CN116413652A - Current transformer calibration system and method - Google Patents

Abstract

The invention discloses a current transformer calibration system, and discloses a corresponding method of the current transformer calibration system, wherein the current transformer calibration system is based on the current comparison type transformer calibration principle, adopts program-controlled precision voltage division and phase shifting technology, The automatic calibration is completed through the automatic zero adjustment of the software algorithm, which improves the work efficiency under the calibration conditions of the high-precision transformer and reduces the labor cost.

Description

A current transformer calibration system and method

technical field

The invention relates to the field of current transformer calibration, in particular to a current transformer calibration system and method.

Background technique

According to the requirements of metrology law and various management standards, it is necessary to carry out periodic verification or calibration of current transformers, which are strong inspection measuring instruments, according to law.

The transformer calibrator is a special equipment for testing or calibrating current transformers. When the traditional transformer calibrator is working, manually turn the knob to observe the pointer of the AC zero indicator. When the pointer approaches zero, record the current angle difference and ratio difference. Although this method of manually turning the knob for zero adjustment has high precision, it has low efficiency and is not suitable for working under electrified conditions. It is difficult for existing methods to guarantee high efficiency under the premise of high efficiency.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, the present invention proposes a current transformer calibration system, which can be based on the current comparison type transformer calibration principle, adopts program-controlled precision voltage division and phase shifting technology, and completes automatic calibration through automatic zeroing through software algorithms.

The present invention also proposes a method corresponding to the above current transformer calibration system.

The current transformer calibration system according to the embodiment of the first aspect of the present invention includes:

The sampling circuit samples the current of the device to be detected through the current transformer to obtain the sampling current;

The precision voltage divider unit uses a high-precision digital-to-analog converter to connect with the microcontroller unit, and can divide the current obtained by sampling to obtain the same-direction component current and the quadrature component current;

A phase shifting unit, connected to the precise voltage dividing unit, including in-phase phase shifting and quadrature phase shifting, capable of changing the output phase angles of the same-direction component current and the quadrature component current;

A micro-controller unit, by controlling the phase shifting unit and the precision voltage dividing unit, adjusts the same-direction component current and the quadrature component current;

The voltage-current conversion unit is capable of converting the input voltage of the sampling current into a current output readable by the instrument.

The current transformer calibration system according to the embodiment of the present invention has at least the following beneficial effects: the system is based on the current comparison type transformer calibration principle, adopts program-controlled precision voltage division and phase shifting technology, and completes automatic calibration through automatic zeroing through software algorithms. The traditional manual calibration process is automated to improve efficiency and reduce labor costs.

According to some embodiments of the present invention, the phase shifting unit includes co-directional phase shifting and quadrature phase shifting, and the output phase of the co-directional phase shifting circuit is 0° or 180°, which can be switched by program control; the output phase of the quadrature phase shifting circuit 90° or 270°, program-controlled switching.

According to some embodiments of the present invention, the number of bits of the high-precision digital-to-analog converter of the precision voltage dividing unit is greater than 12 bits.

According to some embodiments of the present invention, the precision voltage division unit uses the reference input port of the digital-to-analog converter as the signal input, uses the digital input port of the digital-to-analog converter as the voltage division ratio input, and the output value is the voltage after the voltage division value.

According to some embodiments of the present invention, the pressure division formula adopted in the pressure division process is:

Among them, U _o is the output voltage, U _i is the input voltage, D _i is the input data, and n is the number of digits of the digital-to-analog converter.

According to the second aspect embodiment of the present invention

The current transformer calibration method is characterized in that it includes:

Obtain the operating data of the tested current transformer and obtain the sampling current;

Divide the sampling current by using a precision voltage dividing unit, adjust and record the current of the same direction component and the current of the quadrature component so as to meet the calibration conditions;

Change the output phase angle of the current, re-adjust the current of the same direction component and the quadrature component current to meet the calibration conditions.

