Series resonance test device based on inductor voltage measurement

Abstract

The invention discloses a series resonance test device based on inductor voltage measurement, and relates to the technical field of measurement. The invention relates to a variable-frequency power supply, which comprises a variable-frequency power supply, an exciting transformer, a voltage signal measuring unit, a voltage transformer, a current signal measuring unit, a current transformer and a resonance reactor, and is characterized in that the variable-frequency power supply comprises a main control unit, a frequency adjusting unit and a driving output unit, and sweep frequency through the frequency adjusting unit and the driving output unit; a current amplitude-frequency characteristic curve can be measured and obtained through the current signal measuring unit and the current transformer, the resonance angular frequency and two frequency values when the amplitude is reduced by 3dB are obtained based on the current amplitude-frequency characteristic curve, and then a quality factor can be calculated and obtained; the voltage at the tap of the resonance reactor can be measured and obtained through the voltage transformer, and then the voltage on the test capacitor can be calculated and obtained. As a capacitive voltage divider and a grading ring are omitted, the trouble caused by installation and disassembly of the capacitive voltage divider and the grading ring in field tests is solved, and the working efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of measurement technology, and in particular to a series resonance test device based on inductive voltage. Background Technology

[0002] In high-voltage AC power testing, compared with traditional power frequency withstand voltage testing, series resonant testing has lower power supply capacity requirements and is easier to assemble, thus gaining widespread use in the industry since the 1990s. The series resonant test equipment consists of: a frequency and amplitude adjustable power supply, an excitation transformer, a resonant reactor, a resonant test capacitor, and a sampling capacitor voltage divider. When the frequency of the power supply output matches the natural frequency of the series circuit composed of the resonant reactor and resonant capacitor, the circuit resonates, resulting in a high voltage on the capacitive test specimen, which can reach several hundred to over 1000 kV. Given a fixed active power of the frequency converter, the reactive power obtainable on the capacitive test specimen depends on the quality factor Q of the circuit system, and its power is Q times the active power output of the power supply. Because the test power is amplified, this test system can meet relatively large capacity requirements. Due to its performance advantages, the series resonant test system is widely used in the power industry, including for GIS, circuit breakers, generator stator windings, motors, instrument transformers, and other equipment, as well as for withstand voltage testing of cables and other large-capacity equipment.

[0003] A high-voltage capacitive voltage divider consists of a high-voltage arm capacitor and a low-voltage arm capacitor. To reduce the withstand voltage of each capacitor, the high-voltage arm capacitor is often composed of multiple capacitor units connected in series, while the low-voltage arm typically has only one capacitor. These capacitors are assembled using a balanced equipotential shielding structure. One end of the low-voltage arm capacitor is connected to the lower end of the high-voltage arm, and the other end is grounded. In the experiment, the high-voltage capacitive voltage divider is connected in parallel with the capacitive test object, with one end grounded and the other end connected to the high voltage generated by circuit resonance. In the experiment, the voltage division of the series capacitors is used to sample from the low-voltage arm, and the high voltage is calculated according to the capacitive reactance voltage division ratio. This is currently the method for calculating the high voltage in series resonance tests.

[0004] Depending on the voltage level and design structure, high-voltage capacitor dividers are typically several meters to over ten meters long and weigh hundreds of kilograms to tons. The equalizing ring on top of the divider can have a diameter of up to 5 meters and weigh several hundred kilograms. Such large size and weight of the divider and its equalizing ring pose considerable difficulties for the assembly and disassembly of the series resonant withstand voltage field test equipment.

