JP5739309B2 - Digital protection controller - Google Patents

Description

  The present invention relates to a digital protection control device, and more particularly to a digital protection control device having a linearity correction function of an instrument transformer used for analog signal input.

  The digital protection control device inputs an analog quantity such as a voltage or current of the power system, converts it into a digital quantity, executes a predetermined protection calculation process, and is installed in the power system when a power system fault occurs. The circuit breaker is opened and closed to eliminate accidents.

  In this protection calculation process, an accident determination is performed according to the magnitude and phase of analog quantities such as voltage and current. For this reason, voltage transformers VT (Voltage Transformer) and current transformers CT (Current Transformer) for measuring voltage and current of the power system are included in the transformers for measuring instruments (including auxiliary transformers in the subsequent stages). High input accuracy is required. Specifically, since the analog amount of the power system is greatly different between when it is normal and when an accident occurs, high linearity characteristics are required in a wide input range of analog inputs.

  Hereinafter, the characteristics of the instrument transformer will be described. First, FIG. 2 shows the relationship between the primary voltage (horizontal axis) and the primary current (vertical axis) of the instrument transformer. Although they should be proportional to each other, the saturation characteristic 9 is shown by the hysteresis characteristic of the iron core material, and the saturation characteristic varies from instrument transformer to instrument transformer. As a result, an error occurs in the current value when viewed at the rated value.

  Further, FIG. 3 shows the relationship between the input voltage or current (horizontal axis) and the output voltage or current (vertical axis) for a specific instrument transformer. Accordingly, there is no variation between the instrument transformers shown in FIG. In this case, the desired characteristic 10 as an instrument transformer has a relationship in which the output is proportional to the input. On the other hand, the characteristic 11 of the actual instrument transformer is measured as a low value below the rated value when the rated value is taken from the relationship indicating the saturation characteristic 9 (FIG. 2) due to the hysteresis characteristic of the iron core material. Above the value, it is measured as a high value. As described above, the instrument transformer has an error in the low input region and the high input region (relative to the rated value) due to the hysteresis characteristic of the iron core material.

  For this reason, in order to satisfy the linearity characteristics, the size and structure of instrument transformers have been increased. As a result, the input circuit portion including the auxiliary transformer of the digital protection control device is inevitably increased in size, making it difficult to reduce the size of the digital protection control device.

  In response to this problem, in Patent Document 1 and Patent Document 2, as a linearity correction method, input / output characteristics at representative points in all regions of a wide input range of analog input are measured, and this is converted into a function to obtain a correction value.

Japanese Patent Laid-Open No. 5-180878 JP 7-294281 A

  The correction methods of Patent Document 1 and Patent Document 2 need to be implemented for each individual digital protection control device. In addition, since it is necessary to adjust the compatibility with the instrument transformer installed at the site, it is good to be able to perform combination tests and adjustments at the time of shipment from the factory, but there are cases where on-site adjustment is required after installation. For this reason, when the product is mass-produced, it is necessary to make adjustments in each apparatus, which is a difficult method for practical operation.

  In view of the above, an object of the present invention is to provide a digital protection control device that is provided with a linearity error correction function itself and that can easily correct linearity errors.

  From the above, in the present invention, the analog amount of the power system is measured by the instrument transformer, and is taken into the arithmetic unit as a digital value after the sample-and-hold process and the analog-digital conversion process at a constant period. In the protection control device that performs the protection control calculation to detect the accident of the calculation device, the calculation device holds the calculation formula that expresses the characteristics of the input unit including the instrument transformer using its excitation impedance and the theoretical formula and inputs them. Calculate the calculated value and the theoretical value for the analog quantity on the input side of the instrument transformer from the digital value, the calculation formula, and the theoretical formula, and correct the digital value with the calculated value and the theoretical value. Detect accidents.

  In addition, a plurality of instrument transformers for measuring an analog amount of the power system are provided, and the arithmetic unit holds in advance the excitation impedances of the plurality of instrument transformers.

  The arithmetic unit determines an accident from the magnitude of the input digital value, and the calculated value and the theoretical value include information about the magnitude.

  The digital correction value is obtained by multiplying the digital value by the ratio of the calculated value and the theoretical value.

