Capacitive Grading Layers

Capacitive grading layers are concentric cylindrical or conical conductive layers embedded within the insulation of high-voltage bushings. They function as a series of capacitors connected in parallel with the main insulation, creating a controlled voltage gradient along the bushing's length. This prevents excessive electric field concentration at either end, which could cause partial discharges or complete insulation failure. These layers are typically made of conductive foil or metallized paper and are precisely spaced to achieve linear voltage distribution.

The working principle is based on capacitive voltage division. Multiple conductive layers are inserted at specific intervals within the dielectric material. Each layer acts as an electrode, forming capacitors with adjacent layers and the central conductor/ground. This creates a capacitive ladder network that forces the voltage to drop uniformly across the insulation, rather than concentrating at stress points. The capacitance values are designed to be inversely proportional to the distance from the high-voltage end, ensuring equal voltage steps between layers.