KR100737402B1 - Apparatus for Evaluating Burden of a Voltage Transformer using a Decade Resistor and Evaluating Method therefor - Google Patents

Abstract

The present invention uses a variable resistor connected to the secondary side of the voltage transformer under measurement to measure the variation of the voltage transformer's non-error and phase angle error so that the burden of a voltage transformer (VT) that is easy to move and meets field conditions is met. An evaluation apparatus and a method for evaluating a load for a voltage transformer using the same, wherein the reference voltage transformer 40 and the voltage transformer under test 50 are supplied in parallel so that the same high voltage is supplied to the primary side of the reference voltage transformer and the voltage transformer under measurement. The resistance load (Z _b ) 65 connected in parallel to the secondary side of the voltage transformer under measurement 50, the variable resistor 70 is connected in series to the secondary side of the voltage transformer under measurement, and the two voltages The voltage transformer comparator 60 is connected to compare the secondary side voltages of the transformers 40 and 50 so that a small, light weight variable resistor can be brought to the industry and easily As well as to evaluate the load for the voltage transformer, it is possible that the accuracy of the measurement can be greatly increased, and these easily evaluate the accuracy.

Voltage Transformer, Phase Angle Error, Non Error, Comparator, Variable Resistor, Burden, Carrier

Description

Apparatus for Evaluating Burden of a Voltage Transformer using a Decade Resistor and Evaluating Method therefor}

1 is a circuit diagram for explaining the relationship between the characteristics of the voltage transformer and the burden related to the theoretical background of the present invention;

2 is a view showing a circuit configuration of a load evaluation device for a voltage transformer using a variable resistor according to the present invention;

3a and 3b are graphs showing the results of measurement of the error and phase angle error of the voltage transformer measured according to the present invention;

4A and 4B are graphs showing the validity of the error and phase angle error measured according to the present invention.

<Explanation of symbols for the main parts of the drawings>

20: primary side coil,

30: secondary side coil,

40: reference voltage transformer,

50: voltage transformer to be measured,

65: burden for the voltage transformer,

70: variable resistor.

The present invention relates to a voltage transformer (VT), and more particularly, by using a variable resistor connected to the secondary side of the voltage transformer under measurement, by measuring the variation of the error and the phase angle error of the voltage transformer, the movement is simple. The present invention relates to a load evaluation device for a voltage transformer using a variable resistor that meets field conditions and an evaluation method using the same.

In general, voltage transformers are used to drop high voltages to low voltages to precisely measure voltages ranging from AC 220 V to 345 kV at commercial frequencies, and drop the high voltages on the primary side to 110 V on the secondary side. This is to measure the high voltage on the primary side safely and accurately by precisely measuring and converting it into conversion ratio.

The secondary side of the voltage transformer is mainly used to measure the high voltage of the primary side or to measure the amount of electricity by connecting the voltage input terminals of the voltmeter or the wattmeter. In recent years, the power company and the power exchange are operated independently to supply electricity. And accurate metering of the amount of power is required in the distribution phase, the accuracy of the amount of power metering depends on the conversion ratio of the voltage transformer, that is, the accuracy of the non-error.

The error and phase angle error of the voltage transformer are evaluated by using the voltage transformer comparator with the burden of the same condition as the impedance of the load connected to the secondary side. It depends on the burden. Therefore, accurate measurement of the burden is important for the precise measurement of the error and phase angle error of the voltage transformer.

However, in general, an industry or a calibration laboratory that produces a voltage transformer uses a voltage transformer comparison measuring device (error measuring device) to evaluate or calibrate the voltage transformer, and the error and phase angle of the voltage transformer to be measured. It measures the phase angle error, and the voltage transformer to be measured is divided into five grades, class 0.1, class 0.2, class 0.5, class 1 and class 3, depending on the class of error. The errors are about ± 0.1%, ± 0.2%, ± 0.5%, ± 1% and ± 3%, respectively.

The voltage transformer comparator must be able to accurately measure the error to the aforementioned ± 3% range, whereas the voltage transformer comparator can measure the error of the voltage transformer under measurement with a relatively small range of error. Accurate measurement is difficult when measuring the voltage transformer under measurement with a large range of errors.

On the other hand, Figure 2 shows the configuration of the voltage transformer comparison measuring system used in the prior art, the same voltage is supplied in parallel to the primary side of the reference voltage transformer 40 and the voltage transformer under measurement 50, The secondary voltages of the two voltage transformers 40 and 50 are configured to be compared by using the voltage transformer comparison measuring device 60.

