Method for measuring field current and measuring system for field current

Abstract

The application provides a method for measuring excitation current and a system for measuring excitation current, an auxiliary coil is wound on a current transformer, and open circuit voltage U0 of the auxiliary coil is measured; excitation magnetic flux Φ in a core of the current transformer is calculated according to the open circuit voltage U0 of the auxiliary coil and the number of turns N3 of the auxiliary coil m ; a first resistor R 3a and a second resistor R 3b are connected in turn at an open end of the auxiliary coil, and a first voltage U1 corresponding to the first resistor R 3a and a second voltage U2 corresponding to the second resistor R 3b are measured; and excitation current of the current transformer is calculated according to the excitation magnetic flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2. The technical scheme provided by the application can solve the technical problem that the excitation current measurement method in the prior art has a high requirement on weak signal extraction technology.

Description

Technical Field

[0001] The present invention relates to the technical field of excitation current measurement of a current transformer, and in particular to an excitation current measurement method and an excitation current measurement system. Background Art

[0002] Currently, the excellent metering characteristics of current transformers are essential for accurate energy measurement. However, the excitation current of a current transformer during operation directly affects its metering error, or in other words, is the root cause of energy metering errors. Measuring the excitation current has two uses: first, measuring the magnitude of the excitation current can reveal the transformer's error; second, measuring and analyzing the excitation current can reveal the operating state of the transformer core, thereby evaluating the rationality of the transformer core's material selection and structural design.

[0003] The excitation current of a current transformer is the portion of the primary current that generates the magnetic flux in the transformer's core. Because the excitation current is a fraction of the primary current, it is difficult to directly measure the excitation current at different primary currents. Theoretically, the excitation current can be calculated by measuring the primary and secondary currents of the transformer and the difference in their corresponding magnetomotive force. However, the primary current of a current transformer is relatively large and cannot be measured directly, so other methods are needed to measure the excitation current.

[0004] However, existing online current transformer error detection systems require coupling a low-frequency current into the secondary circuit to measure the secondary impedance online. The secondary impedance is then derived from this current and its corresponding voltage. This approach is clearly an active method, requiring a current signal source. The applied current must be sufficiently low to avoid affecting the current transformer's operating state and measurement accuracy. Consequently, it places very high demands on the signal generation and measurement systems and algorithms. Accurate weak signal extraction technology may be a bottleneck for this approach. Summary of the Invention

[0005] The main purpose of the present invention is to provide an excitation current measurement method and an excitation current measurement system to solve the technical problem that the excitation current measurement method in the prior art has high requirements on weak signal extraction technology.

[0006] To achieve the above object, according to one aspect of the present invention, a method for measuring excitation current is provided. The method for measuring excitation current is used to measure the excitation current of a current transformer. The method for measuring excitation current includes:

[0007] Wind the auxiliary coil on the current transformer and measure the open-circuit voltage U0 of the auxiliary coil. Calculate the excitation magnetic flux Φ in the core of the current transformer based on the open-circuit voltage U0 of the auxiliary coil and the number of turns N3 of the auxiliary coil. m ;

[0008] Connect the first resistor R to the open end of the auxiliary coil. 3a and the second resistor R 3b , and measure the first resistor R 3a The corresponding first voltage U1 and the second resistor R 3b The second voltage U2 corresponding to the time;

[0009] According to the excitation magnetic flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 are used to calculate the excitation current of the current transformer.

[0010] Furthermore, according to the excitation flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 are used to calculate the excitation current of the current transformer, including:

[0011] According to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 calculate the core magnetic resistance R of the current transformer m ;

[0012] According to the excitation magnetic flux Φ m and core magnetic resistance R m Calculate the magnetizing current of the current transformer.

[0013] Furthermore, according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 calculate the core magnetic resistance R of the current transformer m ,include:

[0014] According to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 and the principle of the current transformer to establish an equation for solving the core magnetic resistance of the current transformer;

[0015] The excitation current of the current transformer is calculated based on the established equation of the core magnetic resistance of the current transformer.

