A voltage measuring device of a three-phase voltmeter combined with a front-end voltage reduction circuit

Abstract

This application provides a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit. The front-end step-down circuit includes a first voltage divider branch, a second voltage divider branch, and a third voltage divider branch, each connected to the three-phase voltage branch being measured. The voltages at the first voltage divider point of the first voltage divider branch, the second voltage divider point of the second voltage divider branch, and the third voltage divider point of the third voltage divider branch are all within the range of the three-phase voltmeter. The first voltage divider point is connected to the first input point of the three-phase voltmeter, the second voltage divider point is connected to the second input point of the three-phase voltmeter, and the third voltage divider point is connected to the third input point of the three-phase voltmeter. Through the above connection method, this application uses a front-end step-down method with a three-phase star voltage divider network for measuring three-phase voltmeters. The voltage of each phase is reduced to the range before being connected to the input point. The center point of the three-phase star voltage divider network does not need to be grounded, ensuring accurate measurement of high voltages while maintaining safety.

Description

Technical Field

[0001] This application relates to the field of voltage measurement instrument application technology, specifically to a voltage measurement device for a three-phase voltmeter combined with a front-end step-down circuit. Background Technology

[0002] Three-phase voltmeters are widely used as electrical energy metering devices. From the perspective of connection method, three-phase voltmeters are divided into three-phase three-wire voltmeters and three-phase four-wire voltmeters. General-purpose three-phase voltmeters can only directly measure voltage within their range. When measuring high-voltage power at the power frequency exceeding this range, a voltage transformer is required. However, when the output of a high-voltage frequency converter is a PWM pulse wave, a voltage transformer cannot be used. There are two main reasons: (1) The high carrier frequency of the PWM pulse wave causes large iron losses in the voltage transformer, resulting in severe heat generation and potential danger. (2) In applications such as power analysis and waveform recording, the measurement results need to faithfully reflect the original voltage changes. However, voltage transformers have an inductive effect, affecting both phase and amplitude, which can cause measurement distortion. Therefore, some existing technologies employ a voltage divider method, connecting the high voltage to a voltage divider circuit. The voltage after voltage division falls within the range of the three-phase voltage, and the voltage signal after voltage division is input to the three-phase voltmeter for measurement. However, existing voltage divider methods, such as… Figure 1 As shown, the voltage divider circuit formed by resistors R1 and R2 requires a reference voltage to ground, but a three-phase voltmeter has no ground wire and cannot be used. Furthermore, coal mine products require that non-safety signals cannot be directly grounded; therefore, the voltage divider method based on ground voltage cannot meet the explosion-proof safety requirements of coal mines. In addition to the above solutions, existing technology also provides a method of current limiting by connecting a large-resistance electrical component in series between the input terminals of the three-phase voltmeter and the power supply being measured, such as... Figure 2 As shown, once resistor R82 is open-circuited, the voltage at the voltage divider node between R81 and R82 is the same as the voltage of phase L3. The three-phase voltmeter will have a high voltage that far exceeds its range, posing a risk of electric shock to people and equipment and creating a great safety hazard. Utility Model Content

[0003] The technical problem this application aims to solve is that existing three-phase voltmeters are difficult to apply in high-voltage measurement scenarios due to either the need for grounding or the existence of high safety risks. Therefore, this application provides a voltage measurement device for a three-phase voltmeter combined with a front-end step-down circuit.

[0004] This application provides a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit. The front-end step-down circuit includes a first voltage divider branch, a second voltage divider branch, and a third voltage divider branch, which are respectively connected to the three-phase voltage branches being measured.

[0005] The first voltage divider branch includes a first voltage divider element and a second voltage divider element connected in series. The electrical connection point between the first voltage divider element and the second voltage divider element serves as the first voltage divider point. The voltage at the first voltage divider point is within the range of the three-phase voltmeter. The first voltage divider point is connected to the first input point of the three-phase voltmeter.

