Capacitive Voltage Sensor

Abstract

The present application provides a capacitive voltage sensor, which includes: a first capacitor, a second capacitor and an intermediate transformer; one end of the first capacitor is connected to a power supply, the other end of the first capacitor is connected to one end of the second capacitor, and the other end of the second capacitor is grounded; the primary end of the intermediate transformer is connected to the other end of the first capacitor in parallel with the second capacitor; the secondary end of the intermediate transformer includes a current compensation module; the current compensation module includes a coil group, a plurality of control switches and a third capacitor connected in parallel with the coil group; the plurality of control switches are used to adjust the target current of the intermediate transformer, and the target current is used to offset the excitation current of the intermediate transformer. The present application can effectively offset the excitation current of the intermediate transformer through the current compensation module at the secondary end of the intermediate transformer, thereby improving the measurement accuracy of the capacitive voltage sensor.

Description

Technical Field

[0001] The present application relates to the technical field of electrical equipment, and in particular to a capacitive voltage sensor. Background Art

[0002] In power systems, capacitive voltage transformer (CVT) is a common voltage transformer used to convert the voltage signal of the high-voltage system into a low-voltage signal for the convenience of measuring and protecting the equipment. However, in the actual application of capacitive voltage sensors, an excitation current is often generated in the intermediate transformer core, which is caused by the change of magnetic flux in the core. Especially in high-frequency applications such as fault location circuit breakers, the operating frequency of CVT can reach 100 kHz. Under this high-frequency working condition, the intermediate transformer core can easily enter a saturated state. Core saturation means that its magnetic permeability decreases, resulting in an increase in the excitation current. The increase in the excitation current will cause greater interference to the output signal of the CVT, thereby seriously affecting the measurement accuracy of the sensor. Summary of the invention

[0003] The present application provides a capacitive voltage sensor. The present application can effectively offset the excitation current of the intermediate transformer through a current compensation module at the secondary side of the intermediate transformer, thereby improving the measurement accuracy of the capacitive voltage sensor.

[0004] The technical solution of this application is implemented as follows:

[0005] The present application provides a capacitive voltage sensor, which includes a first capacitor, a second capacitor and an intermediate transformer; one end of the first capacitor is connected to a power supply, the other end of the first capacitor is connected to one end of the second capacitor, and the other end of the second capacitor is grounded; the primary end of the intermediate transformer is connected to the other end of the first capacitor in parallel with the second capacitor; the secondary end of the intermediate transformer includes a current compensation module; the current compensation module includes a coil group, a plurality of control switches and a third capacitor connected in parallel with the coil group; the plurality of control switches are used to adjust the target current of the intermediate transformer, and the target current is used to offset the excitation current of the intermediate transformer.

[0006] In the above scheme, the coil group includes multiple sub-coils; one sub-coil is connected in series with a control switch to form a first circuit unit; the control switch is used to control the connection state of the corresponding first circuit unit; multiple first circuit units are connected in parallel to form a parallel circuit; the parallel circuit is connected in parallel with the third capacitor.

[0007] In the above scheme, the capacitive voltage sensor also includes: a frequency detection module and a control module connected to the primary end of the intermediate transformer; the frequency detection module is used to detect the operating frequency of the capacitive voltage sensor according to the voltage of the primary end of the intermediate transformer; the control module is used to adjust the target current of the intermediate transformer by controlling the opening and closing state of the control switch in the current compensation module according to the detected operating frequency and the voltage of the primary end.

[0008] In the above scheme, the control module is also used for: when the detected working frequency is the first frequency, controlling the first control switch among the multiple control switches to be in a closed state; wherein, when the first control switch is in the closed state, the first sub-coil with the first number of coil turns in the current compensation module is in a conducting state, and the first sub-coil is connected in parallel with the third capacitor; when the first control switch is in the closed state, the target current of the intermediate transformer is greater than or equal to the excitation current; when the detected working frequency is the second frequency, controlling the second control switch among the multiple control switches to be in a closed state; wherein, when the second control switch is in the closed state, the first sub-coil and the second sub-coil in the current compensation module are both in a conducting state, and the first sub-coil and the second sub-coil are connected in series and connected in parallel with the third capacitor; the sum of the number of coil turns of the first sub-coil and the second sub-coil is the number of turns of the second coil; when the second control switch is in the closed state, the target current of the intermediate transformer is greater than or equal to the excitation current; the second frequency is greater than the first frequency.

[0009] In the above scheme, the control module is also used to: determine the first magnetic flux density of the iron core of the intermediate transformer according to the first frequency and the voltage of the primary end; determine the first current of the intermediate transformer as the excitation current according to the first magnetic field strength corresponding to the first magnetic flux density; or, determine the second magnetic flux density of the iron core of the intermediate transformer according to the second frequency and the voltage of the primary end; determine the second current of the intermediate transformer as the excitation current according to the second magnetic field strength corresponding to the second magnetic flux density.

[0010] In the above scheme, the multiple sub-coils have different numbers of coil turns respectively; the first number of coil turns is determined by the first frequency, the first current and the capacitance value of the third capacitor; the second number of coil turns is determined by the second frequency, the second current and the capacitance value of the third capacitor; the ratio between the first number of coil turns and the sum of the number of coil turns of the multiple sub-coils is N, and the value of N is any value between 1 / 5 and 1 / 20.

