RU2510030C2 - Device for scale transformation - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device for scale transformation of current comprises an additional load resistance in series with the third outlet winding of the second transformer and the outlet winding of the first transformer. At the same time it is possible that in the device for scale transformation of current the additional load resistance is made in the form of serially connected the additional load resistance galvanically isolated from the main load and the third transformer, so that its primary winding is connected in series with the outlet winding of the first transformer, and they have one common terminal, and the additional load resistance galvanically isolated from the main one is connected to the secondary winding.

EFFECT: high accuracy, small weight and dimensions, expanded range of output capacity of the device corresponding to various types of loads and modes of operation, which makes it possible to widely apply such device in measurement systems and automation systems.

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Description

The invention relates to the field of measurement technology and can be used in systems and devices for measuring electrical quantities of current, power, energy, as well as in protection and automation systems.

Known devices for large-scale current conversion, containing an amplifier, a current transformer with input and output windings, load (see AS No. 918868. BI No. 13, etc.).

The disadvantage of such devices is low accuracy due to the impossibility of compensating the load resistances and the transformer winding more precisely, because scatter and deviation of the transformer and amplifier parameters from the nominal value is possible due to the influence of temperature and over time.

Another disadvantage is the need to use high power amplifiers and with a large output current, because The full load current flows through the amplifier. The consequence of this is the need to use large radiators as a powerful power source for the amplifier.

The next technical solution close to the proposed device is a device (according to AS No. 1045136 BI No. 36, 1983), comprising a first transformer with an input and two output windings, an amplifier whose output is connected in series with the first output winding, the first transformer, the second a transformer and a reference voltage unit, the input of which is connected to the input winding of the first transformer, and the output is in series with the second output winding of the first transformer, the output winding of which is connected to the input of the amplifier, the feedback winding to the outlet.

The disadvantage of this device is the design complexity of the used amplifier at high current and power in the load and, as a consequence, the practical impossibility of using the device at load currents of the order of 5 A.

The closest in technical solution is the device for A. with. No. 1582137. BI No. 28, 1990, containing the first transformer with input and output windings, an amplifier, the second transformer with input and three output windings, the first of which is connected to the amplifier input, load resistance, the third output winding of the second transformer is connected in series with the output winding of the first transformer and load resistance, in parallel to which a circuit is connected, consisting of a series-connected output circuit of the amplifier and the second output winding of the second transformer, the input windings of transformers are connected in series.

The disadvantage of this solution is the limitation of the types of loads simultaneously connected to the output of the device, and their operation modes.

The aim of the invention is to expand the range of output power, for some types of loads, for example, protection systems, automation and high accuracy for measurement systems connected simultaneously.

The goal is achieved in that in series with the third output winding of the second transformer and the output winding of the first transformer, an additional load resistance is introduced. The invention consists in the following.

1. The device for large-scale current conversion comprises a first transformer with input and output windings, an amplifier, a second transformer with input and three output windings, the first of which is connected to the amplifier input, load resistance, the third output winding of the second transformer is connected in series with the output winding of the first transformer and load resistance, in parallel with which a circuit is connected, consisting of a series-connected output circuit of the amplifier and the second output winding of the second transformer, the input windings of both transformers are connected in series, characterized in that additional load resistance is introduced in series with the third output winding of the second transformer and the output winding of the first transformer.

2. The device for large-scale current conversion according to claim 1, characterized in that the additional load resistance is made in the form of series-connected additional load resistance and a third transformer galvanically separated from the main load, so that its primary winding is connected in series with the output winding of the first transformer and they have one common terminal, and an additional load resistance galvanically separated from the main one is connected to the secondary winding.

In the drawing, figure 1, figure 2, presents embodiments of the proposed device for large-scale current conversion.

The device in figure 1 contains a first transformer 1 and a second transformer 2, an amplifier 3, input windings 4 and 5, output windings 6 and 7, 8, 9 of the first 1 and second 2 transformers, respectively, the resistance of the main 10 and additional 11 loads.

The device in figure 2 contains a first transformer 1 and a second transformer 2, an amplifier 3, input windings 4 and 5, output windings 6 and 7, 8, 9 of the first 1 and second 2 transformers, respectively, the main resistance 10 and additional loads, and as an additional load, the primary winding 11 of the third transformer 12 is used, to the secondary winding 13, which is connected galvanically separated from the main additional load resistance 14.

The principle of operation of the proposed device according to figure 1 is as follows.

The input current passing through windings 4 and 5 magnetizes the cores of transformers 1 and 2. In the secondary windings of transformers I and 2, as a result, voltages act and currents flow.

The current I _{10 of the} load 10 is provided mainly due to the voltage induced on the winding 6. Under the action of this voltage through the windings 6, 7 and the load 10, the current I ₆ flows.

The core of transformer 2 is almost demagnetized due to the action of compensating flows created by currents in windings 7 and 9.

