Common-mode current reduction in EMP coupling with the star-quad cable having a reference conductor

The coupling of electromagnetic pulse (EMP) with the star-quad cable having reference conductor is analyzed by using the proposed model, which is based upon multi-conductor transmission line theory. Expressions for common-mode (CM) and differential-mode (DM) currents are developed. Two cases are mainly discussed: the first case is the star-quad cable with a central reference conductor, and the second case with the outside reference conductor. A rigorous comparison between these two cases shows that when the reference conductor is placed at the center, the magnitude of CM current is reduced dramatically, which is beneficial for electromagnetic compatibility (EMC). The CM current magnitude of the outside reference conductor is relatively very high due to the large CM current loop area, which is the least possible for the central reference conductor. There is no significant change in the DM current magnitude for both cases because the DM current has no direct dependence on the CM current loop area. A commercial software, FEKO, which utilizes the method of momentum (MoM), is used to compare the results of our proposed method, which are in good agreement.