JP2012202844A - Current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detector capable of accurately performing temperature compensation of a secondary winding resistance.SOLUTION: The current detector includes a transformer 1, a load resistance 2 connected between secondary-side terminals of the transformer 1, a voltage amplifier 5 which amplifies a voltage developed across the load resistance 2, an input resistance 3 connected to one secondary-side terminal of the transformer 1 in parallel with the load resistance 2, and a feedback resistance 4 which determines an amplification factor of the voltage amplifier 5 together with the input resistance 3. The input resistance 3 is constituted including a thermistor and compensates for temperature characteristics of a winding resistance 11 of the transformer 1.

Description

  The present invention relates to a current detection device used in a protection relay device installed for the purpose of protecting a power system.

  The current detection device used for the protection relay device is generally a system using a transformer. In the current detector, a current flowing in the primary winding can be measured by connecting a burden resistor to both ends of the secondary winding of the transformer and measuring a voltage generated in the burden resistance. However, when the temperature of the transformer changes due to the current flowing in the primary winding and the secondary winding, the secondary winding resistance of the transformer changes, which makes it difficult to accurately measure the current. . In order to solve this problem, a method has been proposed in which a thermistor is inserted so as to cancel the temperature change of the secondary winding resistance in series with the burden resistance (see Patent Document 1).

JP-A-5-34376

  As described above, in the conventional current detection device, the thermistor is inserted in series with the burden resistance so as to cancel the temperature change of the secondary winding resistance. However, in this case, since a burden current flows through the thermistor, the thermistor itself generates heat due to this burden current, and the resistance value of the thermistor changes. For this reason, there is a problem that it is difficult to accurately perform temperature compensation of the secondary winding resistance.

  The present invention has been made in view of the above, and an object of the present invention is to provide a current detection device capable of accurately compensating the temperature of the secondary winding resistance.

  In order to solve the above-described problems and achieve the object, the current detection device according to the present invention is configured such that the number of turns of the primary winding and the secondary winding with respect to the primary current input to the primary winding. A transformer that generates and outputs a secondary current corresponding to the ratio to the secondary winding, a burden resistor connected between the terminals on the secondary side of the transformer, and a voltage generated across the burden resistor. A voltage amplifier to be amplified, an input-side resistor for determining an amplification factor of the voltage amplifier, an input resistor connected in parallel to the burden resistor to one terminal on the secondary side of the transformer, and the input And a feedback resistor that determines the amplification factor of the voltage amplifier together with a resistor, and the input resistor includes a thermistor and compensates for the temperature characteristics of the secondary winding resistance of the transformer. It is characterized by that.

  According to the present invention, the temperature compensation of the secondary winding resistance of the transformer is accurately performed by performing the temperature compensation by using the input resistance of the voltage amplifier for measuring the voltage generated at both ends of the burden resistance as a thermistor. There is an effect that it is possible.

FIG. 1 is a configuration diagram of a current detection device according to the first embodiment. FIG. 2 is a diagram illustrating an example of the temperature characteristics of the inter-terminal voltage of the winding resistor 11 and the burden resistor 2 of the transformer 1. FIG. 3 is a diagram illustrating an example of temperature characteristics of the thermistor resistance value of the input resistor 3 and the gain of the voltage amplifier 5. FIG. 4 is a configuration diagram of the current detection device according to the second embodiment. FIG. 5 is a diagram illustrating an example of temperature characteristics of the winding resistance 11 and the thermistor resistance of the transformer 1. FIG. 6 is a diagram illustrating an example of temperature characteristics of the inter-terminal voltage of the winding resistor 11 of the transformer 1, the input resistor 3 of the voltage amplifier 5 and the burden resistor 2 in combination of the resistor and thermistor. FIG. 7 is a configuration diagram of a conventional current detection device.

  Embodiments of a current detection device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a current detection device according to the present embodiment. In FIG. 1, the current detection device according to the present embodiment includes a transformer 1, a burden resistor 2, a voltage amplifier 5, an input resistor 3 of the voltage amplifier 5, and a feedback resistor 4 of the voltage amplifier 5.

