An AC / DC voltage transformer

Abstract

The present invention discloses an AC / DC voltage transformer, comprising: a high-voltage arm and a low-voltage arm. The low-voltage arm includes: a voltage limiting branch, a total voltage sampling branch, a DC component sampling branch, and an AC component sampling branch. The high-voltage end of the high-voltage arm is connected to the voltage to be measured, and the low-voltage end is connected to the high-voltage end of the low-voltage arm. The low-voltage end of the low-voltage arm is grounded. One end of the voltage limiting branch is connected to the high-voltage end of the low-voltage arm, and the other end is connected to the low-voltage end of the low-voltage arm. One end of the total voltage sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end is connected to the low-voltage end of the low-voltage arm. One end of the DC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end is connected to the low-voltage end of the low-voltage arm. One end of the AC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end is connected to the low-voltage end of the low-voltage arm. The present invention can measure the DC, AC, and total voltage values of the voltage to be measured using only one primary device, effectively reducing the cost and improving the measurement efficiency.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to an AC-DC voltage transformer. Background Art

[0002] In a DC converter station, the voltage between a transformer and a converter valve is composed of an AC voltage and a DC voltage superimposed thereon. Monitoring of the DC voltage and the AC voltage here is particularly important for monitoring the states of the converter station transformer and the converter valve. Currently, only a capacitive voltage divider type AC voltage transformer for measuring the AC voltage is provided at this position, and the DC voltage is not monitored. If it is necessary to measure the AC voltage, the DC voltage, and the total voltage value, it is necessary to set up a DC voltage transformer, an AC voltage transformer, etc., and the number of devices is large and the cost is high.

[0003] In addition, in an existing AC-DC voltage measurement method, the voltage to be measured is first stepped down, and then the low voltage is converted into a digital quantity through a microelectronics technology device, and finally the DC component and the AC component are calculated through a software algorithm. The software requires a complex calculation process, and the calculation process consumes time, affecting the response time of the overall device.

[0004] Therefore, how to simply and effectively measure the DC, AC, and total voltage values of the voltage to be measured is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides an AC-DC voltage transformer, which can measure the DC, AC, and total voltage values of the voltage to be measured by using only one primary device, effectively reducing the cost and improving the measurement efficiency.

[0006] The present invention provides an AC-DC voltage transformer, comprising: a high-voltage arm and a low-voltage arm, wherein the low-voltage arm includes: a voltage limiting branch, a total voltage sampling branch, a DC component sampling branch, and an AC component sampling branch; wherein:

[0007] The high-voltage end of the high-voltage arm is connected to the voltage terminal to be measured, and the low-voltage end of the high-voltage arm is connected to the high-voltage end of the low-voltage arm;

[0008] The low-voltage end of the low-voltage arm is grounded;

[0009] One end of the voltage limiting branch is connected to the high-voltage end of the low-voltage arm, and the other end of the voltage limiting branch is connected to the low-voltage end of the low-voltage arm;

[0010] One end of the total voltage sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the total voltage sampling branch is connected to the low-voltage end of the low-voltage arm;

[0011] One end of the DC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the DC component sampling branch is connected to the low-voltage end of the low-voltage arm;

[0012] One end of the AC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the AC component sampling branch is connected to the low-voltage end of the low-voltage arm.

[0013] Preferably, the high-voltage arm includes: a first resistor and a first capacitor; wherein:

[0014] The first resistor is connected in parallel with the first capacitor;

[0015] One end of the first resistor is connected to the voltage terminal to be measured, and the other end of the first resistor is connected to the high-voltage end of the low-voltage arm;

[0016] One end of the first capacitor is connected to the voltage terminal to be measured, and the other end of the first capacitor is connected to the high-voltage end of the low-voltage arm.

[0017] Preferably, the high-voltage arm is composed of a plurality of resistor-capacitor units connected in series, and each resistor-capacitor unit is composed of a resistor and a capacitor connected in parallel.

[0018] Preferably, the total voltage sampling branch includes: a second resistor and a third resistor; wherein:

[0019] One end of the second resistor is connected to the low-voltage end of the high-voltage arm, and the other end of the second resistor is connected to one end of the third resistor;

[0020] The other end of the third resistor is grounded.

