Large cross-section conductor ac resistance automatic test system and method

Abstract

The application discloses a large-section conductor alternating current resistance automatic testing system and method, and relates to the electrical testing field.The system comprises a computer, an FPGA / real-time system, a D / A converter 1, a D / A converter 2, a D / A converter 3, an A / D converter, a voltage-controlled current source, electrodes, a GIL conductive pipe sample, a through-type high-precision current transformer, a high-precision resistor R, a lock-in amplifier and a coupling transformer with a load Z.The application eliminates the mutual inductance between a current loop and a voltage testing loop and the influence of the self-inductance of a sample, generates a 90-degree leading current voltage based on an equivalent circuit model through the FPGA and the D / A converter, and is used for compensating the voltage on the self-inductance of the sample and the mutual inductance in the voltage testing loop, reducing the phase angle between the voltage on the measured conductor and the exciting current, solving the precision problem of the large-section conductor alternating current resistance testing, and realizing the accurate and automatic measurement of the large-section conductor alternating current resistance.

Description

Technical Field

[0001] This invention belongs to the field of electrical testing, specifically relating to an automatic testing system and method for the AC resistance of large cross-section conductors. Background Technology

[0002] With the continuous growth of national economic demand for electricity, the current carrying capacity and nominal cross-section of conductors are constantly increasing. Due to the skin effect and proximity effect, the AC resistance of conductors is often much larger than the DC resistance. However, at present, there is no universally accepted method for measuring the AC resistance of large cross-section conductors. Therefore, in order to ensure the safe and reliable operation of large cross-section conductors, it is of great application significance to study the AC resistance measurement technology of large cross-section conductors.

[0003] The conductivity of large-section conductors varies depending on the laying environment, thus affecting their transmission capacity and the reliability of the power system. To test the current-carrying capacity of large-section conductors, their electrical performance parameters need to be measured. Among the many parameters for measuring the performance of large-section conductors, the AC resistance of the conductor can more accurately reflect its conductivity. This is because the current-carrying capacity of a large-section conductor under alternating current is closely related to its AC resistance. The AC resistance of a large-section conductor increases due to the skin effect and proximity effect, leading to a decrease in current-carrying capacity. However, many factors can affect the accuracy of the AC resistance test during the testing process. The most significant influencing factor is that the tested object is a large-section conductor with a large equivalent inductance, resulting in a large phase angle between voltage and current. Approaching 90°, the phase angle can be determined from the function error. This results in a large error in AC resistance, severely affecting its testing accuracy. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide an automatic testing system and method for the AC resistance of large cross-section conductors based on voltage compensation technology. A virtual reference voltage is constructed using FPGA technology and a real-time system based on an equivalent circuit model to compensate for the voltage across the self-inductance of the test sample and the mutual inductance in the voltage test circuit. The virtual reference voltage is updated in real-time by the real-time system, reducing the phase angle between the voltage on the tested conductor and the excitation current, thus solving the problem of testing accuracy for the AC resistance of large cross-section conductors and achieving accurate automated measurement of the AC resistance of large cross-section conductors.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An automatic testing system for AC resistance of large cross-section conductors includes: a computer, an FPGA / real-time system, a D / A converter 1, a D / A converter 2, a D / A converter 3, an A / D converter, a voltage-controlled current source, electrodes, a GIL conductive tube sample, a through-hole high-precision current transformer, a high-precision resistor R, a lock-in amplifier, and a coupling transformer with a load Z.

[0007] The computer is electrically connected to the FPGA / real-time system. The computer is used to send data and control commands to the FPGA / real-time system. The computer is also used to perform data analysis, processing and display on the large cross-section conductor AC resistance automatic testing system.

[0008] The FPGA / real-time system is electrically connected to the D / A converter 1, the D / A converter 2, the D / A converter 3, and the A / D converter, respectively. The FPGA / real-time system is used to receive the digital signals from the A / D converters and is also used to output digital signals to the D / A converter 1, the D / A converter 2, and the D / A converter 3, respectively.

