bstract:The space charge in full size 250 kV DC cables was measured using the pulse-electroacoustic method. Measurementsof two types of newly developed DC XLPE cables with 20-mm insulation were taken under a DC voltage of 500 kV with the conductor temperature at: room tempera~ure and at 85 "c. A qualitative analysis of the space-charge distribution and a quantitative analysis of the electric fields in the vicinity of semicon interfaces were conducted. It was shown that the field in the vicinity of the inner semicon tends to increase by 10-40% when the polarity of the applied voltage was reversed, in the case when the conductor was kept at 85 -C.However, the distortion of the electric field was significantly less than that expected in conventional XLPE cables. As the result, the subjected DC cables are considered to have stable DC characteristics from the viewpoint of space chargebehavior.Cross-linked p o l y e~~y l e n~ (XLPE) cables are increasingly taking the place of oil-filled (OF) cables in AC transmission because they are easier to maintain and are less likely to cause fires. While it would be beneficial if XLPE cable cool be used for long-distance DC transmissions such as submarine cables, space charge accumulation is ~hought to be much more significant in a DC electric field than in the AC field in conventional XLPE cables. The current XLPE cables do not provide excellent insulating performance because space charge which accumulates under PE-994-PWRD-0-04-1997 A paper recommended and approved by the IEEE Insulated Conductors Commitfee of the IEEE Power Engineering Society for publication in the IEEE Transactions on Power Delivery. distorts the electric field in insulation. Recently, full-size 250 kV DG XLPE cables with excellent DC performance have been developed. Their insulations are made of XLPE with certain fillers, which limit the influence of a space charge [I].The effect of mixing filler for space charge control can be determined indir~ctly from the results of DC breakdown character is ti^, etc.Space charge distribution can be determined to some extent when the electric field and temperature dependences of resistivity are given. However, in practice, this is apt to be complicated because of factors such as the influence of the captured charge, which cannot be exp~ained from resistiv~~ [2]-[4]. Measuring space charge under an applied DC voltage may bring important information on insulation. Newly developed equipment [5]- [8] was used to carry out space charge measurement nondestructively in full-size 250 kV DC XLPE cables. The space charge measurement results are given in this report. E~P~~I M E N T A L(1) Sample Two cable specimens (sample A, 6) were prepared for this experiment, Each cable was developed as a DC transmission cable and had a conductor cross section of 800 mm2, 20 mm-thick insulation, and semiconducting electrodes 8t the inner side and the outer electrode side. Also, a lead shield was installed as a protective layer. Each cable contained different sort of organic filler to prevent sp...
In oil-immersed power transformers, an insulating oil / pressboard (PB) composite insulation system is generally applied. In order to make power transformers more compact, it is necessary to optimize the insulation design with considering the charge behavior in liquid dielectrics. In addition, environment-friendly insulating oil for transformers is being interested. In this paper, we directly measured the electric field in parallel-plane electrodes and rapeseed ester oil / PB composite insulation system under dc voltage application using Kerr electro-optic technique. From the results, we compared the electric field in rapeseed ester oil with that in mineral oil and discussed the charge behavior in composite system. Finally, we confirmed the basic applicability of rapeseed ester oil for transformers.
Space charge in full size ±250 kV dc cables was measured using a pulse‐electroacoustic method. Two newly developed types of dc XLPE cables with 20 mm thick insulation were subjected to measurements at a dc voltage of 500 kV, keeping the conductor temperature either at room temperature or at 85°C. Qualitative analyses of the space charge distribution and the quantitative analysis of the electric fields in the vicinity of semicon interfaces were made. It was shown that the field in the vicinity of the inner semiconductor tends to increase by 10 to 40% when the polarity of the applied voltage was switched, in the case when the conductor was kept at 85°C. However, the distortion of the electric field was significantly smaller than that expected with conventional XLPE cables. As a result, dc cables are considered to have stable dc characteristics from the viewpoint of space charge behavior. © 1998 Scripta Technica, Electr Eng Jpn, 124(2): 16–28, 1998
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