A measuring device and method for power capacitor characteristic parameters

Abstract

The application discloses a kind of measuring device and measuring method for electric power capacitor characteristic parameter, device includes: the back stage circuit of the interface terminal of discharge circuit is set to control the large current contactor of discharge circuit opening, and the large current contactor is used to control discharge function of discharge circuit;The discharge load of discharge circuit is high-power resistor built-in in host computer;Measuring circuit includes capacitor voltage measuring circuit and current measuring circuit, and data measurement is started by starting data collector: voltage measuring circuit is connected by 2 voltage measurement terminals, 2 electrodes of the electric power capacitor to be tested, measures and obtains the voltage data of all voltage measurement points from discharge start to discharge end;Current measuring circuit measures the discharge current of the electric power capacitor to be tested by current measuring shunt connected in discharge circuit, measures and obtains the current data of all current measurement points from discharge start to discharge end;Voltage and current data are sent to the industrial computer of control circuit.

Description

Technical Field

[0001] This invention relates to the field of power capacitor characteristic parameter measurement technology, and more specifically, to a device and method for measuring the characteristic parameters of power capacitors. Background Technology

[0002] Power capacitors are crucial devices for power regulation and energy storage in power systems, and are widely used in medium-voltage distribution systems. Power capacitors can store and carry enormous amounts of energy; therefore, the current flowing through them can be extremely large during power system faults. To accurately model the power system and calculate the limiting parameters of power transmission and distribution lines under various operating and fault conditions, it is essential to measure the inherent characteristic parameters of the power capacitors. Therefore, type evaluation tests of power capacitors typically require obtaining their accurate LCR (Limited Cycle Resistance) and characteristic frequencies (i.e., natural frequencies and resonant frequencies). Currently, the mainstream method for measuring the internal LCR parameters of capacitors is the time-delayed battery internal resistance measurement method. This method involves injecting a high-frequency signal into the capacitor to obtain feedback of its internal impedance under a high-frequency voltage signal, combined with capacitance measurement under the capacitor's power frequency reference voltage. The measured LCR parameters are then used to calculate the resonant frequency of the power capacitor.

[0003] However, the existing technology for measuring the characteristic parameters of power capacitors is complex, and the accuracy of the measured parameters is difficult to guarantee. Summary of the Invention

[0004] The present invention provides a device and method for measuring the characteristic parameters of power capacitors, thereby solving the problem of how to measure the characteristic parameters of power capacitors.

[0005] To address the aforementioned problems, the present invention provides a measuring device for characteristic parameters of power capacitors, the device comprising: a main unit;

[0006] The host includes a discharge circuit, a measurement circuit, and a control circuit; the discharge circuit includes a high-current contactor, an IGBT electronic switch, and a discharge load; the downstream circuit of the interface terminal of the discharge circuit is equipped with the high-current contactor to control the opening and closing of the discharge circuit, and the high-current contactor is used to control the discharge function of the discharge circuit; the discharge load of the discharge circuit is a high-power resistor built into the host; the high-current contactor enables mechanical isolation between the power capacitor under test and the discharge circuit when the power capacitor is connected to the host.

[0007] The measurement circuit includes a capacitor voltage measurement circuit and a current measurement circuit. Data measurement is initiated by activating the data acquisition unit: the voltage measurement circuit connects to the two electrodes of the power capacitor under test through two voltage measurement terminals, measuring and acquiring voltage data at all voltage measurement points from the start to the end of discharge; the current measurement circuit measures the discharge current of the power capacitor under test through a current measurement shunt connected in the discharge circuit, measuring and acquiring current data at all current measurement points from the start to the end of discharge; the voltage data and the current data are sent to the industrial control computer of the control circuit.

[0008] The control loop includes an industrial computer, a main controller, and peripheral circuits. The industrial computer inputs the test configuration parameters and sends the configuration parameters to the main controller. Based on the configuration parameters and test instructions, the main controller sequentially starts the data acquisition unit, the high-current contactor, and the IGBT electronic switch of the measurement loop.

[0009] Preferably, the device further includes a discharge device comprising three parallel vacuum interrupter circuits. Each vacuum interrupter circuit includes two vertically arranged Z-shaped high-current copper busbars. The two vertically arranged Z-shaped high-current copper busbars surround the outer wall of the vacuum interrupter. An insulating epoxy board is disposed between the two Z-shaped high-current copper busbars. The two Z-shaped high-current copper busbars are connected to the power capacitor being tested.

[0010] Preferably, the contact resistance of the main circuit in the three parallel vacuum interrupter circuits is controlled below 20 microohms, and the asynchrony of the three-phase closing time of the vacuum circuit breaker in the vacuum interrupter circuit is controlled within 1ms.