  The arithmetic device determines an accident from the measured phase difference between the analog quantities of the plurality of power systems, and the calculated value and the theoretical value include information on the phase.

  The digital value includes information corresponding to the phase difference between the measured analog quantities of the plurality of power systems, and the digital correction value includes the phase difference between the calculated value and the theoretical value in the digital value phase difference information. Is required.

  According to the present invention, digital correction can be easily performed even with an instrument transformer such as VT / CT that does not have a desired linearity characteristic.

The figure which shows the processing program of the correction value calculation and error correction calculation which are performed with the arithmetic unit 4. FIG. The figure which showed the relationship between the primary side voltage (horizontal axis) and primary side current (vertical axis) of the instrument transformer. The figure which shows the relationship between the input and output of a specific instrument transformer. The figure which shows schematic structure of the input part of a digital protection control apparatus. The figure which shows the equivalent circuit of the instrument transformer 1 and the analog input circuit 2. FIG. The figure which shows the result of having calculated | required the calculation formula of the input-output voltage of FIG. 3 lower about the phase.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 4 shows a schematic configuration of the input portion of the digital protection control apparatus. Here, the voltage / current of the power system is measured in the instrument transformer 1 such as a voltage transformer or a current transformer. The analog input circuit 2 extracts only the basic waveform of the analog amount, and performs a sample and hold process at intervals of 30 degrees of the analog amount of the power system, for example. In the A / D conversion circuit 3, the analog value sampled and held at intervals of 30 degrees is converted into a digital value and taken into the arithmetic unit (CPU) 4. The arithmetic unit (CPU) 4 executes digital arithmetic processing using the acquired digital data, and executes fault determination of the power system. In the present invention, prior to power system accident determination, correction value calculation and error correction calculation necessary to ensure linearity characteristics are performed using the input digital value.

  In the correction calculation of the present invention, the instrument transformer 1 and the analog input circuit 2 are represented by an equivalent circuit in FIG. First, the instrument transformer 1 is assumed to be an equivalent instrument transformer 1A expressed by a T-type equivalent circuit. A primary winding resistor r1 and a secondary winding resistor r2 are arranged in series on the T-shaped head of the equivalent instrument transformer 1A, and an excitation impedance Z1 is arranged on the T-shaped leg. In the equivalent analog input circuit 2A, this is expressed by an impedance Z2. However, the secondary winding resistance r2 is a value considering the winding ratio n.

  In the equivalent circuit on FIG. 5, the voltage applied to the instrument transformer 1 is Vi, and the voltage obtained from the analog input circuit 2 is Vo. Also, let Z be the total impedance determined by the excitation impedance Z1, the secondary winding resistance r2, and the impedance Z2 of the analog input circuit 2A. At this time, the equivalent circuit in FIG. 5 can be expressed more simply as the equivalent circuit in FIG.

  In this case, in the calculation formula, the output voltage Vo can be derived by calculation in the arithmetic unit (CPU) 4 as a value obtained by multiplying the ratio of the primary winding resistance r1 and the total impedance Z by the input voltage Vi. On the other hand, in the theoretical equation, the output voltage Vo is a value obtained by multiplying the winding ratio n by the input voltage Vi.

  In the input / output characteristics of FIG. 3 described above, the result of the calculation formula in FIG. 5 corresponds to the characteristic 11 of the actual instrument transformer, and the result of the theoretical formula in FIG. 5 is the desired value as the instrument transformer. This corresponds to the characteristic (ideal characteristic) 10. Although FIG. 3 compares the input / output of the instrument transformer from the viewpoint of size, it can also be considered from the viewpoint of phase.

  FIG. 6 shows the calculation formula of the input / output voltage in the lower part of FIG. 3 with respect to the phase. Here, the horizontal axis represents the input voltage, and the vertical axis represents the phase of the output voltage. The phase characteristic 13 is a characteristic in which the phase difference θ with respect to the output at that time is arranged while making the input variable in the calculation formula in the lower part of FIG. 3. On the other hand, no phase difference should occur in the theoretical formula, and a constant value is shown with respect to the input voltage. This theoretical phase difference is represented by 12. According to the result of FIG. 6, when the input voltage rating is used as a reference, the phase difference becomes larger (the delay direction) below the rated value, and becomes smaller (the forward direction) above the rated value.

