Design of Grading Rings for Air-Core Power Reactors

A design technique for improving the impulse voltage distribution along the axial length of a large aircore power reactor is presented. A set of conducting rings is used to linearize the voltage distribution across the reactor windings. The number, the dimensions and the relative locations of the grading rings are determined such that the uniformity of the voltage distribution along the axial length of the reactor is optimized. The electrical stress at the surface of the grading rings is also calculated and found to be below the stress level of the corona inception. The theoretical design and calculation procedure is based on the charge simulation technique. An experimental study is also carried out to verify the effectiveness of the theoretical analysis using large power reactors. Good agreement is obtained.