[0009] The D / A converter 1 is used to convert the digital signal output by the FPGA / real-time system into a first analog voltage, and output the first analog voltage to the voltage-controlled current source;

[0010] The D / A converter 2 is used to convert the digital signal output by the FPGA / real-time system into a second analog voltage, and output the second analog voltage to the lock-in amplifier;

[0011] The D / A converter 3 is used to convert the digital signal output by the FPGA / real-time system into a third analog voltage, and output the third analog voltage to the coupling transformer with load Z to achieve voltage compensation;

[0012] The A / D converter is used to convert the analog voltage on the high-precision resistor R into a digital signal and output it to the FPGA / real-time system;

[0013] The voltage-controlled current source is used to convert the first analog voltage signal into an excitation current signal and output the excitation current signal to the GIL conductive tube sample. The voltage-controlled current source, the through-hole high-precision current transformer, and the GIL conductive tube sample form a current loop.

[0014] The electrode is placed on the GIL conductive tube sample and is used to measure the voltage on the GIL conductive tube sample.

[0015] The GIL conductive tube sample is the object under test, and its AC resistance is measured.

[0016] The through-hole type high-precision current transformer is used to convert the current flowing through the GIL conductive tube sample into a small current output to the high-precision resistor R.

[0017] The high-precision resistor R is used to convert the current signal obtained from the through-type high-precision current transformer into a voltage signal and output it to the A / D converter.

[0018] The lock-in amplifier is used to acquire the compensated A-channel voltage signal on the GIL conductive tube sample and output the compensated A-channel voltage signal to the computer via a USB interface.

[0019] The coupling transformer with load Z is used to output the third analog voltage according to the proportional relationship set by the coupling transformer with load Z. The measured voltage is output to the A path of the lock-in amplifier after being differentially divided with the output voltage of the coupling transformer with load Z, thereby realizing the measurement of the compensated voltage signal.

[0020] Preferably, the automatic AC resistance testing system for large cross-section conductors is divided into a voltage testing circuit and a current excitation and testing circuit.

[0021] Preferably, the voltage test circuit includes: electrodes placed on the surface of the conductor, a lock-in amplifier, a coupling transformer with load Z, an FPGA / real-time system, a D / A converter 2, and a D / A converter 3.

[0022] Preferably, the current excitation and its test circuit include: an FPGA / real-time system, a D / A converter 1, a voltage-controlled current source, a GIL conductive tube sample, a through-hole high-precision current transformer, a high-precision resistor R, and an A / D converter.

[0023] Preferably, the FPGA / real-time system includes: a Real-Time (RT) system, an FPGA chassis, and input / output (I / O) modules.

[0024] An automatic testing method for the AC resistance of a large cross-section conductor, applied to the aforementioned automatic testing system for the AC resistance of a large cross-section conductor, includes:

[0025] An equivalent circuit model of a large cross-section conductor is constructed within the FPGA, and a virtual reference is established using the excitation current and computer-assigned parameters.

[0026] A voltage is applied to the voltage-controlled current source through the FPGA and D / A converter 1 to generate current excitation on the GIL conductive tube sample.

[0027] The current excitation is converted into a voltage signal through a through-hole current transformer and a high-precision resistor R. The A / D converter converts it into a digital signal and transmits it to the computer via the FPGA. The computer calculates the effective value of the current and the phase angle.

[0028] A voltage signal with the same frequency as the current is applied to the lock-in amplifier through the FPGA and D / A converter 2. The voltage signal serves as a reference signal for the lock-in amplifier. Based on the reference signal, the lock-in amplifier obtains the initial voltage information on the GIL conductor under test at the same frequency and transmits it to the computer via the USB interface.

[0029] The computer calculates the parameters of the equivalent circuit model using the effective values ​​of the initial voltage and current, as well as the phase angle, and assigns these values ​​to the FPGA to build a virtual reference.

