A novel approach for basic insulation-level (BIL) enhancement of vacuum interrupters

Abstract

This article introduces a newly developed design method that may be utilized in modern high-voltage vacuum interrupter (VI) design. At first, a typical 24 kV vacuum chamber is modeled using finite-element method. Potential and electric field profiles are derived and analyzed in detail. To continue, the proposed approach which consists of twin metallic rings placed in the porcelain tubular insulator is added to the previous model and the new model is analyzed in three steps: short-, medium- and long-course scenarios. The achieved patterns illustrate the severe reduction in electric field value of the contacts' surface especially for long-course prototype (up to 74.2%). This phenomenon is discussed in detail. Considering the Fowler–Nordheim quantum tunneling equation; a reduction in electric field intensity brings to lower field emission current value which is the most important factor of breakdown during BIL tests. It is important to note that any reduction in electric field value results in decrease in micro-discharge value and microparticle movement, which are the additional reasons for vacuum insulator failure during high-voltage pulse insertion. This means that the inception voltage of the proposed VI can be increased so that higher BILs like 63 kV insulation high voltage requirements are achieved. The reduction rate of field emission current density is reduced to 4.9% of its initial value for or 120-mm course which expresses the effectiveness of this new approach.