In the field of high-voltage and ultra-high-voltage power transmission and transformation engineering, grading rings and corona rings are two kinds of conductive metal components with similar appearance but different functional priorities. They are widely installed on insulator strings, bushings, arresters, converter valves and other high-voltage equipment, aiming to optimize electric field distribution, reduce local field strength, avoid insulation breakdown and restrain corona discharge. Although they are often used together and even integrated into one structure in practical projects, they have clear differences in design purpose, working mechanism and application emphasis.
Grading rings are mainly designed to balance the potential distribution along insulating components. For long insulator strings, high-voltage bushings and other equipment, the voltage distribution is often uneven under high electric field, resulting in excessive electrical stress at both ends, which accelerates insulation aging and reduces the overall withstand voltage level. A grading ring improves the voltage distribution through capacitive coupling, making the potential drop more uniform along the insulator string, so as to give full play to the insulation performance of each unit and enhance the safety and stability of the whole equipment. It is mostly used in 220kV and above AC transmission systems and ±500kV and above DC transmission systems, and is a core component to improve insulation efficiency.
Corona rings focus on suppressing corona discharge at high-voltage terminals and sharp electrodes. When the electric field strength at the tip of a conductor exceeds the critical breakdown strength of air, corona discharge will occur, accompanied by energy loss, sharp noise, ozone corrosion and radio interference, which will damage the equipment and affect the surrounding communication and electronic equipment. A corona ring increases the curvature radius of the electrode surface through its smooth arc structure, weakens the tip effect, reduces the local electric field strength to below the safe threshold, and eliminates corona from the source. It is suitable for all kinds of high-voltage terminals from medium voltage to UHV, with strong universality.
In engineering applications, grading rings and corona rings are mostly made of aluminum alloy with high conductivity, light weight and strong corrosion resistance, and their dimensions, curvature and installation positions are accurately optimized through electric field simulation. In many UHV scenes, the two are designed as an integrated structure, taking into account both potential balancing and corona suppressing functions, forming a full set of electric field optimization solutions.
As the "invisible guards" of the high-voltage power system, grading rings and corona rings rely on simple geometric structures to solve the key problems of electric field concentration and discharge in high-voltage engineering. With the continuous development of the power grid to higher voltage levels, their design and application are more precise and professional, providing a solid guarantee for the safe, efficient and stable operation of modern power transmission and transformation systems.