RU20408U1 - LOAD TRANSFORMER - Google Patents

Abstract

A load transformer containing a magnetic circuit with a closed magnetic circuit and placed on it and covering the primary winding, the secondary winding with a large common cross section, forming two branches located concentrically in the radial direction of the turns, characterized in that the secondary winding is made of a large cross section conductor in the form of a sheet with a width equal to the height of the magnetic circuit window, and the number of turns in the internal and external relative to the primary winding branches of the secondary winding are, respectively, where N - total number of turns of the secondary winding.

Description

Load transformer.

The utility model relates to electrical engineering, in particular to a high-current transformer for the study of the elements of current protection of circuit breakers and protection circuits of electrical installations.

To test the elements of current protection of circuit breakers and protection circuits, AC sources of industrial frequency up to 3-10 kA low voltage are used, which are constructively a double-winding current transformer that contains a magnetic circuit and the windings located on it: primary - high voltage and secondary - high-current, low voltage. A distinctive feature of the design of the secondary winding is that it is performed with a large total cross-section of the turns, so that the transformer operates at low current densities in the secondary winding.

Known load transformer 1, containing a magnetic circuit with a closed magnetic circuit, primary and covering its secondary windings, and the secondary winding is made in the form of a container consisting of separate interconnected elements. The disadvantage of this transformer is the difficulty in ensuring a reliable electrical connection between each other of the constituent elements of the secondary winding and current leads. Connection by welding is difficult, since copper parts (elements) have a high thermal conductivity and during welding the entire structure (secondary winding), in which the primary winding is already enclosed, is very hot. ; A load transformer 2 is also known, which contains one turn of the secondary winding made of a conductor with a large cross section equal to the cross section of the magnetic circuit window, however, in many cases, one turn of the secondary winding does not provide a sufficient current transformation coefficient, which, as you know,

determined by the ratio of the number of turns of the secondary and primary windings. But a simple increase in the turns of the secondary winding leads to an increase in power losses in the secondary winding, since in the area of high currents part of the power falls on the losses associated with overcoming magnetic scattering due to an increase in the inductance of the secondary winding. In some cases, to reduce magnetic scattering by reducing the inductive resistance of the windings, double concentric secondary windings with the same number of turns are used, between which the primary winding is placed.

So, the known transformer 3, selected as a prototype, which contains a magnetic circuit with a closed magnetic circuit and placed on it a secondary winding, covering the primary winding. The secondary winding made of a large cross-section conductor forms two single-turn branches located concentrically in the radial direction.

The disadvantage of the design of the transformer, selected as a prototype, is the lack of accuracy in transmitting the value of the current measured when testing current protection elements of circuit breakers and protection circuits of electrical installations. Indeed, a load transformer is essentially a measuring device. In it, as in any transformer, electric energy is converted and a known power is output. But not power output is the main function of this device. The main function of the load transformer is the issuance of information and, therefore, as in an informational, measuring device, is the accuracy of information transfer. In this case, the accuracy of the load transformer is determined by its transformation coefficient, because, knowing the transformation coefficient from the reading of the ammeter in the master (primary) circuit, it is easy to determine the amount of current in the controlled (secondary) circuit. Accepted to distinguish

)5

2

nominal (Kn) and true (1Ci) transformation ratios. The nominal transformation ratio is the ratio of the primary and secondary currents indicated in the transformer passport. The true transformation coefficient is equal to the ratio of the true values of the primary and secondary currents. The difference between the nominal and the true transformation coefficient is characterized by the current error (f), calculated by the formula:

f (

It is considered that the current error (f) is negative if the actual current

it turns out less than the nominal at which the current element should be triggered

protection. In apparatus engineering, special methods have been developed to reduce current

errors of measuring transformers. As shown in work 4, negative

the current error can be reduced by unwinding from the secondary winding of the current

transformer one or another number of turns. This method of reducing current

the error is called winding correction.