[0030] The FPGA generates an inductive virtual reference voltage that leads the current by 90° based on the real-time excitation current information and the parameter values ​​of the equivalent circuit model. The real-time system ensures the real-time updating of the virtual reference voltage and outputs it to the coupling transformer with load Z through D / A converter 3.

[0031] The coupling transformer with load Z outputs a virtual reference voltage according to the turns ratio, which is applied to the A path of the lock-in amplifier used for voltage acquisition, to achieve voltage differential with the GIL conductor under test;

[0032] The lock-in amplifier acquires the differential voltage, transmits it to the computer via USB interface, and calculates the AC resistance of the tested object.

[0033] An automatic testing method for AC resistance of large cross-section conductors, wherein the equivalent circuit model includes a series connection of resistor and inductor.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) The present invention provides an automatic test system for AC resistance of large cross-section conductors, which uses FPGA technology to have real-time control function and works with a computer to test AC resistance. It has the characteristics of intelligence and high precision.

[0036] (2) The present invention provides an automatic test method for AC resistance of large cross-section conductors. The method is based on an equivalent circuit model and uses FPGA technology and a real-time system to generate a virtual reference voltage to compensate for the voltage on the self-inductance of the test object and the mutual inductance in the circuit. The virtual reference voltage is updated in real time through the real-time system. There is no need to adjust the inductance, so as to achieve automatic compensation, reduce the phase angle between the voltage on the test conductor and the excitation current, solve the test accuracy problem of AC resistance of large cross-section conductors, and realize accurate automatic measurement of AC resistance of large cross-section conductors.

[0037] (3) This method can not only compensate for inductor voltage, but also compensate for voltage when the equivalent circuit model is negative reactance, reduce the phase angle between the voltage on the conductor being measured and the excitation current, thereby achieving accurate automatic measurement and having universality for the equivalent circuit model.

[0038] (4) This method uses current as excitation and employs a through-hole high-precision current transformer and a lock-in amplifier to obtain current and voltage signals on the conductor, which greatly suppresses noise, improves the detection signal-to-noise ratio, and improves the test accuracy. Attached Figure Description

[0039] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0040] Figure 1 This is a schematic diagram of the measurement principle of the automatic AC resistance testing system for large cross-section conductors in this invention.

[0041] Figure 2 This is a schematic diagram of the equivalent circuit of the GIL conductive tube in this invention;

[0042] Figure 3 This is a phasor diagram of the automatic AC resistance testing method for large cross-section conductors in this invention. Detailed Implementation

[0043] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] An automatic testing system for AC resistance of large cross-section conductors includes: a computer, an FPGA / real-time system, a D / A converter 1, a D / A converter 2, a D / A converter 3, an A / D converter, a voltage-controlled current source, electrodes, a GIL conductive tube sample, a through-hole high-precision current transformer, a high-precision resistor R, a lock-in amplifier, and a coupling transformer with a load Z.

[0045] The computer is electrically connected to the FPGA / real-time system. The computer is used to send data and control commands to the FPGA / real-time system. The computer is also used to perform data analysis, processing and display on the large cross-section conductor AC resistance automatic testing system.

[0046] The FPGA / real-time system is electrically connected to the D / A converter 1, the D / A converter 2, the D / A converter 3, and the A / D converter, respectively. The FPGA / real-time system is used to receive the digital signals from the A / D converters and is also used to output digital signals to the D / A converter 1, the D / A converter 2, and the D / A converter 3, respectively.