[0006] The second voltage divider branch includes a third voltage divider element and a fourth voltage divider element connected in series. The electrical connection point of the third voltage divider element and the fourth voltage divider element serves as the second voltage divider point. The voltage of the second voltage divider point is within the range of the three-phase voltmeter. The second voltage divider point is connected to the second input point of the three-phase voltmeter.

[0007] The third voltage divider branch includes a fifth voltage divider element and a sixth voltage divider element connected in series. The electrical connection point of the fifth voltage divider element and the sixth voltage divider element serves as the third voltage divider point. The voltage of the third voltage divider point is within the range of the three-phase voltmeter. The third voltage divider point is connected to the third input point of the three-phase voltmeter.

[0008] Preferably, in some embodiments of the voltage measuring device of a three-phase voltmeter combined with a front-end step-down circuit, the second voltage dividing element in the first voltage dividing branch, the fourth voltage dividing element in the second voltage dividing branch, and the sixth voltage dividing element in the third voltage dividing branch are all electrically connected to a center point, which is connected to the neutral terminal access point inside the three-phase voltmeter.

[0009] Preferably, in some embodiments of the voltage measuring device of a three-phase voltmeter combined with a front-end step-down circuit, the second voltage dividing element in the first voltage dividing branch, the fourth voltage dividing element in the second voltage dividing branch, and the sixth voltage dividing element in the third voltage dividing branch are all electrically connected to a center point, and the center point is connected to the instrument ground terminal access point inside the three-phase voltmeter.

[0010] Preferably, the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit described in some embodiments further includes an isolation transformer:

[0011] The primary side of the isolation transformer is connected to the first voltage dividing point of the first voltage dividing branch, the second voltage dividing point of the second voltage dividing branch, and the third voltage dividing point of the third voltage dividing branch.

[0012] The secondary side of the isolation transformer is connected to the first, second, and third input points of the three-phase voltmeter, and the center point of the secondary side is connected to the neutral terminal or the instrument ground terminal inside the three-phase voltmeter.

[0013] Preferably, in some embodiments, the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit, wherein the voltage ratio of the isolation transformer is adapted according to the voltage division ratio of the first voltage division branch, the second voltage division branch, and the third voltage division branch;

[0014] The voltage turns ratio of the isolation transformer is determined based on the ratio of the impedance of the three-phase voltmeter to the impedance of the front-end step-down circuit.

[0015] Preferably, in some embodiments, the voltage measuring device of a three-phase voltmeter combined with a front-end step-down circuit calibrates the transformation ratio parameter of the three-phase voltmeter by: inputting a set high-voltage signal to the front-end step-down circuit to obtain the output voltage signal of the three-phase voltmeter; and multiplying the ratio of the set high-voltage signal to the output voltage signal by the current transformation ratio parameter of the three-phase voltmeter to obtain the calibrated transformation ratio parameter of the three-phase voltmeter.

[0016] Preferably, in some embodiments, the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit, wherein the set high-voltage signal is a measured value obtained by measuring the input terminal of the front-end step-down circuit using a high-precision AC voltmeter / power analyzer; or, a high-precision voltage source is used to directly output the set high-voltage signal as the given value.

[0017] Preferably, in some embodiments, the voltage measuring device of a three-phase voltmeter combined with a front-end step-down circuit includes at least two electronic components connected in series, comprising the first, third, and fifth voltage divider elements.

[0018] Preferably, in some embodiments, the voltage measuring device of a three-phase voltmeter combined with a front-end step-down circuit includes at least two electronic components connected in parallel, comprising the second, fourth, and sixth voltage divider elements.

[0019] Preferably, in some embodiments of the voltage measuring device of a three-phase voltmeter combined with a front-end step-down circuit, the first, second, third, fourth, fifth, and sixth voltage-dividing elements are all resistive or capacitive elements.

