Diagnosis and Location of Cable Defects Based on Digital Reconstruction of Impedance Spectrum Under Pseudotrapezoidal PFM Excitation

Because the output voltage of the existing high-frequency instrument for the defect detection of long-scale transmission cable is too low, it is necessary to output both high-frequency and high-voltage excitation. A diagnosis and location method of cable defects based on pseudotrapezoidal pulse frequency modulation excitation and impedance spectrum digital reconstruction is proposed. A high-capacity pseudotrapezoidal excitation system based on SiC high-speed inverter is designed to measure the impedance spectrum up to the highest frequency of 7 MHz. Through digital reconstruction, the impedance spectrum with different cable defects can be obtained by the bandwidth extension within the range of 100 kHz–63 MHz. Compared with traditional low-voltage sinusoidal excitation, the location results using the proposed time-space conversion function have a more minor interval oscillation and a faster convergence speed. The accuracy of defect location is improved by 80%, which verifies the effectiveness and accuracy of the proposed method.