[0011] Preferably, the vacuum interrupter circuit includes a release device and an energy storage circuit. The energy storage circuit separates the contacts of the vacuum interrupter and raises them to a restricted position via a spring to complete the opening process. When it is necessary to close the vacuum interrupter to generate an underdamped oscillating current in the power capacitor discharge circuit, the closing process is initiated, and the contacts of the interrupter are quickly pulled back to the tight contact position via the release device and the spring.

[0012] Preferably, the measurement circuit of the discharge device comprises a Rogowski coil and a high-speed current signal recording circuit of the host; the Rogowski coil is used to measure the voltage waveform flowing through the high-current copper busbar during the discharge process and output a voltage signal; the voltage signal enters the current signal current measurement shunt of the host.

[0013] Preferably, when the main controller issues a start-up closing test command, a high-speed AD acquisition signal is simultaneously started, and when the output voltage signal of the Rogowski coil is detected to exceed the minimum threshold, 10ms discharge waveform data is measured and acquired, and the waveform characteristic frequency is calculated through the discharge waveform data.

[0014] According to another aspect of the present invention, the present invention provides a method for measuring the parameters of a power capacitor based on a measuring device, the method comprising:

[0015] The power capacitor to be tested is connected to the host, and the power capacitor is charged when the IGBT electronic switch is off;

[0016] When the voltage of the power capacitor reaches the first preset voltage value, charging of the power capacitor is stopped;

[0017] Set the discharge time T and start the discharge test;

[0018] The high-current contactor is controlled to close. After the high-current contactor is closed to the +++ position, the IGBT electronic switch is started to discharge.

[0019] When the discharge time reaches the discharge time T, the discharge test ends, and the current-time curve and voltage-time curve are recorded.

[0020] Based on the current-time curve and the voltage change ΔV of the power capacitor at the beginning and end of the discharge test, the capacitance value C of the power capacitor is calculated.

[0021] Based on the voltage change ΔV1 at the power capacitor voltage measurement terminal at the moment of discharge test start-up and the circuit current value I1 at the moment of discharge, the internal resistance R of the capacitor is calculated.

[0022] According to another aspect of the present invention, the present invention provides a method for measuring the parameters of a power capacitor based on a measuring device, the method comprising:

[0023] Connect the discharge device to the host computer;

[0024] When the contacts of the vacuum interrupter chamber of the discharge device are in the open state, the power capacitor is charged until it is fully charged.

[0025] When the voltage of the power capacitor reaches the second preset voltage value, the inherent inductance value Lx of the real side of the connection between the power capacitor and the high current copper busbar is input to the host.

[0026] The industrial control computer sends a discharge start test command to the main controller.

[0027] The main controller controls the discharge device to close based on the discharge start test command, and simultaneously measures the output voltage waveform of the Rogowski coil;

[0028] When the voltage waveform is detected to be lower than the minimum voltage threshold, the voltage waveform is stored for a preset time.

[0029] The main frequency of the signal is calculated based on the stored voltage waveform, and the internal inductance Lc and natural vibration frequency f of the power capacitor are calculated based on the inherent inductance value Lx.

[0030] This invention provides a device and method for measuring characteristic parameters of power capacitors. The device includes a main unit; the main unit includes a discharge circuit, a measurement circuit, and a control circuit; the discharge circuit includes a high-current contactor, an IGBT electronic switch, and a discharge load; the downstream circuit of the discharge circuit's interface terminals is equipped with a high-current contactor to control the opening and closing of the discharge circuit, the high-current contactor being used to control the discharge function of the discharge circuit; the discharge load of the discharge circuit is a high-power resistor built into the main unit; the high-current contactor mechanically isolates the power capacitor and the discharge circuit when the power capacitor under test is connected to the main unit; the measurement circuit includes a capacitor voltage measurement circuit and a current measurement circuit, and data measurement is initiated by activating a data acquisition device: voltage... The measurement circuit connects to the two electrodes of the power capacitor under test through two voltage measurement terminals, measuring and acquiring voltage data at all voltage measurement points from the start to the end of discharge. The current measurement circuit measures the discharge current of the power capacitor under test through a current measurement shunt connected in the discharge circuit, measuring and acquiring current data at all current measurement points from the start to the end of discharge. The voltage and current data are sent to the industrial control computer in the control circuit. The control circuit includes an industrial control computer, a main controller, and peripheral circuits. The industrial control computer inputs the test configuration parameters and sends the configuration parameters to the main controller. Based on the configuration parameters and test commands, the main controller sequentially starts the data acquisition unit, high-current contactor, and IGBT electronic switch of the measurement circuit. This invention relates to a power capacitor characteristic parameter testing device, which obtains the internal resistance, internal inductance, and capacitance parameters of the power capacitor by measuring the voltage drop change and characteristic frequency during the discharge process through a high-current discharge test. Attached Figure Description

[0031] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0032] Figure 1 This is a structural diagram of a device for measuring characteristic parameters of a power capacitor according to a preferred embodiment of the present invention.