[0005] Therefore, the voltage U across the capacitor C of the test sample is measured. C Low work efficiency has become a technical problem that urgently needs to be solved. Summary of the Invention

[0006] This invention provides a series resonant test device based on inductive voltage, which solves the problem of measuring the voltage U across the capacitor C of the test sample.C The technical problem of low work efficiency.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A series resonant test device based on inductive voltage includes a frequency converter, an excitation transformer, a voltage signal measurement unit, a voltage transformer (PT), a current signal measurement unit, a current transformer (CT), and a resonant reactor (L). The frequency converter includes a main control unit, a frequency adjustment unit, and a drive output unit. The main control unit is electrically connected to each of the voltage signal measurement unit, current signal measurement unit, frequency adjustment unit, and drive output unit. The frequency adjustment unit is electrically connected to the drive output unit. The drive output unit is electrically connected to the primary winding of the excitation transformer. The resonant reactor (L) and the secondary winding of the excitation transformer are connected in series with the test sample capacitor (C) during measurement. The connection point between the test sample capacitor (C) and the secondary winding of the excitation transformer is grounded. The current transformer (CT) is electrically connected to the current signal measurement unit and is used to obtain the current in the secondary winding of the excitation transformer. The voltage transformer (PT) is electrically connected to the voltage signal measurement unit and is used to obtain the voltage at the tap of the resonant reactor (L).

[0009] A further technical solution includes a measurement module, which is a program module installed on the main control unit. This module is used to obtain the tap voltage division ratio K of the resonant reactor L, obtain the quality factor Q, obtain the voltage U1 at the tap of the resonant reactor L, and calculate the voltage U on the test sample capacitor according to equation (9). C ;

[0010]

[0011] In equation (9), U C U1 is the voltage across the capacitor of the test sample; K is the voltage division ratio of the reactor tap; Q is the quality factor; U1 is the voltage at the tap of the resonant reactor measured by the voltage transformer PT.

[0012] A further technical solution is that the measurement module is also used to obtain the tap voltage division ratio K of the resonant reactor L, which is pre-inputted and calibrated at the factory.

[0013] A further technical solution is that the measurement module is also used to sweep the frequency through the frequency adjustment unit and the drive output unit, measure the current amplitude-frequency characteristic curve through the current signal measurement unit and the current transformer CT, obtain the resonant angular frequency ω0 and the two frequency values ​​ω2 and ω1 when the amplitude drops by 3dB based on the current amplitude-frequency characteristic curve, and calculate the quality factor Q according to formula (5).

[0014]

[0015] In equation (5), Q is the quality factor, ω0 is the resonant angular frequency, and ω2-ω1 is the 3dB bandwidth.

[0016] A further technical solution is that the measurement module is also used to receive the voltage U1 at the tap of the resonant reactor L, which is obtained by the voltage transformer PT and sent by the voltage signal measurement unit.

[0017] A further technical solution includes: a test capacitor C, a resonant reactor L, the secondary winding of the excitation transformer, and the test capacitor C connected in series.

[0018] The beneficial effects of adopting the above technical solution are as follows:

[0019] A series resonant test device based on inductive voltage includes a frequency converter, an excitation transformer, a voltage signal measurement unit, a voltage transformer (PT), a current signal measurement unit, a current transformer (CT), and a resonant reactor (L). The frequency converter includes a main control unit, a frequency adjustment unit, and a drive output unit. The main control unit sweeps the frequency through the frequency adjustment unit and the drive output unit. The current signal measurement unit and the current transformer (CT) can measure and obtain the current amplitude-frequency characteristic curve. Based on the current amplitude-frequency characteristic curve, the resonant angular frequency ω0 and two frequency values ​​ω2 and ω1 when the amplitude drops by 3dB are obtained, and the quality factor Q can be calculated. The voltage U1 at the tap of the resonant reactor L can be measured through the voltage transformer (PT), and the voltage U across the test sample capacitor can be calculated. C Because it eliminates the need for capacitor voltage dividers and their equalizing rings, it solves the problems associated with the installation and disassembly of capacitor voltage dividers and their equalizing rings in field testing, reduces the labor intensity of field testing and installation, and improves work efficiency. Attached Figure Description

[0020] Figure 1 This is the schematic diagram of an RLC series circuit;

[0021] Figure 2 This is a block diagram of the series resonance test device;

[0022] Figure 3 It is a vector diagram showing the voltage vector relationship between R and L in a resonant reactor;

[0023] Figure 4 This is a flowchart of the inductive voltage divider method for measurement. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0026] Example 1:

