RU2685571C1 - Device for measuring leakage inductances of individual windings of a two-winding transformer - Google Patents

Abstract

FIELD: measurement.SUBSTANCE: invention relates to electrical measurements. Essence of invention consists in the fact that in series circuit of device for measurement of inductances of dissipation of separate windings of double-winding transformer additionally includes winding auxiliary two-winding transformer with variable transformation ratio, and free windings of analyzed and auxiliary transformers are connected in series in reverse, wherein transformation coefficient of auxiliary transformer is selected equal to transformer ratio of measured transformer.EFFECT: technical result is high accuracy of measuring inductances of dissipation of separate windings of double-wound transformer.1 cl, 1 dwg

Description

A device for measuring the leakage inductances of individual windings of a transformer refers to electrical measurements and is intended for use in testing two-winding transformers.

The closest to the proposed technical solution (prototype) is the “Device for measuring the leakage inductances and active resistances of each winding of a two-winding transformer”, according to the utility model patent of the Russian Federation: RU 73740 U1 from 27.05.2008, IPC G01R 27/26 - [1]. The device consists of two electrical circuits connected to an alternating current circuit: - the primary winding of the measured transformer and an ammeter are sequentially connected in the first circuit, a voltmeter is connected in parallel to the primary winding; - the second circuit consists of the secondary winding of the transformer to be measured, an ammeter and an adjustable active resistance; a voltmeter is connected to the secondary winding.

The disadvantage of the device [1] is the additional measurement error due to the difference in the phases of the currents flowing through the primary and secondary windings. The phase difference is determined by the presence of adjustable active resistance only in the secondary winding, which is not present in the primary winding.

The solution to the problem of measurement is achieved by eliminating from the prototype adjustable resistance in the circuit of one of the windings of the transformer to be measured. Instead, the current flowing through one of the windings of the transformer to be measured is transformed using an auxiliary two-winding transformer with a variable transformation ratio into the second winding of the transformer to be measured, and the transformation ratio of the auxiliary transformer is chosen equal to the transformation ratio of the transformer being measured. Moreover, the transformed current will have the same phase as the current flowing through the winding of the transformer being measured, since no additional resistance is provided in the auxiliary transformer circuits. Thus, conditions are created that are the same as in the experience of opposition, when the main magnetic flux is absent in the transformer, and only stray fields are present. In this case, the voltage on the windings of the measured transformer will correspond to the leakage inductances of the respective windings.

The measurement proposed by the device produced as follows.

A device for measuring the leakage inductances of individual windings of a two-winding transformer, consists of a series electric circuit including an AC source, an active limiting resistance, one of the transformer windings, the leakage inductance of the magnetic flux of which is required to be measured, an ammeter, and an additional winding of an auxiliary two-winding transformer with a variable transformation coefficient and the free windings of the studied and auxiliary transformers s connected in series in opposition, wherein the auxiliary transformer ratio is chosen equal to the coefficient of transformation of the measured transformer. Voltmeters are connected to the windings of the measured transformer.

The device include, make the setting. During tuning, change the transformation ratio of the auxiliary transformer. At the same time monitor the readings of the ammeter in the primary circuit of the measured transformer. The highest indications of the ammeter in the primary circuit of the measured transformer indicate the achievement of the mode of the measured transformer - opposition mode. In this mode, the measured transformer does not have a main magnetic flux and does not transform the current to either side. Any imbalance caused by an increase or decrease in the transformation ratio of the auxiliary transformer leads to a transformation in one direction or another and a decrease in the current in the primary winding circuit of the measured transformer.

After setting up the device, the current in the primary winding of the measured voltage transformer II is measured at the primary and secondary windings of the measured transformer U1 and U2.

The measurement results are used to calculate the leakage inductances of individual windings.

It is assumed that before the measurement for the measured transformer, the no-load experiment was carried out, during which the transformation ratio of the measured transformer Ktr was determined.

Also before the measurement it is necessary to measure the active resistance of the windings of the measured transformer using a DC bridge.

Calculate the total resistance of the windings:

Calculate the inductive resistance:

The inventive method meets the requirement of "novelty", because it has new features: the auxiliary two-winding transformer with a variable transformation ratio is additionally included in the series circuit, and the free windings of the studied and auxiliary transformers are connected in series with each other, and the transformation ratio of the auxiliary transformer is equal to the transformation ratio of the transformer being measured.

This combination of features provides the device with new features that are not obvious:

- the possibility of a more accurate measurement of the magnetic flux inductance of the primary winding of the transformer being measured, due to the fact that the phases of the currents in the primary and secondary windings are the same, since there is no resistance in the secondary winding circuit to adjust the circuit;

This allows us to conclude that the criterion of "inventive step".