[0033] Figure 2This is a structural diagram of the main unit of the measuring device according to a preferred embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the discharge circuit principle according to a preferred embodiment of the present invention;

[0035] Figure 4 This is a flowchart of a method for measuring the parameters of a power capacitor based on a measuring device according to a preferred embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the test procedure for measuring internal resistance and capacitance according to a preferred embodiment of the present invention;

[0037] Figure 6 A flowchart illustrating a method for measuring the parameters of a power capacitor based on a measuring device according to a preferred embodiment of the present invention; and

[0038] Figure 7 This is a schematic diagram of the test procedure for measuring the internal inductance Lc according to a preferred embodiment of the present invention. Detailed Implementation

[0039] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0040] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0041] Figure 1 This is a structural diagram of a device for measuring characteristic parameters of a power capacitor according to a preferred embodiment of the present invention. The present invention relates to a power capacitor characteristic parameter testing device, used to obtain the internal resistance, internal inductance, and capacitance parameters of a power capacitor by measuring voltage drop changes, characteristic frequencies, etc., during a high-current discharge test.

[0042] This invention provides a power capacitor characteristic parameter measuring device comprising two main components: a measuring host and a short-circuit discharge device. The measuring host can discharge the power capacitor for a short time under low-current overdamped conditions. By measuring the current-time curve and the voltage change curve across the capacitor over time during the discharge process, the actual capacitance and internal DC resistance R of the power capacitor can be calculated. The short-circuit discharge device discharges the power capacitor under underdamped conditions, causing oscillations in the entire circuit discharge process. By measuring the frequency of the oscillating current, the resonant frequency of the circuit can be calculated. Combined with the measured capacitance of the power capacitor, the total inductance of the circuit can be calculated. By measuring the inductance Lx of the external circuit from the same wiring terminal as the power capacitor and subtracting it from the total impedance, the internal inductance Lc of the power capacitor can be obtained. By calculating the measured capacitance C and the internal inductance Lc, the natural oscillation frequency f of the capacitor itself can be accurately calculated.

[0043] To obtain an accurate parameter model of a power capacitor under fault current, this invention provides an automatic testing device that can accurately measure the internal resistance R, internal inductance Lc, capacitance C, and oscillation frequency f of a power capacitor under fault short-circuit conditions. The power capacitor characteristic parameter measuring device consists of two main parts: a measuring host and a discharge device. Its internal schematic diagram and test connection are shown below. Figure 1 As shown.

[0044] like Figure 1 As shown, a measuring device for characteristic parameters of power capacitors includes: a main unit;

[0045] The main unit includes a discharge circuit, a measurement circuit, and a control circuit. The discharge circuit includes a high-current contactor, an IGBT electronic switch, and a discharge load. The downstream circuit of the interface terminal of the discharge circuit is equipped with a high-current contactor to control the opening and closing of the discharge circuit. The high-current contactor is used to control the discharge function of the discharge circuit. The discharge load of the discharge circuit is a high-power resistor built into the main unit. The high-current contactor enables mechanical isolation between the power capacitor under test and the discharge circuit when the power capacitor is connected to the main unit.

[0046] The measurement circuit includes a capacitor voltage measurement circuit and a current measurement circuit. Data measurement is initiated by activating the data acquisition unit: the voltage measurement circuit connects to the two electrodes of the power capacitor under test through two voltage measurement terminals, measuring and acquiring voltage data at all voltage measurement points from the start to the end of discharge; the current measurement circuit measures the discharge current of the power capacitor under test through a current measurement shunt connected in the discharge circuit, measuring and acquiring current data at all current measurement points from the start to the end of discharge; the voltage and current data are sent to the industrial control computer of the control circuit.

[0047] The control loop includes an industrial computer, a main controller, and peripheral circuits. The industrial computer inputs the test configuration parameters and sends them to the main controller. Based on the configuration parameters and test commands, the main controller sequentially starts the data acquisition unit, high-current contactor, and IGBT electronic switch of the measurement loop.