Further, the calibration conditions are:

为同向分量电流，/>

为正交分量电流，/>

为差电流。in,

is the same direction component current, />

is the quadrature component current, />

is the difference current.

Further, the method according to claim 6, characterized in that the number of bits of the high-precision digital-to-analog converter in the precision voltage dividing unit is greater than 12 bits.

Further, the precision voltage division unit uses the reference input port of the digital-to-analog converter as the signal input, and the digital input port of the digital-to-analog converter as the voltage division ratio input, and the output value is the voltage value after the voltage division.

Further, it is characterized in that the pressure division formula adopted in the pressure division process is:

Among them, U _o is the output voltage, U _i is the input voltage, D _i is the input data, and n is the number of digits of the digital-to-analog converter.

Further, the specific steps of the method include:

Step 1: Connect the sampling current and the current transformer to be detected to the same node to obtain the sampling current;

Step 2: Operate the phase shifting unit through the microcontroller, so that the output phase angle of the same-direction component current and the quadrature component current is (0°, 90°);

Step 3: Control the precision voltage divider unit through the microcontroller, so that the output amplitude of the co-directional component current and the quadrature component current is the full-scale amplitude, and read and record the output voltage amplitude synchronously;

Step 4: Decrease the output amplitude of the same-direction component current, read and record the output voltage amplitude synchronously, and enter;

Step 5: If the current amplitude of the same direction component is greater than 0, go to the next step; if the current amplitude of the same direction component is equal to 0, go to step 7;

Step 6: If the output voltage amplitude decreases or remains unchanged compared with the previous amplitude, then make the same direction component current output the current amplitude, and enter step 4; if the output voltage amplitude increases compared with the previous amplitude, then make the same Output the previous state amplitude to the component current and enter the next step.

Step 7: Decrease the output amplitude of the quadrature component current, read and record the output voltage amplitude synchronously, and enter the next step;

Step 8: If the magnitude of the quadrature component current is greater than 0, go to the next step; if the magnitude of the quadrature component current is equal to 0, go to step 10;

Step 9: If the output voltage amplitude decreases or remains unchanged compared with the previous amplitude, then make the quadrature component current output the current amplitude, and enter step 7; if the output voltage amplitude increases compared with the previous amplitude, then make the positive The AC component current outputs the amplitude of the previous state and enters the next step.

Step 10: The microcontroller calculates and records the current in-phase output conversion coefficient, quadrature output conversion coefficient and output voltage, and enters the next step;

Step 11: Let the output phase angles of the same-direction component current and the quadrature component current be (0°, 270°), (180°, 270°), (180°, 90°), and repeat steps 3-10 respectively. After completion , go to the next step;

Step 12: Compare and find the minimum output voltage of the 4 sets of data, and calculate the ratio difference and angle difference according to the corresponding output conversion coefficient and quadrature output conversion coefficient, and complete the calibration.

Additional aspects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and understandable from the description of the embodiments in conjunction with the following drawings, wherein:

Fig. 1 is the functional block diagram of the calibration system for the current transformer under the electrified condition of the embodiment of the present invention;

Fig. 2 is a functional block diagram of the precision voltage dividing unit of the current transformer calibration system shown in Fig. 1 .

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

In order to ensure the stable operation of the power system, regular verification and calibration of current transformers is an indispensable step. However, the existing methods are mainly divided into traditional methods and manual methods. The traditional method has low accuracy. Although the manual method solves the problem Accuracy is a problem, but efficiency is difficult to improve. It cannot meet the regular maintenance needs of large-scale power systems. In order to solve the limitations of the prior art, the present invention proposes a current transformer calibration system and method, which can quickly and automatically adjust zero and realize automatic calibration under the premise of ensuring accuracy.

Embodiment one,

Referring to Fig. 1, the embodiment of the present invention provides a kind of current transformer calibration system, and this system at least comprises following several parts: sampling circuit, phase-shifting unit, precise voltage dividing unit, microcontroller (MCU) unit and voltage current conversion unit.

