Evaluation And Analysis On Shielding Efficiency Of Cables

The transfer impedance is a characteristic parameter that weighs exterior electromagnetic field energy penetration through the cable shielding level. Measuring the transfer impedance is one way to formulate the shielding efficiency of the cable. The theoretical model of transfer impedance has already been proposed. Afterwards also appeared many kinds of improved models. But these models often rely on the simplification assumptions conditions. It is necessary to actually measure the transfer impedance. The measurement of transfer impedance method includes line injection method, absorption pliers method, three coaxial method and so on. We selected three coaxial measuring techniques. We made the power cable core, the cable’s shielding level and the steel pipe constitute the three coaxial structures. In this way we measured the transfer impedance of some kinds of power cables. We used 8/20μ s profile. The electric current which pours into the power cable with the establishment belt shield was 1kA, 2kA, 3kA. The electric current which pours into the power cable with the hoop armor shield was 1kA, 5kA, 10 kA. In the measure process we adopted cables with different measuring technique such as no divergence, the copper tape divergence, the steel belt divergence as well as the copper tape and the steel belt parallel laying aside in the two sides of the power cable. We may see from the test result. In low frequency, transfer impedance is mainly determined by the cable shielding level diffusion and behaviors as the cable shielding level DC resistance. In high frequency, along with frequency increases, electromagnetism energy penetrates through shielding layer hole and seam, coupling to the cable inside, so transfer impedance rapidly increases. On the base of the measurement, we carried on the transfer impedance by the formula to the theoretical calculation of some transfer cable and compared the measurement and the theoretical calculation result. We analyzed the reasons that bring out the measuring error, and hope to build a good foundation to further research and measure later. We introduced the pull-on braid method, and compared with the current probe method. We measured the transfer impedance of some kinds of power cables. In the overlapping frequency range results show excellent agreement.