[0047] The D / A converter 1 is used to convert the digital signal output by the FPGA / real-time system into a first analog voltage, and output the first analog voltage to the voltage-controlled current source;

[0048] The D / A converter 2 is used to convert the digital signal output by the FPGA / real-time system into a second analog voltage, and output the second analog voltage to the lock-in amplifier;

[0049] The D / A converter 3 is used to convert the digital signal output by the FPGA / real-time system into a third analog voltage, and output the third analog voltage to the coupling transformer with load Z to achieve voltage compensation;

[0050] The A / D converter is used to convert the analog voltage on the high-precision resistor R into a digital signal and output it to the FPGA / real-time system;

[0051] The voltage-controlled current source is used to convert the first analog voltage signal into an excitation current signal and output the excitation current signal to the GIL conductive tube sample. The voltage-controlled current source, the through-hole high-precision current transformer, and the GIL conductive tube sample form a current loop.

[0052] The electrode is placed on the GIL conductive tube sample and is used to measure the voltage on the GIL conductive tube sample.

[0053] The GIL conductive tube sample is the object under test, and its AC resistance is measured.

[0054] The through-hole type high-precision current transformer is used to convert the current flowing through the GIL conductive tube sample into a small current output to the high-precision resistor R.

[0055] The high-precision resistor R is used to convert the current signal obtained by the through-type high-precision current transformer into a voltage signal according to a certain ratio, and output it to the A / D converter.

[0056] The lock-in amplifier is used to acquire the compensated A-channel voltage signal on the GIL conductive tube sample and output the compensated A-channel voltage signal to the computer via a USB interface.

[0057] The coupling transformer with load Z is used to output the third analog voltage according to the proportional relationship set by the coupling transformer with load Z. The measured voltage is output to the A path of the lock-in amplifier after being differentially divided with the output voltage of the coupling transformer with load Z, thereby realizing the measurement of the compensated voltage signal.

[0058] The computer obtains the model parameters and AC resistance of the equivalent circuit by acquiring the simulated excitation current signal and obtaining voltage information.

[0059] Furthermore, the automatic AC resistance testing system for large cross-section conductors can be divided into a voltage testing circuit and a current excitation and testing circuit.

[0060] Furthermore, the voltage test circuit includes: electrodes placed on the surface of the conductor, a lock-in amplifier, a coupling transformer with load Z, an FPGA / real-time system, a D / A converter 2, and a D / A converter 3.

[0061] Furthermore, the current excitation and its test circuit include: an FPGA / real-time system, a D / A converter 1, a voltage-controlled current source, a GIL conductive tube sample, a through-hole high-precision current transformer, a high-precision resistor R, and an A / D converter.

[0062] Furthermore, the FPGA / real-time system includes: a Real-Time (RT) system, an FPGA chassis, and input / output I / O modules.

[0063] like Figure 1 As shown, this embodiment consists of a current excitation circuit and its test circuit, and a voltage test circuit. It is applied to the testing of AC resistance of large cross-section conductors. The FPGA / real-time system is a CompactRIO embedded system, and the selected real-time controller is cRIO-9024. The voltage-controlled current source is a voltage-controlled current source based on the Apex PA52A power amplifier. The through-type high-precision current transformer is a Cybertek CTA200 with a current transfer ratio of 1:1000. The high-precision resistor R is a 25Ω non-inductive resistor. The lock-in amplifier is a Signal Recovery 7230 lock-in amplifier. The coupling transformer with load Z is made of permalloy.

[0064] An automatic testing method for the AC resistance of a large cross-section conductor, applied to the aforementioned automatic testing system for the AC resistance of a large cross-section conductor, includes:

[0065] An equivalent circuit model of a large cross-section conductor is constructed within the FPGA, and a virtual reference is established using the excitation current and computer-assigned parameters.

[0066] A voltage is applied to the voltage-controlled current source through the FPGA and D / A converter 1, generating a current excitation effect on the GIL conductive tube sample. The current excitation is converted into a voltage signal through a through-hole current transformer and a high-precision resistor R. The A / D converter converts it into a digital signal and transmits it to the computer via the FPGA. The computer calculates the effective value of the current and the phase angle.

[0067] A voltage signal with the same frequency as the current is applied to the lock-in amplifier through the FPGA and D / A converter 2. The voltage signal serves as a reference signal for the lock-in amplifier. Based on the reference signal, the lock-in amplifier obtains the initial voltage information on the GIL conductor under test at the same frequency and transmits it to the computer via the USB interface.

