KR20080015697A - Resistive impedance type electronic voltage transformer embedded in epoxy insulator for medium voltage power apparatus - Google Patents

Abstract

A resistive impedance type electronic voltage transformer embedded in an epoxy insulator for a medium voltage power apparatus is provided to remove noise due to ferro-resonance without using an iron core and be made smaller and lighter. An electronic voltage transformer(100) for measuring a voltage comprises an input terminal(110), a first resistor(130), a second resistor(140), a molding unit(150), and a voltage adjusting connector(160). The input terminal is connected to a high voltage line. The first resistor is connected to the input terminal. The second resistor is connected to the first resistor in series and one end thereof is grounded. The molding unit made of an insulating material surrounds the first and second resistors. The voltage adjusting connector adjusts an output voltage by being attached and detached from the molding unit and includes an output terminal(120) and a voltage adjusting device. The output terminal outputs a transformed low voltage current by being connected between the first and second resistors. The voltage adjusting device is installed to adjust the output voltage of the output terminal.

Description

Resistive impedance type electronic voltage transformer embedded in epoxy insulator for medium voltage power apparatus}

1 is a schematic configuration diagram of an iron core winding type voltage transformer

2 is a schematic configuration diagram of a capacitor type voltage transformer

3 is a block diagram of an electronic voltage transformer according to an embodiment of the present invention.

4 is a cross-sectional view of an electronic voltage transformer according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100: voltage transformer 110: input terminal

120: output terminal 130, 140: first and second resistor

150 molding part 160 connector

162: adjusting capacitor

The present invention relates to a voltage transformer (Voltage or Potential Transformer: VT or PT) that measures a high voltage (rated primary voltage) used in power equipment and converts it into a low voltage (rated secondary voltage) required for various instruments including a relay. More specifically, the present invention relates to an electronic voltage transformer using a resistor as a voltage dividing means instead of a voltage dividing method using an inductor or a capacitor wound on a conventional iron core.

접속하는 등의 제어회로를 구동한다. In general, domestic distribution systems operating at less than 22.9 kV, including ultra-high voltage transmission and substation systems that are applied up to several hundred kV, continuously measure and use voltages of distribution lines and distributors to ensure reliability and stability of power supply. Distribution system for various purposes such as remote measurement, system protection and automatic control

Drive a control circuit such as a connection.

), 1차 전압 벡터와 180°회전된 2차 전압 벡턱간의 위상차를 나타내는 위상각을 비롯하여 비오차나 위상각의 허용한계를 표시하는 수치로 용도에 따라 0.5급, 1.0급 등으로 분류 되는 계급 등으로 성능을 구분할 수 있으며, 어떤 1 차 전압 값에 비례하는 2차 전압 값으로 변성하는 전압 변성기는 계기용 전압기로 호 칭되기도 한다.Voltage transformers are generally referred to as a variation ratio (transform ratio) divided by the rated primary voltage by the rated secondary voltage, a nominal transformer ratio (Kn), and a transformer ratio (K) of the measured true value (K).

), A phase angle indicating the phase difference between the primary voltage vector and the secondary voltage vector rotated by 180 °, and a numerical value indicating the tolerance or the tolerance of the phase angle. Performance can be distinguished and voltage transformers that transform to secondary voltage values proportional to any primary voltage value are sometimes referred to as instrument voltages.

A device mainly used for detecting a voltage of a distribution line includes a voltage transformer for measuring voltage, and the voltage transformer is mainly divided into an iron core core winding type and a capacitor type voltage transformer.

1 is a view showing a schematic configuration of an iron core core winding type voltage transformer 10, in which an induced current is generated by a primary winding 11 and a primary winding 11 wound on an iron core 14. Winding 12.

The secondary winding 12 may be installed to penetrate the inside of the primary winding 11 as shown, or may be installed on the other side of the iron core 14 spaced apart from the primary winding 11.

One end of the primary winding 11 is connected to the input terminal 13 and the other end is grounded, one end of the secondary winding 12 is connected to the output terminal 15 and the other end is grounded.

The primary and secondary windings 11 and 12 and the iron core 14 are surrounded by a molding portion 16 such as epoxy resin for insulation, and the output voltages are the primary winding 11 and the secondary. It is determined by the winding ratio n of the winding 12, and the voltage, current, and impedance on the primary side can be converted by multiplying 1 / n, n, and 1 / n ² .