[0048] The internal schematic diagram of the main unit of the power capacitor characteristic parameter measuring device of the present invention is as follows. Figure 1 As shown, the device host has a DC current discharge interface. The positive and negative electrodes of the power capacitor are connected to the discharge interface of the device host. The contactor is activated by the device software. Before enabling the IGBT discharge, high-speed signal acquisition begins. The frequency of synchronous sampling of voltage and current signals is no less than 100kHz. The acquired signals include the discharge circuit current I1 and the capacitor voltage V1. The internal resistance of the capacitor is obtained using the formula R = ΔV1 / I1, where ΔV1 is the voltage change of the capacitor before and after discharge initiation, and I is the current value of the capacitor at the instant of discharge. After initiating the IGBT discharge process, the power capacitor characteristic parameter measurement device host of this invention acquires and records the voltage V and current I versus time curves at a frequency of 100kHz during the discharge process. The discharge amount during the discharge process is calculated. The accurate capacitance value C of the capacitor can be calculated using the formula Q = C * ΔV, which represents the voltage difference ΔV before and after the capacitor discharges.

[0049] The main discharge circuit of the power capacitor characteristic parameter measuring device of the present invention consists of a contactor, an IGBT, a high-power discharge resistor, and a voltage and current measuring circuit, as shown in the schematic diagram below. Figure 1 As shown. The contactor has a rated current of 250A, and the high-power resistor is a 5kW resistor connected in parallel, serving as the main load during the discharge process. The electronic control switch is a 200A 1500VIGBT, used for rapid initiation and termination of the discharge process. The voltage measurement signal is connected to the capacitor electrodes in a four-wire configuration via the device's voltage measurement cable. After voltage division, operational amplifier voltage follower, and isolation amplifier, it enters the AD conversion circuit of the device's main unit. The current measurement loop measures the current signal through a shunt connected in the loop.

[0050] Preferably, the device further includes a discharge device comprising three parallel vacuum interrupter circuits. Each vacuum interrupter circuit includes two vertically arranged Z-shaped high-current copper busbars. The two vertically arranged Z-shaped high-current copper busbars surround the outer wall of the vacuum interrupter. An insulating epoxy board is disposed between the two Z-shaped high-current copper busbars. The two Z-shaped high-current copper busbars are connected to the power capacitor under test.

[0051] Preferably, the contact resistance of the main circuit in the three parallel vacuum interrupter circuits is controlled below 20 microohms, and the asynchrony of the three-phase closing time of the vacuum circuit breaker in the vacuum interrupter circuit is controlled within 1ms.

[0052] Preferably, the vacuum interrupter circuit includes a release device and an energy storage circuit. The energy storage circuit separates the contacts of the vacuum interrupter and raises them to a limiting position via a spring to complete the opening process. When it is necessary to close the vacuum interrupter to generate an underdamped oscillating current in the power capacitor discharge circuit, the closing process is initiated, and the contacts of the interrupter are quickly pulled back to the tight contact position via the release device and the spring.

[0053] Preferably, the measurement circuit of the discharge device consists of a Rogowski coil and a high-speed current signal recording circuit of the host; the Rogowski coil is used to measure the voltage waveform of the high-current copper busbar during the discharge process and outputs a voltage signal; the voltage signal enters the current signal current measurement shunt of the host.

[0054] Preferably, when the main control issues a start-up closing test command, the high-speed AD acquisition signal is started synchronously, and when the output voltage signal of the Rogowski coil is detected to exceed the minimum threshold, 10ms discharge waveform data is measured and acquired, and the waveform characteristic frequency is calculated through the discharge waveform data.

[0055] The schematic diagram of the discharge device of the power capacitor characteristic parameter measuring device of this invention is shown below. Figure 1 As shown, the main circuit of the device consists of three 3000A vacuum interrupters. The upper ends of the three interrupters are connected together by a copper busbar, and the lower ends are connected together by another copper busbar. When the discharge device is activated, the three discharge interrupters simultaneously engage. When the first interrupter contacts, a huge discharge current is generated on the electrode plates at both ends of its tip, and this discharge current vibrates at the resonant frequency formed by the circuit's characteristic parameters. Subsequent interrupters can fully absorb the energy of the discharge process when they contact, avoiding the energy of the entire discharge process being applied to a single interrupter contact, which could damage the interrupter. The discharge device is directly connected to the electrodes of a power capacitor, and a Rogowski coil is installed at the lead-out position of the power capacitor electrode to measure the current waveform during the discharge process. The output of the Rogowski coil is connected to the high-speed signal processing circuit of the measurement host. After protection, amplification, and tracking, it enters the high-speed AD conversion module of the TMS320F2812. The acquisition frequency of the control signal is not less than 2MHz to ensure that the characteristic waveform of the instantaneous discharge current can be completely recorded.