[0020] The technical solution provided in this application has the following technical effects compared with the prior art:

[0021] This application provides a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit. The front-end step-down circuit includes a first voltage divider branch, a second voltage divider branch, and a third voltage divider branch, each connected to the three-phase voltage branch being measured. The voltages at the first voltage divider point of the first voltage divider branch, the second voltage divider point of the second voltage divider branch, and the third voltage divider point of the third voltage divider branch are all within the range of the three-phase voltmeter. The first voltage divider point is connected to the first input point of the three-phase voltmeter, the second voltage divider point is connected to the second input point of the three-phase voltmeter, and the third voltage divider point is connected to the third input point of the three-phase voltmeter. Through the above connection method, this application uses a front-end step-down method with a three-phase star voltage divider network for measuring three-phase voltmeters. The voltage of each phase is reduced to the range before being connected to the input point. The center point of the three-phase star voltage divider network does not need to be grounded, which meets the requirements of the three-phase voltmeter measurement scenario and eliminates safety hazards. It is a device that can accurately measure high voltages while ensuring safety. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a prior art method for measuring high voltage by combining a front-end step-down voltage meter with a three-phase voltmeter.

[0023] Figure 2 This is a schematic diagram of a prior art method for measuring high voltage by connecting a large-value resistor in series between the input terminal and the measured terminal of a three-phase voltmeter to limit current.

[0024] Figure 3 This is a schematic block diagram of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0025] Figure 4 This is a block diagram of the internal structure of a three-phase voltmeter according to one embodiment of this application;

[0026] Figure 5 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0027] Figure 6 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0028] Figure 7 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0029] Figure 8 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0030] Figure 9 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0031] Figure 10 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0032] Figure 11 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0033] Figure 12 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0034] Figure 13 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, according to one embodiment of this application.

[0035] Figure 14 This is a schematic diagram of the connection structure of a voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, as described in one embodiment of this application. Detailed Implementation

[0036] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0037] It is readily understood that, based on the technical solution of this application, various structural and implementation methods can be interchanged by those skilled in the art without altering the essential spirit of this application. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this application and should not be considered as the entirety of this application or as limitations or restrictions on the technical solution of the application.

[0038] This embodiment provides a voltage measurement device for a three-phase voltmeter combined with a front-end step-down circuit, such as... Figure 3 As shown, the front-end step-down circuit works in conjunction with a three-phase voltmeter to measure the voltage of a three-phase three-wire system. The three-phase voltmeter can measure the voltage of both "three-phase three-wire" and "three-phase four-wire" systems. Figure 4 As shown, U1, U2, U3, and UN are voltage measurement input terminals. U1, U2, U3, and UN correspond to the first input point, second input point, third input point, and neutral line terminal connection point, respectively. In a three-phase three-wire connection, the voltage signal is input through U1, U2, and U3; in a three-phase four-wire connection, the voltage signal is input through U1, U2, U3, and UN. Figure 5As shown, the front-end step-down circuit includes a first voltage divider branch, a second voltage divider branch, and a third voltage divider branch, each connected to the three-phase voltage branch being measured. Utilizing the voltage divider principle, the three voltage divider branches respectively reduce the three-phase voltages L1, L2, and L3 of the three-phase three-wire system. Each voltage divider branch can employ a resistor voltage divider network, a capacitor voltage divider network, or a hybrid resistor-capacitor voltage divider network, etc. The three voltage divider branches are connected in a star configuration. Specifically: the first voltage divider branch includes a first voltage divider element R11 and a second voltage divider element R12 connected in series. The electrical connection point of the first voltage divider element R11 and the second voltage divider element R12 serves as the first voltage divider point. The voltage at the first voltage divider point is within the range of the three-phase voltmeter, and the first voltage divider point is connected to the first input point U1 of the three-phase voltmeter. The second voltage divider branch includes a third voltage divider element R21 and a fourth voltage divider element R22 connected in series. The electrical connection point serves as the second voltage divider point, and the voltage at the second voltage divider point is within the range of the three-phase voltmeter. The second voltage divider point is connected to the second input point U2 of the three-phase voltmeter. The third voltage divider branch includes a fifth voltage divider element R31 and a sixth voltage divider element R32 connected in series. The electrical connection point of the fifth voltage divider element R31 and the sixth voltage divider element R32 serves as the third voltage divider point, and the voltage at the third voltage divider point is within the range of the three-phase voltmeter. The third voltage divider point is connected to the third input point U3 of the three-phase voltmeter. It can be understood that the voltage divider elements in the above scheme are represented by resistors, but in practical applications, they are not limited to resistors.