[0021] Preferably, the AC component sampling branch includes: a second capacitor and a third capacitor; wherein:

[0022] One end of the second capacitor is connected to the low-voltage end of the high-voltage arm, and the other end of the second capacitor is connected to one end of the third capacitor;

[0023] The other end of the third capacitor is grounded.

[0024] Preferably, the DC component sampling branch includes: a fourth resistor, a fifth resistor and a fourth capacitor; wherein:

[0025] One end of the fourth resistor is connected to the low-voltage end of the high-voltage arm, and the other end of the fourth resistor is respectively connected to one end of the fifth resistor and one end of the fourth capacitor;

[0026] The other end of the fifth resistor is grounded;

[0027] The other end of the fourth capacitor is grounded.

[0028] Preferably, the DC component sampling branch includes: a sixth resistor, a first inductor, and a seventh resistor; where:

[0029] One end of the sixth resistor is connected to the low-voltage end of the high-voltage arm, and the other end of the sixth resistor is connected to one end of the first inductor;

[0030] The other end of the first inductor is connected to one end of the seventh resistor, and the other end of the seventh resistor is grounded.

[0031] Preferably, the output of the low-voltage arm is sampled by a collector and converted into a digital quantity, and the digital quantity is transmitted to the merging unit or the control and protection device through an optical fiber.

[0032] In summary, the present invention discloses an AC-DC voltage transformer, including: a high-voltage arm and a low-voltage arm, where the low-voltage arm includes: a voltage limiting branch, a total voltage sampling branch, a DC component sampling branch, and an AC component sampling branch; where: the high-voltage end of the high-voltage arm is connected to the voltage to be measured, the low-voltage end of the high-voltage arm is connected to the high-voltage end of the low-voltage arm; the low-voltage end of the low-voltage arm is grounded; one end of the voltage limiting branch is connected to the high-voltage end of the low-voltage arm, and the other end of the voltage limiting branch is connected to the low-voltage end of the low-voltage arm; one end of the total voltage sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the total voltage sampling branch is connected to the low-voltage end of the low-voltage arm; one end of the DC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the DC component sampling branch is connected to the low-voltage end of the low-voltage arm; one end of the AC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the AC component sampling branch is connected to the low-voltage end of the low-voltage arm. By measuring the sampled voltages of each branch of the low-voltage arm, the total voltage value and the DC voltage component and AC voltage component contained therein in the high voltage to be measured can be obtained by the present invention, and the DC, AC, and total voltage values of the voltage to be measured can be measured using only one primary device, effectively reducing the cost and improving the measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic structural diagram of Embodiment 1 of an AC-DC voltage transformer disclosed by the present invention;

[0035] Figure 2 It is a schematic circuit diagram of a high-voltage arm disclosed by the present invention;

[0036] Figure 3 Another circuit schematic diagram of the high-voltage arm disclosed by the present invention;

[0037] Figure 4 A structural schematic diagram of Embodiment 2 of an AC-DC voltage transformer disclosed by the present invention;

[0038] Figure 5 Another circuit schematic diagram of the total voltage sampling branch disclosed by the present invention;

[0039] Figure 6 Another circuit schematic diagram of the AC component sampling branch disclosed by the present invention;

[0040] Figure 7 A structural schematic diagram of Embodiment 3 of an AC-DC voltage transformer disclosed by the present invention. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] As Figure 1 shown, an AC-DC voltage transformer disclosed by the present invention includes: a high-voltage arm 11 and a low-voltage arm 12, wherein the low-voltage arm 12 includes: a voltage limiting branch 121, a total voltage sampling branch 122, a DC component sampling branch 123, and an AC component sampling branch 124; wherein:

[0043] The high-voltage end of the high-voltage arm 11 is connected to the voltage terminal to be measured, and the low-voltage end of the high-voltage arm 11 is connected to the high-voltage end of the low-voltage arm 12;

[0044] The low-voltage end of the low-voltage arm 12 is grounded;

[0045] One end of the voltage limiting branch 121 is connected to the high-voltage end of the low-voltage arm 12, and the other end of the voltage limiting branch 121 is connected to the low-voltage end of the low-voltage arm 12;