[0011] In the above solution, the control module is further used to: determine the first sub-coil from the multiple sub-coils according to the number of turns of the first coil; or determine the second sub-coil from the multiple sub-coils according to the number of turns of the second coil.

[0012] In the above scheme, the control module is also used to: determine the control switch to be closed among the multiple control switches based on the detected frequency value of the operating frequency, the current value of the excitation current, the number of coil turns of the multiple sub-coils and the opening and closing states of the multiple control switches; and control the control switch to be closed to be in a closed state.

[0013] In the above scheme, the control module is also used to: when the detected operating frequency is a first frequency, generate and output a first reminder signal, and the first reminder signal is used to remind the control of the first control switch among the multiple control switches to be in a closed state; when the detected operating frequency is a second frequency, generate and output a second reminder signal, and the second reminder signal is used to remind the control of the second control switch among the multiple control switches to be in a closed state.

[0014] The present application provides a pole-mounted circuit breaker, comprising the capacitive voltage sensor provided by the present application.

[0015] This application has the following beneficial effects:

[0016] The present application adds a current compensation module in which a coil group is connected in parallel with a third capacitor at the secondary end of the intermediate transformer of the capacitive voltage sensor, and adjusts the target current of the intermediate transformer through multiple control switches in the current compensation module to effectively offset the excitation current of the intermediate transformer, thereby reducing the output signal error of the capacitive voltage sensor and improving the measurement accuracy of the capacitive voltage sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the circuit structure of the capacitive voltage sensor provided in the embodiment of the present application;

[0018] Figure 2 is another circuit structure schematic diagram of a capacitive voltage sensor provided in an embodiment of the present application;

[0019] Figure 3 is a schematic diagram of the circuit structure of the current compensation module provided in an embodiment of the present application;

[0020] Figure 4 Schematic diagrams of three structures of the current compensation module provided in the embodiments of the present application;

[0021] Figure 5 is a schematic diagram of the iron core magnetization curve of the intermediate transformer provided in an embodiment of the present application;

[0022] Figure 6 It is a schematic diagram of the circuit structure of the intermediate transformer provided in an embodiment of the present application.

[0023] Description of reference numerals:

[0024] First capacitor: 110, second capacitor: 120, intermediate transformer: 130, power supply: 140, equivalent circuit module: 150, equivalent inductance: 150-1, equivalent impedance: 150-2, first sub-coil: 151-1, second sub-coil: 151-2, third sub-coil: 151-3, first control switch: 152-1, second control switch: 152-2, third control switch: 152-3, current compensation module: 160, third capacitor: 170, primary end: 180, iron core: 190, phase sequence detection module: 200, zero-sequence current detection module: 210. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. The described embodiments should not be regarded as limiting the present application. All other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of this application.

[0026] In the following description, reference is made to “some embodiments”, which describe a subset of all possible embodiments, but it will be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0027] In the following description, the terms "first / second / third" involved are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first / second / third" can be interchanged with a specific order or sequence where permitted, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0028] In the embodiments of the present application, the term "module" or "unit" refers to a part of a structure with a predetermined function, and works together with other related parts to achieve a predetermined goal, and can be fully or partially implemented by using software, hardware (such as processing circuits or memory) or a combination thereof.

[0029] Unless otherwise defined, all technical and scientific terms used in the embodiments of the present application have the same meanings as those commonly understood by those skilled in the art. The terms used in the embodiments of the present application are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0030] In practical applications, the capacitive voltage sensor in the related art does not consider the interference of the excitation current generated in the intermediate transformer core on the output signal of the capacitive voltage sensor. Especially in high-frequency applications such as fault location circuit breakers, the operating frequency of the capacitive voltage sensor can reach 100 kHz. Under this high-frequency working condition, the intermediate transformer core can easily enter a saturated state. The saturation of the core means that its magnetic permeability decreases, resulting in an increase in the excitation current. The increase in the excitation current will cause greater interference to the output signal of the capacitive voltage sensor, thereby seriously affecting the measurement accuracy of the sensor.

[0031] Based on the above-mentioned problems existing in the related art, an embodiment of the present application provides a capacitive voltage sensor, which adds a winding (i.e., a coil group) on the secondary side of the intermediate transformer, and connects a capacitor in parallel to the winding to offset the excitation current generated in the iron core of the intermediate transformer. In addition, considering that when the capacitive voltage sensor is under high-frequency working conditions, the capacitor connected in parallel to the winding is not enough to offset the excitation current generated in the iron core. Therefore, the winding is designed as a winding with adjustable turns, so that the capacitor connected in parallel can still offset the excitation current in the iron core at different frequencies, thereby reducing the error of the output signal of the capacitive voltage sensor and improving the measurement accuracy of the capacitive voltage sensor.

[0032] See also Figure 1 , Figure 1 The circuit structure diagram of the capacitive voltage sensor provided in the embodiment of the present application is shown below. Figure 1 The circuit structure shown is explained.