[0027] like Figure 2 As shown, this invention discloses a series resonant test device based on inductive voltage, including a frequency converter, an excitation transformer, a voltage signal measurement unit, a voltage transformer (PT), a current signal measurement unit, a current transformer (CT), a resonant reactor (L), a test capacitor (C), and a measurement module. The frequency converter includes a main control unit, a frequency adjustment unit, and a drive output unit. The main control unit is electrically connected to the voltage signal measurement unit, the current signal measurement unit, the frequency adjustment unit, and the drive output unit, respectively. The frequency adjustment unit is electrically connected to the drive output unit. The drive output unit is electrically connected to the primary winding of the excitation transformer. The resonant reactor (L), the test capacitor (C), and the secondary winding of the excitation transformer are connected in series. The junction of the test capacitor (C) and the secondary winding of the excitation transformer is grounded. The current transformer (CT) is electrically connected to the current signal measurement unit and is used to obtain the current in the secondary winding of the excitation transformer. The voltage transformer (PT) is electrically connected to the voltage signal measurement unit and is used to obtain the voltage at the tap of the resonant reactor (L).

[0028] The measurement module is used to obtain the tap division ratio K of the resonant reactor L, which is pre-calibrated at the factory; it sweeps the frequency through the frequency adjustment unit and the drive output unit, and obtains the current amplitude-frequency characteristic curve through the current signal measurement unit and the current transformer CT; based on the current amplitude-frequency characteristic curve, it obtains the resonant angular frequency ω0 and the two frequency values ​​ω2 and ω1 when the amplitude drops by 3dB; it calculates the quality factor Q according to equation (5); it receives the voltage U1 at the tap of the resonant reactor L obtained by the voltage transformer PT and sent by the voltage signal measurement unit; and it calculates the voltage U on the test capacitor according to equation (9). C .

[0029] The measurement module is a program module installed on the main control unit. After the measurement operation is started, the main control unit runs the measurement module, and accordingly controls the frequency adjustment unit, drive output unit, voltage signal measurement unit, and current signal measurement unit to work, measuring and obtaining the voltage U across the sample capacitor C. C .

[0030] The work process is described below.

[0031] like Figure 4 As shown, based on the series resonant test device, the measurement module is run to obtain the voltage U across the capacitor C of the test sample. C The process includes the following steps:

[0032] Step S1: Obtain the tap division ratio K of the resonant reactor L, which was pre-calibrated at the factory.

[0033] Step S2: The main control unit sweeps the frequency through the frequency adjustment unit and the drive output unit. The main control unit obtains the current amplitude-frequency characteristic curve by measuring the current signal measurement unit and the current transformer CT. Based on the current amplitude-frequency characteristic curve, the resonant angular frequency ω0 and the two frequency values ​​ω2 and ω1 when the amplitude drops by 3dB are obtained. The quality factor Q is calculated according to Equation (5).

[0034] Step S3: The voltage U1 at the tap of the resonant reactor L is obtained by the voltage transformer PT and then communicated to the main control unit via the voltage signal measurement unit.

[0035] Step S4: The main control unit obtains the voltage U1 at the tap of the resonant reactor L, and calculates the voltage U on the test capacitor according to equation (9). C .

[0036] Example 2:

[0037] Example 2 differs from Example 1 in that it also includes a display for displaying measurement data.

[0038] This invention discloses a series resonant test device based on inductive voltage, including a frequency converter, an excitation transformer, a voltage signal measurement unit, a voltage transformer PT, a current signal measurement unit, a current transformer CT, a resonant reactor L, a test sample capacitor C, a display, and a measurement module. The main control unit is electrically connected to the display, and the similarities will not be repeated.

[0039] The technical solution of this application eliminates the need for a capacitor voltage divider and its equalizing ring, solving the problems associated with the installation and disassembly of capacitor voltage dividers and their equalizing rings in on-site testing, reducing the labor intensity of on-site installation, and improving work efficiency. After debugging and testing, the device meets the standards for series resonant high-voltage testing.

[0040] This application comprehensively considers the many factors affecting high-voltage calculation using the inductive voltage divider method. Starting from basic circuit theory, it derives a theoretical formula for calculating the test voltage at the capacitive test specimen from the inductor tap voltage. Based on this theoretical formula, it constructs a program design framework for calculating the test voltage at the test specimen. This program framework includes calculation modules that need to consider many factors. Ultimately, it can accurately and in real-time measure the test voltage during the series resonant high-voltage test, thus achieving the design goal of the inductive voltage divider method.