[0039] As shown in the diagram, in each voltage divider branch, the portion of the branch between the connection point to the three-phase three-wire system and the voltage divider point is called the high-voltage branch, and the portion between the voltage divider point and the center point is called the low-voltage branch. The voltage divider point is the boundary between the high-voltage and low-voltage branches of the voltage divider branch. The voltage divider components constituting the voltage divider branch can be resistors, capacitors, or a combination of both. The high-voltage and low-voltage branches are each composed of at least one voltage divider component connected in series or parallel. By adjusting the impedance of the voltage divider components in the high-voltage and low-voltage branches, the impedance ratio of the high-voltage and low-voltage branches can be changed, thus controlling the voltage entering the three-phase voltmeter within its range.

[0040] In the above embodiments, the front-end step-down circuit includes a first voltage divider branch, a second voltage divider branch, and a third voltage divider branch, each connected to the three-phase voltage branch being measured. The voltages at the first voltage divider point of the first voltage divider branch, the second voltage divider point of the second voltage divider branch, and the third voltage divider point of the third voltage divider branch are all within the range of the three-phase voltmeter. The first voltage divider point is connected to the first input point U1 of the three-phase voltmeter, the second voltage divider point is connected to the second input point U2 of the three-phase voltmeter, and the third voltage divider point is connected to the third input point U3 of the three-phase voltmeter. Through the above connection method, using the front-end step-down method of a three-phase star voltage divider network, the voltage of each phase is reduced to the range and then connected to the input points of the three-phase voltmeter. The center point of the three-phase star voltage divider network does not need to be grounded, that is, no new loop is created by connecting the center point, avoiding mutual interference between the two systems through the voltage divider network. The above solution can meet the measurement scenario requirements of the three-phase voltmeter and has no safety hazards. It is a device that can accurately measure high voltage while ensuring safety.

[0041] As another feasible solution, such as Figure 6 As shown, in the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit, the second voltage dividing element R12 in the first voltage dividing branch, the fourth voltage dividing element R22 in the second voltage dividing branch, and the sixth voltage dividing element R32 in the third voltage dividing branch are all electrically connected to the center point. The center point is connected to the neutral line terminal access point UN inside the three-phase voltmeter. In this scheme, the center point is connected to the neutral line terminal access point UN. UN can form differential pairs with U1, U2, and U3 inside the three-phase voltmeter. When the voltage of UN deviates due to the three-phase voltage imbalance, the voltage vector difference can be calculated with U1, U2, and U3 by measuring the voltage of UN, thereby improving the measurement accuracy of the three-phase voltmeter.

[0042] As another feasible solution, such as Figure 7 As shown, in the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit, the second voltage-dividing element R12 in the first voltage-dividing branch, the fourth voltage-dividing element R22 in the second voltage-dividing branch, and the sixth voltage-dividing element R32 in the third voltage-dividing branch are all electrically connected to the center point. The center point is connected to the instrument ground terminal G inside the three-phase voltmeter. Using this embodiment, when the three-phase voltmeter uses an isolated power supply to form a floating ground system, the influence of common-mode voltage can be reduced, and the measurement accuracy can be improved. Furthermore, as... Figure 8 As shown, as an alternative to improve measurement security, the center point can also be directly connected to the ground.

