Low‐Frequency Oscillation Suppression of FDR Time‐Domain Diagnostic Waveforms for Cable Defects Based on Splicing Technology

ABSTRACT A time domain pulse (TDP) based on the frequency domain reflectometry (FDR) method can be used to diagnose the insulation state of cable defects. However, because of the limitations of the FDR test instrument, the lack of a reflection coefficient spectrum (RCS) in the low‐frequency band (LFB) can result in low frequency oscillation in the time domain reflection signal, which may shield the TDP characteristics of cable defects and then affect the diagnosis of the insulation state of the local defect. To improve the diagnostic performance of the insulation status of local defects in power cables, a low‐frequency stitching technology based on time domain reflectometry (TDR) and FDR is proposed in this work. First, the influence of the RCS in the LFB on the TDP characteristic is analysed through different lower frequency limits. Then, the principles of the proposed low‐frequency stitching technology are introduced in detail, including headend impedance mismatch compensation and the low frequency stitching algorithm. Finally, through simulation and an actual test of two power cables, the effectiveness of the proposed method is verified. The experimental results showed that using the low frequency stitching method could effectively obtain the RCS in the LFB, suppress low‐frequency oscillations in the time domain reflection signal and further enhance the TDP characteristics of the cable defects. Thus, the diagnostic performance of the insulation state of the defect could be improved.