[0016] Furthermore, according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 and the principle of the current transformer establish an equation for solving the core magnetic resistance of the current transformer, including:

[0017] Connect the first resistor R 3aWhen , a first loop voltage equation group is established for the loop formed by the first resistor and the auxiliary coil and the secondary side loop;

[0018] The voltage equations for the first loop are as follows:

[0019]

[0020] in, is the primary side grid current of the current transformer; Connect the first resistor R to the auxiliary coil side test port 3a When , the secondary current of the current transformer; Connect the first resistor R to the auxiliary coil side test port 3a When the first resistor R 3a The voltage at both ends; L2 is the secondary coil inductance of the current transformer; L3 is the auxiliary coil side excitation inductance of the current transformer; M 12 is the mutual inductance between the primary and secondary coils of the current transformer; M 23 is the mutual inductance between the secondary coil and the auxiliary coil of the current transformer; M 13 is the mutual inductance between the primary coil and the auxiliary coil of the current transformer; R 2r is the resistance of the secondary coil of the current transformer; R2 is the secondary load of the current transformer; R 3r is the resistance of the auxiliary coil itself; ω is the angular frequency of the grid current.

[0021] Furthermore, according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 and the principle of the current transformer to establish an equation for solving the core magnetic resistance of the current transformer, and also include:

[0022] Connect the second resistor R 3b When , a second loop voltage equation group is established for the loop formed by the second resistor and the auxiliary coil and the secondary side loop;

[0023] The voltage equations for the second loop are as follows:

[0024]

[0025] in, Connect a second resistor R to the auxiliary coil side test port 3b When , the secondary current of the current transformer; Connect a second resistor R to the auxiliary coil side test port 3b When the second resistor R 3b The voltage across both ends.

[0026] Furthermore, after obtaining the first loop voltage equation and the second loop voltage equation, the measurement method further includes:

[0027] The voltage equations of the first loop and the voltage equations of the second loop are combined to obtain the following equation:

[0028]

[0029] Furthermore, after the first loop voltage equation group and the second loop voltage equation group are combined, the measurement method further includes:

[0030] The equations combining the voltage equations of the first and second loops are modulo-ed, and the auxiliary coil side excitation inductance L3 of the current transformer and the core magnetic resistance R are combined. m The relationship between the core magnetic resistance R of the current transformer is formed. m The equation is as follows:

[0031]

[0032] Furthermore, the auxiliary coil is wound on the current transformer, including:

[0033] The auxiliary coil is sheathed in parallel on the current transformer, and both ends of the auxiliary coil are led out to form a test port on the auxiliary coil side.

[0034] Furthermore, the excitation magnetic flux Φ in the core of the current transformer is calculated based on the open circuit voltage U0 of the auxiliary coil and the number of turns N3 of the auxiliary coil. m ,include:

[0035] Use the following formula to calculate the excitation flux Φ in the core of the current transformer m ;

[0036]

[0037] According to another aspect of the present invention, a system for measuring excitation current is provided, which is applicable to the above-mentioned method for measuring excitation current. The system for measuring excitation current includes:

[0038] A current transformer and an auxiliary coil, wherein the auxiliary coil is wound on the current transformer;

[0039] a first resistor and a second resistor, the first resistor and the second resistor being respectively connected to an open-circuit end of the auxiliary coil;

[0040] A detection component is used to detect the open-circuit voltage U0 of the auxiliary coil, the first voltage U1 when the first resistor is connected, and the second voltage U2 when the second resistor is connected;

[0041] The first calculation unit is used to calculate the excitation flux Φ in the core of the current transformer according to the open circuit voltage U0 of the auxiliary coil and the number of turns N3 of the auxiliary coil. m ;

[0042] The second calculation unit is used to calculate the excitation magnetic flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 are used to calculate the excitation current of the current transformer.

[0043] Applying the technical solution of the present invention requires only an auxiliary coil around the current transformer. By connecting different resistors to the auxiliary coil and combining multiple measured parameters, the current transformer's excitation current can be calculated. This method is not only simple to operate but also highly accurate. The excitation current measurement method provided in this embodiment does not require the external setup and production of a high-frequency signal source, nor does it address the problem of extracting weak signals. It also offers a simple structure, ease of operation, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0045] Figure 1 shows an equivalent circuit principle diagram of a current transformer with an auxiliary coil according to an embodiment of the present invention; and

[0046] Figure 2 A schematic structural diagram of an excitation current measurement system provided according to an embodiment of the present invention is shown.