[0041] The theoretical derivation and technical analysis of the inductive voltage divider method are explained below.

[0042] like Figure 1 The diagram shown is a schematic of an RLC series circuit. In theoretical derivation, the schematic of the series resonant experimental circuit can be equivalent to the RLC series circuit shown in the diagram. It is the output voltage of the excitation transformer. Because the coil wires of the reactor contain internal resistance, it is equivalent to a series connection of a resistor R and an inductor L. The capacitive test specimen is the capacitor C in the figure.

[0043] 1. The approach to determining the test voltage using the inductive voltage divider method.

[0044] The approach to solving the voltage across capacitor C using the inductor voltage divider method is explained below.

[0045] The first step is to find the voltage across the equivalent inductance L. Test voltage on capacitor C of the test sample The relationship between them.

[0046] like Figure 1 As shown, based on existing conclusions, the resonance diagram contains:

[0047]

[0048] In equation (1), Where L is the voltage across the equivalent inductance, and Q is the quality factor. It is the output voltage of the excitation transformer.

[0049]

[0050] In equation (2), The test voltage is applied to capacitor C of the test sample.

[0051] Comparing equations (1) and (2), we have:

[0052]

[0053] Test voltage on capacitor C of the test sample Voltage across the equivalent inductance L The effective values ​​are equal. Therefore, even though L is not grounded, once the voltage across L is known, the voltage across the capacitor C of the test sample can be determined, and this voltage is the test voltage that needs to be calculated.

[0054] The second step is to measure the voltage across the reactor.

[0055] like Figure 1 As shown, the resonant inductor used in the series resonance test is called a reactor. Because the reactor coil has internal resistance, the reactor is equivalent to two elements R and L in the diagram. In actual measurement, a sample is taken at the reactor tap to measure the low voltage of the reactor, obtaining the measured voltage. Then, based on the measured voltage, the calculated voltage across the reactor is obtained proportionally. At this point, the calculated voltage across the reactor is not the voltage across the equivalent inductor L in the diagram. Because the reactor contains pure resistance R, the calculated voltage across the reactor is the vector superposition of the voltages across the equivalent resistance (pure resistance) R and the equivalent inductance (pure inductance) L. The effective value of the voltage across the equivalent inductance L is equal to the effective value of the voltage across the capacitor C. Therefore, by separating the voltages across the equivalent R and equivalent L in the reactor, the effective value of the voltage across the capacitor C can be calculated.

[0056] The third step is to calculate the voltage across the equivalent inductance L from the calculated voltage across the reactor.

[0057] To strip the voltage across R and L in the reactor, the circuit system quality factor Q is used. According to the definition of Q, Q equals the ratio of the peak energy stored in the circuit to the energy consumed by the circuit in one cycle at resonance, i.e.:

[0058] Q=ω0L / R (4)

[0059] In equation (4), Q is the quality factor, ω0 is the resonant angular frequency, the equivalent inductance is L, and the equivalent resistance is R.

[0060] Since the voltage across the equivalent resistance R and the equivalent inductance L has a 90° phase difference, and given the ratio of their reactances Q, the effective value of the voltage across the equivalent inductance L can be determined by vector superposition.

[0061] The fourth step is to measure the Q value of the series circuit.

[0062] The Q value is a key parameter for calculating the voltage across the equivalent resistance R and equivalent inductance L of the stripped reactor, and also a key parameter for calculating the test voltage across the test sample capacitance C. The Q value can be calculated from the perspective of frequency selectivity, specifically using the 3dB bandwidth in the amplitude-frequency response.

[0063] like Figure 1 As shown, if the resonant angular frequency ω0 of the series circuit is measured and the 3dB bandwidth is ω2-ω1, then:

[0064]

[0065] In equation (5), Q is the quality factor, ω0 is the resonant angular frequency, and ω2-ω1 is the 3dB bandwidth.

