在提高配電服務的品質、安全和美觀等因素下，傳統的架空配電系統漸漸轉換成地下配電系統，隨著時間各項因素將使電纜絕緣材料發生劣化乃至故障。由於電纜常見事故多發生在人工接續部份，因此本文為探討地下電纜直線接頭絕緣狀態之研究。
本文利用地下電纜直線接頭的試驗數據進行即時性絕緣狀態診斷，試驗條件為在接頭接續處製作人工瑕疵，施以高電壓直到絕緣擊穿為止，在試驗期間以固定時間擷取試驗電壓與局部放電訊號，所得資料將先進行濾波、化簡、轉換和萃取，形成數個特徵的時間序列資料。接著以固定寬度作平移資料擷取，分別利用常態分配、對數常態分配、伽瑪分配與韋伯分配與樣本資料進行統計適合度檢定，判斷是否符合某種機率分佈。
經由統計分析判斷量測資料的分佈趨勢可知，區域重心符合檢定比率程度為最高，故以此特徵參量作為絕緣探討之代表。觀察每個機率分佈特徵值的演進軌跡，其特徵值在量測資料出現斷點的地方呈現離異值現象，經由既有資料之三倍標準差為門檻，將離異值超出門檻的區域範圍作為即時性絕緣狀態初期、中期、末期的判斷依據。

In order to improve the quality of distribution service, security and appearance, the traditional overhead distribution system have gradually evolved into underground distribution system. With all the factors would lead to the deterioration of electric cable insulation materials. Furthermore, the common accidents of underground cables usually take place in the artificial connecting part. Therefore, this paper interprets underground cable joint insulation status diagnosis.
The thesis draws on the test data of underground cable joint to make real-time insulation diagnosis. Making an artificial defect at the joint connection point and applying high voltage to it until the material breakdown. The experiment voltage and signal of partial discharge are measured at a fixed time interval during experiment. The PD signal will be converted into several time-series characteristic parameters by filtering and simplifying, and then the sample data will be acquired with fixed width by it. Respectively using Normal distribution, Log-Normal distribution, Gamma distribution and Weibull distribution to execute goodness-of-fit test with sample data to verify which kind of probability distribution is suitable.
Through the distribution trend of the measurement data, the highest rate of compliance test is gravity center of discharge. As a result, the characteristic parameter is the insulation representative. From the result of observing each trend of characteristic evolution, the characteristic parameter will appear outliers when the measurement data is with gap. The positions of outliers recorded with third standard deviation threshold are taken as the basis of initial period, middle period and final period of real-time insulation status diagnosis.

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