[0047] The above drawings include the following reference numerals:

[0048] 1. Auxiliary coil; 2. Reversing switch unit; 3. First resistor; 4. Second resistor; 5. Voltmeter; 6. Signal processing and control unit. DETAILED DESCRIPTION

[0049] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0050] Embodiment 1 of the present invention provides a method for measuring excitation current, which is used to measure the excitation current of a current transformer. The method for measuring excitation current includes: winding an auxiliary coil on the current transformer, measuring the open-circuit voltage U0 of the auxiliary coil, and calculating the excitation flux Φ in the iron core of the current transformer based on the open-circuit voltage U0 of the auxiliary coil and the number of turns N3 of the auxiliary coil. m ; Connect the first resistor R to the open end of the auxiliary coil 3a and the second resistor R 3b , and measure the first resistor R 3a The corresponding first voltage U1 and the second resistor R 3b The second voltage U2 corresponding to the time; according to the excitation magnetic flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 are used to calculate the excitation current of the current transformer.

[0051] The excitation current measurement method provided in this embodiment only requires an auxiliary coil around the current transformer. By connecting different resistors to the auxiliary coil and combining multiple measured parameters, the excitation current of the current transformer can be calculated. This method is not only simple to operate but also highly accurate. The excitation current measurement method provided in this embodiment does not require the external establishment and production of a high-frequency signal source, nor does it address the issue of weak signal extraction. Therefore, the excitation current measurement method provided in this embodiment can address the technical issue of existing excitation current measurement methods requiring high weak signal extraction technology.

[0052] In this embodiment, according to the excitation magnetic flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 calculate the excitation current of the current transformer, including: according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 calculate the core magnetic resistance R of the current transformer m ; According to the excitation flux Φ m and core magnetic resistance R m Calculate the excitation current of the current transformer. Using this method can improve the accuracy of the calculation.

[0053] Specifically, in this embodiment, according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 calculate the core magnetic resistance R of the current transformer m , including: according to the first resistor R 3a , the second resistor R3b , the first voltage U1 and the second voltage U2 and the principle of the current transformer are used to establish an equation for solving the core magnetic resistance of the current transformer; the excitation current of the current transformer is calculated according to the established equation of the core magnetic resistance of the current transformer to facilitate calculation.

[0054] In this embodiment, according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 and the principle of the current transformer to establish the equation for solving the core magnetic resistance of the current transformer, including: connecting the first resistor R 3a When , the first loop voltage equation group is established for the loop formed by the first resistor and the auxiliary coil and the secondary side loop; the first loop voltage equation group is as follows:

[0055]

[0056] in, is the primary side grid current of the current transformer; Connect the first resistor R to the auxiliary coil side test port 3a When , the secondary current of the current transformer; Connect a resistor R to the auxiliary coil side test port 3a When the first resistor R 3a The voltage at both ends; L2 is the secondary coil inductance of the current transformer; L3 is the auxiliary coil side excitation inductance of the current transformer; M 12 is the mutual inductance between the primary and secondary coils of the current transformer; M 23 is the mutual inductance between the secondary coil and the auxiliary coil of the current transformer; M 13 is the mutual inductance between the primary coil and the auxiliary coil of the current transformer; R 2r is the resistance of the secondary coil of the current transformer; R2 is the secondary load of the current transformer; R 3r is the resistance of the auxiliary coil itself; ω is the angular frequency of the grid current.

[0057] Using this calculation method, by connecting the first resistor R 3a When the first circuit voltage equation group is established for the circuit formed by the first resistor and the auxiliary coil and the secondary circuit, it is convenient to calculate the core magnetic resistance of the current transformer in the subsequent step, thereby facilitating the calculation of the excitation current of the current transformer.

[0058] Specifically, in this embodiment, according to the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 and the principle of the current transformer to establish the equation for solving the core magnetic resistance of the current transformer, and also include: connecting the second resistor R 3bWhen , the second circuit voltage equation group is established for the circuit formed by the second resistor and the auxiliary coil and the secondary side circuit; the second circuit voltage equation group is as follows:

[0059]

[0060] in, Connect a second resistor R to the auxiliary coil side test port 3b When , the secondary current of the current transformer; Connect a second resistor R to the auxiliary coil side test port 3b When the second resistor R 3b The voltage across both ends.

