CN215953833U - Current transformer's primary winding leakage current compensating circuit and check-up equipment - Google Patents
Current transformer's primary winding leakage current compensating circuit and check-up equipment Download PDFInfo
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Abstract
The utility model discloses a primary winding leakage current compensation circuit and a calibration device of a current transformer, wherein the primary winding leakage current compensation circuit comprises: the circuit comprises a first resistance-capacitance unit, a second resistance-capacitance unit and an operational amplifier; one end of the first resistance-capacitance unit is connected with the connection point, and the other end of the first resistance-capacitance unit is connected with the reverse input end of the operational amplifier; one end of the second resistance-capacitance unit is connected with the current input end of the primary winding of the standard current transformer, and the other end of the second resistance-capacitance unit is connected with the output end of the operational amplifier; the same-direction input end of the operational amplifier is connected with the ground; the compensation circuit can realize the automatic adjustment of the low potential of the primary winding of the standard current transformer, automatically adjust the potential of the serially connected measuring branch connection point to 0 potential and ensure that the N point is always at 0 potential in the test process, and meanwhile, the compensation circuit can play a good compensation effect on the capacitive leakage of the standard current transformer and can ensure the calibration accuracy of the tested current transformer.
Description
Technical Field
The present invention relates to the field of electrical measurement technologies, and in particular, to a primary winding leakage current compensation circuit and a calibration apparatus for a current transformer.
Background
The standard current transformer is a standard device used for calibrating and calibrating large-current measuring devices such as a power transformer, a current sensor and the like. The basic principle is shown in fig. 1. Wherein W1 and W2 are primary winding and secondary winding, and two windings are wound on an iron core together, and primary current produces magnetic flux on the iron core, and secondary winding produces the electric current I2 proportional to primary through the coupling in the secondary setting the number of turns of primary winding and secondary winding is N1 and N2 respectively, then ideally primary current I1 and secondary current I2 satisfy: I1/I2 ═ N2/N1.
However, in the actual current transformer structure, as shown in fig. 2, due to the existence of the distributed parameters, distributed capacitances exist between the primary winding turns, between the primary winding and the shielding structure, and between the primary winding and the housing ground, so that a part of current flows into the ground through the distributed capacitances, or other components, and further the current flowing into and out of the primary winding is not equal, and an error is generated when the magnetic flux generated in the iron core is coupled to the secondary. The capacitive leakage error of the part has a relation with the distribution parameters of the circuit, and in order to stabilize the error of the part, the grounding end of the primary winding is required to be fixed when the current transformer is used, so that the error of the part can be fixed, and a compensation measure is taken. When the standard current transformer is used for error checking, the tested current transformer and the standard current transformer are connected in series for the first time, and the secondary current is connected to the checking device through the same primary current. However, if the connection point of the current transformer is directly grounded, a current flows through the ground loop, so that the primary current of the standard current transformer is not equal to that of the current transformer to be tested, and an error is caused during verification.
In this case, the Wagner grounding technique is generally used for the primary winding, and some researchers have developed a symmetrical branch method, as shown in fig. 3. An adjusting branch consisting of Rw and Cw is added to the current transformer at one time, the middle node of the branch is connected to the ground potential, a command instrument is used for measuring the potential between the grounding node and the connecting point N of the current transformer, and the values of Rw and Cw are adjusted until the command instrument indicates 0. Therefore, the potential of the N point is the ground potential, but the N point is not directly grounded, and the normal work of the two current transformers can be ensured. The simple understanding is that a zero potential is constructed at the grounding point position through the circuit structure, but the part is not really grounded, and the principle of the method is similar to that of a penicillin bridge. The method has the disadvantages that the parameters of the branches are different for different current transformers, and in the testing process, due to the difference of the working characteristics of the current transformers, the state of the command instrument which is not 0 can occur, and the zero setting is required again.
Therefore, a circuit capable of automatically adjusting the N point 0 potential and compensating for the leakage current is required.
Disclosure of Invention
The utility model provides a primary winding leakage current compensation circuit and calibration equipment of a current transformer, which are used for solving the problems that when the current transformer to be tested is calibrated, a connection point is ensured to be at a 0-point position, and the primary winding leakage current of a standard current transformer can be compensated.