  The transformer 1 includes a primary winding 20 and a secondary winding 21, and the number of turns of the primary winding 20 and the secondary winding 21 with respect to the primary current I 1 input to the primary winding 20. A secondary current I2 corresponding to the ratio is generated by the secondary winding 21 and output. The winding resistance 11 is a secondary winding resistance of the transformer 1. A burden resistor 2 is connected between both terminals on the secondary side of the transformer 1. That is, the burden resistor 2 is connected to both ends of the secondary winding. The secondary current I2 generates a voltage VL across the burden resistor 2.

  The voltage amplifier 5 has its input side connected to both ends of the burden resistor 2, and amplifies and outputs the voltage VL. The voltage amplifier 5 is an operational amplifier and constitutes an inverting amplifier circuit 30 together with the input resistor 3 and the feedback resistor 4. The voltage amplifier 5 has two input terminals and one output terminal. The input resistor 3 is connected to the inverting input terminal (−) which is one input terminal of the voltage amplifier 5, and the input resistor 3 is connected to one terminal on the secondary side of the transformer 1 and one end of the burden resistor 2. Yes. The input resistor 3 is connected to one terminal on the secondary side of the transformer 2 in parallel with the burden resistor 2. The non-inverting input terminal (+) which is the other input terminal of the voltage amplifier 5 is connected to the ground. A feedback resistor 4 is connected between the inverting input terminal (−) and the non-inverting input terminal (+) of the voltage amplifier 5. In this current detection device, a voltage signal corresponding to the primary current I1 can be obtained by amplifying the voltage VL by the voltage amplifier 5. The gain (voltage amplification factor) of the voltage amplifier 5 is determined by the ratio of the input resistor 3 and the feedback resistor 4.

  Here, the secondary current I2 itself does not have temperature characteristics, but the winding resistance 11 of the transformer 1 has temperature characteristics as shown in FIG. FIG. 2 is a diagram illustrating an example of the temperature characteristics of the inter-terminal voltage VL of the winding resistor 11 and the burden resistor 2 of the transformer 1. In FIG. 2, the horizontal axis represents temperature T (° C.), the vertical axis represents winding resistance (Ω) or inter-terminal voltage (V), the resistance value of the winding resistance 11 of the transformer 1 is indicated by R, and the burden resistance 2 The voltage between the terminals is indicated by VL. In order to prevent this temperature characteristic from affecting the output, the excitation impedance of the transformer 1 may be designed to be sufficiently larger than the sum of the winding resistance 11 and the burden resistance 2, but if the excitation impedance is increased, There is a problem that the transformer 1 is saturated when a large primary current I1 flows. For this reason, in the case of the transformer 1 that is used in a wide dynamic range such as that used in the protective relay device, the exciting impedance cannot be made sufficiently larger than the sum of the winding resistance 11 and the load resistance 2, so that the burden resistance The voltage VL generated at both ends of 2 is also affected by the temperature characteristics of the winding resistance 2, and has temperature characteristics as shown in FIG. For example, with respect to the transformer 1 used in the protection relay device, if one example of these resistance values is given, the resistance value of the burden resistance 2 to 20 (Ω), the resistance value of the winding resistance 11 (when the temperature is 20 ° C.) to 70 ( Ω), the excitation impedance of the transformer 1 to 350 (Ω), and the ratio of the sum of the resistance values of the winding resistance 11 and the load resistance 2 to the excitation impedance of the transformer 1 is about 0.26, It's not small. In fact, in this case, the voltage VL generated in the burden resistor 2 varies by 0.2% when the temperature changes by 10 ° C. Therefore, the temperature range of the protective relay device varies by ˜1.2% at −10 to 50 ° C. If the required performance is 0.5% or less, for example, it is necessary to compensate for such temperature variation.

