on the line. Fittings, including clamps, hanging plates, bolts, etc., are parts with edges and corners. For lines above 220kV, the high potential gradient at the tip of fittings will produce strong corona without shielding ring.

　　Equalizing and shielding fittings are common electrical protection fittings, including equalizing ring and shielding ring. At present, the grading shield ring of conductor tension insulator string of 500kV transmission line in China generally adopts ear ring. This kind of ear ring is generally set beside insulator tension string and fittings including clamp, hanging plate, bolt, etc., which has both grading and shielding effect. Therefore, it is called grading shield ring. When ring or runway type grading ring is used in UHV transmission line, because ring or runway type grading ring can only grading tension insulator string, it can not shield corona for fittings in UHV transmission line at the same time. Therefore, it is necessary to set a separate shielding ring to shield the fittings in UHV transmission line.

　　In overhead line engineering, UHV shielding parts protect insulators and line fittings to control the visible corona caused by high voltage. With the economic development and the improvement of domestic voltage level, more and more attention has been paid to the harm of corona. The role of grading shield ring can not be underestimated. Grading shield ring, shielding ring and grading shield ring used in China are made of pure aluminum. The support frame and ring body are welded together and connected to the corresponding shielded body by fasteners. In the engineering use, the welding workload is large, and the cases of unqualified strength due to the defects of welding points appear repeatedly. There are huge potential safety hazards and serious economic losses.