  From the above, in the present invention, the correction value is calculated as the difference between the magnitude and phase relationship between the calculation formula obtained from the equivalent circuit and the theoretical formula, and the error correction calculation is performed. These correction value calculation and error correction calculation are executed by the arithmetic unit (CPU) 4 of FIG. FIG. 1 shows a processing program for correction value calculation and error correction calculation executed by the arithmetic unit (CPU) 4.

  In the processing program of FIG. 1, information on the equivalent circuit of FIG. 5 is input to the arithmetic unit (CPU) 4 as a premise. Specifically, as values necessary for executing the calculation formula of FIG. 5, the excitation impedance Z1, the primary winding resistance r1, the secondary winding resistance r2, and the impedance Z2 of the equivalent analog input circuit 2A are arithmetic units (CPU). 4 is obtained by inputting. Here, in particular, since the excitation impedance Z1 of the instrument transformer 1 is information directly related to the variation in characteristics described in FIG. 2, it is technically meaningful to reflect this information in the following calculation formula. .

  Under the above premise, in the processing step S100 of the processing program, the digital value D sampled and held and converted into digital values at intervals of 30 degrees of AC electric quantity is taken. The digital value D corresponds to the output voltage Vo in the calculation formula of FIG.

  Next, in processing step S101, the excitation impedance Z1 of the instrument transformer 1 is taken out from the inputted information of the equivalent circuit of FIG.

In processing step S102, a calculation formula is executed using the digital value D (output voltage Vo of the instrument transformer 1) and the excitation impedance Z1, thereby calculating the input voltage Vi of the instrument transformer 1. The input voltage Vi can be obtained using the formula (1).
[Equation 1]
Vo (= D) = | Z / (Z + r1) | Vi (1)
In the equation (1), the total impedance Z is a value determined by the excitation impedance Z1, the secondary winding resistance r2, and the impedance Z2 of the analog input circuit 2A in the equivalent circuit of FIG.

Similarly, in the processing step S102, a calculation formula is executed using the digital value D (the output voltage Vo of the instrument transformer 1) and the excitation impedance Z1, thereby calculating the phase θ of the input voltage Vi and the output voltage. The phase θ can be obtained using the formula (2).
[Equation 2]
θ = tan ⁻¹ (Vo / Vi) = tan ⁻¹ (Z / (Z + r1)) (2)
Thus, the input voltage Vi and the phase θ obtained by executing the calculation formula reflect the value of the excitation impedance Z1 of the instrument transformer 1. The input voltage and phase obtained by executing the calculation formula in processing step S102 will be expressed as Vic and θc.

Next, in process step S103, the input voltage Vi is calculated | required by theoretical formula (3). In this calculation, the turn ratio n is used.
[Equation 3]
Vo (= D) = n × Vi (3)
In processing step S103, the phase θ is obtained based on the concept of the theoretical formula, but this may be treated as a constant value regardless of the input. For example, it can be set to zero or the phase at the rated value obtained by equation (2). The input voltage and phase obtained by executing the calculation formula in processing step S103 will be expressed as Vir and θr.

In process step S104, a correction value is calculated | required from the calculated value calculated | required with the calculation formula, and the theoretical value calculated | required with the theoretical formula. Here, with respect to the input voltage obtained by the calculation formula and the theoretical formula, the gain ΔG is obtained by the equation (4).
[Equation 4]
ΔG = Vir / Vic (4)
Further, in the processing step S104, the phase difference Δθ is obtained by the equation (5) for the phase θ obtained by the calculation formula and the theoretical formula.
[Equation 5]
Δθ = θr−θc = −θc (θr = 0) (5)
In the processing step S105, the error correction of the equation (6) is performed on the digital value D (the output voltage Vo of the instrument transformer 1), and the error corrected secondary voltage (current) VoA of the instrument transformer 1 is corrected. Get.
[Equation 6]
Vo (= D) × ΔG = VoA (6)
The secondary voltage (current) VoA of the instrument transformer 1 determined in this way is a value reflecting the value of the excitation impedance Z1 of the instrument transformer 1, and as a result, the variation between the instrument transformers is reduced. It is a numerical value that takes into account.