[0033] In some embodiments, the capacitive voltage sensor includes at least: a first capacitor 110, a second capacitor 120 and an intermediate transformer 130; one end of the first capacitor 110 is connected to a power supply 140, the other end of the first capacitor 110 is connected to one end of the second capacitor 120, and the other end of the second capacitor 120 is grounded; the primary end of the intermediate transformer 130 is connected in parallel with the second capacitor 120 to the other end of the first capacitor 110; the secondary end of the intermediate transformer 130 includes a current compensation module; the current compensation module includes a coil group, a plurality of control switches and a third capacitor connected in parallel with the coil group; the plurality of control switches are used to adjust the target current of the intermediate transformer 130, and the target current is used to offset the excitation current of the intermediate transformer 130.

[0034] Here, the first capacitor 110 is a high voltage capacitor, and the second capacitor 120 is a low voltage capacitor. It should be noted that "high voltage" generally refers to the part with a higher voltage level in the power system, such as above 1KV. "Low voltage" generally refers to the part with a lower voltage level in the power system, such as below 1KV. The voltage signal is collected from the second capacitor 120, stepped down by the intermediate transformer 130, and output through the secondary side of the intermediate transformer 130.

[0035] The excitation current of the intermediate transformer 130 is the current caused by the change of magnetic flux in the iron core of the intermediate transformer 130. When the voltage is first applied to the winding at the primary end of the intermediate transformer 130, the magnetic flux in the iron core begins to build up, and the excitation current is small at this time. As the magnetic flux increases, the excitation current also increases until the iron core approaches a saturation state. When the iron core enters a saturation state, even if the increase of the magnetic flux becomes very slow, the excitation current will increase sharply, resulting in the output signal of the capacitive voltage sensor being mixed with undesired components, thereby affecting the accuracy of the capacitive voltage sensor measurement.

[0036] The current cancellation module at the secondary side of the intermediate transformer 130 includes a coil group, a plurality of control switches and a third capacitor connected in parallel with the coil group. The circuit formed by the coil group and the third capacitor in parallel can generate a current with the same frequency and opposite phase as the excitation current, which can form an effect of canceling the excitation current in the circuit.

[0037] Through the embodiment of the present application, the current compensation module of the intermediate transformer 130 can effectively offset the excitation current of the intermediate transformer, thereby improving the purity and stability of the output signal of the capacitive voltage sensor, so that the capacitive voltage sensor can provide more accurate voltage measurement.

[0038] In some embodiments, the inductance and impedance of the primary and secondary ends of the intermediate transformer 130 can also be equivalent to the primary end of the intermediate transformer 130 to generate an equivalent circuit module. The equivalent circuit module is formed by connecting an equivalent inductor and an equivalent impedance in series; the inductance value of the equivalent inductor is equal to the target inductance value; the target inductance value is equal to the sum of the compensation inductance value and the reduced inductance value of the equivalent circuit module, and the reduced inductance value is equal to the leakage inductance value of the primary and secondary ends of the intermediate transformer 130 converted to the inductance value of the primary end of the intermediate transformer 130; the impedance value of the equivalent impedance is equal to the reduced impedance value; the reduced impedance value is equal to the leakage resistance of the primary and secondary ends of the intermediate transformer 130 converted to the impedance value of the primary end of the intermediate transformer 130.

[0039] In this embodiment, another circuit structure of the capacitive voltage sensor is as follows: Figure 2 As shown, Figure 2 middle is the current value flowing through the first capacitor 110, is the current value flowing through the intermediate transformer 130, is the current value flowing through the second capacitor 120, is the power supply voltage value of the power supply 140, is the capacitive reactance value of the first capacitor 110, is the inductive reactance value of the equivalent inductance 150-1, is the converted impedance value, is the impedance value of the intermediate transformer 130, is the capacitive reactance value of the second capacitor 120. , so it can be ignored in stable calculations .

[0040] Therefore, the connection relationship between the first capacitor 110, the second capacitor 120, the intermediate transformer 130, the power supply 140 and the equivalent circuit module 150 composed of the equivalent inductance 150-1 and the equivalent impedance 150-2 in the capacitive voltage sensor can be expressed by the following formulas (1) to (5):

[0041] (1)

[0042] (2)

[0043] (3)

[0044] in, is an imaginary unit, representing ; Indicates the voltage value of the intermediate transformer 130.

[0045] Substituting formula (1) into formula (2) yields:

[0046] (4)

[0047] Substituting formula (3) into formula (4) yields:

[0048] (5)

[0049] Through the embodiment of the present application, after the leakage inductance and leakage resistance of the primary and secondary ends of the intermediate transformer 130 are equivalent to the primary end of the intermediate transformer 130, all parameters (for example, inductance, impedance) can be centrally processed at the primary end, avoiding complex parameter conversion between the primary and secondary ends. This can better understand and predict the behavior of the sensor system under fault and normal operating conditions, thereby improving the stability of the sensor system.

[0050] In some embodiments, the coil group in the current compensation module includes multiple sub-coils; a sub-coil is connected in series with a control switch to form a first circuit unit; the control switch is used to control the connection state of the corresponding first circuit unit; multiple first circuit units are connected in parallel to form a parallel circuit; and the parallel circuit is connected in parallel with a third capacitor.

