Metering protection integrated current transformer based on three-stage core and power equipment

Abstract

The application discloses a kind of based on three-stage core's measurement protection integration current transformer and electric power equipment, the current transformer includes the three-stage core formed by first-stage core to third-stage core in turn superposition winding, the magnetic field sensor for being arranged in the air gap in third-stage core and the signal processor being connected with magnetic field sensor, magnetic field sensor is used to measure the magnetic field intensity in the air gap in third-stage core;Signal processor is used to carry out signal processing to the voltage signal output by magnetic field sensor, and control whether the signal output end after signal processing is connected in parallel with the secondary winding of three-stage core, so that the output current of current transformer meets preset standard.The application can compensate the distorted secondary current caused by core saturation, and can meet the accuracy requirement of measurement current transformer, also can meet the accuracy requirement of protection current transformer, can be used for measurement and protection simultaneously, simplify the configuration of current transformer in power system.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to an integrated current transformer and power equipment based on a three-stage iron core for metering and protection. Background Technology

[0002] Currently, current transformers used in power systems can be divided into two main categories according to their application scenarios: metering current transformers and protection current transformers.

[0003] In power systems, a single current transformer device may contain multiple sets of current transformers of different specifications. However, both metering and protection current transformers still have various shortcomings. Currently, the metering current transformers widely used in power systems are still traditional current transformers composed of a toroidal core and secondary windings. However, with the large-scale grid connection of clean energy and nonlinear loads, the DC and harmonic components in the line current may cause a decrease in the accuracy of metering current transformers, leading to errors in energy metering and losses for the power grid company. In addition, the non-periodic component of the short-circuit current can also cause core saturation, resulting in distortion of the secondary current. Protection current transformers, because they must meet the error requirements under the accurate limit of primary current, have a significantly increased core volume and an air gap, resulting in higher errors when measuring steady-state current.

[0004] In summary, there is an urgent need for a new type of current transformer that retains the high accuracy of metering current transformers, has anti-saturation capability, and meets the error requirements of the primary current under the accuracy limit of protection current transformers. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to provide an integrated metering and protection current transformer based on a three-stage iron core. The output of the magnetic field sensor in this transformer can compensate for the distorted secondary current caused by iron core saturation, avoiding power metering distortion and erroneous operation of relay protection equipment caused by secondary current distortion, thus improving the reliability of power grid operation. Furthermore, it can meet the accuracy requirements of both metering and protection current transformers, and can be used for both metering and protection simultaneously, thereby simplifying the configuration of current transformers in power systems.

[0006] A second objective of this invention is to provide an electrical device.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] An integrated metering and protection current transformer based on a three-stage iron core, comprising:

[0009] The three-stage iron core is formed by sequentially stacking and winding a first-stage iron core, a second-stage iron core, and a third-stage iron core. The first-stage iron core is an annular iron core without air gaps, the second-stage iron core has a small number of air gaps, and the third-stage iron core has a large number of air gaps.

[0010] A magnetic field sensor is installed in an air gap in the third-stage iron core. The magnetic field sensor is used to measure the magnetic field strength in the air gap in the third-stage iron core through its own output voltage signal.

[0011] The signal processor is used to process the voltage signal and control whether the signal output terminal after signal processing is connected in parallel with the secondary winding of the three-stage iron core, so as to control whether the output current of the secondary winding is compensated by the first current signal after signal processing, so that the output current of the current transformer meets the preset standard.

[0012] Optionally, the inner radius and outer radius of each stage of the three-stage iron core are the same.

[0013] Optionally, the heights of the first-stage iron core to the third-stage iron core decrease sequentially.

[0014] Optionally, the signal processor includes an adjustment and amplification module, the input of which is connected to the output of the magnetic field sensor, and the adjustment and amplification module is used to adjust the amplitude of the voltage signal.

[0015] Optionally, the signal processor further includes a voltage-to-current conversion module, the input of which is connected to the output of the adjustment and amplification module, and the voltage-to-current conversion module is used to convert the voltage signal into a second current signal.

[0016] Optionally, the signal processor further includes a power amplification module, the input of which is connected to the output of the voltage-to-current conversion module, and the power amplification module is used to amplify the second current signal to obtain the first current signal.

[0017] Optionally, the signal processor further includes a switching module, the input terminal of which is connected to the output terminal of the power amplifier module, and the output terminal of which is connected in parallel with the secondary winding of the three-stage iron core.

[0018] Optionally, the signal processor further includes a logic judgment module. The input terminal of the logic judgment module is connected to the output terminal of the adjustment amplification module, and the output terminal of the logic judgment module is connected to the control terminal of the switch module. The logic judgment module is used to control the closing and closing of the switch module according to the output signal of the adjustment amplification module, so as to control whether the signal output terminal of the power amplification module is connected in parallel to the secondary winding of the three-stage iron core.

[0019] Optionally, the logic judgment module is specifically used to: control the switch module to turn off when the primary current of the current transformer is small and does not contain a DC component or aperiodic component; and control the switch module to close when the primary current is large or the primary current contains a DC component and aperiodic component.