[0043] In some embodiments of this application, such as Figure 9As shown, the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit also includes an isolation transformer. The primary side of the isolation transformer is connected to the first voltage dividing point of the first voltage dividing branch, the second voltage dividing point of the second voltage dividing branch, and the third voltage dividing point of the third voltage dividing branch. The secondary side of the isolation transformer is connected to the first input point U1, the second input point U2, and the third input point U3 of the three-phase voltmeter, and the center point of the secondary side is connected to the neutral terminal access point UN inside the three-phase voltmeter. In the above scheme, an isolation transformer is added between each voltage dividing branch of the front-end step-down circuit and the three-phase voltmeter to isolate the potentially dangerous high-voltage system being measured from the accessible three-phase voltmeter. In specific implementation, the secondary side of the isolation transformer adopts a star connection, and the center point of the secondary side of the isolation transformer is connected to the neutral terminal access point UN inside the three-phase voltmeter.

[0044] like Figure 10 As shown, as another preferred embodiment, the secondary side center point of the isolation transformer is connected to the instrument ground terminal. Connecting the secondary side center point of the isolation transformer to the instrument ground can reduce the common-mode voltage input to the three-phase voltmeter and improve measurement accuracy.

[0045] As another preferred option, such as Figure 11 As shown, the center point of the secondary side of the isolation transformer is connected to the neutral terminal UN inside the three-phase voltmeter, and simultaneously connected to the ground. This scheme, by connecting the center point of the secondary side of the isolation transformer to the ground and clamping the voltage at the first input point U1, the second input point U2, and the third input point U3, improves the safety of the measurement process and reduces the insulation requirements of the isolation transformer.

[0046] In the above scheme, the isolation transformer is a three-phase transformer or three single-phase transformers forming a three-phase group with their windings connected at the same voltage. The voltage transformation ratio of the isolation transformer is adapted to the voltage division ratio of the first, second, and third voltage division branches; the voltage transformation ratio of the isolation transformer is determined based on the ratio of the impedance of the three-phase voltmeter to the impedance of the front-end step-down circuit. Specifically, by adjusting the transformation ratio of the isolation transformer, its voltage boosting or bucking can be flexibly achieved, making its coordination with the front-end step-down circuit more flexible. When the isolation transformer bucks the voltage, a higher voltage division point is achieved through each voltage division branch, which can reduce the voltage of the first voltage division element R11, the third voltage division element R21, and the fifth voltage division element R31 or increase the voltage of the second voltage division element R12, the fourth voltage division element R22, and the sixth voltage division element R32, increasing the selection range of each component while also well adapting to the input range of the three-phase voltmeter. Correspondingly, when the isolation transformer steps up the voltage, a lower voltage division point is achieved through each voltage division branch. This reduces the primary input voltage of the isolation transformer, lowers the insulation withstand voltage requirements, and reduces its size. Simultaneously, it can better accommodate the input range of the three-phase voltmeter. Adjusting the transformer's turns ratio allows for flexible impedance matching between each voltage division branch and the three-phase voltmeter. The secondary load impedance Z of the isolation transformer... L2 The formula for converting to the primary side is Z′. L2 =k 2 Z L2 ,in: N1 is the number of turns in the primary winding, and N2 is the number of turns in the secondary winding. Choosing a turns ratio of k > 1 significantly increases the resistance of the three-phase voltmeter's input impedance referred to the primary side of the isolation transformer, thus significantly reducing the current shunt from the voltage divider branches. In this case, larger resistance values ​​such as R11 / R12, R21 / R22, and R31 / R32 can be used to achieve good accuracy. This scheme expands the selection range of voltage divider components in each voltage divider path, and also reduces energy consumption because the current flowing through the voltage divider components is reduced.