[0066] Since ω0 is the frequency at resonance, it can be measured by the relative value of the amplitude. ω2 and ω1 are two frequency values ​​when the amplitude drops by 3dB. The amplitude is also a relative value, so it can be measured when there is no calibrated voltage, and the measured Q value is used for voltage calibration.

[0067] 2. Calculation formula for inductor voltage divider method.

[0068] like Figure 2 The diagram shown is a block diagram of a series resonant test circuit designed according to the four-step approach described above. The diagram uses two transformers: a current transformer (CT) and a voltage transformer (PT). The CT is used to measure the high-voltage current, while the PT directly measures the tap voltage of the reactor and indirectly measures the voltage U′ across the resonant reactor. L A sample is taken from the tap of the resonant reactor L, and the signal enters the PT1 input terminal of the voltage transformer PT. The voltage at the tap of the resonant reactor is measured by the voltage transformer PT as U1. The voltage division ratio of the reactor tap is K. Then, the voltage across the resonant reactor is obtained:

[0069] U′ L =KU1 (6)

[0070] In equation (6), U′ L U1 is the voltage across the resonant reactor, K is the tap division ratio of the reactor, and U1 is the voltage at the tap of the resonant reactor measured by the voltage transformer PT.

[0071] Since a reactor is a composite of equivalent resistance R and equivalent inductance L, U′ in equation (6) L It is the result of the superposition of the voltage across the equivalent resistance R and the voltage across the equivalent inductance L.

[0072] like Figure 3 As shown, since the voltages on the equivalent resistance R and the equivalent inductance L have different phases, the superposition should be a vector superposition. Furthermore, the voltage phase on the equivalent resistance R and the voltage phase on the equivalent inductance L are 90° apart. Therefore, this vector superposition can be represented by the right triangle in the figure.

[0073] like Figure 3 As shown, U′ L It is the voltage across the resonant reactor, U L U is the voltage across the equivalent pure inductor L in the resonant reactor. RIt is the voltage across the equivalent pure resistance R in the resonant reactor. The equivalent pure inductance is the same as the equivalent inductance, and the equivalent pure resistance is the same as the equivalent resistance. The voltage U across the pure inductance is... L It is the final required voltage, which is equal to the voltage U across the capacitor of the test sample. C .

[0074] Since the current flowing through R and L is equal, U L with U C The ratio is equal to the ratio of their inductive reactance to their impedance. Using equation (4) again, we have:

[0075]

[0076] In equation (7), U L U is the voltage across the equivalent inductance L of the resonant reactor. R It is the voltage across the equivalent resistance R of the resonant reactor.

[0077] Using formula (7) and Figure 3 The relationship between the right triangles in the diagram can be obtained as follows:

[0078]

[0079] In equation (8), U L It is the voltage across the equivalent inductance L of the resonant reactor, U′ L It is the voltage across the resonant reactor, Q is the quality factor, and U is the voltage across the resonant reactor. L 、U′ L All are effective voltage values.

[0080] Using equations (3) and (6) again, the voltage across the capacitor of the sample can finally be obtained as follows:

[0081]

[0082] In equation (9), U C The voltage across the capacitor of the test sample is given by: K is the tap division ratio of the reactor, which is a calibrated parameter; Q is the quality factor; U1 is the voltage at the tap of the resonant reactor measured by the voltage transformer PT; Q and U1 are quantities that need to be measured in the test.

[0083] like Figure 4 As shown, based on the preceding theoretical derivation, the inductive voltage divider method for measuring voltage includes the following steps.

[0084] Step (1): Calibrate reactor K.

[0085] like Figure 4As shown, the voltage division ratio K of the reactor taps needs to be calibrated before the equipment leaves the factory. Calibration is performed by the equipment manufacturer using existing calibration equipment, such as a series resonant system with a standard voltage divider, at the corresponding voltage level. The calibration process is the reverse of the measurement process during actual use of the equipment; that is, the voltage U across the capacitor sample is measured using the standard voltage divider. C The voltage U1 measured by the voltage transformer is used to calculate the K value using equation (9) based on the Q value of the calibration equipment.

[0086] Step (2): Scan frequency to measure the Q value of the system.