In this configuration, the voltage transformer comparator 60 measures the error and phase angle error of the voltage transformer 50 to be measured, and compares the secondary voltages of the two voltage transformers 40 and 50 to compare the error. And equilibrium with the phase angle error dial to measure the error and phase angle error of the voltage transformer 50 under measurement. The voltage transformer comparison measuring device 60, which is usually used in Korea, is a product of a foreign company, Knopp of USA, Tetex of Switzerland, Soken of Japan, etc. Are similar to each other.

However, the voltage transformer comparison measurement system used in the above-mentioned industries is large and heavy, and it is difficult to carry, and is frequently used for quality control and calibration test of the product. It is almost impossible to get a correction.

For this reason, there is an urgent need for a method of evaluating a voltage transformer measuring device in the field by developing a mobile standard and bringing it to a business in order to evaluate an industrial voltage transformer comparison measuring system.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and a first object of the present invention is to provide a voltage transformer with a variable resistor that can easily take a small and light weight variable resistor to an industry and evaluate the measuring device in the field. To provide a burden evaluation apparatus and an evaluation method using the same.

Further, another object of the present invention is to provide an apparatus and method for evaluating a load for a voltage transformer using a variable resistor which can greatly improve the accuracy of the measurement and can easily evaluate the accuracy.

Objects of the present invention as described above, the reference voltage transformer 40 and the voltage transformer under measurement 50 are connected in parallel so that the same high voltage is supplied to the primary side of the reference voltage transformer and the voltage transformer under measurement. ( _B ) connects the burden (Z _b ) 65 in parallel to the secondary side of (50), connects the variable resistor (70) in series to the secondary side of the voltage transformer under test, and connects two of the two voltage transformers (40, 50). The voltage transformer comparator 60 may be achieved through a load evaluator for a voltage transformer using a variable resistor connected to the differential voltages.

In addition, in the present invention, as the method for evaluating the burden using the burden evaluation device for the voltage transformer using the variable resistor as described above, the reference voltage transformer 40 and the same high voltage is supplied to the primary side of the reference voltage transformer and the voltage transformer under measurement. The voltage transformer 50 under measurement is connected in parallel, the burden Z _b 65 is connected in parallel to the secondary side of the voltage transformer 50 under measurement, and the variable resistor is connected in series with the secondary side of the voltage transformer under measurement. An error evaluation method of a voltage transformer using a voltage transformer burden evaluation device connected to a voltage transformer and connected to a voltage transformer, and the voltage transformer comparison measuring device 60 is connected to compare the secondary voltages of the two voltage transformers 40 and 50.

A method is provided for evaluating the error of a voltage transformer while varying the resistance of the variable resistor 70 according to the following equations:

Where RE ₀ is the no-load error; RE _b is the non-error when burden Z _b is present; Γ ₀ is the phase angle error when there is no burden; Γ _b is when there is burden Z _b Phase angle error; Z ₀ = R ₀ + jX ₀ is the leakage output impedance of the voltage transformer; Z _b = R _b + jX _b is the external burden impedance; G _b = R _b / (R ² _b + X ² _b ) Burden conductance; B _b = X _b / (R ² _b + X ² _b ) is the susceptibility of the burden; R _s is the resistance of the variable resistor)

Other objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and the preferred embodiments associated with the accompanying drawings.

Hereinafter, an apparatus for evaluating the burden of a voltage transformer using a variable resistor according to the present invention will be described in detail with reference to the accompanying drawings showing a preferred embodiment.

2 is a diagram showing the configuration of the voltage transformer burden evaluation apparatus according to the present invention. In the present invention, in addition to the configuration of the conventional voltage transformer comparator, the variable resistor is connected in series to the secondary side of the voltage transformer under measurement. It features.

The present invention is to evaluate the burden for the voltage transformer using a variable resistor, the measurement principle thereof will be briefly described first.

First, the theoretical background of the burden effect of the error and phase angle error of the voltage transformer according to the present invention will be described below with reference to FIG.

A voltage transformer is a type of transformer with a primary coil and a secondary coil wound around an iron core. When there is no internal error at all, the ratio of the primary side high voltage Vp to the secondary side low voltage Vs is equal to the ratio of the primary side winding number n1 to the secondary side winding number n2. However, in practice, since the voltage transformer has an error δ, it can be expressed as Equation (1).

Where N is the rated conversion ratio or winding ratio of the voltage transformer. The actual voltage transformer has a ratio error (RE) and a phase angle error (Γ) because a magnetic saturation phenomenon occurs in the iron core and a voltage drop occurs due to leakage impedance at the primary side 20 and the secondary side 30. have.

1, the impedance (Z _b) (35) of burden (Z _b) When connected to a voltage transformer, load on the secondary side 30 of the voltage transformer (Z _b) is not and when they are connected The relationship between the time error (RE) and the phase angle error (Γ) is given by Equations (2) and (3) below.