Based on the foregoing, it follows that the constructions of the above

load transformers do not allow the possibility of reducing current

error inherent in transformers of this type.

The problem to which the claimed latest model is aimed is to

reducing the current error of the load transformer, which determines

inaccuracy in the transmission of the measured current value when testing current elements

protection while maintaining a sufficiently high coefficient value

transformations.

The specified task is realized due to the special design of the secondary winding

load transformer. Like the transformer selected as a prototype, 3

U “J forming two branches arranged concentrically in the radial direction

turns. In contrast to the prototype, the secondary winding is made of a large cross-section conductor in the form of a sheet with a width equal to the height of the magnetic circuit window, the number of turns

internal to the primary winding of the branch of the secondary winding, and in

„„ N + external to the primary winding branch of the secondary winding of the turns,

where N is the total number of turns of the secondary winding. In FIG. 1 is a schematic representation of an embodiment of a particular embodiment of the inventive load transformer, and FIG. 2 is a connection diagram of windings.

The load transformer contains an armored magnetic circuit type 1 and windings: primary 2 and secondary, which is made in the form of two concentric branches 3 and 4, between which the primary winding 2 is placed. The secondary winding is made of a conductor (copper) in the form of a sheet with a width equal to the height of the window of the magnetic circuit 1 (taking into account the thickness of the insulation layer, which is not shown in Fig. 1). In this particular case, the branches of the secondary winding are made of a copper sheet of a “U-shaped shoulder part located around the central core of the armored magnetic circuit so that the turns of the secondary winding are concentrically and the protrusions forming a single unit with the conductor are current leads 5 and 6 of the branches of the secondary winding 3 and 4 and contact transition 7 between the branches 3 and 4 of the secondary winding. In this case, to ensure the convenience of operation of the load transformer, the protrusions forming the current leads 5, 6 and the contact junction 7 are bent 90 ° to the shoulder of the conductor forming the branches of the secondary winding 3 and 4. In this embodiment, the secondary winding of the transformer consists of 9 turns, and branch 3 consists of four turns, and branch 4 consists of five turns.

J)

4

this the number of turns of the secondary winding becomes less than the nominal number of turns and as a result of this decreases the p.m. secondary winding directed against ppm primary winding, but the latter remains unchanged, because determined only by the primary current and the number of turns of the primary winding. Decrease in ppm secondary winding is accompanied by an increase in ppm magnetization and the resulting magnetic flux, which, in turn, leads to an increase in the emf in the secondary winding and reducing the negative current error.

It was experimentally established that with a small number of turns of the secondary winding of the load transformer made according to the concentric scheme, the number of turns in the internal and external (relative to the primary winding) branches of the secondary winding

 + 1

should be respectively against N / 2 in each of the branches in

22

according to the nominal, where N is the total number of turns of the secondary winding. A load transformer was manufactured and tested for testing current protection elements of circuit breakers and protection schemes for electrical installations, with a small current error at a current in the controlled circuit of about 12 kA.

Literature:

1.a.s. USSR No. 431561, IPC: Н01Р27 / 30.05.06 / 74, Bull. No. 21.

2.a.s. USSR No. 625257, IPC: Н01Р27 / 30.25.09 / 78, Bull. No. 35.

3.p. RF №900327, IPC: Н01Р31 / 06, Publ. descriptions 25.01.82

4.V.V. Afanasyev et al., “Current Transformers, L.: Energy, Leningrad Branch, 1980.

Applicant

about Director NPF / U / / Davydenko Yu.N.

../

Claims (1)

A load transformer containing a magnetic circuit with a closed magnetic circuit and placed on it and covering the primary winding, the secondary winding with a large common cross section, forming two branches located concentrically in the radial direction of the turns, characterized in that the secondary winding is made of a large cross section conductor in the form of a sheet with a width equal to the height of the magnetic circuit window, and the number of turns in the internal and external relative to the primary winding of the branches of the secondary winding is

respectively, where N is the total number of turns of the secondary winding.