Defect and Fault Diagnosis Method for Three-Phase Cross-Bonded Cables Based on High-Frequency High-Voltage Coordinated Excitation

To address severe transmission signal attenuation caused by inter-phase electromagnetic coupling in three-phase cross-bonded cables, which significantly limits the identification of insulation defects and fault types, this paper proposes a broadband impedance spectroscopy differential-frequency decoupling and defect diagnosis method based on three-phase high-frequency, high-voltage coordinated excitation. First, a decoupled transmission line model for three-phase cross-bonded cables is established to systematically analyze how the degree of insulation damage and fault equivalent impedance affect the frequency domain response at the test terminal. Three core diagnostic parameters, namely the fundamental resonant peak amplitude variation ratio, the resonant period change rate, and the initial phase offset, are extracted to construct a multi-dimensional collaborative diagnosis model for accurate defect and fault identification. Second, a high-voltage topology based on proportional optical isolation driving is designed to overcome the gain and bandwidth trade-off of conventional power amplifiers, effectively mitigating excessive high-frequency signal attenuation and low signal-to-noise ratios in long-distance transmission lines. Using this topology, a three-phase differential-frequency coordinated excitation test platform is developed to ensure the accurate, synchronous injection of isolated three-phase differential-frequency sinusoidal waveforms into the cable sending end. Combined with broadband impedance spectra acquired by the test system, the proposed diagnostic model enables the reliable identification of defect and fault types in three-phase cross-bonded cables, offering practical significance for the safe and stable operation of power transmission systems.