In order to solve the above problem, the present invention provides a primary winding leakage current compensation circuit of a current transformer, including: the circuit comprises a first resistance-capacitance unit, a second resistance-capacitance unit and an operational amplifier; wherein the content of the first and second substances,
one end of the first resistance-capacitance unit is connected with a connection point, and the other end of the first resistance-capacitance unit is connected with the reverse input end of the operational amplifier; the connection point is the connection point of the current output end of the primary winding of the standard current transformer and the current input end of the primary winding of the tested current transformer;
one end of the second resistance-capacitance unit is connected with the current input end of the primary winding of the standard current transformer, and the other end of the second resistance-capacitance unit is connected with the output end of the operational amplifier; the first resistance-capacitance unit comprises: the first capacitor and the first resistor are connected in parallel; the second resistance-capacitance unit comprises: the second capacitor and the second resistor are connected in parallel; the value ranges of the first capacitor and the second capacitor are as follows: 1000 μ F to 5000 μ F;
the same-direction input end of the operational amplifier is connected with the ground; according to the principle that the input end of the operational amplifier is virtual short, the potential of the connecting point is equal to the non-inverting input end of the operational amplifier and is 0 potential; according to the principle of virtual disconnection of the input end of the operational amplifier, the current from the connection point to the inverting input end of the operational amplifier is 0; in a loop formed by the operational amplifier and the standard current transformer, the currents of the input end and the output end of the standard current transformer are completely equal, and the operational amplifier can compensate the capacitive leakage current of the standard current transformer.
Preferably, the primary winding leakage current compensation circuit further includes:
the buffer is used for providing current which meets the verification requirement and is equal to the leakage current to be output to a primary winding of the standard current transformer when the leakage current is large;
the input end of the buffer is connected with the output end of the operational amplifier, and the output end of the buffer is connected with the other end of the second resistance-capacitance unit.
Preferably, wherein the buffer is of type BUF 634.
Preferably, the first capacitor, the first resistor, the second capacitor and the second resistor are used for preventing the influence of a direct current offset signal of the operational amplifier on a primary winding of the standard current transformer.
Preferably, the value ranges of the first resistor and the second resistor are both: 100 Ω to 1000 Ω.
Preferably, the model of the operational amplifier is ADA 4522-1.
The utility model also provides a current transformer calibration device, which comprises: a standard current transformer and a primary winding leakage current compensation circuit as described above.
The utility model provides a primary winding leakage current compensation circuit and calibration equipment of a current transformer, which can realize the automatic adjustment of the low potential of the primary winding of a standard current transformer by adding a primary winding leakage current compensation circuit consisting of an operational amplifier at the primary side of the standard current transformer, can play a good compensation effect on the capacitive leakage of the standard current transformer while automatically adjusting the potential of the connecting point of the serially connected measuring branch to 0 potential and ensuring that the N point is always at 0 potential in the test process, and can ensure the calibration accuracy of the tested current transformer.
Drawings
A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
FIG. 1 is a basic schematic diagram of a current transformer;
FIG. 2 is an equivalent circuit diagram of an actual current transformer;
FIG. 3 is a schematic diagram of a current transformer to be tested verified by adopting the Wagner grounding technology;
fig. 4 is a schematic structural diagram of a primary winding leakage current compensation circuit 400 of a current transformer according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a zero potential configuration of a current transformer with an operational amplifier according to an embodiment of the present invention;
FIG. 6 is an exemplary diagram of a primary winding leakage current compensation circuit according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a current transformer calibration apparatus 700 according to an embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the utility model. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Fig. 4 is a schematic structural diagram of a primary winding leakage current compensation circuit 400 of a current transformer according to an embodiment of the present invention. As shown in fig. 4, the primary winding leakage current compensation circuit of the current transformer according to the embodiment of the present invention can automatically adjust the low potential of the primary winding of the standard current transformer, and can perform a good compensation effect on the capacitive leakage of the standard current transformer while automatically adjusting the potential of the connection point of the serially connected measurement branches to 0 potential and ensuring that the N point is always at 0 potential during the test process, thereby ensuring the calibration accuracy of the current transformer to be tested. The primary winding leakage current compensation circuit 400 of the current transformer according to the embodiment of the present invention includes: a first resistance-capacitance unit 401, a second resistance-capacitance unit 402 and an operational amplifier 403.
