CN113777379A - Precise metering current transformer and manufacturing method of double-magnetic-circuit current transformer - Google Patents
Precise metering current transformer and manufacturing method of double-magnetic-circuit current transformer Download PDFInfo
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- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F38/00—Adaptations of transformers or inductances for specific applications or functions
- H01F38/20—Instruments transformers
- H01F38/22—Instruments transformers for single phase ac
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Abstract
The application provides accurate measurement current transformer of dual magnetic circuit includes: the current transformer with the large transformation ratio and the current transformer with the small transformation ratio are arranged on the same circuit, and the current transformer with the large transformation ratio and the current transformer with the small transformation ratio are independent of each other; the number of primary turns of the current transformer with the large transformation ratio is smaller than that of the current transformer with the small transformation ratio; the transformer switching circuit switches the large-transformation-ratio current transformer and the small-transformation-ratio current transformer according to the actual current of the line. The intelligent switching of the current transformer with two independent magnetic circuits meets the requirement for accurate detection of small current.
Description
Technical Field
The application relates to the technical field of electric power metering, in particular to a precise metering current transformer and a manufacturing method of a double-magnetic-circuit current transformer.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The current transformer is an instrument for measuring by converting a large primary side current into a small secondary side current according to the electromagnetic induction principle. The current transformer is composed of a closed iron core and a winding. The primary side winding of the transformer has few turns and is connected in a circuit of the current to be measured.
At present, the existing current transformers conform to national standard accuracy levels of 0.1, 0.2, 0.5 and the like, and the current transformers with special purposes also have standards of 0.2S and 0.5S. Taking the standard of 0.2S as an example, there is no requirement for the accuracy of the current at 1% of the rated current, which results in poor measurement accuracy and no controllability of the large-current transformer for the small current. Some manufacturers improve the accuracy of the current transformers by arranging a plurality of current transformers and adding a complex switching circuit, but in some cases, the installation space is difficult to meet the installation requirement of two transformers, and meanwhile, the multiple transformers are easy to influence each other and difficult to achieve the preset effect.
Disclosure of Invention
In order to solve the problems, the application provides the accurate metering current transformer and the manufacturing method of the double-magnetic-circuit current transformer, and the accurate detection of small current is met through the intelligent switching of the two current transformers with independent magnetic circuits.
The application provides accurate measurement current transformer of dual magnetic circuit includes: the current transformer with the large transformation ratio and the current transformer with the small transformation ratio are arranged on the same circuit, and the current transformer with the large transformation ratio and the current transformer with the small transformation ratio are independent of each other; the number of primary turns of the current transformer with the large transformation ratio is smaller than that of the current transformer with the small transformation ratio; the transformer switching circuit calculates primary current by detecting induced current of the large-transformation-ratio current transformer or the small-transformation-ratio current transformer, when the primary current value is larger than a preset value I1, the transformer switching circuit switches the large-transformation-ratio current transformer to obtain the induced current of a line, and when the current value is smaller than or equal to a preset value I1, the small-transformation-ratio current transformer is switched to obtain the induced current of the line.
Preferably, the transformer switching circuit comprises a CPU controller, and a first controllable switch, a second controllable switch, and a third controllable switch electrically connected to the CPU controller, the first controllable switch is connected in parallel to two output terminals of the large-transformation-ratio current transformer for short-circuiting the large-transformation-ratio current transformer, the second controllable switch is connected in parallel to two output terminals of the magnification unified transformer for short-circuiting the magnification unified transformer, one output terminal of the magnification unified transformer is connected in parallel to one output terminal of the large-transformation-ratio current transformer to form one end externally connected to the external metering circuit, the other output terminals of the magnification unified transformer and the large-transformation-ratio current transformer are respectively connected in series to two sets of switch contacts of the third controllable switch and then connected in parallel to form the other end connected to the external metering circuit, and a first current sensor is connected in series to an output loop of the small-transformation-ratio current transformer; the multiplying power unified transformer is used for being matched with a small-transformation-ratio current transformer to form a current transformation ratio which is the same as that of a large-transformation-ratio current transformer, and the first current sensor is electrically connected with the CPU controller and used for providing a current signal for switching the current transformer.