  Therefore, in this embodiment, in order to compensate for the temperature characteristics of the voltage VL generated at both ends of the burden resistor 2, the input resistor 3 of the voltage amplifier 5 is a thermistor. The gain (G) of the voltage amplifier 5 is determined by the ratio of the input resistor 3 and the feedback resistor 4. By making the input resistor 3 a thermistor having a temperature characteristic that cancels the temperature characteristic of the voltage VL of the burden resistor 2, The gain (G) of the amplifier 5 can cancel the temperature characteristic of the voltage VL of the burden resistor 2 as shown in FIG. Here, FIG. 3 is a diagram illustrating an example of temperature characteristics of the thermistor resistance value of the input resistor 3 and the gain of the voltage amplifier 5. In FIG. 3, the horizontal axis represents temperature T (° C.), the vertical axis represents thermistor resistance value (Ω) or voltage amplification factor (gain) G, the resistance value of the input resistance 3 is represented by RT, and the gain of the voltage amplifier 5 is represented by G. Is shown. As is clear from the comparison between FIG. 2 and FIG. 3, the resistance value RT of the input resistor 3 decreases as the temperature increases so as to cancel out the temperature characteristic of the resistance value R of the winding resistor 11. Therefore, the gain (G) of the voltage amplifier 5 increases as the temperature increases so as to cancel out the temperature characteristics of the voltage VL of the burden resistor 2. Thus, by making the input resistance 3 of the voltage amplifier 5 a thermistor, the temperature characteristic of the current detection device can be improved.

  Further, the input impedance of the voltage amplifier 5 can be made very high compared to the burden resistor 2. Usually, the burden resistor 2 is about several hundred Ω, but the input impedance of the voltage amplifier 5 is 1 MΩ or more. That is, the burden resistor 2 can be set to 1/1000 or less of the input impedance of the voltage amplifier 5. For this reason, when the thermistor is used as the input resistor 3 of the voltage amplifier 5 compared to the case where the thermistor is added in series with the burden resistor 2, the current flowing through the thermistor is 1/1000 or less. Therefore, heat generation due to the current flowing through the thermistor is suppressed, and temperature compensation of the voltage VL of the burden resistor 2 can be performed accurately.

  FIG. 7 is a configuration diagram of a conventional current detection device. In FIG. 7, the same components as those in FIG. 1 are denoted by the same reference numerals. The input resistor 7 is a normal resistor different from the thermistor. In the conventional current detection device, the thermistor 6 is connected in series with the load resistor 2 to one terminal on the secondary side of the transformer 1. That is, by inserting the thermistor 6 in series with the burden resistor 2, the temperature change of the secondary winding resistance is canceled out. However, in this configuration, since the secondary current I2 flows through the thermistor 6, the thermistor 6 itself generates heat, and the resistance value of the thermistor 6 changes. For this reason, in the conventional configuration, it is difficult to accurately compensate the secondary winding resistance.

  As described above, according to the present embodiment, the temperature resistance of the voltage VL of the burden resistor 2 can be accurately compensated by using the input resistor 3 of the voltage amplifier 5 as a thermistor. Moreover, since the input impedance of the voltage amplifier 5 is very high compared to the burden resistor 2 (the burden resistor 2 is 1/1000 or less of the input impedance of the voltage amplifier 5), the input current of the voltage amplifier 5 becomes very small. Therefore, the heat generation of the thermistor is suppressed, and the temperature compensation of the secondary winding resistance can be performed accurately. Therefore, according to the present embodiment, the current detection accuracy of the current detection device is improved.

  In the present embodiment, for example, in a transformer 1 used in a protection relay device, it is difficult to set the excitation impedance of the transformer 1 sufficiently larger than the sum of the winding resistance 11 and the burden resistance 2. In addition, temperature compensation of the voltage VL of the burden resistor 2 can be performed. For example, (burden resistance 2 + winding resistance 11) / (excitation impedance) is 0.1 or more, which is suitable for a configuration that requires temperature compensation of the secondary winding resistance.

Embodiment 2. FIG.
FIG. 4 is a configuration diagram of the current detection device according to the present embodiment. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals. In the first embodiment, the input resistor 3 of the voltage amplifier 5 is a single thermistor. However, in the second embodiment, the input resistor 3 of the voltage amplifier 5 is a combination of a resistor and a thermistor as shown in FIG. It is made to do.

