05_life_test - 438 Montanari et al.: From LDPE to XLPE:...

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Montanari et al.: From LDPE to XLPE: In © estigating the Change of Electrical Properties. Part I 438 From LDPE to XLPE: Investigating the Change of Electrical Properties. Part I: Space Charge, Conduction and Lifetime G.C. Montanari Department of Electrical Engineering University of Bologna, Viale Risorgimento 2 40136 Bologna, Italy C. Laurent, G. Teyssedre Universite Paul Sabatier ´ Laboratoire de Genie Electrique ´ 118 route de Narbonne, 31062 Toulouse, France A. Campus and U.H. Nilsson Borealis AB, Wire & Cable BU 44 486 Stenungsund, Sweden ABSTRACT This paper discusses the results of space charge, conduction current and electrical lifetime measurements performed on widely-used materials for electrical insula - () tion, that is, low density polyethylene LDPE and cross-linked polyethylene XLPE . Space charge accumulation profiles were compared in LDPE, low density polyethylene plus antioxidant LDPE ± AO and XLPE, with consideration of ther - mal treatment effects in LDPE and XLPE. Significant variation decrease of accu - mulated space charge and apparent mobility, as well as slight decrease of conduc - tion current, can be seen going from LDPE to LDPE ± AO and XLPE, which may be associated with formation of deeper trap levels or an increase of their density . On the contrary, electrical life under ac voltage does not show significant differ - ences from LDPE to XLPE. This latter result underlines that life under high ac electrical stress is mostly determined by defects weak points rather than material characteristics associated with charge injection and transport. Index Terms — Space charge, transport, cross-linked polyethylene. 1 INTRODUCTION NVIRONMENTAL, lifecycle and cost-performance E concerns still promote comparative evaluations of cross-linked vs. thermoplastic materials. Regarding high Ž. voltage HV cables, interesting insulating materials, al- ready widely used for years, are thermoplastic low-density polyethylene LDPE or cross-linked polyethylene XLPE . The recent availability of techniques enabling di- rect observation of space charge distribution in insulation, wx such as the pulsed electroacoustic PEA method 1, 2 , has allowed more and more information on mechanisms of charge generation and trapping to be gained, so that basic investigations on the effect of the introduction of Manuscript recei ® ed on 2 July 2003, in final form 28 January 2005. additives, including antioxidant, and of cross-linking by- products, carried out for years, can be re-visited with new knowledge perspectives. A major problem in understanding charge behavior is that XLPE is only apparently a simple material. Differ- ences among base resin LDPE , manufacturing processes and parameters, type of antioxidant and, in general, addi- tives, contaminants and thermal treatment procedures may modify significantly results and, thus, evaluations regard- ing charge injection, transport and trapping features. On the other hand, the need of reliability and increase of per- formance in terms of design stress and life of XLPE,
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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05_life_test - 438 Montanari et al.: From LDPE to XLPE:...

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