Sampling circuit, referring to Fig. 1, CT _n is the standard current transformer, CT _x is the tested current transformer, Z is the load impedance of the tested current transformer, r is the working current sampling resistor, _R0 is the differential current sampling resistor, Sampling the current of the equipment to be detected through the current transformer to obtain the sampling current precision voltage divider unit, which is composed of a high-precision digital-to-analog converter (DAC) and a microcontroller, which can divide the sampled current to obtain the same direction component current and quadrature component currents, the accuracy of the unit directly affects the calibration accuracy of the system.

Referring to Figure 2, U1 and U2 are high-precision DACs, and the number of bits required is greater than 12 bits. The higher the number of bits, the higher the voltage division accuracy; U3 is an MCU, and MPU (microprocessor) or DSP (digital signal processor) can also be used. The basic principle is: use the reference input port of the DAC as the signal input, and use the digital input port of the DAC as the voltage division ratio input, then the output value is the voltage value after the voltage division, and the voltage division formula is:

Among them, U _o is the output voltage, U _i is the input voltage, D _i is the input data, and n is the number of DAC bits.

When adopting 16-bit DAC, namely n=16, formula (1) can be expressed as:

It can be known from the formula (2) that the resolution of the voltage division is 1/65536, which satisfies the condition of high precision voltage division. According to experimental experience, as long as n≥12, it can be called high-precision voltage division.

The phase shifting unit is connected with the precise voltage dividing unit and is divided into co-directional phase shifting and quadrature phase shifting, and changes the output phase angles of the co-directional component current and the quadrature component current. Usually, the output phase of the co-directional phase-shifting circuit is 0° or 180°, which is program-controlled switching; the output phase of the quadrature phase-shifting circuit is 90° or 270°, which is program-controlled switching.

和/>

的值，当满足公式(3)时，即MCU单元读取的输出电压值趋近于0时，实现自动调零，系统完成自动校准。The microcontroller (MCU) unit adjusts the

and />

When the value of , when the formula (3) is satisfied, that is, when the output voltage value read by the MCU unit approaches 0, automatic zero adjustment is realized, and the system completes automatic calibration.

为同向分量电流，/>

为正交分量电流，/>

为差电流。in,

is the same direction component current, />

is the quadrature component current, />

is the difference current.

Through calibration, the ratio difference and angle difference formulas are as follows:

Among them, k _f is the in-phase output transform coefficient, and k _δ is the quadrature output transform coefficient.

The voltage-current conversion unit can convert the input voltage of the sampling current into the current output readable by the instrument.

Embodiment two,

Based on the current transformer calibration system provided in the first embodiment above, the present invention provides a current transformer calibration method:

The method includes the steps of:

Step S100, obtaining the operation data of the current transformer under test, and obtaining the sampling current;

Step S200, using a precision voltage divider to divide the sampling current, adjust and record the current of the same direction component and the current of the quadrature component so as to meet the calibration conditions;

Step S300 , changing the output phase angle of the current, re-adjusting the same-direction component current and the quadrature component current to meet the calibration conditions.

Specifically, according to the device of the above-mentioned embodiment, the steps of the method can be adaptively modified as follows:

Step 1: Connect the sampling current and the current transformer to be detected to the same node to obtain the sampling current.

输出相角为(0°,90°)；Step 2: MCU program-controlled phase-shifting unit, so that

The output phase angle is (0°,90°);

输出幅值为满量程幅值，同步读取记录U₀幅值；Step 3: MCU program-controlled precision voltage divider unit, so that

The output amplitude is the full-scale amplitude, and the amplitude of U ₀ is read and recorded synchronously;

输出幅值减小，同步读取记录U₀幅值；Step 4: Order

The output amplitude decreases, and the amplitude of U ₀ is read and recorded synchronously;

幅值大于0，则进入下一步；如果/>

幅值等于0，则进入步骤7；Step 5: If

If the amplitude is greater than 0, go to the next step; if />

If the amplitude is equal to 0, go to step 7;

输出当前幅值，进入步骤4；如果U₀幅值相较之前幅值增大，则令/>

输出前一状态幅值，进入下一步。Step 6: If the magnitude of U ₀ decreases or remains unchanged compared with the previous magnitude, then let

Output the current amplitude and go to step 4; if the amplitude of U ₀ increases compared with the previous amplitude, then make />

Output the amplitude of the previous state and enter the next step.