Preferably, the transformer switching circuit further comprises a second current sensor and a third current sensor, the second current sensor is connected in series with a connecting line of the large-transformation-ratio current transformer and a third controllable switch, the third current sensor is connected in series with a connecting line of the multiplying-power unified transformer and the third controllable switch, and the second current sensor, the third current sensor and the CPU controller are electrically connected.
Preferably, the first controllable switch, the second controllable switch and the third controllable switch are magnetic latching relays, two output ends of the large-transformation-ratio current transformer are connected in parallel with a normally open contact of the first controllable switch, two output ends of the multiplying power unified transformer are connected in parallel with a normally closed contact of the second controllable switch, an output end of the large-transformation-ratio current transformer is connected in series with a normally closed contact of the third controllable switch, and an output end of the multiplying power unified transformer is connected in series with a normally open contact of the third controllable switch.
Preferably, a signal conditioning module is connected in series between the first current sensor, the second current sensor, the third current sensor and the CPU controller, and a photoelectric isolation module is connected in series between the first controllable switch, the second controllable switch, the third controllable switch and the CPU controller.
Preferably, the transformer switching circuit further comprises a touch screen, a power supply and a memory storage, wherein the touch screen is electrically connected with the CPU controller.
Preferably, the value range of the preset value I1 is 4% -6% of the rated current value of the large-transformation-ratio current transformer, and the transformation ratio of the large-transformation-ratio current transformer to the small-transformation-ratio current transformer is any one of 2, 3 and 4.
Preferably, the switching method of the large-transformation-ratio current transformer and the small-transformation-ratio current transformer is as follows:
when the effective value of the current is smaller than a preset value I1, the first controllable switch is closed first, then the normally closed contact of the third controllable switch is opened, the normally open contact is closed, finally the second controllable switch is opened, the small-transformation-ratio current transformer works, and the large-transformation-ratio current transformer is short-circuited;
when the effective value of the current is detected to be larger than or equal to a preset value I1, the second controllable switch is closed first, then the normally open contact of the third controllable switch is opened, the normally closed electric shock is closed, finally the first controllable switch is opened, and the high-transformation-ratio current transformer is switched back.
Preferably, the multiple redundant current sensing method: the method comprises the steps that a first current sensor measures the induced current of a small-transformation-ratio current transformer, a second current sensor measures the current of a large-transformation-ratio branch, a third current sensor measures the current of a small-transformation-ratio branch, if the transformation ratio of the large-transformation-ratio current transformer to the small-transformation-ratio current transformer is M, when the large-transformation-ratio branch normally works, the detected current ratio of the first current sensor to the second current sensor is equal to M, when the small-transformation-ratio branch normally works, the detected current ratio of the first current sensor to the third current sensor is equal to M, if the detected current ratio of the first current sensor to the second current sensor or the third current sensor is not equal to M, a fault occurs, and a CPU controller can alarm, memorize and disconnect an output main circuit.
The application also provides a manufacturing method of the double-magnetic-circuit current transformer, which comprises the following steps:
the secondary windings of the large-transformation-ratio current transformer and the small-transformation-ratio current transformer are independently fixed on a winding tool, the number of primary windings of the large-transformation-ratio current transformer is smaller than that of the small-transformation-ratio current transformer, a primary wire is wound on the secondary winding of the small-transformation-ratio current transformer for N turns, the primary wire is wound on the secondary windings of the large-transformation-ratio current transformer and the small-transformation-ratio current transformer for N1 turns, N1 is the number of primary windings of the large-transformation-ratio current transformer, and the number of primary windings N2 of the small-transformation-ratio current transformer is N1+ N.
Compared with the prior art, the beneficial effect of this application is:
(1) this application has saved installation space when satisfying the magnetic circuit independence through two magnetic circuit current transformer, through the switching between big transformation ratio and little transformation ratio current transformer, has expanded the measuring range of mutual-inductor, has increaseed the accuracy to the undercurrent detection.