[0061] Using this calculation method, by connecting the second resistor R 3b When the second circuit voltage equation group is established for the circuit formed by the second resistor and the auxiliary coil and the secondary circuit, it is convenient to calculate the core magnetic resistance of the current transformer in the subsequent step, thereby facilitating the calculation of the excitation current of the current transformer.

[0062] In this embodiment, after obtaining the first loop voltage equation and the second loop voltage equation, the measurement method further includes: combining the first loop voltage equation group and the second loop voltage equation group to obtain the following equation:

[0063]

[0064] Specifically, after the first loop voltage equation group and the second loop voltage equation group are combined, the measurement method further includes: taking the module of the equation combining the first loop voltage equation group and the second loop voltage equation group, and combining the auxiliary coil side excitation inductance L3 of the current transformer and the core magnetic resistance R m The relationship between the core magnetic resistance R of the current transformer is formed. m The equation is as follows:

[0065]

[0066] This method can be used to easily calculate the core magnetic resistance of the current transformer and improve the accuracy of the calculation of the core magnetic resistance.

[0067] Specifically, the auxiliary coil is wound on the current transformer, including: the auxiliary coil is sheathed in parallel on the current transformer, and both ends of the auxiliary coil are led out to form the auxiliary coil side test port. This method can facilitate the subsequent measurement process and operation.

[0068] In this embodiment, the excitation magnetic flux Φ in the core of the current transformer is calculated based on the open circuit voltage U0 of the auxiliary coil and the number of turns N3 of the auxiliary coil. m, including: using the following formula to calculate the excitation flux Φ in the core of the current transformer m ;

[0069]

[0070] Specifically, the measurement method in this embodiment addresses the key technical challenge of online monitoring of current transformer metering performance. By acquiring the excitation current, the transformer error can be determined. This excitation current measurement technology and system uses the excitation current as a characteristic quantity and employs an auxiliary coil attached to the current transformer as a key component for acquiring excitation current operating data. By measuring the open-circuit voltage at the auxiliary coil port and the voltage when connected to resistors of varying resistance, an equation is established to calculate the excitation current from the measured voltage, forming a method for online excitation current measurement and transformer error detection.

[0071] Specifically, the method for measuring the excitation current in this embodiment includes the following steps:

[0072] S1: Wind the auxiliary coil on the current transformer to be measured. Assume that the number of turns of the auxiliary coil is N3.

[0073] S2: Measure the open circuit voltage U0 of the auxiliary coil.

[0074] S3: Based on the open circuit voltage U0 and the number of turns N3, the excitation flux Φ in the core of the current transformer to be tested is calculated by the law of electromagnetic induction. m .

[0075] S4: Connect two resistors R at the ends of the auxiliary coil 3a and R 3b , two voltages U1 and U2 are measured.

[0076] S5: Based on the resistor R 3a 、R 3b The voltages U1, U2 and the principle of the transformer form the equation for solving the magnetic resistance of the transformer core.

[0077] S6: Obtain the magnetic resistance R of the transformer core by solving the equation established in S5 m .

[0078] S7: Based on the excitation flux Φ m and the core's magnetic resistance R m Calculate the excitation current of the current transformer to be tested.

[0079] In step S1, the method of winding the auxiliary coil on the current transformer to be tested is similar to the winding method of the secondary coil of the current transformer. The auxiliary coil is sheathed on the current transformer in parallel, and the two ends of the auxiliary coil are led out to form the auxiliary coil side test port. The equivalent circuit principle diagram of the current transformer with the auxiliary coil is shown in FIG. Figure 1 shown.

[0080] In step S3, the excitation flux Φ in the core of the current transformer to be tested is calculated. m The formula is as follows:

[0081]

[0082] Among them, Φ m is the effective value of the excitation flux of the current transformer; U0 is the open-circuit voltage of the port to be measured on the auxiliary coil side; f is the grid current frequency, which is 50Hz; N3 is the number of turns of the auxiliary coil.

[0083] Specifically, the method for forming the equation for solving the transformer core magnetic resistance in step S5 includes the following steps:

[0084] S51: Connect a resistor R at the end of the auxiliary coil 3a When the auxiliary coil circuit and the secondary side circuit are connected, the voltage equations of the first circuit are written as follows:

[0085]

[0086] in, is the grid current on the primary side of the current transformer, which is considered to remain unchanged.

