IEEE 1407-1998 pdf download IEEE Trial-Use Guide for Accelerated Aging Tests for Medium-Voltage Extruded Electric Power Cables Using Water-Filled Tanks
5. Prior tests and preconditioning of specimens
Partial discharge tests should be performed on every test cable to ensure that the cable and terminations aredischarge-free prior to the aging test. The partial discharge test should be carried out according to AEICCS5-94 and AEIC CS6-96.
It is well known that the most commonly used chemical cross-linking agent,dicumyl peroxide, produces anumber of cross-linking agent by-products which include acetophenone, cumyl alcohol, a-methyl styreneand smaller quantities of other by-products. Their formation cannot be avoided, but they are migratory andcan theoretically yolatilize from the cable. Methods for by-product analysis and data for new and agedcables have been reported (Damon, et al,[B7],EPRI Report EL-7076 [B12]).
Silane-cured XLPE does not use dicumyl peroxide as the curing agent and thus contains different cross-linking by-products. No data are available at this time on the effects of the by-products for silane-cured insulaion and the procedures in this clause may not be applicable to silane-cured XLPE. Also no data are availablein the published literature on the effect of cross-linking by-products on EPR-insulated cables.
Residual cross-linking agent by-products may infuence the electrical properties of polymeric insulatingmaterials such as XLPE, tree retardant cross-linked polyethylene (TRXLPE), and EPR. The residuals wildepend on the specific chemical reactions, which occur during manufacture and the rate at which the by-prod.ucts subsequently diffuse through the extruded layers. Although the same cross-linking by-products occur inTRXLPE and EPR, the rate of diffusion will differ from that for XLPE and may vary for different TRXLPEand EPR formulations. In carefully controlled experiments on XLPE molded slabs and ribbons, removedfrom cables, the short-term 60 Hz breakdown strength increased but the impulse breakdown strengthdecreased with increased concentration of by-products (Damon, et al., B7, Eichhorn B9], EPRI Report TR103908 B131. Wartusch and Wagner (B301). The ac breakdown strength of XLPE increased between 10%and 15% when the by-products were present up to 2% but decreased when the by-product concentrationsexceeded 2% (EPRI Report TR-103908 B13)). This study also showed that mixtures of the volatile by-prod.ucts gave synergistic results. The electrical and water treeing resistance was improved by the presence of by.products (Ashcraft B3], Wartusch and Wagner (B301).Although this discussion is not intended to be a comprehensive literature review. the results show that the influence of the by-products on breakdown strength isquite complex
There are limited data available on the effects of by-products on the long-term behavior of either moldedslabs or cables. Controlled tests to examine the long-term effects are difficult to carry out due to the already.mentioned migratory nature of the by-products. An examination of new and service-aged steam-cured XLPEcables showed that the acetophenone level decreased from approximately 3000 ppm to 40 ppm during thefirst two years of installation and that very little (
IEEE 1407-1998 pdf download
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