(2) According to the current transformer, the first controllable switch, the second controllable switch and the third controllable switch are used for switching the large-transformation-ratio current transformer and the small-transformation-ratio current transformer, and dynamic switching between the large-transformation-ratio current transformer and the small-transformation-ratio current transformer is completed on the basis of preventing the transformers from being opened.
(3) The multi-redundancy current detection method is provided through the first current sensor, the second current sensor and the third current sensor, and the self-detection capability of the multi-redundancy current detection method is improved.
(4) This application has saved the energy through magnetic latching relay.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
Figure 1 is a diagram of a dual magnetic circuit transformer implementation of one embodiment of the present invention,
FIG. 2 is a system diagram of one embodiment of the present invention.
FIG. 3 is a schematic diagram of the main circuit of an embodiment of the present invention.
Fig. 4 is a diagram of an embodiment of the present invention.
The specific implementation mode is as follows:
the present application will be further described with reference to the following drawings and examples.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
In the present disclosure, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only relational terms determined for convenience in describing structural relationships of the parts or elements of the present disclosure, and do not refer to any parts or elements of the present disclosure, and are not to be construed as limiting the present disclosure.
As shown in fig. 1 and 4, the present application provides a dual magnetic circuit precision metering current transformer, comprising: two independent big transformation ratio current transformer CT1 and little transformation ratio current transformer CT2 of magnetic circuit and be used for big transformation ratio current transformer CT1 and the transformer switching circuit who switches between little transformation ratio current transformer CT2 of locating on same looks generating line, the next grade of little transformation ratio current transformer CT2 is parallelly connected with multiplying power unified transformer CT3 to be used for forming the same current transformation ratio with big transformation ratio current transformer CT1 with little transformation ratio current transformer CT2 cooperation, make things convenient for outside metering circuit and calculate actual current value according to this application.
The transformer switching circuit calculates primary current by detecting induced current of the large-transformation-ratio current transformer CT1 or the small-transformation-ratio current transformer CT2, when the primary current value is larger than a preset value I1, the transformer switching circuit switches the large-transformation-ratio current transformer CT1 to obtain induced current of a phase bus, and when the current value is smaller than or equal to a preset value I1, the small-transformation-ratio current transformer CT2 is switched to obtain induced current of the phase bus.
TABLE 1
| Percent rated current | 1 | 5 | 20 | 100 | 120 |
| Primary current of | 1 | 5 | 20 | 100 | 120 |
| Secondary current flow | 0.05 | 0.25 | 1 | 5 | 6 |
| Error (+/-) | 0.75 | 0.35 | 0.2 | 0.2 | 0.2 |
TABLE 2
| Percent rated current | 1 | 5 | 20 | 100 | 120 |
| Primary current of | 0.25 | 1.25 | 5 | 25 | 30 |
| Secondary current flow | 0.025 | 0.125 | 0.5 | 2.5 | 3 |
| Error of the measurement | 0.75 | 0.35 | 0.2 | 0.2 | 0.2 |
Table 1 is an error accuracy level table determined by the current transformer with the transformation ratio of 100/5 according to the 0.2S standard, table 2 is an error accuracy level table determined by the current transformer with the transformation ratio of 50/5 according to the 0.2S standard, it can be obtained from tables 1 and 2 that the error of the current transformer becomes large under the condition that the actually used current is small, and when the actual current is less than the rated current by 1%, the national standard has no requirement on the transformer error.
Supposing that the large-transformation-ratio current transformer CT1 is a 100/5 current transformer and the small-transformation-ratio current transformer CT2 is a 50/5 current transformer, the multiplying-power unified transformer CT3 is a 10/5 current transformer, and is used for achieving the purpose that the current transformation ratio effect which is the same as that of the CT1 is obtained by two-stage conversion of the CT2 and the CT3, and table 3 is an error table when switching is performed on the basis that the accuracy level of the national 0.2S standard is met and the primary current value is less than or equal to 5% of the rated current of the CT 1.