[0087] like Figure 4 As shown, when performing high-voltage measurements after the equipment leaves the factory, the key to obtaining high-voltage data is to measure the Q value of the new system after adding the capacitive sample. The system uses frequency sweep to measure the Q value, calculated by equation (5). In equation (5), the 3dB bandwidth refers to the fact that there are two frequencies on the system's amplitude-frequency characteristic curve, and the current amplitude of these frequencies is the peak current. The difference between these two frequencies is the 3dB bandwidth. When sweeping the frequency of the system, a voltage is preset first, and the current amplitude-frequency characteristic curve is obtained by sweeping the frequency. Based on the correspondence between current and frequency on the curve, the Q value is calculated.

[0088] Step (3): Measure the output U1 of the current transformer.

[0089] like Figure 4 As shown, after obtaining the Q value through frequency sweeping, the current transformer output voltage U1 is obtained based on the measurement.

[0090] Step (4): Calculate the voltage of the sample.

[0091] The high pressure on the sample is calculated according to formula (9).

[0092] This application proposes a series resonant high-voltage testing device based on inductive voltage division. This device utilizes inductive voltage division to measure the high voltage across the sample capacitor, eliminating the need for a standard capacitor voltage divider required in series resonant tests and greatly simplifying AC high-voltage field testing. This application is based on rigorous theoretical calculations, which then guide the design of the testing device. The device design incorporates innovative hardware combinations, and the innovative measurement steps are programmed into modules based on theoretical results. After equipment debugging and operation, ideal measurement accuracy is achieved.

Claims

1. An inductance-based pressure sensing series resonant test device, characterized by: The variable frequency power supply includes a main control unit, a frequency adjusting unit and a driving output unit, the main control unit is respectively and individually connected with the voltage signal measuring unit, the current signal measuring unit, the frequency adjusting unit and the driving output unit, the frequency adjusting unit is connected with the driving output unit, the driving output unit is connected with the primary side coil of the excitation transformer, the resonant reactor L and the secondary side coil of the excitation transformer are used to be connected in series with the test capacitor C during measurement, the test capacitor C is grounded at the joint with the secondary side coil of the excitation transformer, the current transformer CT is connected with the current signal measuring unit, the current transformer CT is used to obtain the current in the secondary side coil of the excitation transformer, the voltage transformer PT is connected with the voltage signal measuring unit, and the voltage transformer PT is used to obtain the voltage at the tap of the resonant reactor L.

2. The series resonant test device based on inductive pressure sensing of claim 1, wherein: Also included is a measurement module, which is a program module installed on the main control unit, for obtaining a tap voltage division ratio K of the resonance reactor L, obtaining a quality factor Q, obtaining a voltage U1 at the tap of the resonance reactor L, and calculating a voltage U on the test capacitor according to formula (9) C ; In formula (9), U C is the voltage on the test capacitor; K is the ratio of the reactor tap voltage division; Q is the quality factor; U1 is the voltage at the resonance reactor tap measured by the voltage transformer PT.

3. A series resonant test device based on inductive pressure sensing according to claim 2, characterized in that: The measurement module is further used to obtain the tap voltage division ratio K of the resonant reactor L pre-factory calibrated in advance.

4. The series resonant test device based on inductive pressure sensing of claim 2, wherein: The measurement module is further used to sweep frequency through the frequency adjusting unit and the driving output unit, measure the current amplitude-frequency characteristic curve through the current signal measuring unit and the current transformer CT, obtain the resonant angular frequency ω0 and the two frequency values ω2 and ω1 when the amplitude drops by 3dB based on the current amplitude-frequency characteristic curve, and calculate the quality factor Q according to formula (5). In formula (5), Q is the quality factor, ω0 is the resonant angular frequency, and ω2-ω1 is the 3dB bandwidth.

5. The series resonant test device based on inductive pressure sensing of claim 2, wherein: The measurement module is further used to receive the voltage U1 at the tap of the resonant reactor L sent by the voltage signal measuring unit after the voltage transformer PT is measured.

6. The series resonant test device based on inductive pressure sensing of claim 1, wherein: The test capacitor C is further included, and the resonant reactor L, the secondary side coil of the excitation transformer and the test capacitor C are connected in series.

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