地下電纜為現今都市的主要輸送電力設施，而常見的地下電纜瑕疵多發生在人為施工接續部份，在長期運轉下可能發生不可預期的故障，因此藉由長期監控地下電纜直線接頭是目前降低事故方法之一。在進行長期性監控局部放電訊號時，因為資料隨時間增加而累積，在實務上會發生設備記憶體空間限制。
本研究提出一套即時性的地下電纜接頭絕緣狀態評估方法，包含固定時間擷取試驗電壓與局部放電訊號，將擷取的資料進行化簡、轉換和萃取，為解決資料累積的問題，將其萃取後的資料以固定寬度作平移方式，計算特徵值與絕緣狀態評估值，並且將特徵值超出評估值的區域認定為絕緣狀態轉變時期，當評估值為3倍標準差時，可有效鑑別出兩次特徵值超出評估值，此為絕緣初期、中期與末期之依據。最後，比較有無小波濾波處理下，發現無小波濾波可以有效進行絕緣狀態判斷，並且改善程式運算速度與程式複雜度。

Underground cables are the main apparatus of electricity transmission in recent urban. The common defects usually existed in the artificial connection part. Under a long-term operation, these defects might become unexpected accident. In recent, a long-term monitoring of underground cable joint is a method to avoid accident. Increasing with time during long-term monitoring, the data size might reach the limit of measuring device.
This research proposed a real-time insulation status assessment method for underground cable joint. This method includes the acquisition of test voltage and PD signal, simplification, transformation, and extraction. In order to solve the problem of limitation of data, the extracted data will be shifted by a fixed width to calculate a feature and assessment value of insulation status. The duration, which feature is over the assessment value, is represented as the transition period of insulation status. When the assessment value is 3 times the standard deviation, two transition periods can be effectively detected. These two transition periods were used to determine the insulation status, including early, middle and final term. Finally, no matter using wavelet filtering or not, this method can assess insulation status effectively. Finally, comparing the use of wavelet filtering, the diagnosis of insulation status without wavelet filtering was feasible and improved the operation speed and program complexity.

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