[0051] In this embodiment, the circuit structure of the current compensation module is as follows: Figure 3 As shown, the current compensation module 160 in the intermediate transformer 130 may include a coil group, a plurality of control switches and a third capacitor 170 connected in parallel with the coil group. The coil group may include a first sub-coil 151-1, a second sub-coil 151-2 and a third sub-coil 151-3, and the plurality of control switches may be a first control switch 152-1, a second control switch 152-2 and a third control switch 152-3, respectively. The first sub-coil 151-1, the second sub-coil 151-2, the third sub-coil 151-3, the first control switch 152-1, the second control switch 152-2 and the third control switch 152-3 form a parallel circuit, and the parallel circuit is connected in parallel with the third capacitor 170 to form the current compensation module 160. For the sub-coils in the above coil group and the control switches in the plurality of control switches, this embodiment is only exemplified. There is no specific restriction on the number of sub-coils and control switches, and it can be expanded according to actual needs.

[0052] The control switch refers to the control switch in the current compensation module 160. The control switch is an electrical component, and the main function of the control switch is to connect or disconnect the current path in the circuit; the control switch in the embodiment of the present application can be a mechanical switch (including a toggle switch, a button switch, a knob switch, a rocker switch, etc.), an electronic switch (such as a transistor switch, a relay, a solid-state relay, etc.), a magnetic switch (such as an electromagnetic relay) or a liquid switch, etc. The third capacitor 170 connected in parallel with the coil group can be a capacitor with a fixed capacitance value. The third capacitor 170 can be used to adjust the phase of the secondary side current of the intermediate transformer 130 so that the phase difference between the secondary side current and the excitation current is 180 degrees, thereby achieving mutual cancellation.

[0053] Through the embodiments of the present application, by opening or closing the control switch, it can be determined whether the sub-coil connected in series with the control switch participates in the entire current compensation module 160, that is, the number of sub-coils in the control current compensation module 160 can be controlled, thereby flexibly changing the current value flowing through the current compensation module 160.

[0054] In some embodiments, the capacitive voltage sensor also includes: a frequency detection module and a control module connected to the primary end of the intermediate transformer 130; the frequency detection module is used to detect the operating frequency of the capacitive voltage sensor according to the voltage of the primary end of the intermediate transformer 130; the control module is used to adjust the target current of the intermediate transformer 130 by controlling the opening and closing state of the control switch in the current compensation module 160 according to the detected operating frequency and the voltage of the primary end.

[0055] In this embodiment, the frequency detection module is connected to the primary side of the intermediate transformer 130. The frequency detection module can be used to collect the voltage of the primary side of the intermediate transformer 130, and determine the working frequency of the capacitive voltage sensor according to the waveform data of the voltage of the primary side of the intermediate transformer 130, that is, to detect and obtain the working frequency of the capacitive voltage sensor, and send the voltage of the primary side and the working frequency to the control module. The control module is used to receive the working frequency and the voltage of the primary side sent by the frequency detection module, and determine how to control the opening and closing state of the control switch according to a preset algorithm or logic, and adjust the target current of the intermediate transformer 130 to be greater than or equal to the excitation current of the intermediate transformer 130.

[0056] Through the embodiments of the present application, the voltage at the primary end of the intermediate transformer 130 is collected through the frequency detection module, and the operating frequency of the capacitive voltage sensor is detected, and the control module is used to automatically adjust the target current of the intermediate transformer 130 according to the detected operating frequency and the voltage at the primary end, so that the automatic adjustment system can quickly respond to changes in the operating frequency and the voltage at the primary end, thereby adjusting the target current in real time, so that the current compensation module 160 can offset the excitation current of the intermediate transformer 130 in real time, thereby realizing automatic control and optimization of the capacitive voltage sensor.

[0057] In some embodiments, the control module is also used to: when the detected operating frequency is a first frequency, control a first control switch among multiple control switches to be in a closed state; wherein, when the first control switch is in a closed state, a first sub-coil having a first number of coil turns in the current compensation module 160 is in a conducting state, and the first sub-coil is connected in parallel with the third capacitor 170; when the first control switch is in a closed state, a target current of the intermediate transformer 130 is greater than or equal to the excitation current; when the detected operating frequency is a second frequency, control a second control switch among multiple control switches to be in a closed state; wherein, when the second control switch is in the closed state, both the first sub-coil and the second sub-coil in the current compensation module 160 are in a conducting state, and the first sub-coil and the second sub-coil are connected in series and connected in parallel with the third capacitor 170; the sum of the number of coil turns of the first sub-coil and the second sub-coil is the number of turns of the second coil; when the second control switch is in a closed state, the target current of the intermediate transformer 130 is greater than or equal to the excitation current; the second frequency is greater than the first frequency.