Where each argument is:

RE ₀ : Rain error when there is no burden,

RE _b : Rain error when burden Z _b ,

Γ ₀ : phase angle error without burden

Γ _b : phase angle error when there is a burden Z _b ,

Z ₀ = R ₀ + jX ₀ : Leakage output impedance of voltage transformer,

Z _b = R _b + j X _b : impedance of external burden.

G _b = R _b / (R ² _b + X ² _b ): Conductance of the burden

B _b = X _b / (R ² _b + X ² _b ): Susceptance of burden

As in equations (2) and (3), the error and phase angle error when there is a burden vary with the burden value. The 1% error in the measurement of the burden value (Z _b = R _b + jX _b ) causes a 1% error in the non-error and phase angle error. Therefore, the accurate measurement of the burden value is important to obtain the correct non-error and phase angle error of the voltage transformer.

In the present invention, as shown in Figure 2, characterized in that the variable resistor is further installed in the circuit configuration of the conventional voltage transformer comparison measurement system, the variable resistor has a resistance ratio of DC resistance and AC resistance By connecting a variable resistor of 0.1% or less, i.e., X _s / R _s <10 ^-3 in series with the secondary side of the voltage transformer under test (70 in Fig. 2), the burden for the voltage transformer can be measured more accurately and easily. It was made with attention to the existence.

Accordingly, in the present invention, as shown in FIG. 2, the configuration of the load evaluating apparatus for the voltage transformer is configured such that the same high voltage is supplied to the primary side 20 of the reference voltage transformer 40 and the voltage transformer under test 50. 40) and the voltage transformer 50 to be measured are connected in parallel.

Further, the load Z _b 65 is connected in parallel to the secondary side 30 of the voltage transformer 50 under measurement, and the variable resistor 70 is connected in series to the secondary side 30 of the voltage transformer 50 under measurement. ) And the voltage transformer comparison measuring device 60 is connected to compare the voltages of the secondary side 30 of the two voltage transformers 40 and 50.

In this case, the error (RE) and the phase angle error of the voltage transformer can be expressed as follows.

In formulas (2) and (3), R _o is R _o Replaced by + R _s , which can be represented by equations (4) and (5).

_b 가 상수이므로, 식(4)의 비오차, RE_b(R_o, R_s)와 식(5)의 위상각 오차, Γ_b(R_o, R_s)는 모두 가변 저항기의 저항값(R_s)에 비례한다. 따라서 R_s의 값을 변화시켜 가면서 측정한 RE_b(R_o, R_s)와 Γ_b(R_o, R_s)를 R_s의 1차 함수로 플로팅(plotting)하여 기울기를 얻으면 각 부담의 (RE_o-1)G_b 와 서셉턴스(B_b)가 된다. 이렇게 얻어진 컨덕턴스(G_b)와 서셉턴스(B_b)로부터 부담의 부담 값과 역률은 식(6)에 의해 얻어진다.RE _o , RE _b , in Eqs. (4) and (5) at any particular burden

_{Since b} is a constant, the error in equation (4), RE _b (R _o , R _s ) and the phase angle error of equation (5), Γ _b (R _o , R _s ) are both proportional to the resistance value R _s of the variable resistor. Therefore going to change the value of R _s measured RE _b (R _o, R _s) and Γ _b (R _o, R _s) to the floating (plotting) as a linear function of R _s get the slope of each load ( RE _o -1) G _b and susceptance (B _b ). The burden value and the power factor of the burden from the conductance G _b and the susceptance B _b thus obtained are obtained by equation (6).

Where V _b is obtained by measuring the voltage across the load using a multimeter.

The actual equipment used in the construction of the voltage transformer burden evaluation apparatus of FIG. 2 is manufactured by Knopp, USA, and models are WP-14000-4 and Knopp KVTs, respectively. The to-be-measured voltage transformer was measured using a model 2261 manufactured by Yokogawa, Japan, while the primary voltage was 440V and the secondary voltage was maintained at 110V. 2, the external burden (Z _b) (65) is in parallel to the voltage transformer secondary side, it is a Gen Rad's variable resistor 70, one represented by R _s voltage transformer connected in series to the secondary side .

In the configuration of the present invention, the error and phase angle error of the voltage transformer under measurement are measured while varying the resistance of the variable resistor 70 connected in series (between 1 kV and 100 kPa).

Accordingly, the present invention also connects the reference voltage transformer 40 and the measured voltage transformer 50 in parallel so that the same high voltage is supplied to the primary side of the reference voltage transformer and the voltage transformer under measurement, and the voltage transformer 50 to be measured. Connect the burden (Z _b ) 65 in parallel to the secondary side of the circuit, connect the variable resistor 70 in series to the secondary side of the voltage transformer under test, and adjust the secondary voltages of the two voltage transformers 40 and 50. An error evaluation method of a voltage transformer using a voltage transformer burden evaluation device to which a voltage transformer comparison measuring device 60 is connected so as to compare the voltage, while changing the resistance of the variable resistor 70 according to Equations (4, 5) above. Provides a way to assess the burden on the transformer.

