RU2174281C1 - Method for drying solid insulation of transformer windings in sealed tank - Google Patents

Abstract

FIELD: electrical engineering; in-service drying of winding insulation. SUBSTANCE: method involves repeated drying cycles including circulation of transformer oil contacting solid insulation of transformer windings followed by moisture removal. Each cycle includes build-up of electric field in solid insulation prior to oil circulation which is maintained for 2-4 h and moisture removal from transformer oil by centrifuging or freezing. Electric field is built up by applying dc voltage between winding conductors and transformer ground. EFFECT: enhanced drying effectiveness; provision for dispensing with evacuating equipment. 1 tbl

Description

 The invention relates to electrical engineering, in particular to methods of drying in a sealed tank of solid insulation of transformer windings during their operation.

A known method of drying the solid insulation of transformers, including heating the solid insulation by contact with heated oil while evacuating, turning off the heating, continuing evacuation until the insulation temperature reaches 40-50 ^o C, and throughout the cycle, the residual pressure is maintained at a level not exceeding 5 mm Hg, and the cycle can be repeated many times (SU 671664, class H 02 K 15/12, 08/15/80).

 The known method provides a sufficiently quick drying due to the intensification of the process.

 However, the known drying method is applied at very low residual pressure in the tank. In addition, this method is quite energy intensive.

 A known method of drying the insulation of an electric machine without supplying heat, in which a constant voltage is applied between the conductors of the windings and the body of the machine, connecting the positive pole of the DC voltage source to the conductors of the windings, and the negative to the body, while the insulation of the electric machine is affected by microwave radiation (SU 1688354 , CL H 02 K 15/12, 10.30.91).

 The known method allows to intensify the drying process by increasing the mobility of water molecules, destroying their thin shells and depolarizing space charges in the metal of the windings and casing, and also provides energy savings.

 However, the known method is not applicable to drying the solid insulation of the transformer windings during operation.

 The closest analogue of the present invention is a method of drying the solid insulation of transformer windings in a sealed tank by repeating cycles involving the circulation of transformer oil in contact with the solid insulation of the transformer windings and the subsequent removal of moisture (SU 1365265, class H 02 K 15/12, 01/07/08 )

 Moreover, in the known method, the transformer oil is circulated after it is heated, and the moisture is removed from the vapor-air medium by circulating it while freezing it.

In the known method, the heated transformer oil is brought into contact with the solid insulation of the transformer windings to heat the latter. After reaching an insulation temperature of 75-85 ^o C turn off the oil heater, stop the circulation of oil and circulate the air, which is a medium that carries moisture from the solid insulation of the transformer windings.

 The drying process is controlled by a change in the amount of moisture in the trap and a change in the moisture content of solid insulation.

The total drying time of the solid insulation of the transformer TDTG-40500/110 / 38.5 / 6.6 (initial moisture - 3.55%, final moisture 1.02%) in a known manner is 240 hours; the number of cycles for removing moisture from the insulation - 10; total amount of removed condensate 230.8 l; the temperature of oil heating in each cycle is 90 ^o C; respectively, the heating temperature of the insulation is 80-88 ^o C.

 The known method allows efficient drying of solid insulation in containers not designed for vacuum, does not require the use of vacuum equipment.

 However, the known method is time-consuming (240 hours), as well as energy-intensive.

 A new technical result from the use of the present invention is the intensification of the process while reducing the energy intensity of the process, due to the drying of the heat supply.

 This result is achieved by the fact that in the method of drying the solid insulation of transformer windings in an airtight tank by repeating cycles involving the circulation of transformer oil in contact with the solid insulation of the transformer windings and the subsequent removal of moisture, an electric circuit is created in the solid insulation of the transformer windings before circulating the transformer oil in each cycle field by applying a constant voltage between the conductors of the windings and the transformer housing, which is maintained for 2 to 4 hours, and moisture is removed from cold oil by centrifugation or freezing.

 Before the transformer oil is circulated, it is not heated, and moisture is removed from the cold transformer oil (at room temperature) by centrifugation or freezing.

 The process is carried out at a high residual pressure.

 An electric field is created in the solid insulation of the transformer windings by applying a constant voltage between the winding conductors and the transformer case, connecting the positive pole of the DC voltage sources to the winding conductors, and the negative to the case.

 The created electric field contributes to a change in the mobility of water molecules from the mass of solid insulation to its surface in contact with circulating cold oil, which is a medium that carries away moisture released from the solid insulation.

 The claimed method is implemented on a transformer TDTG-40500/110 / 38.5 / 6.6, the technological parameters of drying are presented in the table.

 Water is removed from the transformer oil by centrifugation, passing a circulating oil enriched in water through a centrifuge.

 The drying process is continued until the insulation tolerance value is reached.

 Analysis of the table shows that the drying time in the proposed method is much shorter and is 84 hours, which is 3 times less than in the prototype method. The energy consumption by the proposed method implemented in example 1 is ≈12 kWh, and in the prototype method, the total energy consumption (oil heating, oil circulation, circulation of the vapor-air mixture, etc.) is more than ≈200 times.

 Thus, the proposed method for drying the solid insulation of transformer windings ensures the preservation of the quality of insulating materials due to a significant reduction in drying time and the absence of heating of transformer oil, a decrease in the downtime of equipment, as well as a very significant reduction in the energy intensity of drying.

Claims (1)

 The method of drying the solid insulation of transformer windings in an airtight tank by repeating cycles involving the circulation of transformer oil in contact with the solid insulation of the transformer windings and the subsequent removal of moisture, characterized in that before the transformer oil is circulated in each cycle in the solid insulation of the transformer windings, an electric field is created by applying a constant voltage between the conductors of the windings and the transformer housing, maintain an electric field for 2 to 4 hours, and remove Moisture is carried out from cold transformer oil by centrifugation or freezing.

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