[0056] This invention provides a power capacitor characteristic parameter measurement device based on short-circuit discharge, which relates to power capacitor quality inspection and testing. It provides a new method and device for measuring characteristic parameters that are closer to the actual operating conditions of power capacitors, solving the difficulties in measuring power capacitor characteristic parameters under actual short-circuit conditions. The test process is simple and the measurement accuracy is high. The test results are closer to the LCR and inherent oscillation frequency characteristic parameters of power capacitors under power frequency and high current conditions, and the measurement results are more convincing and of reference significance. This invention uses a DC voltage system to charge a power capacitor. After reaching a specified voltage, the capacitor is discharged under overdamped conditions using IGBT control. The current value during the discharge process is recorded at 100kHz. The charge amount during charging is obtained by integrating the current and time. By comparing the capacitor voltage change before and after discharge, the true capacitance C is calculated. The internal DC resistance R of the capacitor can be calculated by rapidly recording the voltage drop and current value at the moment of discharge. The discharge circuit resistance is reduced to allow the capacitor to discharge in an underdamped state. The characteristic frequency of the discharge circuit waveform is measured, and the total inductance Lt of the circuit is calculated by combining the capacitor capacitance and resonant frequency. Then, under power frequency conditions, the external inductance Le of the discharge circuit is measured with a large current and subtracted from the total impedance Lt to obtain the internal inductance L of the capacitor. The LCR value of the capacitor measured using a large current discharge method is closer to the actual operating conditions of the capacitor, providing more guidance for the design and calculation of relevant parameters in power systems. Furthermore, the experimental process is simple, and the measured parameters are more accurate.

[0057] like Figure 4 As shown, the present invention provides a method for measuring the parameters of a power capacitor based on a measuring device, the method comprising:

[0058] Step 401: Connect the power capacitor to be tested to the host and charge the power capacitor with the IGBT electronic switch off;

[0059] Step 402: When the voltage of the power capacitor reaches the first preset voltage value, stop charging the power capacitor;

[0060] Step 403: Set the discharge time T and start the discharge test;

[0061] Step 404: Control the high-current contactor to close. After the high-current contactor is closed to the ++ position, start the IGBT electronic switch to discharge.

[0062] Step 405: When the discharge time reaches the discharge time T, end the discharge test and record the current-time curve and voltage-time curve;

[0063] Step 406: Based on the current-time curve and the voltage change ΔV of the power capacitor at the beginning and end of the discharge test, calculate the capacitance value C of the power capacitor;

[0064] Step 407: Based on the change in voltage ΔV1 at the power capacitor voltage measurement terminal at the moment of discharge test start-up and the circuit current value I1 at the moment of discharge, calculate the internal resistance R of the capacitor.

[0065] like Figure 6 As shown, the present invention provides a method for measuring the parameters of a power capacitor based on a measuring device, the method comprising:

[0066] Step 601: Connect the discharge device to the main unit;

[0067] Step 602: When the contacts of the vacuum interrupter of the discharge device are in the open state, charge the power capacitor until it is fully charged;

[0068] Step 603: When the voltage of the power capacitor reaches the second preset voltage value, input the inherent inductance value Lx of the real side of the connection between the power capacitor and the high current copper busbar to the host.

[0069] Step 604: Send the discharge start test command to the main controller via the industrial control computer;

[0070] Step 605: The main controller controls the discharge device to close based on the discharge start test command, and simultaneously measures the output voltage waveform of the Rogowski coil;

[0071] Step 606: When the voltage waveform is detected to be lower than the minimum voltage threshold, start storing the voltage waveform for a preset time;

[0072] Step 607: Calculate the main frequency of the signal and the inherent inductance value Lx based on the stored voltage waveform. Calculate the internal inductance Lc and the inherent vibration frequency value f of the power capacitor.

[0073] To obtain an accurate parameter model of a power capacitor under fault current, this invention provides an automatic testing device that can accurately measure the internal resistance R, internal inductance Lc, capacitance C, and oscillation frequency f of a power capacitor under fault short-circuit conditions. The power capacitor characteristic parameter measuring device consists of two main parts: a measuring host and a discharge device. Its internal schematic diagram and test connection are shown below. Figure 1 As shown.

[0074] The internal schematic diagram of the measuring host of the power capacitor characteristic parameter measuring device is as follows: Figure 2As shown, the measuring host has two discharge interface terminals and two capacitor voltage measurement terminals. The discharge interface terminals are connected to the capacitor electrodes through a high-current cable. The main body of the measuring device mainly includes a discharge circuit, a measurement circuit, and a control circuit.