[0046] One end of the total voltage sampling branch 122 is connected to the high-voltage end of the low-voltage arm 12, and the other end of the total voltage sampling branch 122 is connected to the low-voltage end of the low-voltage arm 12;

[0047] One end of the DC component sampling branch 123 is connected to the high-voltage end of the low-voltage arm 12, and the other end of the DC component sampling branch 123 is connected to the low-voltage end of the low-voltage arm 12;

[0048] One end of the AC component sampling branch 124 is connected to the high-voltage end of the low-voltage arm 12, and the other end of the AC component sampling branch 124 is connected to the low-voltage end of the low-voltage arm 12.

[0049] In the above embodiment, the AC-DC voltage transformer includes a high-voltage arm and a low-voltage arm. The high-voltage end of the high-voltage arm receives the voltage terminal to be measured, the low-voltage end is connected to the high-voltage end of the low-voltage arm, and the low-voltage end of the low-voltage arm is grounded. The voltage at the high-voltage end of the high-voltage arm and the sampling voltage of the low-voltage arm have a certain voltage division ratio, and the voltage division ratio depends on the selection of the resistance and capacitance values of the high-voltage arm and the low-voltage arm. The total voltage sampling branch, the DC component sampling branch, and the AC component sampling branch have the same frequency response characteristics as the high-voltage arm. By measuring the sampling voltage of the measurement branch of the low-voltage arm, the total voltage value of the high voltage to be measured and its internal DC component and AC component can be obtained. Among them, the voltage division ratio can be the same or designed to be different. Compared with the existing voltage transformers, the AC-DC voltage transformer provided in this embodiment shares a high-voltage arm for each branch of the low-voltage arm when measuring non-pure DC or pure AC voltages. Through different branches of the low-voltage arm, the corresponding secondary voltages can be output respectively, and then the voltage value to be measured and its internal AC component and DC component can be obtained through the voltage division ratio, without the need for secondary equipment to collect and process data, effectively reducing the cost and improving the measurement efficiency.

[0050] Specifically, as Figure 2 shown, the high-voltage arm can be composed of a parallel connection of a first resistor R1 and a first capacitor C1, where:

[0051] One end of the first resistor R1 is connected to the voltage terminal to be measured, and the other end of the first resistor R1 is connected to the high-voltage end of the low-voltage arm;

[0052] One end of the first capacitor C1 is connected to the voltage terminal to be measured, and the other end of the first capacitor C1 is connected to the high-voltage end of the low-voltage arm.

[0053] Specifically, as Figure 3 shown, the high-voltage arm can also be composed of a resistor and a capacitor in parallel to form a resistance-capacitance unit, and multiple resistance-capacitance units are connected in series to form the high-voltage arm. As Figure 3 shown, the resistor R11 and the capacitor C11 are connected in parallel to form a resistance-capacitance unit, the resistor R12 and the capacitor C12 are connected in parallel to form a resistance-capacitance unit, the resistor R13 and the capacitor C13 are connected in parallel to form a resistance-capacitance unit, the resistor R14 and the capacitor C14 are connected in parallel to form a resistance-capacitance unit, and the resistor R15 and the capacitor C15 are connected in parallel to form a resistance-capacitance unit.

[0054] When applied to high-voltage measurement, since the high-voltage end of the high-voltage arm is usually connected to the high voltage to be measured and the voltage difference between the low-voltage end of the high-voltage arm and the ground potential is very small, the high-voltage arm generally consists of a resistor and a capacitor connected in parallel to form a resistor-capacitor unit, and then multiple resistor-capacitor units are connected in series. Using the structure of multiple resistor-capacitor units connected in series to form the high-voltage arm is beneficial to improving the insulation ability, and under lightning impulse voltage and switching impulse voltage, the voltage can be evenly distributed under the action of each resistor-capacitor unit, reducing the uneven voltage distribution coefficient and avoiding damage to the resistor due to overload. This technical solution can be used in the high-voltage and ultra-high-voltage fields.