[0058] In this embodiment, the first control switch may be one or more of a plurality of control switches, and the first sub-coil is a sub-coil connected in series with the first control switch in the current compensation module 160, and the first sub-coil has a first number of coil turns. When the detected operating frequency is the first frequency, the first control switch is controlled to be closed, and the first sub-coil connected in series with the first control switch is in a conducting state, so that the first sub-coil is connected in parallel with the third capacitor 170 to form the current compensation module 160 in the intermediate transformer 130. For example, the first control switch may be the first control switch 152-1, and the first sub-coil is the first sub-coil 151-1, such as Figure 4 As shown in Figure (a), the first sub-coil 151-1 is connected in parallel with the third capacitor 170 to form a current compensation module 160 in the intermediate transformer 130. After the first sub-coil is connected in parallel with the third capacitor 170, the target current generated by the current compensation module 160 is greater than or equal to the excitation current, that is, the amplitude of the target current is greater than or equal to the amplitude of the current excitation current, and the phase is opposite, and the sum of the target current and the excitation current is greater than or equal to zero, thereby achieving the cancellation of the excitation current.

[0059] When the detected operating frequency is the second frequency, and the second frequency is greater than the first frequency, since the capacitance value of the third capacitor 170 in the current compensation module 160 is fixed, it is necessary to add a second sub-coil on the basis of the first sub-coil, that is, by increasing the number of coil turns of the coil connected in parallel with the third capacitor 170 in the current compensation module 160, to ensure effective compensation of the excitation current. The second control switch is a control switch connected in series with the first sub-coil and the second sub-coil, respectively. By closing the second control switch, the first sub-coil and the second sub-coil in the current compensation module 160 are both in the on state, and the first sub-coil and the second sub-coil are connected in series and connected in parallel with the third capacitor 170. For example, the second control switch can be the second control switch 152-2, the first sub-coil is the first sub-coil 151-1, and the second sub-coil is the second sub-coil 151-2. Figure 4 As shown in FIG. 1 (b), the first sub-coil 151-1 and the second sub-coil 151-2 are connected in series and then connected in parallel with the third capacitor 170 to form the current compensation module 160 in the intermediate transformer 130. The second control switch can also be the third control switch 152-3, the first sub-coil is the first sub-coil 151-1 and the second sub-coil 151-2, and the second sub-coil is the third sub-coil 151-3. Figure 4As shown in Figure (c), the first sub-coil 151-1, the second sub-coil 151-2 and the third sub-coil 151-3 are connected in series and then connected in parallel with the third capacitor 170 to form a current compensation module 160 in the intermediate transformer 130. At this time, the target current generated by the current compensation module 160 is greater than or equal to the excitation current, that is, the amplitude of the target current is greater than or equal to the amplitude of the current excitation current, and the phase is opposite, and the sum of the target current and the excitation current is greater than or equal to zero, thereby achieving the cancellation of the excitation current.

[0060] Through the embodiment of the present application, the excitation current of the intermediate transformer 130 can be accurately calculated according to the voltage at the primary side and the detected operating frequency. And according to the excitation current, the sub-coil in parallel with the third capacitor 170 in the current compensation module 160 can be automatically adjusted by flexibly controlling the opening and closing of the control switch in the current compensation module 160, so that the amplitude of the target current of the intermediate transformer is greater than or equal to the amplitude of the excitation current, and the phase is opposite, so as to achieve effective compensation of the excitation current.

[0061] In some embodiments, the control module is also used to: determine a first magnetic flux density of the iron core of the intermediate transformer based on a first frequency and a voltage at the primary end; determine a first current of the intermediate transformer as an excitation current based on a first magnetic field strength corresponding to the first magnetic flux density; or, determine a second magnetic flux density of the iron core of the intermediate transformer based on a second frequency and a voltage at the primary end; determine a second current of the intermediate transformer as an excitation current based on a second magnetic field strength corresponding to the second magnetic flux density.

[0062] In this embodiment, the calculation process of the excitation current is as follows: First, the magnetic flux density of the core of the intermediate transformer 130 is determined according to the following formula (6):

[0063] (6)

[0064] in, is the magnetic flux density (i.e., the first magnetic flux density or the second magnetic flux density), is the voltage at the primary side of the intermediate transformer 130, is the detected operating frequency (i.e., the first frequency or the second frequency), is the number of turns of the coil at the primary end, is the cross-sectional area of ​​the core.

[0065] Then, according to Figure 5 The core magnetization curve shown in the figure determines the magnetic flux density The corresponding magnetic field strength (ie, the first magnetic field strength or the second magnetic field strength). Figure 5The first curve 501 in the graph represents the magnetization curve of a ferrite toroid (FT) of model FT-3KM, the second curve 502 represents the magnetization curve of a ferrite toroid of model FT-3KL, and the third curve 503 represents the magnetization curve of manganese-zinc ferrite (Mn-Zn Ferrite). Finally, the excitation current of the intermediate transformer 130 is determined according to the following formula (7):

[0066] (7)

[0067] in, is the excitation current (i.e. the first current or the second current of the intermediate transformer), is the magnetic field strength of the iron core, is the effective length of the coil at the primary end.

[0068] Through the embodiments of the present application, the magnetic flux density of the core of the intermediate transformer can be accurately determined based on the detected operating frequency and the voltage at the primary end, and thus the excitation current of the intermediate transformer can be accurately determined based on the magnetic field strength corresponding to the magnetic flux density.

