RU2603723C2 - Device for transformer magnetization current measurement, which operates under load - Google Patents

Abstract

FIELD: electromechanics.

SUBSTANCE: invention relates to electromechanics. Device for transformer with variable coefficient of transformation magnetization current measurement, which operates under load, consisting of shunts included in transformer primary and secondary windings circuits. At that, shunts measuring terminals are connected in series opposed.

EFFECT: current measurement.

1 cl, 3 dwg

Description

The device relates to electrical mechanics, can be used for demonstration, educational or research purposes.

The closest analogues, the purpose of which is to measure the magnetizing current of a transformer with a variable transformation coefficient, operating under load, have not been identified.

The shunt terminals are connected in such a way that the voltage drop from the secondary current i ′ ₂ (t) is subtracted from the voltage drop from the current i ₁ (t). The oscilloscope in such a circuit should show the magnetizing current i _m (t), since i _m (t) = i ₁ (t) -i ₂ (t). But this is true only with the exact selection of shunts, when the same current flowing through the shunts will create voltage drops on the measuring terminals of the shunts, the ratio of which is equal to the transformation coefficient of the transformer. It is not possible to select the ratio between the rated currents of the shunts exactly equal to the transformation coefficient of the transformer (in this case, the same current flowing through the shunts will create voltage drops on the measuring terminals of the shunts whose ratio is equal to the transformation coefficient of the transformer) using standard shunts.

The shunts installed in the primary and secondary windings are standard. The ratio between the rated currents of the shunts is chosen as close as possible to the transformation ratio of the transformer.

Before measurement it is necessary to make scaling.

During scaling, a reduced voltage is applied to the transformer, while saturation is excluded and I _m (t) is negligible. The load turns on. The magnetizing current is measured by an oscilloscope according to the described scheme.

Undervoltage is necessary in order to exclude magnetizing current during setup. In this case, with correctly selected shunts, the voltage drops across the shunts are equal and the oscilloscope connected to the series-connected shunts should show 0 regardless of the load.

If these conditions are not fulfilled accurately, a sinusoid will be observed on the oscilloscope screen. This is the difference in voltage drops on shunts. To calibrate, change the position of the autotransformer engine (transformer ratio). By changing the transformation coefficient, a straight line is achieved on the oscilloscope screen (signal absence). It is this position of the autotransformer engine (transformer transformation ratio) that will correspond to the scaled circuit. The circuit is ready for measurements.

In order to make sure that the measurement results are correct, the following experiments can be done.

- Measurements are carried out at reduced voltage and various loads. In all cases, the oscilloscope readings should be zero.

- Measurements to idle. Gradually increase the supply voltage. In this case, the magnetizing current should increase, and then become a non-sinusoidal characteristic shape.

The inventive device meets the requirement of "novelty", since from the current level of technology there are no devices for measuring the magnetizing current of a transformer with a variable transformation ratio operating under load.

The device allows to obtain a new quality - to provide the ability to measure the magnetizing current of a transformer with a variable transformation ratio, operating under load. This allows us to conclude that the criterion of "inventive step".

In FIG. 1 shows a diagram of a device for measuring the magnetizing current of a transformer with a variable transformation ratio, operating under load: 1 - autotransformer with a variable transformation ratio; 2 - a shunt in the primary winding circuit; 3 - a shunt in the secondary circuit; 4 - load resistance (rheostat).

In FIG. Figure 2 shows the oscillograms of the magnetizing current i _m (t) at various transformation ratios of the autotransformer (a, b, c) and in the saturation mode of the transformer primary winding (d).

If the autotransformer transformation coefficient is greater than the resistance ratio of shunts 2 and 3, then the magnetizing current i _m (t) has the form (a);

If the autotransformer transformation coefficient is less than the resistance ratio of shunts 2 and 3, then the magnetizing current i _m (t) has the form (b);

If the autotransformer transformation coefficient is equal to the ratio of the resistances of shunts 2 and 3, then the magnetizing current i _m (t) has the form (c);

In FIG. Figure 3 shows the real waveforms of the magnetizing current at a weak (a) and stronger saturation of the magnetic circuit (b).

A device for measuring the magnetizing current of a transformer operating under load consists of a transformer with a variable transformation ratio 1, the secondary winding of which is connected to the load, shunts 2 and 3, connected to the primary and secondary winding circuits, the measuring terminals of which are connected in series (see Fig. 1 )

The ratio between the rated currents of the shunts is chosen as close as possible to the transformation ratio of the transformer. The terminals of shunts 2 and 3 are connected so that the voltage drop from the current of the secondary winding i ′ ₂ (t) at shunt 3 is subtracted from the voltage drop at the shunt 2 from the current i ₁ (t). The oscilloscope in such a circuit should show the current i _m (t), since i _m (t) = i ₁ (t) -i ₂ (t).

During scaling, the position of the autotransformer engine is changed (transformation ratio of the transformer).

On the oscilloscope screen, depending on the position of the autotransformer engine (transformer transformation coefficient), one of the pictures depicted in FIG. 2.

When the transformation ratio exceeds the ratio of the resistances of the shunts 2 and 3, the magnetizing current will have the form shown in FIG. 2a.

When the transformation coefficient is less than the ratio of the resistances of the shunts 2 and 3, the magnetizing current will have the form shown in FIG. 2b.

By changing the transformation coefficient, a straight line is achieved on the oscilloscope screen (Fig. 2c - signal absence). It is this position of the autotransformer engine (transformer transformation coefficient) that will correspond to the scaled circuit, and the transformation coefficient is equal to the ratio of the resistances of shunts 2 and 3. The circuit is ready for measurements.

In FIG. Figure 3 shows the real waveforms of the magnetizing current for a weak (a) and stronger saturation of the magnetic circuit (b).

The device was tested using a commercially available laboratory transformer (LATR) 8A; 0-250 V. Used shunts:

in the primary winding 5 A; 75 mV;

in the secondary winding 10 A; 75 mV.

Load 4 - laboratory rheostat 10 A; 0-22 ohms.

Power was supplied from a laboratory potential regulator (an adjustable source of alternating sinusoidal voltage).

The test results allow us to conclude that the claimed invention meets the criterion of "industrial applicability".

Claims (1)

A device for measuring the magnetizing current of a transformer with a variable transformation coefficient, operating under load, consisting of shunts included in the circuit of the primary and secondary windings of the transformer, and the measuring terminals of the shunts are connected in series.

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