[0047] More preferably, to avoid errors from the front-end step-down circuit affecting the measurement results of the three-phase voltmeter, the transformation ratio parameter of the three-phase voltmeter is adjusted by calibration. Specifically, the transformation ratio parameter of the three-phase voltmeter is calibrated as follows: a set high-voltage signal is input to the front-end step-down circuit to obtain the output voltage signal of the three-phase voltmeter; the calibrated transformation ratio parameter of the three-phase voltmeter is obtained by multiplying the ratio of the set high-voltage signal and the output voltage signal by the current transformation ratio parameter of the three-phase voltmeter. This solution eliminates the error caused by the front-end step-down circuit by calibrating the transformation ratio parameter of the three-phase voltmeter, ensuring that the overall measuring device composed of the front-end step-down circuit and the three-phase voltmeter meets the accuracy requirements. To ensure adjustment accuracy, the set high-voltage signal is a measured value obtained by measuring the input terminal of the front-end step-down circuit using a high-precision AC voltmeter / power analyzer; or, a high-precision voltage source is used to directly output the set high-voltage signal as the given value.

[0048] Preferably, to improve the safety performance of the measuring device, the first voltage divider element R11, the third voltage divider element R21, and the fifth voltage divider element R31 include at least two electronic components connected in series. Similarly, the second voltage divider element R12, the fourth voltage divider element R22, and the sixth voltage divider element R32 include at least two electronic components connected in parallel. Figure 12 As shown, the first voltage divider includes R111 and R112 connected in series; the third voltage divider includes R211 and R212 connected in series; and the fifth voltage divider includes R311 and R312 connected in series. The second voltage divider includes R121 and R122 connected in parallel; the fourth voltage divider includes R221 and R222 connected in parallel; and the sixth voltage divider includes R321 and R322 connected in parallel. Figure 12 Only one schematic diagram of the scheme is given in the text. Figure 5 Correspondingly, in practical applications, the same deformation method can also be applied to... Figures 6-11 The voltage divider components forming the high-voltage section collectively bear the voltage required for the high-voltage section. If any one of these components experiences a short-circuit fault, the remaining components in the entire voltage divider branch can still withstand the required voltage. Similarly, in the low-voltage section, the voltage divider components forming the low-voltage section simultaneously bear the required voltage, and if any one of these components experiences an open-circuit fault, the remaining components in the entire voltage divider branch can still withstand the required voltage, ensuring the safety of the measurement process. In practical applications, assuming the required insulation withstand voltage is 3000V, Table 1 provides specific examples of the minimum withstand voltage values ​​required for each resistor in the first voltage divider branch in the event of a single fault, where R121 / / R122 represents the equivalent resistance after R121 and R122 are connected in parallel.

[0049] Table 1. Examples of single-fault resistance value selection

[0050]

[0051] Therefore, resistors with the resistance values ​​shown in Table 2 can be selected to meet the requirement of a withstand voltage greater than the withstand voltage limit.

[0052] Table 2 Resistor Value Selection

[0053] resistance Pressure resistance limit R111 4.00MΩ 2400V R112 5.00MΩ 2500V R121 2.00MΩ 600V R122 2.00MΩ 600V

[0054] The resistance values ​​for other voltage divider branches can be selected with reference to the resistance value selection results for the first voltage divider branch.

[0055] like Figure 13 and Figure 14 As shown, in the voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit, the first voltage divider element, the second voltage divider element, the third voltage divider element, the fourth voltage divider element, the fifth voltage divider element, and the sixth voltage divider element can be either resistive or capacitive. Figure 13 In this system, a full-capacitor approach is used to implement each voltage-dividing branch. By adjusting the capacitive reactance of the high-voltage branch and the low-voltage branch, the voltages entering the three input points of the three-phase voltmeters U1, U2, and U3 can be controlled within the range. Figure 14 In the high-voltage branch circuit, a capacitor is used, and a resistor is used in the low-voltage branch circuit. By adjusting the capacitive reactance of the high-voltage branch circuit and the impedance of the low-voltage branch circuit, the voltages entering the three input points of the three-phase voltmeters U1, U2, and U3 are controlled within the range.