TABLE 3
According to the table 1, the table 2 and the table 3, it can be found that when the actual primary current of the original 100/5 current transformer is 5% of the rated current of the current transformer, the error standard is already increased to 0.35%, and when the actual primary current is 1% of the rated current of the current transformer, the error standard is expanded to 0.75%, after the current transformer is used, the current transformer is switched to the small-transformation-ratio current transformer CT2 when the actual primary current is 5% of the rated current of the large-transformation-ratio current transformer CT1, the error standard of the current transformer is 0.2%, and when the actual primary current is 1% of the rated current of the large-transformation-ratio current transformer CT1, the error standard of the current transformer is between 0.2% and 0.35%, so that the current transformer has an enlarged accurate measurement range, and the measurement error is reduced under the condition of small current. Fig. 4 is a graph of an error curve of the present application, where a is the error curve of the present application and b is the error curve of an individual transformer.
Preferably, the value range of the preset value I1 is 4% -6% of the rated current value of the large-transformation-ratio current transformer CT1, and the transformation ratio of the large-transformation-ratio current transformer CT1 to the small-transformation-ratio current transformer CT2 is any one of 2, 3 and 4.
The application also provides a manufacturing method of the double-magnetic-circuit current transformer, which comprises the following specific steps:
the number of primary turns of the large-transformation-ratio current transformer CT1 is smaller than that of the small-transformation-ratio current transformer CT2, the secondary windings of the large-transformation-ratio current transformer CT1 and the small-transformation-ratio current transformer CT2 are independently fixed on a winding tool, a primary wire is wound on the secondary winding of the small-transformation-ratio current transformer CT2 for N turns, and a secondary wire is wound on the secondary windings of the large-transformation-ratio current transformer CT1 and the small-transformation-ratio current transformer CT1 for N1 turns at the same time, N1 is the number of primary turns of the large-transformation-ratio current transformer, and the number of primary turns N2 of the small-transformation-ratio current transformer is N1+ N.
Assuming that the transformation ratio of the large-transformation-ratio current transformer CT1 is 100/5, the transformation ratio of the small-transformation-ratio current transformer CT2 is 50/5, the number of primary turns of the large-transformation-ratio current transformer CT1 is 3, the number of secondary turns of the large-transformation-ratio current transformer CT1 is 60, the number of primary turns of the small-transformation-ratio current transformer CT2 is 6, and the number of secondary turns of the small-transformation-ratio current transformer CT2 is 60, a primary wire is wound on a secondary winding of the small-transformation-ratio current transformer CT2 for 3 turns, and then the primary wire is simultaneously wound on secondary windings of the large-transformation-ratio current transformer CT1 and the small-transformation-ratio current transformer CT2 for 3 turns, that is, the transformation ratio requirements of the large-transformation-ratio current transformer CT1 and the small-transformation-ratio current transformer CT2 are met under the condition of saving installation space, the transformation ratio of the CT3 is 10/5, and the CT2 and CT3 obtain the current transformation ratio effect same as that of the CT1 through two-stage transformation, which is convenient for metering of the metering circuit.
As shown in fig. 2 and 3, the present application is further explained below according to the case of the present application applied to three-phase current detection, and includes a large-transformation-ratio current transformer ACT1, a small-transformation-ratio current transformer ACT2, a transformer switching circuit, a magnification unified transformer ACT3, a C-phase large-transformation-ratio current transformer CCT1 and a small-transformation-ratio current transformer CCT2, a transformer switching circuit, a magnification unified transformer CCT3 on a phase, an a mutual inductor switching circuit including a CPU controller and a first controllable switch a-1K, a second controllable switch a-2K, and a third controllable switch electrically connected to the CPU controller, the first controllable switch a-1K being connected in parallel to two output terminals A1S1 and A1S2 of the large-transformation-ratio current transformer ACT1 for short-circuiting the large-transformation-ratio current transformer ACT1, the second controllable switch a-2K being connected in parallel to two output terminals A3S2 and A3S3 of the magnification unified transformer ACT3 for short-circuiting the magnification transformer ACT3, an output end A3S2 of the multiplying power unified transformer ACT3 is connected in parallel with an output end A1S2 of a large-transformation-ratio current transformer ACT1 to form one end AS2 externally connected to an external metering circuit, the multiplying power unified transformer ACT3 and the other output end A3S3 and A1S1 of the large-transformation-ratio current transformer ACT1 are respectively connected in series with two groups of switch contacts A-3K1 and A-3K2 of a third controllable switch and then connected in parallel to form the other end AS1 connected to the external metering circuit, and a first current sensor ACY1 is connected in series in an output loop of the small-transformation-ratio current transformer ACT 2; the specific connection relation of a large-transformation-ratio current transformer CCT1, a small-transformation-ratio current transformer CCT2, a multiplying power unified transformer CCT3, a first controllable switch C-1K, a second controllable switch C-2K, a third controllable switch and a first current sensor CCY1 of the C phase is consistent with that of the A phase.