[0069] In some embodiments, the plurality of sub-coils have different numbers of coil turns respectively; the number of turns of the first coil is determined by the first frequency, the first current and the capacitance value of the third capacitor 170; the number of turns of the second coil is determined by the second frequency, the second current and the capacitance value of the third capacitor 170. The ratio of the number of turns of the first coil to the sum of the number of turns of the plurality of sub-coils is N, and the value of N is any value between 1 / 5 and 1 / 20.

[0070] In this embodiment, the multiple sub-coils in the coil group may have different numbers of coil turns. When the operating frequency and the excitation current are known, the minimum number of coil turns required to offset the excitation current through the current offset module 160 can be determined according to the operating frequency and the excitation current. Further, the first coil number of turns or the second coil number of turns is determined according to the minimum number of coil turns and the number of coil turns of the multiple sub-coils. The minimum number of coil turns can be determined by the following formula (8):

[0071] (8)

[0072] in, is the current value of the target current, is the angular frequency of the alternating current, , is the frequency value of the operating frequency; is the capacitance value of the third capacitor 170, is the minimum number of coil turns.

[0073] When the detected operating frequency is the first frequency and the excitation current is the first current, in order to make the target current generated by the current compensation module 160 greater than or equal to the excitation current, the current value of the first current is used as the minimum current value of the target current. The minimum number of coil turns required to offset the excitation current by the current compensation module 160 can be determined by the above formula (8). In the case where there is a coil turn number equal to the minimum coil turn number among the coil turns of the multiple sub-coils, or the sum of the coil turns of the multiple sub-coils connected in series is equal to the minimum coil turn number, the minimum coil turn number can be determined as the first coil turn number. In the case where there is no coil turn number equal to the minimum coil turn number among the coil turns of the multiple sub-coils, or the sum of the coil turns of the multiple sub-coils connected in series is equal to the minimum coil turn number, the coil turn number of the multiple sub-coils greater than the minimum coil turn number can be determined as the first coil turn number, or the sum of the coil turns greater than the minimum coil turn number can be determined as the first coil turn number. That is, the number of turns of the first coil may be greater than or equal to the minimum number of turns of the coil, so that the target current generated by the current compensation module 160 is greater than or equal to the excitation current, thereby achieving effective compensation of the excitation current.

[0074] When the detected operating frequency is the second frequency and the excitation current is the second current, in order to make the target current generated by the current cancellation module 160 greater than or equal to the excitation current, the current value of the second current is used as the minimum current value of the target current. The minimum number of coil turns required to cancel the excitation current by the current cancellation module 160 can be determined by the above formula (8). In the case where there is a coil turn of a sub-coil connected in series with a sub-coil having the first number of coil turns among the multiple sub-coils, and the sum of the coil turns obtained by adding the first number of coil turns is equal to the minimum number of coil turns, the minimum number of coil turns can be determined as the second number of coil turns; and in the case where there is no coil turn of a sub-coil connected in series with a sub-coil having the first number of coil turns among the multiple sub-coils, and the sum of the coil turns obtained by adding the first number of coil turns is equal to the minimum number of coil turns, the sum of the coil turns greater than the minimum number of coil turns can be determined as the second number of coil turns. That is, the second number of coil turns can be greater than or equal to the minimum number of coil turns, so that the target current generated by the current cancellation module 160 is greater than or equal to the excitation current, thereby achieving effective cancellation of the excitation current.

[0075] When the capacitive voltage sensor operates in the non-saturated region (that is, in the normal state), the number of coil turns required in the current compensation module 160 is assumed to be 100 turns. When the operating frequency increases sharply to 100 KHZ, the capacitive voltage sensor operates in the saturated region, and the number of coil turns required in the current compensation module 160 is assumed to be 1000 turns. The ratio of the number of coil turns in the above two cases is 1 / 10. It should be noted that when there is a problem with the distribution line, the operating frequency usually increases sharply, and the amplitude of the sharp increase is very large. Therefore, when the line fails, the number of coil turns required in the current compensation module 160 is usually 10 times that of the normal situation, so it is necessary to determine the ratio N between the number of turns of the first coil and the sum of the number of turns of the coils of the multiple sub-coils as a value between 1 / 5 and 1 / 20.

[0076] Through the embodiments of the present application, based on the detected operating frequency, excitation current, and capacitance value of the third capacitor 170, the number of coil turns of the sub-coil connected in parallel with the third capacitor 170 in the current compensation module 160 can be accurately determined, thereby effectively adjusting the target current used to offset the excitation current of the intermediate transformer 130.

[0077] In some embodiments, the control module is further configured to: determine a first sub-coil from a plurality of sub-coils according to the number of turns of the first coil; or determine a second sub-coil from a plurality of sub-coils according to the number of turns of the second coil.

