SU1365149A1 - Method of heating up power transformer - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to oil power transformers. The method of heating the oil transformer is that one winding of the transformer is short-circuited, the other winding is connected to a DC source, and the connection of each phase of the winding alternates with a change of polarity after a certain time. A formula is given for calculating the time after which the polarity is changed. 2 hp f-ly, 3 ill., 2 tab. i (L

Description

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The invention relates to electrical engineering and can be used for oil-filled power transformers during heating prior to opening for the purpose of inspecting the active part, monitoring heating for assessing the insulation state of the windings and conducting drying.

The aim of the invention is to provide a uniform heating of the windings, an increase in the heating power, a decrease in the temperature of the windings during forced heating from a DC source.

FIG. Figures 1 and 2 show the connection diagram of a 3-phase 2-winding transformer on the switch in FIG. 3 time diagrams of the switch operation.

The switch can be made on contactors or power semiconductor devices, its operation is controlled by a software device in accordance with FIG. 3, where and, Ug, Up voltage of phases, Uj - effective value of voltage.

Example. A 2-winding three-phase transformer is connected to a direct current source through a switch. Alternately, in accordance with FIG. 3, connect the phases of the high (or low) voltage winding for a time determined by the above formula, as a result of which currents flow alternately in the phases of the high and low voltage windings, which also heat the transformer.

In calculations, the calculation is: P, 0.00738

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In tab. Figure 1 shows the times for various heating power control laws, which are derived from averaged parameters.

The transformer is heated to an average oil temperature of +20 ° C at an ambient temperature of -25 s. If heating is performed at a variable power, then the switching time is calculated for maximum power (current).

The transformer is heated to an average oil temperature of +55 ° C (the temperature of the upper oil layers is 70-75 s) at an ambient temperature of -25 ° C to dry the insulation. These calculations are given in Table. 2

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When connecting the windings with a triangle, the switching time of the DC source and the remagnetization of the core in Table. 1 and 2 must be multiplied by 0.866 and 1.3, respectively.

The use of the proposed method in comparison with the known heating methods makes it possible to obtain the passage of currents through all phases of the windings and thereby ensure their uniform heating, increase the maximum heating power of the transformer by 2-3 times and thereby extend the heating range for drying in negative temperatures, illustrated by relationship 2 in FIG. 1, built for the maximum allowable temperature of the windings +105 C, and the data table. 2; to obtain a predetermined reduction in the heating time of the transformer when forced with a lower temperature of the windings, as illustrated in Table. 1, In a specific example, the temperature of the windings is reduced by 2.1 times.

In addition, when heated with a large excess of oil temperature relative to the environment, a natural force can be obtained at a constant voltage of the power source. In this case, the force is removed as the resistance of the windings increases due to their heating. For data table. 2 power at the beginning of heating 1.32 above the established power.

The use of heating forces with a winding temperature significantly lower than acceptable for this class of insulation makes it possible to reduce winding temperature control requirements.

and control heating power,

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Claims (3)

1. A method of warming up a power transformer, which involves passing an electric current through the phases of one IB-coil with another winding short-circuited by connecting the phases of the winding to a DC source, characterized in that, in order to evenly heat the windings, increase the heating power and decrease the temperature windings during power up, the connection of each phase of the winding to the DC source alternate with the change of polarity through time with f.  and 4. in 3t Wi de t is the half-period of voltage variation on the phases; t is the time between successive turn-ons of the contactors of the switch connecting the phases of the winding to the DC source; C - nominal frequency; 1) RFC heating and nominal short circuit power in proportions of the corresponding nominal values of the transformer; B, V - nominal induction 20 and a change in the induction of different phases to the same-name field of the primary magnetic field of the current source alternate with a time shift of 2t. Table 1 current during pemagk  AND Gz, breaking the magnetic circuit t (by the amount and В 2В ;; - when connecting the phases of the supply winding star; - - -y to. 4 and - at connection by a triangle; g, g - resistances of the phases of the windings, respectively, supply and short-circuited. 2. A method according to claim 1, characterized in that each phase is connected to a direct current source in a half period t for a time of 2 t. 3. Method according to paragraphs. 1 and 2, characterized in that the connection different phases to the same name field of the current source alternate with a time shift of 2t. Constant winding temperature + 50 ° С Constant source voltage Constant heating power Constant winding temperature +105 C (by a known method), 54 Constant winding temperature +105 С 2.55 Constant voltage the source 1.82 00 OO 0.65 table 2 0.78 1.1 0.385 0.81 . ::::::: i :::::::::: i ::: ::: i ::: Constant power 1,58 0,63 Heating is not possible due to insufficient power. Srig. one / fo / iMyfTJOfTJop (Rig. G i :::: :::: iz :: 1.06 1.26