[0087] S52: Connect a resistor R at the end of the auxiliary coil 3b The auxiliary coil circuit and the secondary side circuit are listed to write the second circuit voltage equation group:

[0088]

[0089] S53: The two sets of equations in step S51 and step S52 are combined to obtain the following equation:

[0090]

[0091] S54: Modulo the equation obtained in step S53, and combine the excitation inductance L3 of the auxiliary coil side of the current transformer and the core magnetic resistance R m The relationship between the core magnetic resistance R of the transformer is formed. m The equation is:

[0092]

[0093] Furthermore, in step S7, the excitation current of the current transformer to be tested is calculated by the following formula:

[0094]

[0095] The second embodiment of the present invention provides an excitation current measurement system, which is applicable to the excitation current measurement method provided in the above-mentioned first embodiment. The excitation current measurement system includes: a current transformer, an auxiliary coil 1, a first resistor 3, a second resistor 4, a detection component, a first calculation unit and a second calculation unit. The auxiliary coil 1 is wound on the current transformer; the first resistor 3 and the second resistor 4 are respectively used to be connected to the open-circuit end of the auxiliary coil 1, so that the first resistor 3 and the second resistor 4 are respectively connected to the auxiliary coil 1. The detection component is used to detect the voltage at the port of the auxiliary coil 1. The detection component is used to detect the open-circuit voltage U0 of the auxiliary coil 1, the first voltage U1 when the first resistor 3 is connected, and the second voltage U2 when the second resistor 4 is connected. The detection component can be a voltmeter 5. The first calculation unit is used to calculate the excitation magnetic flux Φ in the iron core of the current transformer based on the open-circuit voltage U0 of the auxiliary coil 1 and the number of turns N3 of the auxiliary coil 1. m The second calculation unit is used to calculate the excitation magnetic flux Φ m , the first resistor R 3a , the second resistor R 3b , the first voltage U1 and the second voltage U2 are used to calculate the excitation current of the current transformer.

[0096] With such a structural setting, the detection operation is simple, the detection accuracy is high, and there is no need to set up and produce an external high-frequency signal source, and thus there is no problem in extracting the signal.

[0097] Specifically, when the first resistor 3 and the second resistor 4 are connected respectively, the detection component detects the voltage across the first resistor 3 and the voltage across the second resistor 4 respectively.

[0098] like Figure 2 The excitation current measurement system in this embodiment is shown in FIG. The excitation current measurement system in this embodiment further includes: a reversing switch unit 2 and a signal processing and control unit 6 .

[0099] Specifically, the reversing switch unit 2 may be a double-throw controllable switch.

[0100] The auxiliary coil 1 is wound around the current transformer, with two terminals A and B. The reversing switch unit 2 interface comprises a moving terminal P, two fixed terminals U and V, and a control signal input terminal C. The moving terminal P is connected to terminal A of the auxiliary coil 1, and the two fixed terminals U and V are connected to the first resistor 3 and the second resistor 4, respectively. The control signal input terminal C is connected to the signal processing and control unit 6, which is used to receive control signals to achieve different states of opening the terminals of the auxiliary coil 1 and connecting the first resistor 3 and the second resistor 4. The voltmeter 5 is connected in parallel to the terminals of the auxiliary coil 1 for voltage measurement. The input terminal IN1 of the signal processing and control unit 6 receives measurement data from the voltmeter 5, the input terminal IN2 receives secondary current data of the current transformer, and the output terminal O1 outputs the control signal of the reversing switch unit 2. Preferably, the signal processing and control unit 6 can be an existing device, and the voltmeter 5 is an existing instrument with high measurement accuracy.

[0101] The devices and materials required for implementation include: a typical low-voltage current transformer, such as a 75A / 5A transformer, with a secondary coil with 15 turns N2; a 0-100V AC power supply with adjustable power frequency; a high-precision digital millivoltmeter; a high-precision digital ammeter (5A range); a double-throw controllable switch; three precision resistors of known resistance values, such as 1 ohm, 2 ohm, and 0.1 ohm; a large resistor, such as 10 ohm; a signal processing and control unit 6; several thin copper wires; and a DC resistance meter. The implementation steps are as follows:

[0102] (1) Wind the copper wire onto the current transformer as auxiliary coil 1. The number of turns N3 can be 2 turns. Measure the DC resistance R of the auxiliary coil 1. 3r =7.86 milliohms and the DC resistance of the transformer secondary coil R 2r =63.69 milliohms.

