RU213924U1 - Transformer with a reduced value of the magnetizing current when working under load - Google Patents

Abstract

The utility model relates to the field of electrical engineering. The technical result consists in reducing the magnetizing current when operating under load in a transformer with increased magnetic flux leakage due to the redistribution of leakage inductances towards the predominance of the primary winding inductance. A transformer with a reduced value of the magnetizing current when operating under load consists of a magnetic circuit, primary and secondary windings wound on a magnetic circuit. The primary and secondary windings are close together. A choke is additionally included in the primary winding circuit, formed by a wire wound along a magnetic core rod free from windings. 2 ill.

Description

The utility model relates to the field of electrical engineering, to electromagnetic transformers and concerns single-phase and three-phase power transformers with increased magnetic flux leakage.

Transformers with increased magnetic flux leakage include transformers used in transformer substations. The increased leakage of the magnetic flux reduces the short-circuit currents in the secondary circuit and makes it possible to make short-circuit protective devices (circuit breakers, fuses, oil circuit breakers, etc.) cheaper, with a weaker arc extinguishing system. The increased leakage of the magnetic flux of power transformers determines the increased short circuit voltage. So the short circuit voltage of power transformers used at transformer substations has a value of 5.5% to 12%.

The prototype of the claimed device is a transformer with increased magnetic flux leakage inductance, consisting of a magnetic circuit, primary and secondary disk windings wound on a magnetic circuit in such a way that the secondary winding is divided in half into two sections, and an undivided primary winding is located between the halves of the winding, according to a patent for useful RF model RU 186814 U1 - [1]. A transformer of this design has a leakage inductance of the primary winding 2 times higher than the leakage inductance of the magnetic flux of the secondary winding. The leakage inductance of the magnetic flux of each winding is proportional to the square of the number of turns covered by the magnetic leakage flux. The magnetic flux covers the primary winding completely. The secondary winding is divided into two sections. The inductance of each section, reduced to one number of turns, is 4 times less, since the sections contain 2 times fewer turns than the solid primary winding. When connected in series, the leakage inductance of the individual sections of the secondary winding is added. As a result, the total reduced inductance of the secondary winding is 2 times less than the leakage inductance of the primary. The possibility of redistributing the leakage inductance of individual transformer windings has been studied in the literature: Markwardt E.G. "On the scattering of transformer windings". "Electricity", 1937, No. 11, p. 60-63 - [2].

The disadvantage of such a device is the increased magnetizing current when the transformer is under load.

The disadvantage is explained by the insufficient redistribution of the leakage inductance of the windings in the direction of the predominance of the primary winding. As described above, the prototype design assumes the maximum possible ratio of the leakage inductance of the primary winding and the leakage inductance of the secondary winding reduced to the number of turns of the primary winding, equal to 2 and not more.

The magnetizing current is determined by the value of the main magnetic flux of the transformer. When the transformer is operating under load, it decreases by an amount proportional to the voltage drop across the leakage inductance and the active resistance of the primary winding. This will have a particularly strong effect on transformers with increased leakage inductance of the magnetic flux.

The predominance of the leakage inductance of the primary winding determines the increased voltage drop on the leakage inductance of the primary winding during operation under load, and therefore reduces the main magnetic flux and magnetizing current. But the design of the prototype does not allow you to make a transformer with a predominance of the leakage inductance of the primary winding over the leakage inductance of the secondary winding, reduced to the number of turns of the primary winding by more than 2 times.

This determines the increased magnetizing current when operating under load, as a result of not using all the potential possibilities of redistributing leakage inductances towards the predominance of the leakage inductance of the primary winding.

The proposed transformer with increased leakage inductance of the magnetic flux consists of a magnetic circuit, primary and secondary windings wound on a magnetic circuit, and to reduce the value of the magnetizing current of the transformer under load by redistributing the leakage inductance of individual windings in the direction of the predominance of the leakage inductance of the primary winding and increasing the voltage drop on the leakage inductance of the primary winding from the load current, a choke is additionally included in the primary winding circuit, formed by a wire wound on a magnetic core free from windings.

The leakage inductance of the magnetic flux of the transformer windings is minimal, which is achieved by bringing the primary and secondary windings closer together (with concentric windings, the distance between the windings decreases; with disk windings, the windings move towards each other). A significant part of the inductive resistance of the transformer is determined by the inductance of the choke connected in series to the primary winding circuit, and in order to reduce the mass, size and cost of the choke, the steel of the magnetic core rod, free from windings, is used. The inductor is wound not around the core of the magnetic circuit, but along the free core of the magnetic circuit. With this arrangement, the inductor winding creates a magnetic flux perpendicular to the main magnetic flux and, due to this, practically does not load the magnetic circuit in the direction of the main magnetic flux.

The proposed transformer can be used both independently instead of the prototype, and in conjunction with the technical solutions of the prototype, in which case the effect will be summed up.

The essence of the proposed technical solution is that in a transformer with increased leakage inductance of the magnetic flux when operating under load, consisting of a magnetic circuit, primary and secondary windings wound on a magnetic circuit, a choke is additionally included in the primary winding circuit, formed by a wire wound on a free windings of the magnetic core. At the same time, by changing the design of the transformer with increased leakage of the magnetic flux, it was possible to achieve a decrease in the magnetizing current under load, due to the redistribution of the leakage inductances of individual windings in the direction of the predominance of the primary winding inductance to a greater extent than when using the prototype.