[0068] The computer calculates the parameters of the equivalent circuit model using the effective values ​​of the initial voltage and current, as well as the phase angle, and assigns these parameters to the FPGA to construct a virtual reference. The FPGA generates an inductive virtual reference voltage with a 90° lead current based on the real-time excitation current information and the parameter values ​​of the equivalent circuit model. The real-time system ensures the real-time updating of the virtual reference voltage and outputs it to the coupling transformer with load Z through D / A converter 3. The coupling transformer with load Z outputs the virtual reference voltage according to the turns ratio, which is applied to the A-path of the lock-in amplifier used for voltage acquisition, realizing the voltage difference with the GIL conductor under test. The lock-in amplifier acquires the differential voltage and transmits it to the computer via the USB interface, and calculates the AC resistance of the tested object.

[0069] Furthermore, the equivalent circuit model can be a resistor and inductor connected in series, a resistor and capacitor connected in parallel, or a resistor and inductor connected in series and then in parallel with a capacitor, etc. Since the large cross-section conductor sample selected in this invention is a GIL conductive tube sample, the equivalent circuit model of this patent is a resistor and inductor connected in series.

[0070] In a specific embodiment, the specific steps of the automatic testing method for the AC resistance of a large cross-section conductor are as follows:

[0071] An equivalent circuit model of a large-section conductor is constructed within the FPGA. In this embodiment, the large-section conductor is equivalent to an inductor L. x and resistance R x For a series circuit, the equivalent circuit model is as follows: Figure 2 As shown; a voltage is applied to the voltage-controlled current source via the FPGA and D / A converter 1, generating current excitation on the GIL conductor; the current collected by the through-hole current transformer is... The voltage signal is obtained through a high-precision resistor R. This signal is converted into a digital signal by an A / D converter and sent to a computer via the FPGA. The computer calculates the effective value of the current and the phase angle. A voltage signal with the same frequency as the current is applied to the lock-in amplifier through the FPGA and the D / A converter 2. This signal serves as the reference signal for the lock-in amplifier. Based on the reference signal, the lock-in amplifier obtains the initial voltage information on the measured GIL conductor at the same frequency. And transmitted to the computer via USB interface; initial voltage information for:

[0072]

[0073] In the formula: R x This is the equivalent resistance of the GIL transistor.

[0074] L x This is the equivalent inductance of the GIL transistor;

[0075] The initial voltage across the GIL transistor;

[0076] R is the equivalent resistance on the GIL transistor. x Apply voltage;

[0077] The equivalent inductance L on the GIL transistor x Apply voltage;

[0078] This represents the current flowing through the GIL transistor.

[0079] The computer calculates the parameters L0 of the equivalent circuit model using the effective values ​​of the initial voltage and current, as well as the phase angle, and assigns these values ​​to the FPGA to construct a virtual reference. The FPGA then generates an inductive virtual reference voltage with a 90° lead current based on the real-time excitation current information and the parameter values ​​of the equivalent circuit model. The real-time system ensures the real-time updating of the virtual reference voltage and outputs it to the coupling transformer with load Z via D / A converter 3. The coupling transformer with load Z outputs the virtual reference voltage according to the turns ratio n:1, which is applied to path A of the lock-in amplifier to obtain the voltage relative to the conductor reactance. Compensation voltage signals of equal magnitude but opposite direction Compensation voltage signal for:

[0080]

[0081] In the formula: The transformer ratio of the coupled transformer with load Z;

[0082] This is the compensation voltage applied to the A-channel of the lock-in amplifier;

[0083] The mutual inductance L between the current loop and the voltage test loop h The voltage on;

[0084] L0 represents the inductance parameters in the virtual conductor model built on the FPGA.

