【正文】 ltage dependence and hysteresis response. The losses are rather high probably due to a joint. The capacitance plots show no voltage dependence. The cable is most likely in a good condition and not deteriorated by water trees. The cable will remain in service for many years. The last group is a cable with two joints, cable 3. At both ends of the cable there are cables from the mid 80s and in the middle there is a cable from the beginning of the 70s. This cable shows a voltage independent leakage current response with no hysteresis. The capacitance did not 7 show any voltage dependence either. This indicates that the cable is in good condition and not deteriorated by water trees. The leakage current response is most likely an effect of the two cable joints. The cable will probably remain in service for many years. Regarding the measurements made in 1998 it is difficult to say how reliable they were. What could be said on the other hand, is that even though three of the cables were judged as old and four of the cables were judged as critical for nine years ago they are still operating. The insulation diagnostic instruments that were found in the literature study are all offline instruments. The technique used in the instruments varies. General Electric’s IDA 200 HVU, now manufactured and sold by Pax diagnostics and called Idax206 VAX230, measures the dissipation factor tanδ at a variable frequency sweep between Hz. Bauer’s PHG 70 and PHG 80 and sebaKMT’s VLF and HV diagnostics HVA 30, 30,5 and 60 measures the dissipation factor tanδ at a fixed very low frequency, VLF. Tettex Midas, 2820 and 2877 measures the dissipation factor tanδ at powerline frequency. Omicron’s CPC 100 with CP TD1 also measures the dissipation factor tanδ , however, at a frequency sweep between 1570 Hz. sebaKMT’s CDS measures the losses with the isothermal relaxation current, IRC method. The measurement techniques used in these instruments are considered to be nondestructive at a voltage level up to 0 V . The fault location instruments found in the literature study are all based on the same technology, the time domain reflectometry. SebaKMT provides four instruments the Surgeflex 15, 25, 32 and the Teleflex T30E. Surgeflex 15 and 25 and Teleflex T30E are batterypowered and portable instruments. PFL401500/2020 is supplied by Megger and is a batterypowered portable instrument. The 5150 first response cable fault locator by Hipotronics is also portable and batterypowered. The failure statistics from the Stockholm grid shows that the major number of faults is connected to underground cables. The largest fault category for high voltage, low voltage and service cables are lack of maintenance or worn out cables. The second large category for all threevoltage levels is unknown. A more extensive investigation of the failure statistics from the Eker246。 Energi’s grid is more extensive. There has been access to statistics reported to Darwin, Eker246。, due to that the soil consists of sand and gravel that has a draining quality. Another reason that Eker246。 Energi’s medium voltage cables, which had been diagnosed in 1998. The measurements were analysed in order to estimate the condition of the cables. An evaluation was done in order to try to find out if the measurements made in 1998 were trustworthy. Qualitative models of different water trees were developed in order to demonstrate the behaviour of these water trees. The instrument used in the fieldmeasurements is called IDA200 HVU, which is an instrument that measures the dissipation factor at variable low frequencies at diverse voltage levels. The technique is developed at report also contains an overview of different mercial instruments for XLPEcable diagnostic and cable fault location instruments. This overview gives information on mercial available diagnostic instruments, and which technique they use. In the report the theory for different techniques used in diverse instruments are revealed. Failure statistics from Fortum’s Stockholm grid and Eker246。還應該有關于失敗的原因和影響的信息。 另外 ， 如果有協(xié)議或建立了各期刊中 /高電壓電纜 將提高對 中 /高壓電網(wǎng)條件 的 知識。 是 Energi那里得到的紙質(zhì)報告是失敗的 。這些例子表明，很多信息 在 報告程序 時 丟失 。 更可 靠的故障信息在 Eker246。 當信息進行了檢查一下 AT Eker246。然而， 由于 挖掘，客戶故障， 以及 在車站 5次洪水造成 17故障 ， Eker246。 的交聯(lián)聚乙烯電纜電 網(wǎng)故障次數(shù)為 每 100公里 ，這被認為是 比較 低 的 。該 統(tǒng)計報告 說明， 電纜 Eker246。對高電壓大故障類別，低電壓和 服務電纜的電纜 還沒有需要 維修或磨損 。 SebaKMT 提供了四個文書 Surgeflex 15， 25， 32，泰利福 T 30E， Surgeflex 15， 25和泰利福 T 30E是電池供電