[0020] To achieve the above objectives, a second aspect of the present invention provides a power equipment, including the aforementioned integrated current transformer for metering and protection based on a three-stage iron core.

[0021] This invention has at least the following technical effects:

[0022] 1. The three-stage iron core structure is adopted as the iron core of the current transformer, which not only retains the high permeability of the complete iron core, but also initially has the anti-saturation capability.

[0023] 2. A magnetic field sensor placed in the air gap of the third-stage iron core is used to compensate for the distorted secondary current. This can solve the problem of iron core saturation and secondary current distortion when the current transformer measures the primary current containing DC bias or non-periodic components. It can be widely used to measure currents with more complex waveforms.

[0024] 3. By adopting a connection method that links the secondary winding of the current transformer to the output of the signal processing module in parallel, the high accuracy of the current transformer for metering is retained, while also meeting the accuracy limit coefficient required for the current transformer for protection.

[0025] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the integrated metering and protection current transformer based on a three-stage iron core according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of a three-stage iron core according to an embodiment of the present invention. Detailed Implementation

[0028] The following describes this embodiment in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0029] The following description, with reference to the accompanying drawings, illustrates an integrated current transformer and power equipment based on a three-stage iron core for metering and protection, according to this embodiment.

[0030] Figure 1 This is a schematic diagram of the integrated metering and protection current transformer based on a three-stage iron core according to an embodiment of the present invention.

[0031] like Figure 1 As shown, the integrated current transformer for metering and protection based on a three-stage iron core includes a three-stage iron core 5, a magnetic field sensor 7, and a signal processor 13.

[0032] Among them, the three-stage iron core 5 is formed by the first-stage iron core 1, the second-stage iron core 2 and the third-stage iron core 3 being stacked and wound in sequence. The first-stage iron core 1 is an annular iron core without air gaps 4, the second-stage iron core 2 has a small number of air gaps 4, and the third-stage iron core 3 has a large number of air gaps 4.

[0033] In this embodiment, the inner radius and outer radius of each core stage are the same, and the heights of the first core stage 1 to the third core stage 3 decrease sequentially.

[0034] Specifically, the inner radius of each core stage is 70 mm, and the outer radius of each core stage is 130 mm; the first core stage 1 is a complete annular core with a height of 90 mm; the second core stage 2 has a height of 60 mm and a small number of air gaps, such as 4 air gaps 4, each with a length of 5.6 mm; the third core stage 3 has a height of 50 mm and a large number of air gaps, such as 40 air gaps 4, each with a length of 5 mm.

[0035] Furthermore, such as Figure 2 As shown, the magnetic field sensor 7 is installed in one of the air gaps 4 of the third-stage iron core 3, and its output terminal is connected to the input terminal of the signal processor 13. The magnetic field sensor 7 is used to measure the magnetic field strength in the air gap 4 of the third-stage iron core 3 through its own output voltage signal. The signal processor 13 is used to process the voltage signal and control whether the signal output terminal after signal processing is connected in parallel with the secondary winding 6 of the third-stage iron core 5, so as to control whether the output current of the secondary winding 6 is compensated through the first current signal after signal processing, so that the output current of the current transformer meets the preset standard.

[0036] Specifically, the magnetic field sensor 7 outputs a voltage signal, which reflects the magnetic field strength within the air gap 4 of the third-stage iron core 3. The signal processor 13 processes this voltage signal and, when the first-stage iron core 1 is not saturated, controls the signal output terminal after signal processing to not be connected in parallel with the secondary winding 6 of the third-stage iron core 5, i.e., no compensation is needed for the output current of the secondary winding 6. When the first-stage iron core 1 is saturated, controls the signal output terminal after signal processing to be connected in parallel with the secondary winding 6 of the third-stage iron core 5, and compensates for the output current of the secondary winding 6 through the processed first current signal, so that the output current of the current transformer meets the preset standard.

[0037] In one embodiment of the present invention, the signal processor 13 includes an adjustment amplification module 8, a voltage-to-current conversion module 9, a power amplification module 10, and a switching module 11 connected in sequence, wherein the output terminal of the switching module 11 is connected in parallel with the secondary winding 6 of the three-stage iron core 5. The signal processor 13 also includes a logic judgment module 12, the input terminal of which is connected to the output terminal of the adjustment amplification module 8, and the output terminal of the logic judgment module 12 is connected to the control terminal of the switching module 11.

[0038] In this embodiment, the adjustment amplification module 8 is used to adjust the amplitude of the voltage signal. The voltage-to-current conversion module 9 is used to convert the voltage signal into a second current signal. The power amplification module 10 is used to amplify the second current signal to obtain a first current signal. The logic judgment module 12 is used to control the closing and closing of the switch module 11 according to the output signal of the adjustment amplification module 8, so as to control whether the signal output terminal of the power amplification module 10 is connected in parallel to the secondary winding 6 of the three-stage iron core 5.