[0075] The discharge circuit of the measuring host of this invention consists of a high-current contactor, an IGBT electronic switch, and a discharge load. A 250A / 630V high-current contactor for controlling the opening and closing of the control circuit is connected to the downstream circuit of the discharge interface terminal. When the contactor is energized, the discharge function of the circuit is enabled. A 200A / 1500V IGBT electronic switch is connected downstream of the contactor as the main control switch for starting and ending the discharge process. The load of the discharge circuit uses two 5kW / 2Ω high-power resistors built into the measuring device host. Throughout the discharge process, the high-power contactor ensures the safety and controllability of the test process. When connecting the capacitor electrodes to the measuring device host, the contactor mechanically isolates the capacitor and the discharge load to ensure safety. When the internal IGBT experiences a breakdown fault, the contactor can quickly disconnect the capacitor from the internal discharge circuit. Using an IGBT as the main discharge switch avoids overvoltage and measurement noise caused by mechanical node bounce, and also allows for precise control of the discharge time.

[0076] The main measuring circuit of the measuring device includes two main circuits: capacitor voltage measurement and discharge current measurement. Its schematic diagram is shown below. Figure 2 As shown. The main panel of the measuring device has two voltage measurement terminals for connecting the two electrodes of the capacitor under test. A resistor divider circuit is connected after the measurement terminals, and the voltage is stepped down and then output by a fast operational amplifier OP42. The OP42 is followed by an isolation operational amplifier ISO122, which isolates the capacitor voltage signal after voltage division and sends it to the sampling input channel of the AD7656 ADC. The voltage signal after AD conversion is acquired and temporarily stored by the main controller chip TMS32F2812 of the measuring device. A 200A / 200mV current measuring shunt connected to the discharge circuit is used to measure the discharge current during discharge. The shunt's output voltage signal is first amplified by a fast operational amplifier, then followed by the fast operational amplifier OP42 (mentioned later) and output to the sampling input channel of the AD7656 ADC. The current signal after AD conversion and the capacitor voltage signal are synchronously acquired and temporarily stored in the main controller TMS320F2812. During the test, the main controller records and stores all voltage and current measurement points collected from the start of discharge to the point of discharge contact. Then, all the measured data is transmitted to the industrial control computer for processing through the communication USB interface between the main controller and the industrial control computer.

[0077] The control loop of the measuring device consists of an industrial computer, a main controller, and its peripheral circuits. The industrial computer's software interface allows input of test control parameters such as discharge current and discharge duration. The industrial computer transmits these configuration parameters to the main controller, TMS320F2812, and then uses commands to start the test. Upon receiving the configuration parameters and the test start command, the main controller sequentially activates the contactor, sampling circuit, and IGBT switch via its I / O pins and drive circuit, and synchronously reads the voltage and current data from the AD converter.

[0078] The discharge device schematic diagram of the power capacitor characteristic parameter measuring device of the present invention is shown below. Figure 1 As shown, its leads are two Z-shaped high-current copper busbars. Figure 3 As shown, two copper busbars extend close to the outer wall of the arc-extinguishing chamber, minimizing the area enclosed by the two busbars. They are then separated by a 3mm insulating epoxy board. On the other side of the copper busbars, they are directly bolted to the electrodes of the power capacitor under test. The gap between the two copper busbars is kept as small as possible to reduce the cross-sectional area enclosed by the main circuit of the discharge device, thus minimizing the external inductance. The discharge circuit of the power capacitor characteristic parameters discharge device consists of three vacuum arc-extinguishing chambers connected in parallel. The contact resistance of its main circuit is controlled below 20 microohms. The asynchrony of the three-phase closing time of the vacuum circuit breaker in the vacuum arc-extinguishing chamber circuit is controlled within 1ms to ensure that the energy of the test chamber capacitor is distributed as evenly as possible across the three vacuum arc-extinguishing chamber circuits, reducing damage to the vacuum arc-extinguishing chambers themselves from high-current surges. Using a vacuum arc-extinguishing chamber as the main control switch for discharge avoids waveform abnormalities caused by repeated breakdown discharges at the moment of switch contact, and also avoids ionization or explosion caused by air heating and expansion due to high current switching.

[0079] The control circuit of the arc-extinguishing chamber of the power capacitor discharge device provided by this invention is as follows: Figure 1 The circuit consists of a release device and an energy storage circuit. The energy storage circuit uses a spring to separate the contacts of the arc-extinguishing chamber and raise them to the limit position to complete the opening process. When it is necessary to close the arc-extinguishing chamber to generate an underdamped oscillating current in the power capacitor discharge circuit, the closing process is initiated. The release device and spring quickly pull the contacts of the arc-extinguishing chamber back to the contact position and press them tightly together.

