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Sorted by type: Papers

  • Papers

    • English The Oil-Moisture Problem of Aged Transformers

      (Papers) 2014-05-02 08:23:44 by Altmann, Bukvis

      Summary: Experimental verification of diagnostic methods


    • Czech Voda ve vystárlých transformátorech

      (Papers) 2007-05-27 10:22:02 by Inh. Altmann

      Summary: Řádně ošetřovaný a standardně zatěžovaný systém olej-celuloza výkonového transformátoru reprezentuje velmi spolehlivý celek. Proto je vždy velmi frustrující pozorovat jak je tento systém, zvláště u vystárlých a navhlých transformátorů, devastován chybnou diagnostikou a nevhodným ošetřením. Je ovšem nutno vždy předem zdůraznit, že našim cílem je náležité vysušení transformátoru nikoliv pouze jeho olejové náplně. To znamená, že musíme bezpečné odstranit dilutovanou vodu z jeho celulozových materiálů. Naproti tomu množství vody dilutované a vázané vody obsažené v olejové náplni tohoto stroje je ve srovnání z množstvím dilutované vody v celuloze natolik malé, že jej můžeme z hlediska vysoušení transformátoru zanedbat. Transformátorový olej v tomto ohledu slouží pouze jako „nosič“ a to v první řadě jako „nosič“ informace kolik dilutované vody je obsaženo v celuloze. KF metoda která měří současně jak vodu dilutovanou tak vázanou vodu v oleji, je proto pro určení množství dilutované vody v celuloze nejen nevhodná, ale dokonce nebezpečná – relativně suchý transformátor je považován za navlhlý.


    • English The water problem of aged transformers

      (Papers) 2007-05-27 10:17:22 by Ing. Altmann

      Summary: If properly maintained and loaded, the oil-cellulose system of power transformers generally represent a very robust and reliable system. It is therefore always very frustrating to observe the devastation of aged transformers due to improper diagnostics and incorrect maintenance. It should be emphasised in advance that our dehydration target is to properly dehydrate a transformer and not only its oil filling . This means to remove diluted water from its cellulose materials. From this point of view the amount of diluted and bonded water in its oil filling is negligible. The oil serves here only as a „porter“ of information of how much diluted water is actually accumulated in the cellulose. The reading of diluted water in the oil by a suitable and precise humidity sensor therefore represents an ideal solution of our diagnostic problem. In contrast the KF method, which reads the content of diluted and bonded water simultaneously, is clearly unsuitable and even dangerous because, for example, a relatively dry aged transformer can be considered as a wet one.


    • English Infrared Verification

      (Papers) 2005-02-02 11:07:13 by Altmann

      Summary: The preliminary verification of the TRAFOSEAL function by the unfrared camera.

      Download "Infrared Verification" Size: 823.67 KB (English)

    • English Dielectric Diagram

      (Papers) 2004-08-26 12:29:37 by Altmann

      Summary: A Dielectric diagram is the logical extension of the current diagnostic method, which evaluates the degree of a transformer’s water contamination by means of Nielsen diagram. The Nielsen diagram provide us with the required temperature invariant (Cp (%)) by which we can unequivocally analyse the moisture problem of a given transformer. The Dielectric diagram will subsequently show us the actual dielectric problem of a given transformer by the means of the Ud-curve (Cp=const) for the whole range of its operational temperatures.

      Download "Dielectric Diagram" Size: 269.49 KB (English)

    • English The Oil-Moisture Diagnostic Problem of Aged Transformers

      (Papers) 2004-04-26 13:18:40 by Altmann

      Summary: The present indirect diagnostic method of taking an oil sample for the estimation of water contamination of power transformers is based on the parallel measurement of two values - water content in the oil by the Karl Fisher method C w,KF (ppm) and the average temperature of the transformer oil cellulose system T(C). This method can sometimes lead to inaccurate, contradictory and quite curious diagnostic results. An example of a diagnostic discrepancy, is when the aged oil in a transformer is replaced by new oil. Following the oil change, the C w,KF value is always higher in the aged oil compared to the new oil at the same transformer temperature. This discrepancy is hard to accept and understand. Let's say, we have a transformer with 10,000 kg oil and 1,000 kg of cellulose. Before and after the oil change the transformer is operated at the same temperature (T= 50C). The water in oil results are (C w,KF) 30 ppm in the aged oil and 20 ppm in the new oil. According to a Nielsen Equilibrium chart ([L2] - Fabre-Pichon Diagram), before the oil change the water content in the cellulose (Cp) is 4.3 %, or 43 kg (1000 x 0.043). However using the same chart, the new oil value gives a water content of 3.2 % or 32 kg of water ? With the aged oil a maximum of (10,000 x 0.000030) 0.3 kg of water will be in the oil, and 0.2kg for the new oil. Why is there a variance of 11kg of water, and how can the water disappear just by changing the oil ?


    • English Impact of Vacuum Treatment on DGA

      (Papers) 2004-04-26 13:14:39 by Altmann

      Summary: State of the art for the diagnosis of undesired changes in the Insulating Systems of oil-immersed transformers is DGA - Dissolved Gas in oil Analysis [L1]. By the detecting variations of the individual gases over longer periods, it is possible to estimate the type, the size and in certain cases the localisation of the damage. The introduction of new vacuum treatment methods for transformers has raised worries weather results of DGA would not be deteriorated or changed in an unwanted manner