[0039] Specifically, when the logic judgment module 12 analyzes the output signal of the adjustment and amplification module 8 and finds that the primary current of the current transformer is small and contains no DC or aperiodic components, i.e., the first-stage iron core 1 is not saturated, and the output of the magnetic field sensor 7 is extremely small and does not require compensation, the control switch module 11 is turned off. When the analysis finds that the primary current is large or contains DC and aperiodic components, causing the first-stage iron core 1 to saturate, the output current of the secondary winding 6 needs to be compensated, the output value of the magnetic field sensor 7 increases rapidly, and the control switch module 11 is closed. It should be noted that in this embodiment, the superimposed signal after parallel connection can be measured by the metering protection device 14.

[0040] In addition, the effectiveness of the present invention is verified by finite element simulation, wherein the primary current is set as rated current (effective value of 600 amperes), steady-state symmetrical short-circuit current (effective value of 18000 amperes), and asymmetrical short-circuit current (peak value of 25455.8 amperes, primary time constant of 100 milliseconds, and initial short-circuit angle of 0 degrees).

[0041] Simulation results show that when the primary current is the rated current (RMS value of 600 Amperes), the composite error output by this invention is 0.0132%; when the primary current is a steady-state symmetrical short-circuit current (RMS value of 18000 Amperes), the composite error output by this invention is 0.109%; and when the primary current is an asymmetrical short-circuit current (peak value of 25455.8 Amperes, primary time constant of 100 ms, and initial short-circuit angle of 0 degrees), the composite error output by this invention is 0.325%. These simulation results verify the advantages of this invention.

[0042] In summary, this invention employs a three-stage core structure as the transformer core, retaining the high permeability of a complete core while also providing preliminary anti-saturation capability. The invention utilizes a magnetic field sensor placed in the air gap of the third-stage core to compensate for distorted secondary current, solving the problem of core saturation and secondary current distortion when measuring primary currents containing DC bias or aperiodic components. This allows for wide application in measuring currents with complex waveforms. Furthermore, the invention uses a parallel connection between the transformer's secondary winding and the signal processing module output, maintaining the high accuracy of metering current transformers while meeting the accuracy limit coefficient requirements of protective current transformers.

[0043] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0044] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A current transformer integrating metering and protection based on a three-stage iron core, characterized in that, include: The three-stage iron core is formed by sequentially stacking and winding a first-stage iron core, a second-stage iron core, and a third-stage iron core. The first-stage iron core is an annular iron core without air gaps, the second-stage iron core has a small number of air gaps, and the third-stage iron core has a large number of air gaps. The inner radius and outer radius of each stage of the three-stage iron core are the same, and the height of the first-stage iron core to the third-stage iron core decreases sequentially. A magnetic field sensor is installed in an air gap in the third-stage iron core. The magnetic field sensor is used to measure the magnetic field strength in the air gap in the third-stage iron core through its own output voltage signal. The signal processor is used to process the voltage signal and control whether the signal output terminal after signal processing is connected in parallel with the secondary winding of the three-stage iron core, so as to control whether the output current of the secondary winding is compensated by the first current signal after signal processing, so that the output current of the current transformer meets the preset standard.

2. The integrated metering and protection current transformer based on a three-stage iron core as described in claim 1, characterized in that, The signal processor includes an adjustment and amplification module, the input of which is connected to the output of the magnetic field sensor, and the adjustment and amplification module is used to adjust the amplitude of the voltage signal.

3. The integrated metering and protection current transformer based on a three-stage iron core as described in claim 2, characterized in that, The signal processor further includes a voltage-to-current conversion module, the input of which is connected to the output of the adjustment and amplification module, and the voltage-to-current conversion module is used to convert the voltage signal into a second current signal.

4. The integrated metering and protection current transformer based on a three-stage iron core as described in claim 3, characterized in that, The signal processor further includes a power amplifier module, the input of which is connected to the output of the voltage-current conversion module, and the power amplifier module is used to amplify the second current signal to obtain the first current signal.

5. The integrated metering and protection current transformer based on a three-stage iron core as described in claim 4, characterized in that, The signal processor also includes a switching module, the input terminal of which is connected to the output terminal of the power amplifier module, and the output terminal of which is connected in parallel with the secondary winding of the three-stage iron core.

6. The integrated metering and protection current transformer based on a three-stage iron core as described in claim 5, characterized in that, The signal processor further includes a logic judgment module. The input terminal of the logic judgment module is connected to the output terminal of the adjustment and amplification module, and the output terminal of the logic judgment module is connected to the control terminal of the switch module. The logic judgment module is used to control the closing and closing of the switch module according to the output signal of the adjustment and amplification module, so as to control whether the signal output terminal of the power amplification module is connected in parallel to the secondary winding of the three-stage iron core.

7. The integrated metering and protection current transformer based on a three-stage iron core as described in claim 6, characterized in that, The logic judgment module is specifically used for: When the primary current of the current transformer is small and does not contain a DC component or aperiodic component, the switch module is controlled to turn off; when the primary current is large or contains a DC component and aperiodic component, the switch module is controlled to close.

8. An electrical device, characterized in that, Including the integrated metering and protection current transformer based on a three-stage iron core as described in any one of claims 1-7.

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