[0085] This achieves the compensation voltage and the voltage difference on the measured GIL conductor; the phasors mentioned above are as follows: Figure 3 As shown, the lock-in amplifier obtains the differential voltage. The data is transmitted to the computer via USB interface, and the AC resistance R of the tested object is obtained. x :

[0086]

[0087] In the formula: U is The modulus;

[0088] I am The modulus;

[0089] for and The phase angle between them;

[0090] To excite the current to flow through the mutual inductance L between the current loop and the voltage test loop h The generated voltage.

[0091] Depend on It can be seen that the AC resistance R of the tested GIL conductive tube can be calculated using the formula for the functional error of system uncertainty. x The relative error is:

[0092]

[0093] In the formula: This represents the relative error of the AC resistance of the GIL conductive tube.

[0094] ΔU is the absolute error of the measured U;

[0095] ΔI is the absolute error of the measured I;

[0096] For measurement Relative error:

[0097] γ U The relative error of the measured U is determined by the performance of the lock-in amplifier;

[0098] γI The relative error of the measured I is determined by the performance of the through-type high-precision current transformer and the accuracy of the high-precision resistor R.

[0099] Δφ is the absolute error of the measured phase angle, which is determined by the performance of the lock-in amplifier.

[0100] The 7230 lock-in amplifier and CTA200 precision current transformer used in this example can suppress noise and improve the detection signal-to-noise ratio, therefore γ U γ I and It is very small, and has little impact on the relative error of AC resistance. Because As the value approaches infinity, it eventually becomes the main factor affecting the AC resistance error. This method utilizes the aforementioned FPGA technology and real-time system voltage compensation method to eliminate the mutual inductance L between the current loop and the voltage test loop. h and the self-perceived L of the test sample x The effect is that, based on the equivalent circuit model, an inductive voltage with a 90° lead current is generated through FPGA and D / A converter 3. After being stepped down by a coupling transformer with load Z, it is used to compensate for the voltage on the self-inductance of the test object and the mutual inductance in the test circuit, forming a differential voltage. This reduces the phase angle between the voltage on the tested conductor and the excitation current, thereby significantly reducing the error of AC resistance, solving the accuracy problem of AC resistance testing of large cross-section conductors, and realizing accurate automated measurement of AC resistance of large cross-section conductors.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the spirit and scope of this invention. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An automatic testing system for the AC resistance of a large cross-section conductor, characterized in that, include: Computer, FPGA / real-time system, D / A converter 1, D / A converter 2, D / A converter 3, A / D converter, voltage-controlled current source, electrodes, GIL conductive tube sample, through-hole high-precision current transformer, high-precision resistor R, lock-in amplifier and coupling transformer with load Z; The computer is electrically connected to the FPGA / real-time system. The computer is used to send data and control commands to the FPGA / real-time system. The computer is also used to perform data analysis, processing and display on the voltage-compensated large cross-section conductor AC resistance automatic testing system. The FPGA / real-time system is electrically connected to the D / A converter 1, the D / A converter 2, the D / A converter 3, and the A / D converter, respectively. The FPGA / real-time system is used to receive the digital signals from the A / D converters and is also used to output digital signals to the D / A converter 1, the D / A converter 2, and the D / A converter 3, respectively. The D / A converter 1 is used to convert the digital signal output by the FPGA / real-time system into a first analog voltage, and output the first analog voltage to the voltage-controlled current source; The D / A converter 2 is used to convert the digital signal output by the FPGA / real-time system into a second analog voltage, and output the second analog voltage to the lock-in amplifier; The D / A converter 3 is used to convert the digital signal output by the FPGA / real-time system into a third analog voltage, and output the third analog voltage to the coupling transformer with load Z to achieve voltage compensation; The A / D converter is used to convert the analog voltage on the high-precision resistor R into a digital signal and output it to the FPGA / real-time system; The voltage-controlled current source is used to convert the first analog voltage signal into an excitation current signal and output the excitation current signal to the GIL conductive tube sample. The voltage-controlled current source, the through-hole high-precision current transformer, and the GIL conductive tube sample form a current loop. The electrode is placed on the GIL conductive tube sample and is used to measure the voltage on the GIL conductive tube sample. The GIL conductive tube sample is the object under test, and its AC resistance is measured. The through-hole type high-precision current transformer is used to convert the current flowing through the GIL conductive tube sample into a small current output to the high-precision resistor R. The high-precision resistor R is used to convert the current signal obtained from the through-type high-precision current transformer into a voltage signal and output it to the A / D converter. The lock-in amplifier is used to acquire the compensated A-channel voltage signal on the GIL conductive tube sample and output the compensated A-channel voltage signal to the computer via a USB interface. The coupling transformer with load Z is used to output the third analog voltage according to the proportional relationship set by the coupling transformer with load Z. The measured voltage is output to the A path of the lock-in amplifier after being differentially divided with the output voltage of the coupling transformer with load Z, thereby realizing the measurement of the compensated voltage signal.