The claimed utility model solves the problem of reducing the magnetizing current of a transformer operating under load.

The claimed device meets the requirement of "novelty", as it has a new feature: the primary winding circuit additionally includes a choke formed by a wire wound on a magnetic core free from windings.

The technical result of the proposed solution is to reduce the magnetizing current during operation under load in a transformer with increased leakage of magnetic flux due to the redistribution of leakage inductances in the direction of the predominance of the primary winding inductance.

The technical result is achieved by the fact that in order to reduce the magnitude of the magnetizing current of the transformer under load by redistributing the leakage inductances of individual windings towards the predominance of the leakage inductance of the primary winding and increasing the voltage drop on the leakage inductance of the primary winding from the load current, a choke formed by a wire is additionally included in the primary winding circuit, wound on a core of a magnetic circuit free from windings.

In FIG. 1 shows a transformer with a reduced value of the magnetizing current under load, where: 1 - primary winding; 2 - secondary winding; 3 - magnetic circuit; 4 - a choke included in the primary winding circuit, formed by a wire wound on a magnetic core free from windings.

In FIG. 2 shows a diagram of an experimental setup for testing the utility model.

The proposed transformer with increased leakage inductance of the magnetic flux consists of a magnetic circuit 3, primary and secondary windings 1 and 2, and to reduce the magnitude of the magnetizing current of the transformer under load by redistributing the leakage inductance of individual windings in the direction of the predominance of the leakage inductance of the primary winding 1 and increasing the voltage drop across the inductance leakage of the primary winding from the load current, a choke is additionally included in the primary winding circuit, formed by a wire wound on a magnetic core free from windings.

To experimentally verify the effectiveness of the proposed device, experiments were carried out with a transformer from a converted welding transformer TD-300. The scheme for conducting experiments is shown in Fig. 2.

In the course of the experiments, a comparison was made of the magnetizing current, the transformer under load for a transformer with a conventional arrangement of windings and for a transformer, in the primary winding circuit of which an additional choke is included, formed by a wire wound on a magnetic core free from windings.

The magnetizing current of the transformer under load was measured using the method known from the RF patent RU 2328749 C1 - [3]. The essence of the method is that shunts are installed in the primary and secondary windings. The ratio between the rated currents of the shunts is chosen equal to the transformation ratio of the transformer. The shunt terminals are connected so that the voltage drop from the secondary current is subtracted from the voltage drop from the primary current. The oscilloscope in such a circuit will show the magnetizing current.

Compare two transformers:

- the first transformer with increased magnetic flux leakage, converted from a welding transformer with spaced primary and secondary windings;

- the second transformer with increased leakage of the magnetic flux, converted from a welding transformer with close primary and secondary windings and additionally wound on a core of the magnetic circuit free from windings, included in the primary winding circuit (the claimed transformer); The number of turns of the inductor is chosen so as to equalize the short circuit voltage of the compared transformers (the total resistance of the transformer windings). Due to the convergence of the windings of the proposed transformer, the total inductive resistance of the windings is reduced, and by adding a choke to the primary winding circuit, it is restored at the same level, that is, the leakage inductance of the individual windings is redistributed towards the predominance of the primary winding circuit inductance.

The following results are obtained:

under equal conditions and the same load, the magnetizing current of the proposed transformer, in the primary circuit of which an additional inductor is included, formed by a wire wound on a magnetic core free from windings, always turned out to be less than that of a conventional transformer. During the experiments, a large amount of data was obtained for various levels of supply voltage, various loads. So for one of the modes under the same conditions, the magnetizing current of a conventional transformer under load was 6 A, and for the proposed transformer with a choke, 2.1 A.

Experimental data allow us to conclude that the claimed invention meets the criterion of "industrial applicability".

The higher the leakage inductance of the transformer, the greater the effect can be achieved. So, for power transformers of power supply systems, it is advisable to use such a winding design for a voltage level of 110 kV and higher, where the short circuit voltage is 12.5%.

Sources of information:

1. RF patent for utility model No. 186814 MPK H01F 30/04 (2006.01), "Transformer with a reduced value of the magnetizing current when operating under load", authors: Gukov D.V., Zagulyaev S.D., Ivankov S.M. , Zakirov T.R., Romanenko S.I., bul. No. 4 dated February 5, 2019 (prototype).

2. E. G. Marquardt. "On the scattering of transformer windings". "Electricity", 1937, No. 11, p. 60-63.

3. RF patent No. 2328749 MPK G01R 19/00, “Method of measuring the magnetizing current of a transformer operating under load”, authors: Gukov D.V., Gukov A.D., Prutchikov I.O., Kamlyuk V.V., Soldatov V.N., Prokofiev V.E., Spiridonov A.E., bul. No. 19 dated 10.07.2008

Claims (1)

A transformer with a reduced value of the magnetizing current when operating under load, consisting of a magnetic circuit, primary and secondary windings wound on a magnetic circuit, characterized in that the primary and secondary windings are brought together, and a choke is additionally included in the primary winding circuit, formed by a wire wound along a free windings of the magnetic core.

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