Grading Rings/Capacitors

Grading rings (also called corona rings) are metallic rings installed at strategic points on high-voltage bushings to control and equalize electric field gradients, reducing corona discharge and preventing insulation failure. Capacitors in this context refer to capacitive grading elements embedded within bushing insulation to create uniform voltage distribution along the bushing length. Together, these components ensure reliable operation of high-voltage equipment by managing electrostatic stress.

Grading rings work by providing a smooth conductive surface that redistributes electric field lines, preventing concentration at sharp edges. Capacitive grading uses series-connected capacitor layers within the bushing insulation to create a controlled capacitive voltage divider, ensuring linear voltage drop along the bushing axis. This combination prevents partial discharges, reduces thermal stress, and maintains dielectric integrity under high-voltage conditions.