For AC/DC, it can be high voltage evenly distributed around the object to ensure the potential of every position around the ring consistent. The purpose of the ring is very extensive, it can be divided into; Arrester corona ring, lightning protection; Corona ring, insulator corona ring, transformer corona ring, corona ring of high voltage test equipment, power transmission line corona ring.
Meanwhile, in a lot of supporting precision measurement of electrical equipment, often used shielding corona ring, or shield ring.
The corona discharge of some grading rings is serious on 500 kV compact transmission line,due to the improper structure design and installation. In order to suppress the corona and avoid the same fault in the future,it is necessary to optimize the structure of the grading ring. Consequently,the grading rings having obvious corona discharge were found out by observing hardware fittings along lines with UVI (ultraviolet imager),then the electric field distribution of the grading rings was calculated using three-dimension FEM(finite element method). After analyzing the electric field distribution to get the causes of corona discharge,the structure of grading ring was optimized to reduce the maximum electric field intensity on its surface from 3868 V/mm to 2475 V/mm. According to the optimization proposals,new grading rings were manufactured and hung on operating lines. The observations by UVI show that the new ones have no corona discharge on their spheres and bodies which validate the optimizations. This study can provide experiences and references for the design of anti-corona hardware fittings on high voltage transmission lines
Grading rings
Grading rings reshape the electric field, reducing corona discharge on the insulator, high RIV levels, and power losses. If corona persists, it may damage the polymer material and lead to insulator failure.
Corona discharges can form on the metallic ends of an insulator when the electric-field intensity exceeds the dielectric strength of the surrounding air. Several factors that affect the onset of corona are air pressure, humidity, end fitting material, and voltage level. If the end fitting has sharp edges or is irregular in shape, corona can result from a concentration of the electric field.
The elevation at which insulator is applied is an important consideration when specifying grading rings. Tests have shown that corona extinction and inception levels decrease with increasing altitude; approximately a 1% change for every 1000 feet above sea level. However, the effect is not as significant below 3000 feet since the bulk of corona tests occur near this level. Therefore, corona extinction levels must be adjusted for applications above 3000 feet.
Grading rings are selected according to the corona extinction level. A variety of ring shapes and sizes are necessary to meet the requirements of the different voltage levels and insulator configurations. Generally, by increasing a corona rings diameter or thickness the inception level increases.
Aluminium tube rings supplying for Transmission line Insulators
1. Assembly Corona Ring outside diameter is 320mm,inner diameter is 220mm, Tube diameter is 50mm, tube Wall thickness is 2.5mm, mounting hole diameter is 18.87mm
2. Surface finish is polished bright (debur and no break sharp
edges
3. Ring body material is 1060 aluminum alloy, ring holding clamp material are Al 1060
4.Corona Assy ring set includes two aluminum holding clamps and one corona ring body and 2 sets of M.S galvanized/304 stainless material fasteners. Each M.S galvanized fastener sets(2 pcs M8 bolts, 2 nuts, 2 spring washers, 2 flat gaskets)
“toroid” type discharge shields manufacturer for HV bushings/lightning Arresters, Corona rings,corona electrode,grade rings,corona shields manufacturing
1.Double corona electrode for 525kV bushings;
2.Bracket using φ50 aluminium tube to weld cross type,connecting with the support tube flexbily,it can adjust the distance up and down to the φ9 hole in each support tube;
3.Flange,bracket and M12 bolt are welded between or fix.