输出幅值减小，同步读取记录U₀幅值，进入下一步；Step 7: Order

The output amplitude decreases, read and record U ₀ amplitude synchronously, and enter the next step;

幅值大于0，则进入下一步；如果/>

幅值等于0，则进入步骤10；Step 8: If

If the amplitude is greater than 0, go to the next step; if />

If the amplitude is equal to 0, go to step 10;

输出当前幅值，进入步骤7；如果U₀幅值相较之前幅值增大，则令/>

输出前一状态幅值，进入下一步。Step 9: If the magnitude of U ₀ decreases or remains unchanged compared with the previous magnitude, then let

Output the current amplitude and go to step 7; if the amplitude of U ₀ increases compared with the previous amplitude, then make />

Output the amplitude of the previous state and enter the next step.

Step 10: MCU calculates and records the current k _f , k _δ , U ₀ data, and enters the next step;

输出相角为(0°,270°)、(180°,270°)、(180°,90°)，分别重复步骤3-10，完成后，进入下一步；Step 11: Order

The output phase angles are (0°, 270°), (180°, 270°), (180°, 90°), repeat steps 3-10 respectively, and go to the next step after completion;

Step 12: Compare and find the minimum U ₀ of the 4 sets of data, calculate the ratio difference and angle difference according to the corresponding k _f , k _δ according to the formula (2-3), and complete the calibration.

Further, the method proposed in the present invention can be based on the

The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Accordingly, the present invention can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein. The solutions in the embodiments of the present invention can be realized by using various computer languages, for example, the object-oriented programming language Java and the literal translation scripting language JavaScript.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It should be understood that each procedure and/or block in the flowchart and/or block diagram, and a combination of procedures and/or blocks in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions may be provided to a general purpose computer, special purpose computer, embedded processor, or processor of other programmable data processing equipment to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing equipment produce a An apparatus for realizing the functions specified in one or more procedures of the flowchart and/or one or more blocks of the block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to operate in a specific manner, such that the instructions stored in the computer-readable memory produce an article of manufacture comprising instruction means, the instructions The device realizes the function specified in one or more procedures of the flowchart and/or one or more blocks of the block diagram.

These computer program instructions can also be loaded onto a computer or other programmable data processing device, causing a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process, thereby The instructions provide steps for implementing the functions specified in the flow chart or blocks of the flowchart and/or the block or blocks of the block diagrams.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.

Claims (11)

1. A current transformer calibration system, comprising:

the sampling circuit is used for sampling the current of the equipment to be detected through the current transformer to obtain sampling current;

the precise voltage dividing unit is connected with the microcontroller unit by adopting a high-precision digital-to-analog converter and can divide the sampled current to obtain the same-direction component current and the orthogonal component current; the phase shifting unit is connected with the precise voltage dividing unit and comprises an in-phase shifting unit and a quadrature phase shifting unit, and can change the output phase angles of the same-direction component current and the quadrature component current;

the micro-controller unit is used for adjusting the same-direction component current and the orthogonal component current by controlling the phase shifting unit and the precise voltage dividing unit;

the voltage-current conversion unit can convert the input voltage quantity of the sampling current into the current quantity output readable by the instrument.

2. The system of claim 1, wherein the phase shifting unit comprises a homodromous phase shifting and a quadrature phase shifting, the homodromous phase shifting circuit outputting a phase of 0 ° or 180 °, programmed switching; the output phase of the quadrature phase shift circuit is 90 degrees or 270 degrees, and program control is switched.

3. The system of claim 1, wherein the high precision digital to analog converter of the precision voltage divider unit has a number of bits greater than 12 bits.