  Processing steps S106 and after are processing in a normal protection control device. Here, the magnitude is obtained using the input value VoA obtained as an instantaneous value (a discrete value at intervals of 30 degrees), and an accident determination is performed. In FIG. 1, since the correction process has been completed, a method for obtaining a known size can be applied as it is.

  In the embodiment of FIG. 1, error correction processing is performed for each of the discrete values at intervals of 30 degrees. However, this applies an average value, an execution value, and a maximum value by applying a method for obtaining a known size. Etc., the gain ΔG in step S104 may be corrected.

  Further, when the processing in the protection control device in the processing step S106 is a phase comparison type protection controller, an accident determination is performed by obtaining a phase difference between AC amounts. In this case, the value of the excitation impedance Z1 of the instrument transformer 1 can be reflected by adding the phase difference Δθ obtained by the equation (5) to the phase difference between the AC amounts. Variations between the transformers can be eliminated.

  In the calculation formula of the present invention, the excitation impedance Z1 needs to be taken into the arithmetic unit 4 and set in advance. On the other hand, an instrument transformer is installed for each phase, line, voltage, or current, and the protection control device may realize a protection function in units of lines, so as an excitation impedance Z1 used in the protection control device. The value of each of these instrument transformers must be captured. In addition, the process of FIG. 1 needs to be performed individually for each input.

  According to the present invention described above, since the correction arithmetic expression substantially depends on the shape of the winding core, the correction function can be shared, and the work for calculating the correction value for each instrument transformer can be shortened. it can.

  Conventionally, small transformers such as VT and CT could not be used to obtain desired characteristics. However, the desired characteristics cannot be obtained by using the correction method of the present invention. Small VT and CT can also be easily used.

  Further, by combining with high performance large VT and CT, it is possible to realize a wide dynamic range that ensures linearity characteristics, and to provide a further highly accurate digital protection control device. However, if it is completely saturated, it must be excluded.

1: Instrument transformer 1A: Equivalent instrument transformer 2: Analog input circuit 2A: Equivalent analog input circuit 3: A / D conversion circuit 4: Arithmetic unit (CPU)
9: Saturation characteristic 10: Desirable characteristic as an instrument transformer 11: Characteristic of actual instrument transformer 12: Theoretical phase 13: Phase characteristic r1: Primary winding resistance r2: Secondary winding resistance N : Winding ratio Vo: output voltage Vi: input voltage θ: phase ΔG: gain Z1: excitation impedance Z2: impedance Z

Claims (6)

Protective control calculation that measures the amount of analog in the power system with an instrument transformer, takes it into the arithmetic unit as a digital value after sample-and-hold processing and analog-to-digital conversion processing at a fixed period, and detects the power system accident in the arithmetic unit In the protection control device that implements
The arithmetic device holds a calculation formula representing the characteristics of the input unit including the transformer for the instrument using its excitation impedance and a theoretical formula, and from the input digital value, the calculation formula and the theoretical formula, the instrument A calculated value and a theoretical value are obtained for an analog quantity on the input side of the transformer, and an accident in the power system is detected by a digital correction value obtained by correcting the digital value with the calculated value and the theoretical value. Protection control device. The protection control device according to claim 1,
A protection control device comprising a plurality of instrument transformers for measuring an analog quantity of a power system, wherein the arithmetic device holds in advance the respective excitation impedances of the plurality of instrument transformers. In the protection control device according to claim 1 or 2,
The protection control device according to claim 1, wherein the arithmetic device is configured to determine an accident from the magnitude of the input digital value, and the calculated value and the theoretical value include information about the size. The protection control device according to claim 3,
The protection control device according to claim 1, wherein the digital correction value is obtained by multiplying the digital value by a ratio of the calculated value and the theoretical value. In the protection control device according to claim 1 or 2,
The arithmetic unit is configured to determine an accident from a measured phase difference between analog amounts of a plurality of power systems, and the calculated value and the theoretical value include information on a phase. The protection control device according to claim 5,
The digital value includes information corresponding to the measured phase difference between the analog quantities of the plurality of power systems, and the digital correction value includes the phase difference between the calculated value and the theoretical value in the digital phase difference information. A protection control device characterized by being obtained in consideration of the above.

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