報告書番号

H15017

タイトル（和文）

油隙欠陥を含むOFケーブル油浸紙‐絶縁油複合絶縁系での部分放電特性に与える油圧および電界の影響

タイトル（英文）

Effect of Oil Pressure and Electric Field on Partial Discharge Characteristics of Oil Impregnated Insulation System for Oil-Filled Cable with an Oil Gap

概要 （図表や脚注は「報告書全文」に掲載しております）

近年，経年OFケーブル接続部の解体調査で，油中ガス分析によって異常なしと判定されたにも関わらず，ケーブル絶縁層や補強絶縁層で部分放電（PD : Partial Discharge）の痕跡が認められる事例が報告されている。そのため，油中ガス分析の精度向上やPD測定による劣化診断手法が注目されている。当所では後者の実現可能性を見極めるため，ケーブル絶縁層におけるPD現象に着目した検討を進めてきた。これまでに油隙欠陥を含む油浸紙‐絶縁油複合絶縁系において，275 kVOFケーブル設計電界・許容油圧の下限値付近にてPDの継続性やPD特性を明らかにした。しかし，それ以外の設計電界・油圧条件下での検証が課題であった。そこで，各種設計電界・許容油圧条件下でのPDの継続性やPD特性を検証した。その結果，275 kV設計電界下では，油隙欠陥部の劣化状況によっては0.2 MPaG以下でPDが継続する可能性があることを明らかにした。また，油隙欠陥部の観察により，絶縁体が劣化して気泡が残存しやすいとPDが継続しやすいことを確認した。PDが継続した場合について，PD特性平均値を調べたところ，電荷量の最大値はほとんど変化しないが，設計電界の低下や油圧の増加で発生回数は減少することを確認した。

概要 （英文）

Effects of oil pressure and the electric field for the oil-filled (OF) cable on partial discharge (PD) characteristics of the oil impregnated insulation system with an oil gap were investigated in this study. Firstly, we investigated continuity of PDs in the presence of bubbles in the range of oil pressure from atmosphere pressure to 0.25 MPaG and at the electric fields adopted in the designs of OF cables at 66, 77 kV, 154 kV and 275 kV. As a result, when the insulation in the oil gap was not deteriorated due to PDs, PDs disappeared at the any oil pressure and the electric fields adopted in the designs of OF cables at 66, 77 kV and 154 kV. PDs continued at the oil pressure lower than 0.05 MPaG and the electric field adopted in the design of OF cable at 275 kV. On the other hand, when the insulation in oil gap was deteriorated due to the generation of PDs for an hour at the oil pressure of atmosphere pressure and 20 kV/mm, PDs disappeared at the oil pressure higher than 0.05 MPaG and the electric fields adopted in the designs of OF cables at 66, 77 kV and 154 kV. PDs continued at the oil pressure lower than 0.2 MPaG and the electric field adopted in the design of OF cable at 275 kV. Secondly, we observed inside condition of the oil gap by using a transparent electrode with ITO layer, and it was revealed that bubbles tended to remain in the oil gap when insulation in the oil gap was deteriorated due to PDs. Finally, we investigated the PD charge magnitude and number when PDs continued. As a result, it was found that the average number of PDs decreased with the decrease in the electric field and the increase in the oil pressure. It was also found that the average value of the maximum PD charge magnitude seems not to change in the range of the oil pressure and the electric field investigated in this study.

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