[0080] The power capacitor discharge device provided by this invention comprises a Rogowski coil and a high-speed current signal recording circuit of the measurement host. The Rogowski coil, installed in the main discharge circuit, measures the large current waveform flowing through the copper busbar during discharge. Its output signal is a high-frequency voltage signal, which enters the current signal measurement terminal of the measurement host. After passing through a current-limiting resistor and a fast diode for voltage limiting protection, it enters the fast operational amplifier OP42 for processing. The output voltage signal from the Rogowski coil is amplified by the OP42 and then enters the next stage fast operational amplifier OP42 follower circuit, before being output to the high-speed AD converter of the main controller TMS320F2812 for acquisition. The sampling frequency of the high-speed AD converter is configured at 2MHz. When the main controller issues a start-up closing test command, the high-speed AD acquisition signal is started synchronously. When the output voltage signal of the Rogowski coil exceeds a minimum threshold, the measured signal is stored. Because the acquisition frequency is very high and the oscillating current frequency is relatively high, only the initial 10ms waveform is recorded during the measurement process to reduce the number of measurement points that need to be stored. After the discharge process is completed, the measured 10ms discharge waveform data is transmitted from the main controller TMS320F2812 to the industrial computer via the USB communication interface. The industrial computer can display the actual measured 10ms oscillating current waveform and calculate the characteristic frequency signal of the waveform through software.

[0081] The power capacitor characteristic parameter measuring device provided by this invention has the following typical operating procedure when measuring the capacitance and internal resistance of a power capacitor: Figure 5 As shown. The detailed testing workflow is described below:

[0082] (1) Connect the ground wire and power wire of the characteristic parameter measurement terminal;

[0083] (2) Connect the electrodes of the uncharged power capacitor to the discharge terminal and capacitor voltage measurement terminal of the measurement host of the characteristic parameter measurement device;

[0084] (3) With the discharge circuit contactor and IGBT not turned on, charge the capacitor to about 200V.

[0085] (4) Remove the power capacitor charging device;

[0086] (5) Configure the discharge time T of the discharge device, and then start the discharge test;

[0087] (6) The main unit of the characteristic parameter measuring device controls the internal contactor to engage first;

[0088] (7) Ensure that the contactor inside the discharge device is closed to the ++ position, start the IGBT switch to discharge, maintain the discharge time T and then shut down the discharge process, and record and save the curves of discharge current and capacitor voltage versus time during this process.

[0089] (8) The main unit of the discharge device calculates the capacitance C of the capacitor based on the recorded current-time curve and the change in capacitor voltage ΔV before and after the discharge begins. The specific calculation formula is as follows: And Q=C*ΔV, where I is the current during the discharge process, Q is the amount of charge during the discharge process, and T is the discharge duration;

[0090] (9) The main unit of the discharge device calculates the internal resistance R of the capacitor based on the change value ΔV1 of the voltage measurement terminal of the capacitor at the moment of discharge start and the circuit current value I1 at the moment of discharge. The calculation formula is R=ΔV1 / I1.

[0091] (10) After the calculation is completed, the characteristic parameter measurement host displays the measured internal resistance R, capacitance C, voltage versus time curve and discharge current versus time curve of the test process on the LCD screen of the industrial control computer. The sampling frequency of the curve is 100kHz and the time resolution is 0.01us.

[0092] The power capacitor characteristic parameter measuring device of the present invention, when measuring the inductance and resonant frequency of a capacitor, has the following typical test procedure: Figure 7 As shown, the detailed experimental procedure is described below:

[0093] (1) Connect the ground wires of the discharge device and the main unit of the measuring device;

[0094] (2) Install the Rogowski coil for measuring current waveform, and then connect the power capacitor to the copper busbar of the discharge device;

[0095] (3) While ensuring that the contacts of the vacuum interrupter of the discharge device are in the open state, charge the capacitor to a voltage of approximately 500V-1000V.

[0096] (4) Connect the discharge device to the copper busbar of the capacitor and input the measured inherent inductance value Lx to the host of the measuring device. Then send the discharge start test command from the industrial control computer to the main controller TMS320F2812.

[0097] (5) After receiving the start test command, the main controller chip TMS320F2812 controls the discharge device to close and simultaneously measures the output voltage waveform of the Rogowski coil.

[0098] (6) When the output voltage waveform of the Rogowski coil is detected to exceed the minimum voltage threshold, the voltage waveform is stored and the storage time is not less than 10ms.

[0099] (7) The main controller chip transmits the recorded and stored output voltage waveform data from the Rogowski coil to the industrial computer;

[0100] (8) The industrial control computer calculates the main frequency of the signal based on the received voltage waveform signal;

[0101] (9) The industrial control computer calculates the internal inductance of the capacitor and the natural vibration frequency of the capacitor based on the calculated main frequency of the signal and the inductance of the discharge device itself and the capacitance value of the capacitor.

