Sensitivity improvement of multi-type defect location and identification in long cables based on beat signal

Abstract Multi-type defects usually coexist in long cables, while conventional frequency-domain reflectometry techniques struggle with weak noise immunity and the inability to determine the defect types. To address these issues, this paper proposes a method based on the beat signal to simultaneously locate and identify multiple defects in long cables. Specifically, the method involves injecting a frequency modulated continuous wave into the cable head and obtaining the beat signal by mixing the incident and reflected signals. The defect location is determined by analyzing the time delay of the reflected signal within the beat signal. Additionally, the defect type is recognized based on the characteristic that the coefficients of beat signal periodic components have the same sign as the reflection polarities at the defect positions. To validate the effectiveness of the method, simulation analyses, coaxial cable experiments, and field tests on a 330 kV cable were conducted. The results demonstrate that the proposed method can accurately locate the concentrated defects, determine the range of distributed defects, and efficiently identify the defect types. The relative location error is less than 0.9%. Compared to the reflection coefficient spectrum method, the proposed method enhances noise immunity by 40 dBV and extends the one-way measurement range by 18.18%.