4. The system of claim 1, wherein the precision voltage dividing unit uses a reference input of the digital-to-analog converter as a signal input, uses a digital input of the digital-to-analog converter as a voltage dividing ratio input, and outputs a voltage value after voltage division.

5. The system of claim 4, wherein the partial pressure process employs a partial pressure formula of:

wherein U is _o To output voltage U _i For input voltage, D _i For input data, n is the number of bits of the digital-to-analog converter.

6. A method of calibrating a current transformer, comprising:

acquiring operation data of a current transformer to be detected to obtain sampling current;

dividing the sampling current by using a precise voltage dividing unit, and adjusting and recording the same-direction component current and the orthogonal component current to enable the same-direction component current and the orthogonal component current to meet the calibration condition;

changing the output phase angle of the current, and re-aligning the same-directional component current and the orthogonal component current to enable the same-directional component current and the orthogonal component current to meet the calibration condition.

7. The method of claim 6, wherein the calibration conditions are:

wherein,,

for the same directional component current, +.>

For orthogonal component currents>

Is a differential current.

8. The method of claim 6, wherein the number of high precision digital to analog converter bits in the precision voltage divider unit is greater than 12 bits.

9. The method of claim 6, wherein the precision voltage dividing unit uses a reference input of a digital-to-analog converter as a signal input, uses a digital input of the digital-to-analog converter as a voltage dividing ratio input, and outputs a voltage value after voltage division.

10. The method of claim 6, wherein the partial pressure process employs a partial pressure formula of:

wherein U is _o To output voltage U _i For input voltage, D _i For input data, n is the number of bits of the digital-to-analog converter.

11. The method according to claim 6, characterized in that the specific steps of the method comprise:

step 1: the sampling current and the current transformer to be detected are connected into the same node, and the sampling current is obtained;

step 2: operating the phase shifting unit by the microcontroller to enable the output phase angles of the homodromous component current and the orthogonal component current to be (0 DEG, 90 DEG);

step 3: the precise voltage dividing unit is controlled by the microcontroller, so that the output amplitude of the same-direction component current and the quadrature component current is the full-scale amplitude, and the output voltage amplitude is synchronously read and recorded;

step 4: the output amplitude of the same-direction component current is reduced, the output voltage amplitude is synchronously read and recorded, and the current enters;

step 5: if the amplitude of the same-direction component current is greater than 0, entering the next step; if the amplitude of the same-directional component current is equal to 0, the step 7 is entered;

step 6: if the amplitude of the output voltage is reduced or unchanged compared with the previous amplitude, the current amplitude of the same-direction component current is output, and the step 4 is carried out; if the amplitude of the output voltage is increased compared with the previous amplitude, the same-direction component current is enabled to output the previous state amplitude and enter the next step.

Step 7: the output amplitude of the orthogonal component current is reduced, the output voltage amplitude is synchronously read and recorded, and the next step is carried out;

step 8: if the amplitude of the orthogonal component current is greater than 0, entering the next step; if the quadrature component current magnitude is equal to 0, then step 10 is entered;

step 9: if the amplitude of the output voltage is reduced or unchanged compared with the previous amplitude, the orthogonal component current is enabled to output the current amplitude, and the step 7 is entered; if the output voltage amplitude is increased compared with the previous amplitude, the quadrature component current is made to output the previous state amplitude and enter the next step.

Step 10: the microcontroller calculates and records the current in-phase output conversion coefficient, the quadrature output conversion coefficient and the output voltage, and then enters the next step;

step 11: the output phase angles of the homodromous component current and the orthogonal component current are (0 degree, 270 degrees), 180 degrees, 270 degrees and 180 degrees, 90 degrees, and the steps 3 to 10 are respectively repeated, and after the completion, the next step is carried out;

step 12: and comparing and finding out the minimum output voltage of 4 groups of data, and calculating the ratio difference and the angle difference according to the corresponding output transformation coefficient and the orthogonal output transformation coefficient to finish calibration.

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