[0103] (2) Connect an AC power supply in series with a 10-ohm resistor, and then connect it to a current transformer. By adjusting the power supply voltage, different primary currents I1 can be applied to the current transformer. This primary current simulates the grid current.

[0104] (3) Connect the load R2 of the current transformer (such as a 0.1 ohm resistor) and the ammeter in series, and then connect them to the secondary side port of the current transformer.

[0105] (4) The controllable switch is called the first resistor 3 (ie R 3a ) of 1 ohm resistor and 2 ohm resistor is called the second resistor 4 (that is, R 3b ) is connected to the mutual inductor and the signal processing and control unit 6.

[0106] (5) When the auxiliary coil 1 is open, adjust the voltage so that the current on the secondary side of the transformer reaches a certain value, such as 1A; and record the open-circuit voltage U0 = 21.83mV at the auxiliary coil 1 port at this time.

[0107] (6) Control the switch moving point and connect the first resistor R 3a , record the voltage U1=21.59mV corresponding to the auxiliary coil port, and record the transformer secondary side current I 2a =0.9971A; then connect the second resistor R 3b , record voltage U2 = 21.71mV and current I 2b =0.9986A; Finally, disconnect the second resistor R 3b The time required to connect each resistor is approximately 0.5 milliseconds.

[0108] (7) After the measurement is completed, the following calculations are started:

[0109] (a) Calculate the excitation flux:

[0110]

[0111] (b) Calculate the core magnetic resistance:

[0112]

[0113] (c) Calculate the excitation current of the transformer

[0114]

[0115] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: (1) Passivity, no need to set up and produce a high-frequency signal source externally. The existing transformer online detection technology requires an additional high-frequency signal source to couple a high-frequency small current signal to the secondary circuit, and calculate the secondary impedance from the current and the corresponding voltage to obtain the transformer error. In contrast, the present invention proposes a technology for measuring the transformer excitation current for the first time. By adding an auxiliary coil to the transformer and measuring the open-circuit voltage of the auxiliary coil port and the voltage when the port is connected to resistors of different resistance values, an equation for calculating the excitation current can be established, thereby realizing the excitation current measurement and transformer error online detection. This is an innovative passive method. (2) No high-frequency small signal extraction problem. Since the existing transformer online detection adopts an active method, the external high-frequency current signal must be small enough to avoid affecting the working state and measurement accuracy of the transformer, making the extraction of the signal extremely difficult, and there is a bottleneck in the accurate extraction of weak signals. The present invention only needs to measure the power frequency voltage induced by the change in the magnetic flux of the transformer core in the auxiliary coil, and this power frequency voltage is generally above the millivolt level, which greatly reduces the difficulty of signal acquisition. (3) The structure is simple, easy to implement, and low cost. There is no need for an external high-frequency signal source and a complex weak signal extraction circuit. It is only necessary to add an auxiliary coil and corresponding measurement, calculation, and storage units to the transformer. The system structure is simple, the algorithm is easy to implement, the various units are easy to integrate, and mass production is easy, and the cost is low.

[0116] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0117] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to actual proportional relationships. The techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values ​​should be interpreted as being merely exemplary and not as limitations. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0118] In the description of this application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of this application; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0119] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0120] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of this application.

[0121] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for measuring excitation current, characterized in that: The excitation current measurement method is used to measure the excitation current of a current transformer, and the excitation current measurement method includes: Wind the auxiliary coil on the secondary side of the current transformer and measure the open circuit voltage of the auxiliary coil , according to the open circuit voltage of the auxiliary coil and the number of turns of the auxiliary coil Calculate the excitation flux in the core of the current transformer ; The first resistor is connected to the open end of the auxiliary coil in sequence. and the second resistor , and measure the first resistor connected The first voltage corresponding to and connect the second resistor The second voltage corresponding to ; According to the excitation magnetic flux , the first resistor The second resistor , the first voltage and the second voltage The excitation current of the current transformer is calculated.

2. The method for measuring the excitation current according to claim 1, characterized in that: According to the excitation magnetic flux , the first resistor The second resistor , the first voltage and the second voltage Calculating the excitation current of the current transformer, including: According to the first resistor The second resistor , the first voltage and the second voltage Calculate the core magnetic resistance of the current transformer ; According to the excitation magnetic flux and the core reluctance The excitation current of the current transformer is calculated.