[0078] In this embodiment, when the number of turns of the first coil is known, the sub-coil having the first number of turns is determined as the first sub-coil from the multiple sub-coils, and the first control switch connected in series with the first sub-coil can be controlled to be closed. When the number of turns of the second coil is known, the number of turns of the second coil is subtracted from the number of turns of the first sub-coil to obtain a coil turn difference, and the sub-coil having the coil turn difference and connected in series with the first sub-coil having the first number of turns is determined as the second sub-coil from the multiple sub-coils. When the first sub-coil and the second sub-coil are determined, the second control switch connected in series with the first sub-coil and the second sub-coil is controlled to be closed.

[0079] Through the embodiments of the present application, based on the number of turns of the first coil or the number of turns of the second coil, the sub-coil connected in parallel with the third capacitor 170 in the current compensation module 160 can be accurately determined, thereby automatically controlling the control switch connected in series with the sub-coil to close, thereby achieving effective compensation of the excitation current.

[0080] In some embodiments, the control module is also used to: determine the control switch to be closed among multiple control switches based on the detected frequency value of the operating frequency, the current value of the excitation current, the number of coil turns of multiple sub-coils, and the open and closed states of multiple control switches; and control the control switch to be closed to be in a closed state.

[0081] In this embodiment, when the frequency value of the currently detected operating frequency, the current value of the excitation current, the number of coil turns of the multiple sub-coils in the coil group, and the control switches that are currently closed (i.e., the control switches in the closed state) and which control switches are in the open state are known, the number of coil turns of the coil required to offset the excitation current, i.e., the number of coil turns of the coil group connected in parallel with the third capacitor 170 in the current offset module 160, can be determined according to the above formula (8), so as to judge which control switch among the multiple control switches needs to be closed, i.e., determine the control switch to be closed among the multiple control switches.

[0082] Through the embodiments of the present application, the control module can flexibly control the control switch in the current compensation module 160 according to the current known data, so as to achieve effective compensation of the excitation current.

[0083] In some embodiments, the control module is also used to: when the detected operating frequency is a first frequency, generate and output a first reminder signal, and the first reminder signal is used to remind the control of a first control switch among multiple control switches to be in a closed state; when the detected operating frequency is a second frequency, generate and output a second reminder signal, and the second reminder signal is used to remind the control of a second control switch among multiple control switches to be in a closed state.

[0084] In this embodiment, the control module can also determine the number of coil turns of the coil required to offset the excitation current, that is, the number of coil turns of the coil group connected in parallel with the third capacitor 170 in the current offset module 160, according to the detected operating frequency and excitation current through the above formula (8), so as to determine which control switch among the multiple control switches needs to be closed. Then, a reminder signal is generated based on the switch identifier of the control switch, and a reminder signal is sent to the user terminal to remind the user to manually close the control switch corresponding to the switch identifier carried in the reminder signal. Since the first frequency is different from the second frequency, and the first current is different from the second current, the switch identifiers carried in the first reminder signal and the second reminder signal are different, and the corresponding first control switch and second control switch are also different.

[0085] Through the embodiment of the present application, the control module can also automatically determine which control switch among the multiple control switches should be closed according to the detected operating frequency and excitation current, and generate a reminder signal to timely remind the user to control the opening and closing status of the multiple control switches. The user can also judge whether the control switch corresponding to the switch identifier carried in the closing reminder signal can effectively offset the excitation current according to the reminder signal, thereby improving the flexibility of the implementation process.

[0086] In some embodiments, the secondary side of the intermediate transformer 130 also includes a phase sequence detection module and a zero-sequence current detection module; the phase sequence detection module is used to detect the phase sequence of the voltage or current at the secondary side of the intermediate transformer 130; the zero-sequence current detection module is used to detect the zero-sequence current at the secondary side of the intermediate transformer 130.

[0087] In this embodiment, the circuit structure of the intermediate transformer 130 is as follows: Figure 6 As shown, the intermediate transformer 130 also includes a primary side 180 and an iron core 190, and the secondary side of the intermediate transformer 130 also includes a phase sequence detection module 200 and a zero-sequence current detection module 210. If the phase sequence of the voltage or current at the secondary side of the intermediate transformer 130 is wrong, the capacitive voltage sensor may be damaged or operate abnormally. The phase sequence detection module 200 can trigger a protection action when the phase sequence is wrong to prevent the capacitive voltage sensor from being damaged. When a ground fault occurs in the system, a zero-sequence current will be generated at the secondary side of the intermediate transformer 130, and the zero-sequence current is an abnormal current. The zero-sequence current detection module 210 can detect this abnormal current, thereby triggering a protection action.

[0088] Through the embodiments of the present application, a phase sequence detection module 200 and a zero-sequence current detection module 210 are added to the secondary side of the intermediate transformer 130. Through real-time monitoring and rapid response of the phase sequence detection module 200 and the zero-sequence current detection module 210, the fault can be prevented from expanding and the safety and stability of the system can be improved.

[0089] An embodiment of the present application provides a pole-mounted circuit breaker, which at least includes the capacitive voltage sensor provided in the embodiment of the present application.