[0055] As Figure 4 shown, a kind of AC-DC voltage transformer disclosed by the present invention includes: a high-voltage arm 41 and a low-voltage arm 42, wherein the low-voltage arm 42 includes: a voltage-limiting branch 421, a total voltage sampling branch 422, a DC component sampling branch 423 and an AC component sampling branch 424; among them: the high-voltage arm 41 includes: a first resistor R1 and a first capacitor C1; the total voltage sampling branch 422 includes: a second resistor R2 and a third resistor R3; the AC component sampling branch 424 includes: a second capacitor C2 and a third capacitor C3; the DC component sampling branch 423 includes: a fourth resistor R4, a fifth resistor R5 and a fourth capacitor C4;

[0056] One end of the first resistor R1 is connected to the voltage terminal to be measured, and the other end of the first resistor R1 is connected to the high-voltage end of the low-voltage arm;

[0057] One end of the first capacitor C1 is connected to the voltage terminal to be measured, and the other end of the first capacitor C1 is connected to the high-voltage end of the low-voltage arm;

[0058] One end of the voltage-limiting branch 421 is connected to the high-voltage end of the low-voltage arm, and the other end of the voltage-limiting branch 421 is connected to the low-voltage end of the low-voltage arm;

[0059] One end of the second resistor R2 is connected to the low-voltage end of the high-voltage arm, and the other end of the second resistor R2 is connected to one end of the third resistor R3;

[0060] The other end of the third resistor R3 is grounded;

[0061] One end of the second capacitor C2 is connected to the low-voltage end of the high-voltage arm, and the other end of the second capacitor C2 is connected to one end of the third capacitor C3;

[0062] The other end of the third capacitor C3 is grounded;

[0063] One end of the fourth resistor R4 is connected to the low-voltage end of the high-voltage arm, and the other end of the fourth resistor R4 is respectively connected to one end of the fifth resistor R5 and one end of the fourth capacitor C4;

[0064] The other end of the fifth resistor R5 is grounded;

[0065] The other end of the fourth capacitor C4 is grounded.

[0066] In the above embodiment, when measuring the total voltage, the sampled voltage is U56, and the voltage division ratio k can be taken as R1:R3. As Figure 4 shown, the voltage U to be measured is the voltage between nodes 1 and 6, which includes an AC voltage component Uac and a DC voltage component Udc, and U = Uac + Udc. To improve the reliability of the measurement, the measurement channels can be divided into a multi-path parallel structure. As Figure 5 shown, one set of monitoring instruments can be separately connected to both ends of R31, R32, R33, R34, and R35.

[0067] In the AC voltage component sampling branch, the isolation capacitor (second capacitor) C2 and the voltage sampling capacitor (third capacitor) C3 are in series. The isolation capacitor C2 functions to isolate the DC thermal current of the high-voltage arm from entering the sampling voltage capacitor C3. The AC sampled voltage is U36. When measuring the AC voltage, when C1 is much smaller than C2 and C3, and C2 = C3, the AC voltage division ratio k1 can be taken as C3:C1, then To improve the reliability of the device, the measurement channels can be divided into a multi-path parallel structure. As Figure 6 shown, one set of monitoring instruments can be separately connected to both ends of C31, C32, C33, C34, and C35.

[0068] In the DC component sampling branch, the front-end resistor (fourth resistor) R4 and the DC component sampling resistor (fifth resistor) R5 are in series, and the filter capacitor (fourth capacitor) C4 is in parallel with the DC component sampling resistor R5. The filter capacitor C4 functions to remove the AC component part in this branch. The filter capacitor C4 should select an appropriate capacitance value according to the frequency of the AC component in U, and as large as possible should be selected. The advantages of a large capacitor C4 are, first, it can well remove the AC component, and second, it can effectively reduce the peak value of the AC component. The DC component sampled voltage is U46. When measuring the DC voltage, take R1 much larger than R2, R3, R4, and R5, R2 and R3 much larger than R4 and R5, R2 = R3, R4 = R5, and ensure that then the voltage division ratio k2 for DC component measurement can be taken as R1:R3,

