Design of Field-Controlled Multi-Layer Insulation System

A novel method is proposed and validated experimentally to increase the breakdown voltage of an insulating system for applications in the electrical insulation of large power equipment. The method relies on controlling the electric field within a multilayer insulation system. The insulation system is constructed from n layers of insulation and m very thin conducting strips placed between successive insulating layers. The conducting strip at each layer is symmetrically shifted by a constant distance determined from a shifting factor which is calculated to maximize the withstand voltage of the insulation. The potential distribution within the composite insulation is determined from the solution of the Laplace equation for different design parameters, and it is shown that the field can be reduced for a proper choice of the dimensions of the system. A composite insulation system based on the proposed method has been fabricated and tested for ac (60 Hz) and impulse voltages. Substantial improvements in the withstand voltage are obtained over an identically sized system without the conducting strips, thus validating the analysis presented in this paper.