  Specifically, the input resistor 3 includes a resistor 60, a thermistor 61 connected in series to the resistor 60, a resistor 63 connected in parallel to the resistor 60 and the thermistor 61, and a resistor 60 and the thermistor 61 connected in series. And configured resistor 62. In FIG. 4, the resistance value of the resistor 60 is represented by R1, the resistance value of the thermistor 61 is represented by RT1, the resistance value of the resistor 62 is represented by R3, and the resistance value of the resistor 63 is represented by R2. The resistance value of the input resistor 3 is represented by Rin.

  FIG. 5 is a diagram illustrating an example of temperature characteristics of the winding resistance 11 and the thermistor resistance of the transformer 1. The temperature characteristic (R) of the winding resistor 11 is proportional to the temperature as shown in FIG. 5, but a generally available thermistor has a logarithmic temperature characteristic (RT) as shown in FIG. The thermistor of the first embodiment has a linear temperature characteristic (RT) as shown in FIG.

In order to perform temperature compensation using such a thermistor having a logarithmic temperature characteristic, for example, the input resistor 3 is configured by combining the thermistor 61 and the resistors 60, 62, 63 as shown in FIG. As described above, the resistance value Rin of the input resistor 3 can be set by combining the thermistor 61 with resistors 60, 62, and 63 that cancel the temperature characteristic (R) of the winding resistor 11. The input resistance Rin is obtained by the following equation.
Rin = 1 / (1 / (R1 + RT1) + 1 / R2) + R3
Here, if the values of R1, R2, and R3 are appropriately selected, the resistance value of the input resistor 3 can be canceled by the temperature characteristic R of the winding resistor 11 as shown in FIG. FIG. 6 is a diagram illustrating an example of temperature characteristics of the inter-terminal voltage of the winding resistance 11 of the transformer 1, the input resistance 3 composed of a combination of resistance and thermistor, and the burden resistance 2. In FIG. 6, the horizontal axis represents temperature T (° C.) and the vertical axis represents resistance (Ω) or voltage (V). V 0 represents the voltage between the terminals of the burden resistor 2. Although the method of configuring the input resistor 3 with the thermistor 61 and the plurality of resistors 60, 62, 63 is not limited to the illustrated example, the illustrated example provides the simplest and sufficient configuration.

  In this way, it is possible to use a thermistor that is generally available, so that temperature correction can be performed at low cost. Further, since the temperature characteristic of the gain of the voltage amplifier 5 can be finely adjusted using the resistors 60, 62, 63, there is an effect that the temperature can be corrected more accurately. Other effects of the present embodiment are the same as those of the first embodiment.

  In the above description, the case of the current detection device used for the protection relay device installed for the purpose of protecting the power system as an application of the present invention has been described as an example. However, the present invention is also used for a device for detecting current using other transformers. it can.

  The present invention is useful as a current detection device applicable to a protection relay device installed for the purpose of protecting a power system.

DESCRIPTION OF SYMBOLS 1 Transformer 2 Burden resistance 3 Input resistance 4 Feedback resistance 5 Voltage amplifier 11 Winding resistance 20 Primary winding 21 Secondary winding 30 Inversion amplification circuit 60, 62, 63 Resistance 61 Thermistor

Claims (5)

A transformer that generates and outputs a secondary current corresponding to a turns ratio of the primary winding and the secondary winding to the primary current input to the primary winding;
A burden resistor connected between the terminals on the secondary side of the transformer;
A voltage amplifier that amplifies the voltage generated at both ends of the burden resistor;
An input-side resistor for determining an amplification factor of the voltage amplifier, the input resistor being connected to one terminal on the secondary side of the transformer in parallel with the burden resistor;
A feedback resistor that determines the amplification factor of the voltage amplifier together with the input resistor;
With
The current detection device is characterized in that the input resistance includes a thermistor and compensates for temperature characteristics of the secondary winding resistance of the transformer.   The current detection device according to claim 1, wherein the input resistance is constituted by a single thermistor.   The current detection device according to claim 1, wherein the input resistance includes a single thermistor and a plurality of resistors.   The current detection apparatus according to claim 1, wherein the burden resistance is 1/1000 or less of an input impedance of the voltage amplifier.   5. The current according to claim 1, wherein a sum of resistance values of the burden resistance and the secondary winding resistance is 0.1 times or more of an excitation impedance of the transformer. Detection device.

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