[0090] In some embodiments, a pole-mounted circuit breaker is a switch device installed on a columnar support in an electric power system, which is mainly used in a distribution network to perform functions such as circuit opening and closing, fault removal, and load control. The pole-mounted circuit breaker can be used in high-voltage (such as 10kV, 35kV, etc.) and low-voltage (such as 380V, 220V, etc.) distribution systems. When a short circuit or overload occurs in the distribution system, the pole-mounted circuit breaker can quickly disconnect the circuit to protect the system and equipment from damage. The pole-mounted circuit breaker can be an oil-less circuit breaker, an SF6 circuit breaker, or a vacuum circuit breaker. The pole-mounted circuit breaker includes at least the capacitive voltage sensor provided in the embodiment of the present application, that is, the capacitive voltage sensor is integrated in the pole-mounted circuit breaker, so that the pole-mounted circuit breaker not only improves the operating efficiency of the power grid, but also enhances the self-monitoring and self-protection capabilities of the power grid, providing strong technical support for the operation of the smart grid.

[0091] The above is only an embodiment of the present application and is not intended to limit the protection scope of the present application. Any modifications, equivalent substitutions and improvements made within the spirit and scope of the present application are included in the protection scope of the present application.

Claims

1. A capacitive voltage sensor, characterized in that: include: A first capacitor, a second capacitor, an intermediate transformer, and a frequency detection module and a control module connected to the primary end of the intermediate transformer; One end of the first capacitor is connected to a power supply, the other end of the first capacitor is connected to one end of the second capacitor, and the other end of the second capacitor is grounded; The primary end of the intermediate transformer is connected in parallel with the second capacitor; The secondary side of the intermediate transformer includes a current compensation module; the current compensation module includes a coil group, a plurality of control switches and a third capacitor connected in parallel with the coil group; the coil group includes a plurality of sub-coils; a sub-coil is connected in series with a control switch to form a first circuit unit; the control switch is used to control the on state of the corresponding first circuit unit; a plurality of first circuit units are connected in parallel to form a parallel circuit; the parallel circuit is connected in parallel with the third capacitor; The frequency detection module is used to detect the operating frequency of the capacitive voltage sensor according to the voltage at the primary end of the intermediate transformer; The control module is used to: adjust the target current of the intermediate transformer by controlling the opening and closing state of the control switch in the current compensation module according to the detected operating frequency and the voltage of the primary end, and the target current is used to offset the excitation current of the intermediate transformer; The control module is also used for: when the detected working frequency is the first frequency, controlling the first control switch among the multiple control switches to be in a closed state; wherein, when the first control switch is in the closed state, the first sub-coil with the first number of coil turns in the current compensation module is in a conducting state, and the first sub-coil is connected in parallel with the third capacitor; when the first control switch is in the closed state, the target current of the intermediate transformer is greater than or equal to the excitation current; when the detected working frequency is the second frequency, controlling the second control switch among the multiple control switches to be in a closed state; wherein, when the second control switch is in the closed state, the first sub-coil and the second sub-coil in the current compensation module are both in a conducting state, and the first sub-coil and the second sub-coil are connected in series and connected in parallel with the third capacitor; the sum of the number of coil turns of the first sub-coil and the second sub-coil is the number of turns of the second coil; when the second control switch is in the closed state, the target current of the intermediate transformer is greater than or equal to the excitation current; the second frequency is greater than the first frequency; The control module is also used to: determine the first magnetic flux density of the iron core of the intermediate transformer according to the first frequency and the voltage at the primary end; determine the first current of the intermediate transformer as the excitation current according to the first magnetic field strength corresponding to the first magnetic flux density; or, determine the second magnetic flux density of the iron core of the intermediate transformer according to the second frequency and the voltage at the primary end; determine the second current of the intermediate transformer as the excitation current according to the second magnetic field strength corresponding to the second magnetic flux density.

2. The capacitive voltage sensor according to claim 1, characterized in that: The multiple sub-coils respectively have different numbers of coil turns; The number of turns of the first coil is determined by the first frequency, the first current and the capacitance value of the third capacitor; the number of turns of the second coil is determined by the second frequency, the second current and the capacitance value of the third capacitor; The ratio of the number of turns of the first coil to the sum of the number of turns of the multiple sub-coils is N, and the value of N is any value between 1 / 5 and 1 / 20.

3. The capacitive voltage sensor according to claim 2, characterized in that: The control module is also used for: Determining the first sub-coil from the plurality of sub-coils according to the number of turns of the first coil; or, The second sub-coil is determined from the plurality of sub-coils according to the number of turns of the second coil.

4. The capacitive voltage sensor according to claim 3, characterized in that: The control module is also used for: Determine a control switch to be closed among the multiple control switches according to the detected frequency value of the operating frequency, the current value of the excitation current, the number of coil turns of the multiple sub-coils, and the open and closed states of the multiple control switches; And control the control switch to be closed to be in a closed state.

5. The capacitive voltage sensor according to claim 1, characterized in that: The control module is also used for: When the detected operating frequency is the first frequency, a first reminder signal is generated and output, wherein the first reminder signal is used to remind and control a first control switch among the plurality of control switches to be in a closed state; When the detected operating frequency is the second frequency, a second reminder signal is generated and output, where the second reminder signal is used to remind a second control switch among the plurality of control switches to be in a closed state.

6. A pole mounted circuit breaker, characterized in that: A capacitive voltage sensor comprising any one of claims 1 to 5.

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