[0056] The solutions described in the above embodiments of this application enable the use of a three-phase voltmeter to measure the voltage of a high-voltage power supply that exceeds its range, while ensuring safety.

[0057] As needed, the above technical solutions can be combined to achieve the best technical effect.

[0058] The above are merely the principles and preferred embodiments of this application. It should be noted that, for those skilled in the art, several other modifications can be made based on the principles of this application, and these modifications should also be considered within the scope of protection of this application.

Claims

1. A voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit, characterized in that: The front-end step-down circuit includes a first voltage divider branch, a second voltage divider branch, and a third voltage divider branch, which are respectively connected to the three-phase voltage branch being measured, wherein: The first voltage divider branch includes a first voltage divider element and a second voltage divider element connected in series. The electrical connection point between the first voltage divider element and the second voltage divider element serves as the first voltage divider point. The voltage at the first voltage divider point is within the range of the three-phase voltmeter. The first voltage divider point is connected to the first input point of the three-phase voltmeter. The second voltage divider branch includes a third voltage divider element and a fourth voltage divider element connected in series. The electrical connection point of the third voltage divider element and the fourth voltage divider element serves as the second voltage divider point. The voltage of the second voltage divider point is within the range of the three-phase voltmeter. The second voltage divider point is connected to the second input point of the three-phase voltmeter. The third voltage divider branch includes a fifth voltage divider element and a sixth voltage divider element connected in series. The electrical connection point of the fifth voltage divider element and the sixth voltage divider element serves as the third voltage divider point. The voltage of the third voltage divider point is within the range of the three-phase voltmeter. The third voltage divider point is connected to the third input point of the three-phase voltmeter.

2. The voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit according to claim 1, characterized in that: The second voltage divider element in the first voltage divider branch, the fourth voltage divider element in the second voltage divider branch, and the sixth voltage divider element in the third voltage divider branch are all electrically connected to the center point, which is connected to the neutral terminal access point inside the three-phase voltmeter.

3. The voltage measuring device of the three-phase voltmeter combined with the front-end step-down circuit according to claim 1, characterized in that: The second voltage divider element in the first voltage divider branch, the fourth voltage divider element in the second voltage divider branch, and the sixth voltage divider element in the third voltage divider branch are all electrically connected to the center point, which is connected to the instrument ground terminal connection point inside the three-phase voltmeter.

4. The voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit according to claim 1, characterized in that, It also includes isolation transformers: The primary side of the isolation transformer is connected to the first voltage dividing point of the first voltage dividing branch, the second voltage dividing point of the second voltage dividing branch, and the third voltage dividing point of the third voltage dividing branch. The secondary side of the isolation transformer is connected to the first, second, and third input points of the three-phase voltmeter, and the center point of the secondary side is connected to the neutral terminal or the instrument ground terminal inside the three-phase voltmeter.

5. The voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit according to claim 4, characterized in that: The voltage ratio of the isolation transformer is adapted to the voltage division ratio of the first voltage division branch, the second voltage division branch, and the third voltage division branch; The voltage turns ratio of the isolation transformer is determined based on the ratio of the impedance of the three-phase voltmeter to the impedance of the front-end step-down circuit.

6. The voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit according to claim 1, characterized in that: The first voltage divider, the third voltage divider, and the fifth voltage divider each include at least two electronic components connected in series.

7. The voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit according to claim 6, characterized in that: The second, fourth, and sixth voltage divider components each include at least two electronic components connected in parallel.

8. The voltage measuring device for a three-phase voltmeter combined with a front-end step-down circuit according to any one of claims 1-7, characterized in that: The first, second, third, fourth, fifth, and sixth voltage divider elements are all resistive or capacitive elements.

Images