Transformer oil is a liquid dielectric obtained by distilling oil. The dielectric properties of the transformer oil are directly dependent on the degree of its wetting and contamination by various impurities: the more moisture and mechanical impurities in the oil, the lower its electrical strength.
The damaged transformers that have been in service for a long time come in for repair, so the oil in them is usually so much moistened and soiled that it can only be reused after cleaning and drying.
The transformer oil purification from the mechanical impurities and moisture contained in it is carried out with the help of special apparatuses - centrifuges and filter press, brief information about the device and the principle of operation of which are given below.
The centrifuge (Fig. 91, a) is a mobile device, on the platform of which there is a body 1 with a drum inside, gear pumps 2, an electric motor 5, an electric heater 4 and a filter 5. The drum consists of a large number of cone-shaped plates with holes. The plates are located on the common shaft parallel one above the other with a very small gap between them; they serve to separate the liquid into a multitude of thin layers and thereby increase the intensity of oil purification.
Humidified and contaminated oil is pumped into the centrifuge by pump 2 through the central inlet. The apparatus also has three outlet openings with sleeves, of which the upper outlet serves to drain the oil if the drum is excessively contaminated or the centrifuge is suddenly stopped, the middle outlet is for the outlet of the cleaned oil and the lower one for draining the water separated. (separated) from the oil. For more intensive removal of water, the oil is heated by an electric heater to 50 - 60 ° C.
The mechanical admixtures of large fractions are retained by the filter 5 installed on the inlet pipe of the oil pipeline. The filter is a thin metal mesh with small holes. The centrifuge can operate in one of two modes, determined by the degree of moisture of the oil.
When cleaning weakly moistened oil, the centrifuge operates in the normal mode, i.e., in the mode of removing moisture and mechanical impurities, and if it is necessary to clean the highly moistened oil, the centrifuge is rearranged (by rearrangement of the plates) to another mode of operation-the removal of water from the oil. The productivity of a centrifuge operating in normal mode is about 1600 l / h.
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