[0069] As Figure 7As shown in the figure, a AC / DC voltage transformer disclosed by the present invention includes a high-voltage arm 71 and a low-voltage arm 72. The low-voltage arm 72 includes a voltage limiting branch 721, a total voltage sampling branch 722, a DC component sampling branch 723, and an AC component sampling branch 724. Specifically, the high-voltage arm 71 includes a first resistor R1 and a first capacitor C1; the total voltage sampling branch includes 722 a second resistor R2 and a third resistor R3; the AC component sampling branch 724 includes a second capacitor C2 and a third capacitor C3; the DC component sampling branch 723 includes a sixth resistor R6, a first inductor L1, and a seventh resistor R7;

[0070] One end of the first resistor R1 is connected to the voltage terminal to be measured, and the other end of the first resistor R1 is connected to the high-voltage end of the low-voltage arm;

[0071] One end of the first capacitor C1 is connected to the voltage terminal to be measured, and the other end of the first capacitor C1 is connected to the high-voltage end of the low-voltage arm;

[0072] One end of the voltage limiting branch 721 is connected to the high-voltage end of the low-voltage arm, and the other end of the voltage limiting branch 721 is connected to the low-voltage end of the low-voltage arm;

[0073] One end of the second resistor R2 is connected to the low-voltage end of the high-voltage arm, and the other end of the second resistor R2 is connected to one end of the third resistor R3;

[0074] The other end of the third resistor R3 is grounded;

[0075] One end of the second capacitor C2 is connected to the low-voltage end of the high-voltage arm, and the other end of the second capacitor C2 is connected to one end of the third capacitor C3;

[0076] The other end of the third capacitor C3 is grounded;

[0077] One end of the sixth resistor R6 is connected to the low-voltage end of the high-voltage arm, and the other end of the sixth resistor R6 is connected to one end of the first inductor L1;

[0078] The other end of the first inductor L1 is connected to one end of the seventh resistor R7, and the other end of the seventh resistor R7 is grounded.

[0079] In the above embodiment, when measuring the total voltage, the sampled voltage is U56, and the voltage division ratio k can be taken as R1:R3. As Figure 4 shown, the voltage U to be measured is the voltage between nodes 1 and 6, which includes an AC voltage component Uac and a DC voltage component Udc, and U = Uac + Udc. To improve the reliability of the measurement, the measurement channels can be divided into a multi-path parallel structure. As Figure 5 shown, a set of monitoring instruments can be separately connected to both ends of R31, R32, R33, R34, and R35.

[0080] In the AC voltage component sampling branch, the isolation capacitor (second capacitor) C2 and the voltage sampling capacitor (third capacitor) C3 are connected in series. The isolation capacitor C2 serves to isolate the DC thermal current of the high-voltage arm from entering the sampling voltage capacitor C3. The AC sampling voltage is U36. When measuring the AC voltage, when C1 is much smaller than C2 and C3, and C2 = C3, the AC voltage division ratio k1 can be taken as C3:C1. Then To improve the reliability of the device, the measurement channels can be divided into a multi-parallel structure. For example Figure 6 As shown, one set of monitoring instruments can be separately connected to both ends of C31, C32, C33, C34, and C35.

[0081] In the DC component sampling branch, the front-end resistor (sixth resistor) R6, the isolation inductor (first inductor) L1, and the DC component sampling resistor (seventh resistor) R7 are connected in series. The isolation inductor L1 serves to isolate the AC thermal current of the high-voltage arm from entering the sampling resistor R7. The isolation inductor L1 needs to select an appropriate inductance value according to the frequency of the AC component in U to play a good role in isolating the AC. The DC component sampling voltage is U46. When measuring the DC voltage, when R1 is much larger than R2, R3, R6, and R7, R2 and R3 are much larger than R6 and R7, R2 and R3 are equal, and R6 and R7 are equal, the DC voltage division ratio is approximately R1 / R3, Udc≈U46×(R1 / R3), and it is ensured that R1×C1≈(R2 + R3)×(C2×C3) / (C2 + C3).

[0082] It should be noted that the output of the low-voltage arm in the AC-DC voltage transformer provided by the present invention can also be sampled by a collector and converted into a digital quantity, and the digital quantity is transmitted to the merging unit or the control and protection device through an optical fiber.

