Diagnosis and Localization of Moisture Defects in HV Cable Water-Blocking Buffer Layer Based on Characteristic Impedance Variation

To identify and localize buffer layer moisture defects in high-voltage (HV) cables, this article verifies the effectiveness of the frequency-domain reflectometry (FDR) method theoretically and experimentally by analyzing the impact of moisture on the characteristic impedance of the cable. This article first analyzes the relationship between the electrical parameters of the buffer layer and the characteristic impedance of the cable. Subsequently, the electrical parameters were tested for buffer layer samples at different degrees of moisture, and the characteristic impedance of the cable was calculated. The results indicate that the characteristic impedance of the cable decreases after moisture exposure primarily due to a significant increase in the dielectric constant of the buffer layer. As the degree of moisture increases, the characteristic impedance gradually decreases until it becomes stable. This is mainly due to its rate of change being inversely related to the square of the dielectric constant of the buffer layer. This provides a theoretical basis for the implementation of the FDR method. Finally, this article conducted FDR tests on HV cables with different degrees of moisture, demonstrating that the FDR method can effectively locate buffer layer moisture defects.