The multiplying power unified transformers ACT3 and CCT3 are used for being matched with the small-transformation-ratio current transformers ACT2 and CCT2 to form a current transformation ratio the same as that of the large-transformation-ratio current transformers ACT1 and CCT1, and the first current sensors ACY1 and CCY1 are electrically connected with the CPU controller to provide current signals for switching the current transformers.
Taking the direction A as an example, the transformer switching circuit further comprises a second current sensor ACY2 and a third current sensor ACY3, the second current sensor ACY2 is connected in series in a connecting line between the output end A1S1 of the large-transformation-ratio current transformer ACT1 and a switch contact A-3K2 of a third controllable switch, the third current sensor ACY3 is connected in series in a connecting line between the multiplying power unified transformer ACT3 and the switch contact A-3K1 of the third controllable switch, and the second current sensor ACY2, the third current sensor ACY3 and the CPU controller are electrically connected. The first current sensor ACY1 measures the induction current of the small-transformation-ratio current transformer ACT2, the second current sensor ACY2 measures the current of the large-transformation-ratio branch, the third current sensor ACY3 measures the current of the small-transformation-ratio branch, if the transformation ratio of the large-transformation-ratio current transformer ACT1 to the small-transformation-ratio current transformer ACT2 is M, when the large-transformation-ratio branch normally works, the detected current ratio of the first current sensor ACY1 to the second current sensor ACY2 is equal to M, when the small-transformation-ratio branch normally works, the detected current ratio of the first current sensor ACY1 to the third current sensor ACY3 is equal to M, and if the detected current ratio of the first current sensor ACY1 to the second current sensor ACY2 or the third current sensor ACY3 is not equal to M, a fault occurs, and the CPU controller can alarm and memorize and disconnect the main output circuit. As described above, the C-phase transformer switching circuit further includes the second current sensor CCY2 and the third current sensor CCY3, and the specific connection relationship is consistent with that of the a phase.
The first controllable switch A-1K, C-1K, the second controllable switch A-2K, C-2K and the third controllable switch are magnetic latching relays, preferably, taking phase A as an example, two output ends A1S1 and A1S2 of the large-transformation-ratio current transformer ACT1 are connected in parallel with normally open contacts of the first controllable switch A-1K, two output ends A3S3 and A3S2 of the multiplying-ratio unified transformer ACT3 are connected in parallel with normally open contacts of the second controllable switch A-2K, a switch contact A-3K2 of the third controllable switch connected in series with an output end A1S1 of the large-transformation-ratio current transformer ACT1 is a normally closed contact, a switch contact A-3K1 of the third controllable switch connected in series with an output end A3S3 of the multiplying-ratio unified transformer 3 is a normally open contact, the purpose of preferentially using the large-transformation-ratio current transformer is achieved, and the use rule of the ACT1 is met.
The first current sensors ACY1 and CCY1 of the a-phase and the C-phase, the second current sensors ACY2 and CCY2, and the third current sensors ACY3 and CCY3 are hall current sensors.
A signal conditioning module is connected between the first current sensors ACY1 and CCY1 of the A phase and the C phase, the second current sensors ACY2 and CCY2, the third current sensors ACY3 and CCY3 and the CPU controller in series, the signal conditioning module comprises signal amplification, filtering, analog-to-digital conversion circuits and the like, and photoelectric isolation modules are connected between the first controllable switches A-1K and C-1K, the second controllable switches A-2K and C-2K and the third controllable switches and the CPU controller in series.
The mutual inductor switching circuit further comprises a touch screen, a power supply and a memory storage, wherein the touch screen is electrically connected with the CPU controller, the touch screen is used for man-machine interaction, and the memory storage is used for storing alarm information.