The figure shows a device for measuring the leakage inductance of the transformer winding: (1) - active resistance, limiting the current in the circuit; (2) - a transformer in which the leakage magnetic flux inductance of the windings is measured; (3) - a transformer with a variable transformation ratio, in the process of adjustment is set equal to the transformer ratio of the transformer (2); (4), (5) - voltmeters connected respectively to the primary and secondary circuits of the transformer, the leakage inductance of which is measured; (6), (7) - ammeters connected respectively to the primary and secondary circuits of the transformer, the leakage inductance of which is measured;

The device consists of the measured transformer (2), the primary winding of which is connected to the active resistance, which limits the current in the circuit (1), with the primary winding of the auxiliary transformer with a variable transformation ratio (3) and an ammeter connected to the alternating current circuit. The secondary windings of the measured transformer (2) and auxiliary transformer (3) are interconnected. An ammeter (7) is connected to the secondary windings, and the voltage on the windings of the transformer to be measured is monitored by voltmeters (4) and (5).

The transformation ratio of the auxiliary transformer (3) is chosen equal to the transformation ratio of the measured transformer.

The measurement proposed by the device produced as follows.

The device include, make the setting. During tuning, change the transformation ratio of the auxiliary transformer (3). At the same time monitor the readings of the ammeter (6) in the primary circuit of the measured transformer. The highest indications of the ammeter (6) in the primary circuit of the measured transformer indicate the achievement of the mode of the measured transformer - the mode of inhibition.

After setting up the device, measurements are made of the currents in the primary winding of the transformer to be measured (2) I _{1 by an} ammeter (6) and the secondary winding by 12 ammeters (7), voltages on the primary and secondary windings of the measured transformer U ₁ and U _{2 by} voltmeters (4) and (5) .

The measurement results are used to calculate the leakage inductances of individual windings.

The device was tested when measuring the magnetic flux leakage inductance of the transformer OSM-1.0U3 windings; P = 1.0 kVA; f = 50 (60) Hz;

The transformer involved concentric windings with rated voltages of 220 V and 110 V. A winding of 220 V was wound closer to the magnetic conductor.

To measure the preliminary experience was carried out idling during which the ratio was determined Ktr = 1.9428; Ktr ² = 3,774;

The resistances of the windings were measured by a DC bridge:

R1 = 0.198 Ohm;

R2 = 0.07 ohm; R2 '= 0.07 * 3.774 = 0.26418 Ω; R2'2 = 0.26418 ² = 0.06979 Ohm;

In the assembled circuit, active resistance was involved — a rheostat of 0–200 ohms; 2 A;

During calibration, the circuit changed the transformation ratio of the auxiliary transformer to achieve the highest current in the primary winding circuit of the transformer being measured. The largest current was 1.75 A;

Voltages on the windings in the mode of opposition were measured by an electronic voltmeter B3-38

The effective value of U ₂₂₀ = 0.83 B;

The effective value of U ₁₁₀ = 0.33 B;

Current I ₁ = 1.75 A;

Calculate the total resistance of the windings:

Z ₁ = 0.83 / 1.75 = 0.474 Ω;

Z ₂ = 0.33 / (1.75 * 1.9428) = 0.097 Ohm; Z ₂ '= 0.097 * 3.774 = 0.366 Ohm;

Calculate the inductive resistance:

X ₁ = Root (0.474 ² -0.198 ² ) = 0.43 Ohm;

X ₂ '= Root (0.366 ² -0.06979 ² ) = 0.359 Ohm;

X ₁ / X ₂ '= 1.19

L ₁ = X _1/2 * 3.14 * 50 = 0.43 / 314 = 0.001369 GN;

L ₂ '= X _{2/2 * 3.14 * 50 =} 0.359 / 314 = 0.001143 Gn;

Then, the windings of the transformer to be measured were changed (primary with secondary) and measurements were repeated. The discrepancy of the obtained data does not exceed 5%, which allows to make a conclusion about the compliance of the claimed invention with the criterion "industrial applicability".

Information sources

1. Patent for useful model of the Russian Federation: RU 73740 U1 of 27.05.2008, IPC G01R 27/26, authors: Sakhno OI, Sakhno LI, Voronin VN, “Device for measuring leakage inductances and active resistances of each winding of a two-winding transformer ”is a prototype.

Claims (1)

A device for measuring the leakage inductances of individual windings of a two-winding transformer, consisting of a series electric circuit including an alternating current source, an active limiting resistance, one of the transformer windings, the leakage inductance of the magnetic flux of which is required to be measured, and an ammeter, a voltmeter that is differently connected to the measured winding the fact that the coil of the auxiliary double-winding transformer with variable transformation ratio, and the free windings of the investigated and auxiliary transformers are connected in series with each other, and the transformation ratio of the auxiliary transformer is chosen equal to the transformation ratio of the measured transformer.

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