Sheath Voltage Limiter Defects Detection Method Based on Harmonic Phasor Differences of Sheath Current for Cross-Bonded HV Cable

The sheath voltage limiter (SVL) defect is a typical defect in HV cable cross-bonding systems that threatens cable system safety. Traditional surge arrester detection and time-domain sheath current analysis methods fail to accurately identify SVL defects due to environmental complexities and parameter variations. This paper proposes a defect diagnosis method based on harmonic phasor difference of sheath currents. By establishing a frequency-domain equivalent model of cross-bonded HV cables combined with SVL nonlinear resistance characteristics, harmonic currents under defect conditions are treated as harmonic sources injected into the sheath loop. Transfer functions analyze the impacts of SVL defects on sheath currents, revealing that harmonic content during SVL defects is significantly higher than under normal conditions and other defect types. Through simulation analysis using 110kV cable as the case study, diagnostic criteria based on harmonic content of sheath current phasor differences were established: When SVL defects occur in sheath loop 1, the 3rd, 5th, 7th, and 9th harmonic content variation ranges of the head-to-tail sheath current phasor difference in this loop are 1.88%~21.31%, 0.79%~8.98%, 0.17%~1.94%, and 0.11%~1.10% respectively; When SVL defects occur in sheath loop 2, the 3rd, 5th, 7th, and 9th harmonic content variation ranges of the head-to-tail sheath current phasor difference in this loop are 1.30%~23.71%, 0.55%~9.99%, 0.12%~2.16%, and 0.07%~1.22% respectively; When SVL defects occur in sheath loop 3, the 3rd, 5th, 7th, and 9th harmonic content variation ranges of the head-to-tail sheath current phasor difference in this loop are 1.53%~16.15%, 0.65%~6.81%, 0.14%~1.47%, and 0.08%~0.83% respectively. The harmonic content of phasor differences is significantly affected by ground impedance and phase currents, while the influence of phase voltage is insignificant. Compared with existing methods, this approach takes into account the effects of complex environmental factors and effectively resolves the issue of traditional diagnostic methods being unable to distinguish between SVL defects and other types of grounding defects, thereby improving the accuracy of SVL defect diagnosis.