3. The method for measuring the excitation current according to claim 2, characterized in that: According to the first resistor The second resistor , the first voltage and the second voltage Calculate the core magnetic resistance of the current transformer ,include: According to the first resistor The second resistor , the first voltage and the second voltage and the principle of the current transformer to establish an equation for solving the core magnetic resistance of the current transformer; The excitation current of the current transformer is calculated according to the established equation of the core magnetic resistance of the current transformer.

4. The method for measuring the excitation current according to claim 3, characterized in that: According to the first resistor The second resistor , the first voltage and the second voltage The principle of the current transformer is to establish an equation for solving the core magnetic resistance of the current transformer, including: Connect the first resistor When , a first loop voltage equation group is established for the loop formed by the first resistor and the auxiliary coil and the secondary side loop; The first loop voltage equations are as follows: ； in, is the primary side grid current of the current transformer; Connect the first resistor to the auxiliary coil side test port When , the secondary side current of the current transformer; Connect the first resistor to the auxiliary coil side test port When the first resistor The voltage across the terminals; is the secondary coil inductance of the current transformer; is the excitation inductance of the auxiliary coil side of the current transformer; is the mutual inductance between the primary side coil and the secondary side coil of the current transformer; is the mutual inductance between the secondary coil of the current transformer and the auxiliary coil; is the mutual inductance between the primary side coil of the current transformer and the auxiliary coil; is the resistance of the secondary coil of the current transformer itself; is the secondary side load of the current transformer; is the resistance of the auxiliary coil itself; is the grid current angular frequency.

5. The method for measuring the excitation current according to claim 4, characterized in that: According to the first resistor The second resistor , the first voltage and the second voltage The principle of the current transformer is to establish an equation for solving the core magnetic resistance of the current transformer, and further includes: Connect the second resistor When , a second loop voltage equation group is established for the loop formed by the second resistor and the auxiliary coil and the secondary side loop; The second loop voltage equations are as follows: ； in, Connect the second resistor to the auxiliary coil side test port When , the secondary side current of the current transformer; Connect the second resistor to the auxiliary coil side test port When the second resistor The voltage across both ends.

6. The method for measuring the excitation current according to claim 5, characterized in that: After obtaining the first loop voltage equation and the second loop voltage equation, the measurement method further includes: The first loop voltage equation group and the second loop voltage equation group are combined to obtain the following equation: 。 7. The method for measuring the excitation current according to claim 5, characterized in that: After the first loop voltage equation group and the second loop voltage equation group are jointly established, the measurement method further includes: The equation of the first loop voltage equation group and the second loop voltage equation group is modulo, and the auxiliary coil side excitation inductance of the current transformer is combined. and core magnetic resistance The relationship is formed to solve the core magnetic resistance of the current transformer The equation is as follows: 。 8. The method for measuring the excitation current according to claim 1, characterized in that: Winding the auxiliary coil on the current transformer includes: The auxiliary coils are sheathed in parallel on the current transformer, and two ends of the auxiliary coils are led out to form auxiliary coil side test ports.

9. The method for measuring the excitation current according to claim 1, characterized in that: According to the open circuit voltage of the auxiliary coil and the number of turns of the auxiliary coil Calculate the excitation flux in the core of the current transformer ,include: The excitation flux in the core of the current transformer is calculated using the following formula: ; 。 10. A system for measuring excitation current, characterized in that: The method for measuring the excitation current according to any one of claims 1 to 9, wherein the excitation current measurement system comprises: a current transformer and an auxiliary coil, wherein the auxiliary coil is wound on the secondary side of the current transformer; a first resistor and a second resistor, wherein the first resistor and the second resistor are respectively connected to an open circuit end of the auxiliary coil; A detection component for detecting the open circuit voltage of the auxiliary coil , the first voltage when the first resistor is connected and the second voltage when the second resistor is connected ; The first calculation unit is configured to calculate the open circuit voltage of the auxiliary coil according to the open circuit voltage of the auxiliary coil. and the number of turns of the auxiliary coil Calculate the excitation flux in the core of the current transformer ; The second calculation unit is used to calculate the excitation magnetic flux according to the , the first resistor The second resistor , the first voltage and the second voltage The excitation current of the current transformer is calculated.

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