A Virtual Impedance Matching Method for the FDR-Based Cable Defect Location

Nowadays Frequency domain reflection (FDR) method are widely used to diagnose the power cable defects and faults. However, in FDR tests, the unmatched impedance can be caused by the signal connection wire between the FDR analyzer and the power cable, and leads to a large signal reflection and defect misdiagnosing. Thus, in this work, a virtual impedance matching method for the FDR-based cable defect location is proposed to alleviated the negative impact of the signal connection wire. First, the transmission line model of the power cable is established, and the idea of the FDR method is introduced. Second, the reason causing the unmatched impedance is analyzed, and a reflection coefficient extraction method and the characteristic impedance estimation method are proposed to gain the front-end reflection coefficient and the impedance of the signal connection wire. Then, the impedance of the signal connection wire is eliminated from the front-end reflection coefficient spectrum. Thus, the negative impact of the signal connection wire is also alleviated, and a virtual impedance matching is achieved. At last, both a 50 m SYV50-5-1 type coaxial signal cable and a 500 m 10 kV XLPE power cable are used in the experiment to show the performance of the proposed method. The experiment results show that with the proposed virtual impedance matching method, the front-end reflection is almost eliminated, and the cable defect can be easy recognized.