2 is a view showing a schematic configuration of a capacitor-type voltage transformer 20, in which the first and second capacitors 23 and 24 for voltage dividing are installed in the insulator 25 in series. The input terminal 21 is connected to the first capacitor 23, and one end of the second capacitor 24 is grounded.

The output terminal 22 is connected between the first and second capacitors 23 and 24, and when the voltage at the input terminal 21 is U1 and the voltage at the output terminal 22 is U2, U2 = C1 / (C1 + C2). )

Therefore, the output voltage is determined by the capacitances C1 and C2 of the first and second capacitors 23 and 24.

However, the conventional voltage transformer has some problems as follows.

The iron core core winding type voltage transformer 10 generally has a large output voltage of 50 V to 110 V, and thus is mainly used in power equipment such as relays or power meters, and a range of measurement voltages satisfying measurement errors required by a class of a certain transformer. In addition to being narrow, the measurement accuracy is inferior, which makes it possible to measure over a wide range of voltages and is not suitable for use in digital relays or power IT applications requiring high precision.

In addition, due to the core core, the transformer itself is very heavy, and the noise due to the iron resonance phenomenon. In addition, when the secondary winding 12 is shorted or connected with an extremely low impedance, an excessive short current is induced in the secondary winding 12 and the secondary winding 12 is broken, and the secondary winding Burnout of (12) is spread to the insulation breakdown of the primary winding 11, the risk of occurrence until the accident of the distribution line to which the primary winding 11 is connected.

The capacitor-type voltage transformer 20 can solve many of the problems of the iron core core winding voltage transformer 10 described above, but the capacitors 23 and 24 are made of the same epoxy resin as the insulator 25. In this case, it is difficult to obtain the exact output voltage that was intended due to the change in capacitance caused by temperature change.

In addition, when an epoxy resin molding of the insulator 25 and a capacitor made of a different type of dielectric are embedded, an explosion may occur due to a thermal problem that may occur at an interface of dissimilar materials. In addition, due to stray capacitance caused by epoxy resin of the dielectric insulator 25, there is a problem that the precise output voltage originally intended is not obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to precisely control an output voltage of a transformer at a low voltage to increase the accuracy and reliability of voltage measurement.

It also aims to provide an electronic voltage transformer that can be used in digital relays or power IT.

It is also an object of the present invention to provide an electronic voltage transformer that can improve mechanical strength while miniaturizing and reducing the transformer itself.

The present invention, the input terminal is connected to the high-voltage line in order to achieve the above object; A first resistor connected to the input terminal; A second resistor connected in series with the first resistor and having one end grounded; An insulating material molding part surrounding the first resistor and the second resistor; An apparatus for adjusting an output voltage by detaching the molding part, the apparatus comprising: an output terminal connected between the first resistor and the second resistor to output a modified low voltage; and a voltage adjusting means installed to adjust the output voltage of the output terminal. The branch provides a voltage measuring voltage transformer including a voltage adjusting connector.

The voltage adjusting means is preferably an adjusting capacitor connected in parallel with the second resistor with respect to the output terminal.

The voltage adjusting connector is preferably detachable by coupling the molding portion and the bolt nut method.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention.

The electronic voltage transformer 100 according to the embodiment of the present invention is distinguished from the conventional capacitor type voltage transformer 20 in that the first and second resistors are used as voltage dividers.

That is, as shown in the block diagram of FIG. 3, the first resistor 130 and the second resistor 140 are connected in series with respect to the input terminal 110, and one end of the second resistor 140 is grounded. . The first and second resistors 130 and 140 are surrounded by a molding part 150 made of an insulator such as epoxy.

The output terminal 120 is connected between the first resistor 130 and the second resistor 140. Therefore, when the resistance values of the first and second resistors 130 and 140 are R1 and R2, respectively, the input voltage is U1. Output voltage U2 is theoretically U1 * R2 / (R1 + R2).

More rigorously, however, U2 is represented by the following equation since the first stray capacitance C1 between the input terminal 110 and the output terminal 120 and the second stray capacitance C2 between the output terminal 120 and the ground terminal must be considered. It can be expressed as 1.

(Equation 1)

Here, if R1C1 = R2C2, the ideal relationship of U2 = U1 * R2 / (R1 + R2) holds.

Therefore, in order to obtain a desired output voltage, the first and second stray capacitances C1 and C2 as well as the resistance values R1 and R2 of the first and second resistors 130 and 140 must be known. Since the first and second floating capacitances C1 and C2 are determined by the geometry or material of the dielectric, the size of the first and second floating capacitances C1 and C2 may be relatively accurately determined through calculation.