[0083] In summary, the present invention can directly monitor the total voltage value of the voltage to be measured and the analog voltage signals corresponding to its DC voltage component and AC voltage component, which is simple and easy to test, and does not require secondary equipment to collect and process data. In addition, the high-voltage arm is a resistor-capacitor voltage division structure, and the capacitors therein can equalize the voltage under lightning impulse voltage and switching impulse voltage, evenly distributing the voltage to the resistors of the high-voltage arm to avoid damage to the resistors due to overload. This technical solution can be used in the high-voltage and ultra-high-voltage fields.

[0084] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0085] Those skilled in the art may further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0086] The steps of the methods or algorithms described in combination with the embodiments disclosed herein can be directly implemented by hardware, software modules executed by a processor, or a combination of the two. The software modules can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0087] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An AC / DC voltage transformer, characterized in that, Comprising: A high-voltage arm and a low-voltage arm, wherein the low-voltage arm includes: a voltage limiting branch, a total voltage sampling branch, a DC component sampling branch, and an AC component sampling branch; where: The high-voltage end of the high-voltage arm is connected to the voltage to be measured terminal, and the low-voltage end of the high-voltage arm is connected to the high-voltage end of the low-voltage arm; The low-voltage end of the low-voltage arm is grounded; One end of the voltage limiting branch is connected to the high-voltage end of the low-voltage arm, and the other end of the voltage limiting branch is connected to the low-voltage end of the low-voltage arm; One end of the total voltage sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the total voltage sampling branch is connected to the low-voltage end of the low-voltage arm; One end of the DC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the DC component sampling branch is connected to the low-voltage end of the low-voltage arm; One end of the AC component sampling branch is connected to the high-voltage end of the low-voltage arm, and the other end of the AC component sampling branch is connected to the low-voltage end of the low-voltage arm; The AC component sampling branch includes: a second capacitor and a third capacitor; where: One end of the second capacitor is connected to the low-voltage end of the high-voltage arm, and the other end of the second capacitor is connected to one end of the third capacitor; The other end of the third capacitor is grounded.

2. The AC-DC voltage transformer according to claim 1, wherein The high-voltage arm includes: a first resistor and a first capacitor; where: The first resistor is connected in parallel with the first capacitor; One end of the first resistor is connected to the voltage to be measured terminal, and the other end of the first resistor is connected to the high-voltage end of the low-voltage arm; One end of the first capacitor is connected to the voltage to be measured terminal, and the other end of the first capacitor is connected to the high-voltage end of the low-voltage arm.

3. The AC / DC voltage transformer according to claim 1, wherein The high-voltage arm is composed of a plurality of resistor-capacitor units connected in series, where each resistor-capacitor unit is composed of a resistor and a capacitor connected in parallel.

4. The AC-DC voltage transformer according to claim 2 or 3, characterized in that, The total voltage sampling branch includes: a second resistor and a third resistor; where: One end of the second resistor is connected to the low-voltage end of the high-voltage arm, and the other end of the second resistor is connected to one end of the third resistor; The other end of the third resistor is grounded.

5. The AC / DC voltage transformer according to claim 2 or 3, characterized in that, The DC component sampling branch includes: a fourth resistor, a fifth resistor, and a fourth capacitor; where: One end of the fourth resistor is connected to the low-voltage end of the high-voltage arm, and the other end of the fourth resistor is respectively connected to one end of the fifth resistor and one end of the fourth capacitor; The other end of the fifth resistor is grounded; The other end of the fourth capacitor is grounded.

6. The AC-DC voltage transformer according to claim 2 or 3, characterized in that, The DC component sampling branch includes: a sixth resistor, a first inductor, and a seventh resistor; where: One end of the sixth resistor is connected to the low-voltage end of the high-voltage arm, and the other end of the sixth resistor is connected to one end of the first inductor; The other end of the first inductor is connected to one end of the seventh resistor, and the other end of the seventh resistor is grounded.

7. The AC-DC voltage transformer according to claim 1, characterized in that, The output of the low-voltage arm is sampled by a collector and converted into a digital quantity, and the digital quantity is transmitted to a merging unit or a control and protection device through an optical fiber.

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