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  • A rectifier transformer ageing study using optical fibre temperature sensors, transformer thermal modelling, and EIMV physical-chemical diagnostics : Elektronski vir
    Gradnik, Timotej ; Končan-Gradnik, Maja
    Four 59 MVA rectifier transformers built in 1988 are of vital importance to the TALUM aluminium plant in Slovenia. After the dielectric failure of one of these transformers in 2004, an internal ... inspection was carried out. DP tests of paper samples of the rectifier's winding insulation showed that the paper insulation's mechanical strenght in the hot-spot region had already been reduced significantly after 15 years of operation at a low load profile. Therefore, the question of what a normal expected lifetime should be for the three remaining rectifier transformers arose. After refurbishment in 2005 a decision was made to equip the new windings of the failed transformer with 14 optical fibre temperature sensors for on-line measurements of hot-spot, winding, and various oil temperatures. The temperature measurements were collected with the optical sensors during the first 8 months of transformer operation in 2006, as well as a thermal model was constructed for this transformer. The termal model has been adapted also for the other three transformers of a similar construction type, operating in parallel. Thermal modelling has enabled a more appropriate transformer cooling system setting and consequently a prolongation of remaining expected lifetime. The results ofcomplex physical chemical transformer diagnostics conducted from 1988-2007 on these four transformers are also discussed, together with their expected lifetime evaluations based on oil and paper analysis. Combining the load-dependent results of direct temperature measurements with the result of physical-chemical diagnostics allowed us to compare different methods of estimating the ageing rate of the four rectifier transformers. Reasons for theearly ageing are clarifield, together with suggested actions to reduce the ageing rate and to prolong the rest of lifetimes of these four transformers.
    Vir: Final programme [Elektronski vir] (2007, [9] f.)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2007
    Jezik - angleški
    COBISS.SI-ID - 29115653

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