RU2265253C1 - Transformer reducing error of in-service potential transformers - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: primary winding of additional potential transformer having transformation ratio of unity is connected to low-voltage measuring winding of in-service potential transformer so that potential transformer cascade is formed and its measurement error equals sum of errors of in-service transformer and additional transformer whose error throughout entire range of loads connected to its secondary winding is equal in absolute value to that of in-service transformer and its error polarity is reverse to that of in-service transformer. Additional potential transformer has magnetic circuit, primary and secondary windings; magnetic circuit has a number of cores wound with ferromagnetic material ribbon and inserted one into other or placed one onto other and separated by nonmagnetic spacers. Secondary winding is wound on magnetic circuit assembled of separate cores so that part of its turns passed via through holes in nonmagnetic spacers covers at least one core.

EFFECT: enhanced measurement accuracy.

1 cl, 1 dwg

Description

The invention relates to electrical engineering and can be used to improve the accuracy of measurements of voltage transformers in operation.

Currently, methods are known for reducing the error of voltage transformers by unwinding a certain number of turns from the primary winding of a transformer or adding a certain number of turns to the primary winding of a transformer (the so-called winding correction) [1]. However, this can only be done during the manufacturing process of the transformer at the factory. In this case, in the case of winding the turns from the secondary winding of the transformer, a certain constant error value is added to the value of the transformer error, measured in the entire permissible range of load changes and in the entire permissible range of variation of the primary voltage of the transformer.

Similarly, when winding additional turns to the secondary winding of the transformer, some constant error value will be subtracted from the error value of the transformer in the entire allowable load range and in the entire allowable voltage range of the transformer. Therefore, there are such values of loads and such voltage values at which the error value exceeds the value normalized by GOST.

The closest in technical essence and the achieved result is a voltage transformer in which the secondary winding is wound on the magnetic circuit in such a way that some part of the turns passing only part of the cross section of the magnetic circuit is passed through the holes made in the magnetic circuit. The magnitude of the error in the voltage of such a transformer depends on the magnitude of the load of the transformer [2].

With a small load, the number of turns of the secondary winding is almost equal only to the number of turns covering the full cross section of the magnetic circuit, and at full load, the number of turns of the secondary winding is almost equal to the total number of turns, which includes those turns that cover only part of the cross section of the magnetic circuit.

However, the known transformer has a significant drawback. It can be made with magnetic cores that are assembled from laminated plates with holes stamped in these plates. The use of magnetic cores wound with a tape made of ferromagnetic material is unacceptable, since if a through hole is made in any surface of the magnetic circuit (end or cylindrical), the layers of the tape made of ferromagnetic material will inevitably be closed, which will lead to an increase in the open circuit losses and magnetization current of the magnetic circuit, which , in turn, will lead to an unacceptable increase in error, which cannot be eliminated by using a secondary winding, part of which turns covers only part of the cross section of the magnetic circuit.

The objective of the invention is to reduce the error of voltage transformers in operation.

This problem is solved in such a way that the primary winding of the additional low-voltage transformer is connected to the low-voltage terminals of the measuring winding of the voltage transformer in operation, the transformation coefficient of which is unity, and the magnetic circuit and the secondary winding are made in such a way that in the entire allowable range of measured voltage and the entire range of permissible loads connected to the secondary winding of the additional transformer, the absolute value of the error in voltage is approximately equal to the absolute value of the error in voltage of the transformer in operation, and its sign is opposite to the sign of the error in voltage of the transformer in operation.

This is achieved by the fact that the magnetic circuit of an additional transformer made according to this invention contains two or more cores wound from a ferromagnetic tape, superimposed on one another by end surfaces and separated from each other by spacers of non-magnetic material, and the secondary winding is wound on a magnetic circuit assembled from individual cores, so that some part of the turns passing through the through hole in the gaskets of non-magnetic material covers only part of the cross section of the magnet toprovoda (one or more cores).

This is also achieved if the magnetic circuit of the auxiliary transformer contains two or more cores wound from ferromagnetic tape, inserted into each other and separated from each other by spacers of non-magnetic materials, and the secondary winding is wound onto a magnetic circuit assembled from separate cores so that some part of the turns passing through holes in gaskets of non-magnetic material, covers only part of the cross section of the magnetic circuit (one or more cores).

This is also achieved by the fact that two or more magnetic cores of an additional transformer containing 3 or more cores wound from a ferromagnetic tape, inserted into each other and separated from each other by spacers of non-magnetic material, are superimposed on each other by end surfaces and separated from each other gaskets of non-magnetic material, and the secondary winding is wound on these magnetic cores, so that some of its turns passing through the through holes in gaskets of non-magnetic material Covers only a part sectional cores (one or more cores).

Figures 1 and 2 show additional voltage transformers made according to this invention, the magnetic cores of which contain two or more cores 1.1, 1.2 ... 1.n, wound from a ferromagnetic tape, and the secondary windings 2 with several turns 3.1 ... 3 .n, covering only part of the cross section of the magnetic cores (one or more cores), passing through the through holes 4.1 ... 4.n in gaskets of non-magnetic material 5.1 ... 5.n, are led out by taps 6 and 7.

The primary winding is not indicated in the drawings.