Preferably, one end of the first resistance-capacitance unit 401 is connected to a connection point, and the other end of the first resistance-capacitance unit is connected to an inverting input end of the operational amplifier; the connection point is the connection point of the current output end of the primary winding of the standard current transformer and the current input end of the primary winding of the tested current transformer.
Preferably, one end of the second rc unit 402 is connected to a current input end of a primary winding of a standard current transformer, and the other end of the second rc unit is connected to an output end of the operational amplifier.
Preferably, the first capacitor, the first resistor, the second capacitor and the second resistor are used for preventing the influence of a direct current offset signal of the operational amplifier on a primary winding of the standard current transformer.
Preferably, the value ranges of the first capacitor and the second capacitor are both: 1000 μ F to 5000 μ F.
Preferably, the value ranges of the first resistor and the second resistor are both: 100 Ω to 1000 Ω.
Preferably, the non-inverting input of the operational amplifier 403 is connected to ground. According to the principle that the input end of the operational amplifier is virtual short, the potential of the connecting point is equal to the non-inverting input end of the operational amplifier and is 0 potential; according to the principle of virtual disconnection of the input end of the operational amplifier, the current from the connection point to the inverting input end of the operational amplifier is 0; in a loop formed by the operational amplifier and the standard current transformer, the currents of the input end and the output end of the standard current transformer are completely equal, and the operational amplifier can compensate the capacitive leakage current of the standard current transformer.
Preferably, the model of the operational amplifier is ADA 4522-1.
Preferably, the primary winding leakage current compensation circuit further includes:
the buffer is used for providing current which meets the verification requirement and is equal to the leakage current to be output to a primary winding of the standard current transformer when the leakage current is large;
the input end of the buffer is connected with the output end of the operational amplifier, and the output end of the buffer is connected with the other end of the second resistance-capacitance unit.
Fig. 5 is a schematic diagram of a zero potential structure of a current transformer configured with an operational amplifier according to an embodiment of the present invention. As shown in fig. 5, a precision operational amplifier is added to the primary side of the standard current transformer CT1, the non-inverting input terminal of the operational amplifier is grounded, the inverting input terminal of the operational amplifier is connected to the connection point N for checking the current transformer to be tested, and the output terminal of the operational amplifier is connected to the current input terminal of the primary winding of the standard current transformer, i.e., the terminal I1. The CT2 is the measured transformer. According to the principle that the input end of the operational amplifier is virtually short, the potential of N is equal to the non-inverting input end, namely 0 is meant. According to the principle of the virtual break of the input end of the operational amplifier, the current from the point N to the inverting input end of the operational amplifier is 0. In a loop formed by the operational amplifier and the CT1, due to the distribution parameters of the standard current transformer CT1, the capacitive leakage current flowing into the grounding conductor passes through the grounding end of the operational amplifier and then flows back to the CT1 through the output end, so that the input current and the output current of the CT1 are completely equal, and the effect of compensating the capacitive leakage current of the CT1 is realized. A feedback loop formed by adding one operational amplifier at a time to a standard current transformer realizes that the capacitive leakage of the current transformer is well compensated while the connecting point of the series measurement branch is adjusted to 0 potential. When the current compensation circuit is used for checking the current transformer to be tested, the output of the circuit can be adjusted according to the change of the current measured by the current transformer, and the effect is always kept.
In addition, the current leakage compensation circuit cannot be connected to the measured transformer, and if the current leakage compensation circuit is connected to the measured transformer, the error of the measured transformer can be changed, which is not allowed.