With a loop gain of 10-100, which is ensured by choosing the gain of the amplifier 3 and the number of turns of the windings 8, 9 of the transformer 2, the magnetic flux in the core of the transformer 2 can be made very small. Therefore, with sufficient accuracy, the relation is valid for transformer 2

$$I_{\mathrm{one}}{W}_5-I_6{W}_7-I_9{\mathrm{<figure-callout\; id="9"\; label="W"\; filenames="00000006.png"\; state="\{\{state\}\}">W</figure-callout>}}_9=0\left(\mathrm{one}\right)$$

where I ₁ is the input current of transformers 1 and 2;

I ₆ - current winding 6;

I ₉ - current through the winding 9;

W ₅ , W ₇ , W ₉ - the number of turns of the windings 5, 7, 9.

We neglect the current of winding 8, because with a large input impedance of the amplifier, its effect is negligible. From (1) we have:

$${\mathrm{<figure-callout\; id="9"\; label="I"\; filenames="00000006.png"\; state="\{\{state\}\}">I</figure-callout>}}_9=I_{\mathrm{one}}\left({\mathrm{<figure-callout\; id="5"\; label="W"\; filenames="00000006.png"\; state="\{\{state\}\}">W</figure-callout>}}_5/W_9\right)-I_6\left({\mathrm{<figure-callout\; id="7"\; label="W"\; filenames="00000006.png"\; state="\{\{state\}\}">W</figure-callout>}}_7/W_9\right)\left(2\right)$$

Since the load resistance 10 is selected sufficiently small compared to the equivalent resistances of current sources I ₆ and I ₉ (winding resistances 6, even without taking into account the additional resistance 11, and amplifier 3), the total load current I _{10 is} practically determined as the sum of the currents I ₆ and I ₉

$${\mathrm{<figure-callout\; id="10"\; label="I"\; filenames="00000006.png"\; state="\{\{state\}\}">I</figure-callout>}}_{10}=I_6+I_9.\left(3\right)$$

In view of (2), we have

$${\mathrm{<figure-callout\; id="10"\; label="I"\; filenames="00000006.png"\; state="\{\{state\}\}">I</figure-callout>}}_{10}=I_{\mathrm{one}}\left({\mathrm{<figure-callout\; id="5"\; label="W"\; filenames="00000006.png"\; state="\{\{state\}\}">W</figure-callout>}}_5/W_9\right)+I_6\left(\mathrm{one}-{\mathrm{<figure-callout\; id="7"\; label="W"\; filenames="00000006.png"\; state="\{\{state\}\}">W</figure-callout>}}_7/W_9\right)\left(\mathrm{four}\right)$$

If W ₇ = W ₉ , then regardless of the distortions introduced by the transformer 1, the conversion result is proportional to the value of I ₁ . The number of turns of the winding 6 is practically chosen so that the ratio W ₆ = W ₄ (I ₁ / I _10nom ) is _satisfied ,

Where I _10nom - the nominal value of the load current 10 at a given current value I ₁ .

In this case, the main power is transmitted to the loads 10 and 11 through the transformer 1 and only part of the power dissipated by the load 10 is formed by the amplifier 3.

Moreover, despite the fact that the load of the first 1 transformer due to the additional load 11 from the protection and automation systems increases several times, compared with the load 10 from the measuring systems, the power of the amplifier 3 will increase slightly to ensure accuracy in the load 10, so how it is proportional not to the power of transformer 1, but to its error. So, with an error of transformer 1 equal to 0.5% and a load power of 10 from measuring systems 1.0 W will be a fraction of a percent of amplifier 3, a power equal to 0.5% of the allocated to load 10 will be required, i.e. equal to 0.05 watts.

Thus, unlike the prototype, it is possible to connect to the device both protection and automation systems requiring high power with moderate error of the order of 0.5%, and accurate measuring circuits requiring low power, but small error of the order of 0.1%.

The principle of operation of the device according to figure 2, differs from the previous one in that the galvanically shared load resistance 14 is provided by an additional third transformer 12 to its primary winding with a proportionality factor (W ₁₃ / W ₁₁ ) ² . This solution provides the necessary ratio of currents in loads 10 and 14, as well as their galvanic separation. A slight increase in the current error in the load 14, due to the error of the transformer 12, does not matter much, given that the accuracy for the measuring load 10 remains almost unchanged, i.e. not more than 0.1%, while the current in the load resistance 14 corresponds to a protection and automation system, where the accuracy requirements are not so high.

High accuracy, small weight and dimensions, an expanded range of output power of the device, corresponding to different types of loads and operating modes, will make it possible to widely use such a device in measuring systems and automation systems.

Claims (2)

1. The device for large-scale current conversion comprises a first transformer with input and output windings, an amplifier, a second transformer with input and three output windings, the first of which is connected to the amplifier input, load resistance, the third output winding of the second transformer is connected in series with the output winding of the first transformer and load resistance, in parallel with which a circuit is connected, consisting of a series-connected output circuit of the amplifier and the second output winding of the second transformer, the input windings of both transformers are connected in series, characterized in that additional load resistance is introduced in series with the third output winding of the second transformer and the output winding of the first transformer. 2. The device for large-scale current conversion according to claim 1, characterized in that the additional load resistance is made in the form of series-connected additional load resistance and a third transformer galvanically separated from the main load, so that its primary winding is connected in series with the output winding of the first transformer and they have one common terminal, and an additional load resistance galvanically separated from the main one is connected to the secondary winding.

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