On the electrodynamics of partial discharges in voids in solid dielectrics

نویسنده

  • A.
چکیده

Until1 now paper 3-phase belt type cables were succesfully used for voltages upto 20 kV in great parts of the world. Replacement of paper by extruded insulation has been unsuccesfull and service voltages no higher than 5 kV can be applied because of the large discharges and uncontrolled field in the interstices at the core and the belt. Belt-type cables remained paper-insulated for that reason. A breakthrough has been obtained when a non-woven fibrous tape was applied to the cores to improve the longitudinal water tightness. As these tapes are very poor dielectrics, with low breakdown stress, it was expected that the breakdown tests would be impaired. At the contrary, the life expectancy was raised from less than 10 years to more than 30 years at 10 kV. Further study revealed that this dielectric improvement was caused by a considerable reduction of the discharges in the interstices of the cable: reductions of several hundred times were measured. INTRODUCTION To obtain a waterstop in the longitudinal direction of a 3-phase belted cable, a thin non-woven tape was applied to the core insulation and to the interstices between the belt insulation and the core insulation (Figure l), Kreuger, Morshuis et al. [l]. The discharge diagram of this cable and a non-taped cable are shown in Figure 2 . The research on the discharge mechanism of voids filled with a nonwoven, fibrous tape was initiated by the discharge limiting effect of the tape in the cable and by the fact that the cable life was significantly increased. To study the discharge mechanism of these taped cables a model was built that represented the interstices in the cable. EXPERIMENTAL METHOD The testcircuit for measuring partial discharges consists of a 50 Hz high voltage source that can deliver a programmable number of half or whole 50 Hz periods. This set-up makes it possible to study subsequent discharges or Lichtenberg figures during specific time intervals. A balanced discharge detection system is used (Figure 3 ) combined with a storage facility. Lichtenberg figures can be P.H.F. Morshuis is with the High Voltage Laboratory of the Technical University of Delft, The Netherlands. F.H. Kreuger is professor of High Voltage Technology at the Technical University of Delft, The Netherlands. Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on July 01,2010 at 11:38:59 UTC from IEEE Xplore. Restrictions apply.

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تاریخ انتشار 2017