The desired output voltage can be obtained by determining the resistance values R1 and R2 of the first and second resistors 130 and 140 by considering the first and second floating capacitances C1 and C2 obtained through the calculation.

However, due to various factors in the manufacturing process of the voltage transformer 100, the floating capacitances C1 and C2 often deviate from a pre-calculated value, so it is difficult to accurately obtain a desired output voltage.

In particular, since the first and second resistors 130 and 140 have already been molded using epoxy, the first and second resistors 130 and 140 may be replaced or the size of the first and second floating capacitances C1 and C2 may be precisely determined. It is almost impossible to change the output voltage by adjusting it.

Therefore, the embodiment of the present invention uses the voltage adjusting connector 160 that can be attached and detached from the outside of the molding unit 150 in preparation for such a case.

An adjustment capacitor 162 is installed inside the voltage adjusting connector 160, and one side includes an output terminal 120 for providing a current transformed to an external circuit.

Therefore, the molding unit 150 is provided with a coupling means such as a bolt or nut groove for coupling the voltage adjusting connector 160, the corresponding voltage adjusting connector 160 is provided with a corresponding means.

When the voltage adjusting connector 160 is coupled, the output line inside the molding unit 150 and the adjusting capacitor 162 of the voltage adjusting connector 160 should be connected in parallel with each other. That is, the adjusting capacitor 162 is connected to the output terminal 120 in parallel with the second resistor 140.

Assuming that the capacitance of the adjusting capacitor 162 is C3, the output voltage U2 may be expressed by Equation 2 below.

(Equation 2)

Also in this case, if R1C1 = R2 (C2 + C3), an ideal relationship of U2 = U1 * R2 / (R1 + R2) is established.

If the magnitudes of the first and second stray capacitances C1 and C2 are known or known correctly, the capacitance C3 of the adjusting capacitor 162 required to obtain a desired output voltage U2 may be determined through Equation 2 above.

Even when the first and second floating capacitances C1 and C2 cannot be accurately measured, an appropriate adjustment capacitor 162 is provided through a trial and error method in which an output capacitor U2 is measured by combining an adjustment capacitor 162 having an arbitrary capacitance. ) To get the desired output voltage.

4 is a cross-sectional view showing the actual configuration of the voltage transformer 100 according to an embodiment of the present invention, the shape of the molding unit 150 constituting the insulator is exemplary.

The upper input terminal 110 is connected to the high voltage line, the lower ground terminal 154 is connected to the ground line. The voltage adjusting connector 160 coupled to the lower end of the molding unit 150 includes an adjusting capacitor therein and supplies a low voltage current to an external control circuit through an output terminal.

Although the preferred embodiment of the present invention has been described above, the scope of the present invention is not limited thereto, and the scope of the present invention is included in the range equivalent to the technical idea described in the following claims.

According to the present invention, by precisely controlling the output voltage of the voltage transformer at a low voltage, it is possible to increase the accuracy and measurement reliability of the voltage measurement, through which it can be utilized in the field of digital relay or power IT.

In addition, since the iron core is not used, noise caused by iron resonance can be eliminated, and the transformer itself can be miniaturized and lightened. In addition, it is possible to prevent accidents caused by secondary short circuits.

In addition, the broadband frequency response characteristics can be realized compared to the capacitor type voltage transformer, and the linearity is excellent.

In addition, by embedding a resistor in the epoxy molded body can improve the mechanical strength, can reduce the risk of explosion, it can significantly improve the productivity.

Claims (3)

An input terminal connected to the high voltage line; A first resistor connected to the input terminal; A second resistor connected in series with the first resistor and having one end grounded; An insulating material molding part surrounding the first resistor and the second resistor; A device for adjusting an output voltage by attaching and detaching the molding part, the output terminal being connected between the first resistor and the second resistor to output a modified low voltage current, and a voltage adjustment provided to adjust the output voltage of the output terminal. A voltage adjusting connector having means; Electronic voltage transformer for measuring voltage The method of claim 1, The voltage regulating means is a voltage measuring electronic voltage transformer, characterized in that for adjusting the capacitor connected in parallel with the second resistor in the output terminal. The method of claim 1, The voltage adjusting electronic voltage transformer for the voltage adjusting connector is detachable by combining the molding part with a bolt nut method.

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