The switching method and the multi-redundancy current detection method of the large-transformation-ratio current transformer CT1 and the small-transformation-ratio current transformer CT2 are described by taking an A phase as an example:
the switching method comprises the following steps:
when the effective value of the current is less than or equal to a preset value I1, the first controllable switch A-1K is closed, then the normally closed contact A-3K2 of the third controllable switch is opened, the normally open contact A-3K1 is closed, finally the second controllable switch A-2K is opened, the small-transformation-ratio current transformer ACT2 works, and the large-transformation-ratio current transformer ACT1 is short-circuited; when the effective value of the current is detected to be larger than a preset value I1, the second controllable switch A-2K is closed, then a normally open contact A-3K1 of the third controllable switch is opened, a normally closed contact A-3K2 is closed, finally the first controllable switch A-1K is opened, and the current is switched back to the large-transformation-ratio current transformer ACT 1. The action sequence of each magnetic latching relay is controlled by a CPU controller, the action holding time is 50ms, the interval time is 50ms, and the current transformer is ensured not to be opened on the basis of saving energy.
The multi-redundancy current detection method comprises the following steps:
the first current sensor ACY1 measures the induction current of the small-transformation-ratio current transformer ACT2, the second current sensor ACY2 measures the current of the large-transformation-ratio branch, the third current sensor ACY3 measures the current of the small-transformation-ratio branch, if the transformation ratio of the large-transformation-ratio current transformer ACT1 to the small-transformation-ratio current transformer ACT2 is M, when the large-transformation-ratio branch normally works, the detected current ratio of the first current sensor ACY1 to the second current sensor ACY2 is equal to M, when the small-transformation-ratio branch normally works, the detected current ratio of the first current sensor ACY1 to the third current sensor ACY3 is equal to M, and if the detected current ratio of the first current sensor ACY1 to the second current sensor ACY2 or the third current sensor ACY3 is not equal to M, a fault occurs, and the CPU controller can alarm and memorize and disconnect the main output circuit.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Although the embodiments of the present application have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present application, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive effort by those skilled in the art.
Claims (10)
1. Accurate measurement current transformer of dual magnetic circuit, its characterized in that includes:
the transformer switching circuit comprises a large-transformation-ratio current transformer, a small-transformation-ratio current transformer and a transformer switching circuit, wherein the two independent magnetic circuits are arranged on the same circuit;
the number of primary turns of the current transformer with the large transformation ratio is smaller than that of the current transformer with the small transformation ratio;
the transformer switching circuit calculates primary current by detecting induced current of the large-transformation-ratio current transformer or the small-transformation-ratio current transformer, when the primary current value is larger than a preset value I1, the transformer switching circuit switches the large-transformation-ratio current transformer to obtain the induced current of a line, and when the current value is smaller than or equal to a preset value I1, the transformer switching circuit switches the small-transformation-ratio current transformer to obtain the induced current of the line.
2. The dual magnetic circuit precision metering current transformer of claim 1, wherein:
the transformer switching circuit comprises a CPU controller, a first controllable switch, a second controllable switch and a third controllable switch, wherein the first controllable switch, the second controllable switch and the third controllable switch are electrically connected with the CPU controller, the first controllable switch is connected in parallel with two output ends of a high-transformation-ratio current transformer for short-circuiting the high-transformation-ratio current transformer, the second controllable switch is connected in parallel with two output ends of a multiplying-ratio unified transformer for short-circuiting the multiplying-ratio unified transformer, one output end of the multiplying-ratio unified transformer is connected in parallel with one output end of the high-transformation-ratio current transformer to form one end externally connected to an external metering circuit, the other output ends of the multiplying-ratio unified transformer and the high-transformation-ratio current transformer are respectively connected in series with two groups of switch contacts of the third controllable switch and then connected in parallel to form the other end connected to the external metering circuit, and a first current sensor is connected in series in an output loop of the low-transformation-ratio current transformer;
the first current sensor is electrically connected with the CPU controller and used for providing a current signal for switching the current transformer.
