Typical Defects Detection of I&C Cables in Nuclear Power Plants Based on Time-Frequency Domain Reflection Method

Abstract

In order to enhance the safe and stable operation of instrumentation and control (I&C) cables in nuclear power plant (NPP), time-frequency reflection method (TFDR) based on SPWVD (Smooth Pseudo Wigner-Ville Distribution) is proposed to detect and locate typical defects in I&C cables. Firstly, the defect information of the cable was obtained by the reflected signal produced by a linear Frequency Modulation (FM) Gaussian signal. Secondly, the receiving signals were processed by SPWVD to obtain time-frequency domain distribution. Thirdly, time-frequency cross-correlation (TFCC) of the incident and reflected signals were analyzed and normalized from the results of time-frequency distribution. Finally, evaluation and localization of typical defects of I&C cables were discussed. In this paper, a 50 meters I&C cable was prepared to simulate several typical defects, including short circuit, open circuit, and metal shield damage. Subsequently, TFDR method was adopted to detect these defects to verify the reliability of this technology. The experiment shows that the cross term generated by WVD reduces the reliability of the detection, SPWVD can effectively eliminate cross term by windowing and convolved process. By adopting TFDR with SPWVD, artificial defects can be accurately detected. The measured positions of the defects are approach to the actual locations of the defects. The measuring errors are less than 2%.