FA491CD1d01 - E M Transactions DII Dielectrics aird...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
EM Transactions DII Dielectrics aird Electrical liisiilatioii Vol. 7 No. 3, June 2OUO 401 The lnfluence of Defects on the Short-term Breakdown Characteristics and Long-term dc Performance LDPE Insulation ABSTRACT Extruded polyethylene is used as the bulk insulation for ac IIV cables because nf its high clcc- tric resistivity and breakdown strength. Although the inaterial at present has limited use in dc power cables, it is used extensively in submarine optical coiniiiunication cable syslcms. This paper reports on the study of the short-term characteristics and long-term yerforinauce of low- density polyethyleiie (LDIT) insulation under dc electric stress. l’be results are preseuted iii which controlled defects as found in practical systems (voids, iiietallic and non-iiwtallic parti- cles) were introduced into well characterized polyiiier material so that their influence on elec- trical strength and breakdown inechanisins could be deterinined. Samples were compression- iiiolded under laboratory conditioos and scibjected to ramp-to-failure aid clcctrical aging tests at various stresses. Weibull statistics are used to analyae the results. Examination of elec- trically aged samples indicates an nxidation degradation around the defects due lo stress eu- liancenient. From the failed samples a value of ‘TI, in the inverse power inodcl was estimated. The residual life of aged samples also was examined. 1 INTRODUCTION ONSlllil~hlil.ll clfurt hasbrcn inadc lo improve the electrical pcr- c formanre of solid yolymcric insulalion systems. Tlowevcr, thcrc is dlsu considcrabic evidcisc [l 1 that defects in the iiiakrial cm catisc prenialurc elcclrical iailiire. Ccntwlly, thcrc arc four kinds nl dcfccls; voids, inclusiuns (metallic and non-mctallic), Iprofrusioiis from scnii- conducting layers and inhomogencitics (cryslalline scalc). Hoth clcctri- cal and walcr trccs caii bc iniliatcd al these dcfccls, leading to prema- ture failure. A number of exyeriincntal invesliji,itioiis [2,3[ have shown that tlic liictiinc oi polychylenc (IT) instilaicit cal~lcs can be reduced duc to the inclusions. Coppard cf 01. 141 investigated ihc dfcci oi irregular alu- minim pirticlcs on tlic dicleclsic breakdown of 111; aid showed that ac clcclric breakdown sti dccrrases rapidly with an increase in prlicle conccntration. The rcsulls were cxplaincd based on Llic boiid percob- tionmodel dcvclopcd by Duxburp ?I nl. (51. I Iowrvcr, deiccls asc fouiid to be singular and randomly dislributcd in tlic matrrial. \%rk carried out by Hagcn and lldstad [il, 7) showed that addilion ol conducting iruii aiid copper particles reduced sliori tciin ac breakdown slrcss of thc material fsom 107 kV/mm to 70 and 35 kV/mm for sphcrically and irregularly shaped prticlcs, rcspcclively. I’or glass particlcs Ihc breakdown stress was seduced to 55 kV/mni, regardless of thc shape of the particles.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

FA491CD1d01 - E M Transactions DII Dielectrics aird...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online