3. The dual magnetic circuit precision metering current transformer of claim 2, wherein:
the transformer switching circuit further comprises a second current sensor and a third current sensor, the second current sensor is connected in series with a connecting line of the large-transformation-ratio current transformer and a third controllable switch, the third current sensor is connected in series with a connecting line of the multiplying-power unified transformer and the third controllable switch, and the second current sensor, the third current sensor and the CPU controller are electrically connected.
4. The dual magnetic circuit precision metering current transformer according to any one of claims 2 or 3, wherein:
the first controllable switch, the second controllable switch and the third controllable switch are magnetic latching relays, two output ends of the large-transformation-ratio current transformer are connected in parallel to a normally open contact of the first controllable switch, two output ends of the multiplying-power unified transformer are connected in parallel to a normally open contact of the second controllable switch, an output end of the large-transformation-ratio current transformer is connected in series to a normally closed contact of the third controllable switch, and an output end of the multiplying-power unified transformer is connected in series to a normally open contact of the third controllable switch.
5. The dual magnetic circuit precision metering current transformer of claim 4, wherein:
and signal conditioning modules are connected among the first current sensor, the second current sensor, the third current sensor and the CPU controller in series, and photoelectric isolation modules are connected among the first controllable switch, the second controllable switch, the third controllable switch and the CPU controller in series.
6. The dual magnetic circuit precision metering current transformer of claim 2, wherein:
the mutual inductor switching circuit further comprises a touch screen, a power supply and a memory storage, wherein the touch screen, the power supply and the memory storage are electrically connected with the CPU controller.
7. The dual magnetic circuit precision metering current transformer of claim 2, wherein:
the value range of the preset value I1 is 4% -6% of the rated current value of the large-transformation-ratio current transformer, and the transformation ratio of the large-transformation-ratio current transformer to the small-transformation-ratio current transformer is any one of 2, 3 and 4.
8. The dual magnetic circuit precision metering current transformer of claim 3, wherein:
the switching method of the large-transformation-ratio current transformer and the small-transformation-ratio current transformer comprises the following steps:
when the effective value of the current is smaller than a preset value I1, the first controllable switch is closed first, then the normally closed contact of the third controllable switch is opened, the normally open contact is closed, finally the second controllable switch is opened, the small-transformation-ratio current transformer works, and the large-transformation-ratio current transformer is short-circuited;
when the effective value of the current is detected to be larger than or equal to a preset value I1, the second controllable switch is closed first, then the normally open contact of the third controllable switch is opened, the normally closed electric shock is closed, finally the first controllable switch is opened, and the high-transformation-ratio current transformer is switched back.
9. The dual magnetic circuit precision metering current transformer of claim 8, wherein:
the multi-redundancy current detection method comprises the following steps: the method comprises the steps that a first current sensor measures the induced current of a small-transformation-ratio current transformer, a second current sensor measures the current of a large-transformation-ratio branch, a third current sensor measures the current of a small-transformation-ratio branch, if the transformation ratio of the large-transformation-ratio current transformer to the small-transformation-ratio current transformer is M, when the large-transformation-ratio branch normally works, the detected current ratio of the first current sensor to the second current sensor is equal to M, when the small-transformation-ratio branch normally works, the detected current ratio of the first current sensor to the third current sensor is equal to M, if the detected current ratio of the first current sensor to the second current sensor or the third current sensor is not equal to M, a fault occurs, and a CPU controller can alarm, memorize and disconnect an output main circuit.
10. The manufacturing method of the double-magnetic circuit current transformer is characterized by comprising the following steps:
the secondary windings of the large-transformation-ratio current transformer and the small-transformation-ratio current transformer are independently fixed on a winding tool, the number of primary windings of the large-transformation-ratio current transformer is smaller than that of the small-transformation-ratio current transformer, a primary wire is firstly wound on the secondary winding of the small-transformation-ratio current transformer for N turns, then the primary wire is simultaneously wound on the secondary windings of the large-transformation-ratio current transformer and the small-transformation-ratio current transformer for N1 turns, N1 is the number of primary windings of the large-transformation-ratio current transformer, and the number of primary windings N2 of the small-transformation-ratio current transformer is N1+ N.
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