| Title |
Statistical Analysis of Conventional and Revised Index R for Reliable Degradation Diagnosis in Underground Distribution Cables |
| Authors |
김가현(Ga-Hyun Kim) ; 서예슬(Ye-Seul Seo) ; 임장섭(Jang-Seob Lim) |
| DOI |
https://doi.org/10.5370/KIEE.2026.75.8.1887 |
| Keywords |
Water tree; VLF tanδ; MMU Index R; Kepco Index; Skirt factor |
| Abstract |
This paper compares the MMU Index R with the newly proposed KEPCO Index to improve insulation diagnostics for underground distribution cables. The MMU Index R, used in Very Low Frequency (VLF) tanδ diagnostics, relies on the Skirt factor, which was unobtainable for about 15% of the field data studied. The KEPCO Index excludes this volatile factor, applying instead the trend line slopes and standard deviations of Tangent Delta (TD) and its differential (DTD) as weights. Across about 6,000 field data points, the indices differed in virtual versus trend line use, normalization, and Skirt factor use. Some data judged defective by the MMU Index R were judged normal by the KEPCO Index; for these, DTD lay solely within Grade C to E. Such discrepancies could misclassify a defective cable as normal, a latent risk to supply stability. Whether this stems from the KEPCO Index design or from Skirt calculation errors remains unclear, requiring further study of the groups where the indices disagree. |