Hereinafter, the results of measuring the error and phase angle error according to the present invention will be described.

3A and 3B are graphs of the measurement results of the error and phase angle error at 15VA, power factor 0.8, 60Hz, and 110V, where the ratio of the measured voltage transformer measured when the secondary side is open is unburdened. The error RE _o = 0.178% and the slope in the straight line A + B _x drawn in FIG. 3A is (RE _o -1) G _b by equation (4). Therefore, the conductance of the burden can be obtained. It can be seen that the slope B is the susceptance B _b of the burden in the straight line A + B _x plotted in FIG. 3B according to equation (5). The results of the measurement of the conductance (G _b ) and susceptance (B _b ) of the burdens measured at 1.25 VA, 2.5 VA, 5 VA, and 10 VA in the same way are summarized together with the results of 15 VA. The first and third columns are shown respectively. The burden value and the power factor of the burden can be obtained by Equation (6). The burden values and the power factor obtained in the above ranges are collectively shown in the last two columns of Table 1.

Rated / Power Factor of Burden Conductance (G _b ) Susceptance (B _b ) Burden Power factor 1.25 VA / 0.8 0.0000795 0.0000627 1.226VA 0.785 2.5 VA / 0.8 0.0001605 0.0001233 2.449VA 0.793 5 VA / 0.8 0.0003263 0.0002421 4.917VA 0.803 10 VA / 0.8 0.0006575 0.0004917 9.934VA 0.801 15 VA / 0.8 0.0009658 0.0007342 14.679VA 0.796

On the other hand, Figure 4a, Figure 4b is a direct load automatic evaluation system using a power meter experimentally established to verify the validity of the technology that can measure the burden value and power factor of the burden using the voltage transformer burden evaluation apparatus of the present invention It is a graph showing the result compared with the measured value, the y-axis value in the drawing is a relative error (Relative error) is defined as follows.

The vertical bar is the uncertainty of the values measured by the two methods, it can be seen that the measurement results are consistent with each other uncertainty can confirm the effectiveness of the present invention.

According to the voltage transformer burden evaluation apparatus according to the present invention described above, not only can a small and light weight variable resistor be brought to the industry, but also the measuring device can be easily evaluated in the field, and the accuracy of the measurement can be greatly improved. The effect of being able to easily evaluate is achieved.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

Claims (4)

The reference voltage transformer 40 and the voltage transformer under test 50 are connected in parallel so that the same high voltage is supplied to the primary side of the reference voltage transformer and the voltage transformer under measurement. The burden (Z _b ) 65 is connected in parallel to the secondary side of the voltage transformer 50 under measurement, The variable resistor 70 is connected in series with the secondary side of the voltage transformer under measurement, Voltage transformer using a variable resistor, characterized in that the voltage transformer comparison measuring device 60 is connected to compare the secondary voltages of the two voltage transformers (40, 50). The apparatus of claim 1, wherein the resistance ratio of the DC resistance and the AC resistance is 0.1% or less, that is, X _s / R _s <10 ^-3 . 3. The burden evaluator for voltage transformer using a variable resistor according to claim 1 or 2, wherein said primary side voltage is 440V and said secondary side voltage is 110V. The reference voltage transformer 40 and the voltage transformer under test 50 are connected in parallel so that the same high voltage is supplied to the primary side of the reference voltage transformer and the voltage transformer under measurement. Wherein the measured voltage charge on the secondary side of the transformer (50) (Z _b) connecting (65) in parallel, and connected to a variable resistor 70 in series with the secondary side of the measured voltage transformer, and the two voltage transformers ( As an error evaluation method of a voltage transformer using the voltage transformer burden evaluation device to which the voltage transformer comparison measuring device 60 is connected to compare the secondary voltages 40 and 50, Method for evaluating the burden for a voltage transformer using a variable resistor, characterized in that for evaluating the error of the voltage transformer while changing the resistance of the variable resistor 70 according to the following equations (8) and (9):

Here, RE ₀ is the error when there is no burden; RE _b is the error when burden Z _b is present; Γ ₀ is the phase angle error at no burden; Γ _b is the phase angle error when the burden Z _b is present; Z ₀ = R ₀ + jX ₀ is the leakage output impedance of the voltage transformer; Z _b = R _b + j X _b is the impedance of the external burden; G _b = R _b / (R ² _b + X ² _b ) is the conductance of the burden; B _b = X _b / (R ² _b + X ² _b ) is the susceptance of the burden; R _s is the resistance of the variable resistor.

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