Fig. 6 is an exemplary diagram of a primary winding leakage current compensation circuit according to an embodiment of the present invention. As shown in fig. 6, U1 in the primary winding leakage current compensation circuit can use a low offset voltage precision operational amplifier ADA4522-1, U2 is a buffer, and can use BUF634 optionally, to ensure that the circuit can provide sufficient current output when the leakage current is large. The first capacitor C1, the first resistor R1, the second capacitor C2 and the second resistor R2 are used together for preventing the influence of the DC offset signal of the amplifier on the primary winding of the standard current transformer. The values of C1 and C2 should be as large as possible, generally 1000 muF to 5000 muF can be selected, the resistance can be selected from 100 omega to 1000 omega, and the adjustment is needed according to the current transformer loop. Point a is connected to point N in fig. 5, and point B is connected to the current input terminal of the primary winding of CT1, i.e., terminal I1. When the tested current transformer is verified, the potential of the connecting point can be in a 0 potential state, and the winding leakage current is compensated.
Fig. 7 is a schematic structural diagram of a current transformer calibration apparatus 700 according to an embodiment of the present invention. As shown in fig. 7, a current transformer calibration apparatus 700 provided in an embodiment of the present invention includes: a standard current transformer 701 and a primary winding leakage current compensation circuit 702. The sequential winding leakage current compensation circuit 702 is the same as the primary winding leakage current compensation circuit 400 of the current transformer according to the embodiment of the present invention, and is not described herein again.
The utility model has been described with reference to a few embodiments. However, other embodiments of the utility model than the one disclosed above are equally possible within the scope of the utility model, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application 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, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the utility model without departing from the spirit and scope of the utility model, which is to be covered by the claims.
Claims (7)
1. A primary winding leakage current compensation circuit of a current transformer, the primary winding leakage current compensation circuit comprising: the circuit comprises a first resistance-capacitance unit, a second resistance-capacitance unit and an operational amplifier; wherein the content of the first and second substances,
one end of the first resistance-capacitance unit is connected with a connection point, and the other end of the first resistance-capacitance unit is connected with the reverse input end of the operational amplifier; the connection point is the connection point of the current output end of the primary winding of the standard current transformer and the current input end of the primary winding of the tested current transformer;
one end of the second resistance-capacitance unit is connected with the current input end of the primary winding of the standard current transformer, and the other end of the second resistance-capacitance unit is connected with the output end of the operational amplifier; the first resistance-capacitance unit comprises: the first capacitor and the first resistor are connected in parallel; the second resistance-capacitance unit comprises: the second capacitor and the second resistor are connected in parallel; the value ranges of the first capacitor and the second capacitor are as follows: 1000 μ F to 5000 μ F;
the same-direction input end of the operational amplifier is connected with the ground; according to the principle that the input end of the operational amplifier is virtual short, the potential of the connecting point is equal to the non-inverting input end of the operational amplifier and is 0 potential; according to the principle of virtual disconnection of the input end of the operational amplifier, the current from the connection point to the inverting input end of the operational amplifier is 0; in a loop formed by the operational amplifier and the standard current transformer, the currents of the input end and the output end of the standard current transformer are completely equal, and the operational amplifier can compensate the capacitive leakage current of the standard current transformer.
2. The primary winding leakage current compensation circuit of claim 1, further comprising:
and the input end of the buffer is connected with the output end of the operational amplifier, and the output end of the buffer is connected with the other end of the second resistance-capacitance unit.
3. The primary winding leakage current compensation circuit of claim 2, wherein said buffer is of type BUF 634.
4. The primary winding leakage current compensation circuit of claim 1, wherein the first capacitor, the first resistor, the second capacitor and the second resistor are used to prevent the dc offset signal of the operational amplifier from affecting the primary winding of the standard current transformer.
5. The primary winding leakage current compensation circuit of claim 1, wherein the first resistor and the second resistor both have a value range of: 100 Ω to 1000 Ω.
6. The primary winding leakage current compensation circuit of claim 1, wherein the operational amplifier is model ADA 4522-1.
7. A current transformer calibration apparatus, characterized in that the calibration apparatus comprises: a standard current transformer and a primary winding leakage current compensation circuit according to any one of claims 1 to 6.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202120451022.5U CN215953833U (en) | 2021-03-02 | 2021-03-02 | Current transformer's primary winding leakage current compensating circuit and check-up equipment |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202120451022.5U CN215953833U (en) | 2021-03-02 | 2021-03-02 | Current transformer's primary winding leakage current compensating circuit and check-up equipment |
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| CN215953833U true CN215953833U (en) | 2022-03-04 |
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