2. The automatic testing system for AC resistance of large cross-section conductors according to claim 1, characterized in that, The automatic AC resistance testing system for large cross-section conductors is divided into a voltage testing circuit and a current excitation and testing circuit.

3. The automatic testing system for AC resistance of large cross-section conductors according to claim 2, characterized in that, The voltage test circuit includes: electrodes placed on the surface of the conductor, a lock-in amplifier, a coupling transformer with load Z, an FPGA / real-time system, a D / A converter 2, and a D / A converter 3.

4. The automatic testing system for AC resistance of large cross-section conductors according to claim 2, characterized in that, The current excitation and its test circuit include: FPGA / real-time system, D / A converter 1, voltage-controlled current source, GIL conductive tube sample, through-hole high-precision current transformer, high-precision resistor R and A / D converter.

5. The automatic testing system for AC resistance of large cross-section conductors according to claim 4, characterized in that, The FPGA / real-time system includes: a Real-Time (RT) system, an FPGA chassis, and input / output (I / O) modules.

6. An automatic method for testing the AC resistance of a large cross-section conductor, applied to the automatic testing system for the AC resistance of a large cross-section conductor as described in any one of claims 1 to 5, characterized in that, include: An equivalent circuit model of a large cross-section conductor is constructed within the FPGA, and a virtual reference is established using the excitation current and computer-assigned parameters. A voltage is applied to the voltage-controlled current source through the FPGA and D / A converter 1 to generate current excitation on the GIL conductive tube sample. The current excitation is converted into a voltage signal through a through-hole current transformer and a high-precision resistor R. The A / D converter converts it into a digital signal and transmits it to the computer via the FPGA. The computer calculates the effective value of the current and the phase angle. A voltage signal with the same frequency as the current is applied to the lock-in amplifier through the FPGA and D / A converter 2. The voltage signal serves as a reference signal for the lock-in amplifier. Based on the reference signal, the lock-in amplifier obtains the initial voltage information on the GIL conductor under test at the same frequency and transmits it to the computer via the USB interface. The computer calculates the parameters of the equivalent circuit model using the effective values ​​of the initial voltage and current, as well as the phase angle, and assigns these values ​​to the FPGA to build a virtual reference. The FPGA generates an inductive virtual reference voltage that leads the current by 90° based on the real-time excitation current information and the parameter values ​​of the equivalent circuit model. The real-time system ensures the real-time updating of the virtual reference voltage and outputs it to the coupling transformer with load Z through D / A converter 3. The coupling transformer with load Z outputs a virtual reference voltage according to the turns ratio, which is applied to the A path of the lock-in amplifier used for voltage acquisition, to achieve voltage differential with the GIL conductor under test; The lock-in amplifier acquires the differential voltage, transmits it to the computer via USB interface, and calculates the AC resistance of the tested object.

7. The automatic testing method for the AC resistance of a large cross-section conductor according to claim 6, characterized in that, The equivalent circuit model includes a series connection of resistors and inductors.

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