Figure 3 also shows an additional voltage transformer made according to this invention, which consists of a magnetic circuit containing 3 or more cores 1.1, 1.2 ... 1.n, wound from a ferromagnetic tape, as inserted into each other and separated by spacers from non-magnetic material 2.1, 2.2 ... 2.n, and superimposed on each other by end surfaces and separated from each other, in turn, by spacers of non-magnetic material 3.1 ... 3.n, from the secondary winding 4, wound on the magnetic circuit , with several turns, ooh covering only part of the cross section of the magnetic circuit (one or more cores) 5.1 ... 5n, passing through the through holes 6.1 ... 6.n in gaskets of non-magnetic material, with taps from the secondary winding 7 and 8.

The primary winding is not indicated in the drawings.

From the consideration of the figures in which the design of the additional transformer is presented (for example, Fig. 1), it follows that gaskets of non-magnetic material 5.1 ... 5n subdivide the cross section of the magnetic circuit into parallel sections (cores 1.1, 1.2 ... 1.n), and coils 3.1 ... 3.n, passing in the holes 4.1 ... 4.n, cover only part of the cross section of the magnetic circuit, for example, core 1.1.

Due to the fact that the winding direction of these turns coincides with the direction of winding the remaining turns 2 of the secondary winding, the direction of the flow created by the turns 3.1 ... 3.n in the cores 1.2 ... 1.n coincides with the direction of the flow created by the turns 2 , and the magnetic fluxes in the cores 1.2 ... 1.n are summed, and in the core 1.1 the flux created by the coils 3.1 ... 3.n is directed towards the flux created by the coils 2, and therefore the magnetic flux created by the coils 3.1 ... 3.n is subtracted from the magnetic flux created by the turns 2. Thus, the values of induction and magnetic pro the tightness in areas near the turns 3.1 ... 3.n in the core 1.1 and in the cores 1.2 ... 1.n are different.

At insignificant load currents (up to 25% of the nominal), a large fraction of the flow created by turns 2 of the secondary winding passes through the cores 1.2 ... 1.n in areas near the turns 3.1 ... 3.n. Due to the magnetizing action of the coils 3.1 ... 3.n in the sections of the cores 1.2 ... 1.n located near the coils 3.1 ... 3.n, the induction and magnetic permeability are significantly increased, and in the core 1.1. in the areas located near the turns 3.1 ... 3.n, the induction value and magnetic permeability are insignificant due to the demagnetizing effect of the flow created by the turns 3.1 ... 3.n in this core and directed against the flow created by the turns 2 in the same core. In this case, the coils 3.1 ... 3.n almost do not adhere to the flow created by the coils 2 in the entire magnetic circuit. This increases the transformation coefficient of the voltage transformer, and the working number of turns of the secondary winding is equal to the number of turns of pos.2, which reduces the voltage on the secondary winding. In this case, the absolute value of the error in the voltage decreases slightly.

With an increase in the load current, the redistribution of the magnetic flux between the cores of the magnetic circuit occurs at the place of winding coils 3.1 ... 3.n. In cores 1.2 ... 1.n, induction approaches the induction of saturation due to the magnetizing action of the flux created by turns 3.1 ... 3.n in these cores. The magnetic permeability in these cores is reduced. And in core 1.1, induction increases, but does not yet reach saturation induction due to the demagnetizing effect of the flux created by turns 3.1 ... 3.n, and the magnetic permeability is maintained significant.

Most of the magnetic flux passing through the core 1.1 in the place of winding the coils 3.1 ... 3.n now coheses with the coils 3.1 ... 3.n, and the number of coils in the secondary winding, which now consists of coils 2 and turns 3.1 ... 3.n. In this case, the voltage on the secondary winding increases and the absolute value of the error in the voltage decreases significantly, and with a certain number of turns 3.1 ... 3.n, the error in the voltage can become positive.

Thus, in the entire range of measured voltages and in the entire range of loads connected to the secondary winding of the additional transformer, with a certain number of turns 3.1 ... 3.n and a certain number of cores 1.2 ... 1.n covered by turns 3.1 ... 3.n, the absolute value of the error in the voltage of the additional transformer is selected in such a way that it turns out to be approximately equal to the absolute value of the error in the voltage of the voltage transformer in operation, and its sign is opposite to the sign of the heat voltage in the transformer in operation.

Sources of information taken into account when preparing the application

1. Transformers. Issue 27. Voltage Transformers. A.M. Dymkov, V.M. Kibel, Yu.V. Tishenin. M.: Energy, 1975, p. 36 ÷ 38.

2. Current transformers. V.V. Afanasyev et al. L .: ENERGY, Leningrad Branch, 1980, p. 48 ÷ 50.

Claims (1)

A voltage transformer to reduce the error of voltage transformers in operation, having a transformation coefficient equal to unity, connected by the terminals of its primary winding to the terminals of the measuring winding of the voltage transformer in operation, and containing a primary winding, a magnetic circuit consisting of at least two cores wound with a tape of ferromagnetic material, said cores being inserted into each other or superimposed on each other by end surfaces E and separated from each other by spacers of non-magnetic material, and a secondary winding wound on the magnetic circuit so that a part of turns passes through the through holes in the pads of a nonmagnetic material, covering at least one of said cores.

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