[0102] (10) The industrial control computer displays the actual measured internal inductance Lc of the capacitor, the natural vibration frequency value f of the capacitor, and the current-time waveform obtained during the test.

[0103] In this invention, the capacitor inductance value Lc is measured when the capacitor is in a short-circuit underdamped state, and its value is closer to the actual inductance under fault current conditions.

[0104] This invention is based on the LCR parameters and resonant frequencies of power capacitors measured under high current conditions. These parameters are closer to the values ​​required for power system operation and fault condition modeling, and are more instructive for parameter calculation and system design under various conditions and operating conditions of power systems.

[0105] The LCR parameters of power capacitors measured under high-current discharge and underdamped discharge conditions in this invention are more suitable for the calculation and design of limit parameters of power capacitors under various extreme operating conditions.

[0106] The invention has been described with reference to a few embodiments. However, as will be known to those skilled in the art, and as defined in the appended claims, other embodiments besides those disclosed above fall equivalently within the scope of the invention.

[0107] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / / the [device, component, etc.]” ​​are openly interpreted as at least one instance of the device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

Claims

1. A measuring device for characteristic parameters of a power capacitor, the device comprising: Host; The host includes a discharge circuit, a measurement circuit, and a control circuit; the discharge circuit includes a high-current contactor, an IGBT electronic switch, and a discharge load; the downstream circuit of the interface terminal of the discharge circuit is equipped with the high-current contactor to control the opening and closing of the discharge circuit, and the high-current contactor is used to control the discharge function of the discharge circuit; the discharge load of the discharge circuit is a high-power resistor built into the host; the high-current contactor enables mechanical isolation between the power capacitor under test and the discharge circuit when the power capacitor is connected to the host. The measurement circuit includes a capacitor voltage measurement circuit and a current measurement circuit. Data measurement is initiated by activating the data acquisition unit: the voltage measurement circuit connects to the two electrodes of the power capacitor under test through two voltage measurement terminals, measuring and acquiring voltage data at all voltage measurement points from the start to the end of discharge; the current measurement circuit measures the discharge current of the power capacitor under test through a current measurement shunt connected in the discharge circuit, measuring and acquiring current data at all current measurement points from the start to the end of discharge; the voltage data and the current data are sent to the industrial control computer of the control circuit. The control loop includes an industrial computer, a main controller, and peripheral circuits. The industrial computer inputs the test configuration parameters and sends the configuration parameters to the main controller. Based on the configuration parameters and test commands, the main controller sequentially starts the data acquisition unit, the high-current contactor, and the IGBT electronic switch of the measurement loop. The discharge device includes three parallel vacuum interrupter circuits. Each vacuum interrupter circuit includes two vertically arranged Z-shaped high-current copper busbars. The two vertically arranged Z-shaped high-current copper busbars surround the outer wall of the vacuum interrupter. An insulating epoxy board is installed between the two Z-shaped high-current copper busbars. The two Z-shaped high-current copper busbars are connected to the power capacitor under test. The contact resistance of the main circuit in the three parallel vacuum interrupter circuits is controlled below 20 microohms, and the asynchrony of the three-phase closing time of the vacuum circuit breaker in the vacuum interrupter circuit is controlled within 1ms. The power capacitor to be tested is connected to the host, and the power capacitor is charged when the IGBT electronic switch is off; When the voltage of the power capacitor reaches the first preset voltage value, charging of the power capacitor is stopped; Set the discharge time T and start the discharge test; The high-current contactor is controlled to close. After the high-current contactor is closed to the +++ position, the IGBT electronic switch is started to discharge. When the discharge time reaches the discharge time T, the discharge test ends, and the current-time curve and voltage-time curve are recorded. Based on the aforementioned current-time curve, and the voltage changes of the power capacitor at the beginning and end of the discharge test. Calculate the capacitance C of the power capacitor; Based on the voltage change at the power capacitor voltage measurement terminal at the instant of discharge test start-up 1. The internal resistance R of the capacitor is calculated from the circuit current value I1 at the moment of discharge; Connect the discharge device to the host computer; When the contacts of the vacuum interrupter chamber of the discharge device are in the open state, the power capacitor is charged until it is fully charged. When the voltage of the power capacitor reaches the second preset voltage value, the inherent inductance value Lx of the real side of the connection between the power capacitor and the high current copper busbar is input to the host. The industrial control computer sends a discharge start test command to the main controller. The main controller controls the discharge device to close based on the discharge start test command, and simultaneously measures the output voltage waveform of the Rogowski coil; When the voltage waveform is detected to be lower than the minimum voltage threshold, the voltage waveform is stored for a preset time. The main frequency of the signal is calculated based on the stored voltage waveform, and the internal inductance Lc and natural vibration frequency f of the power capacitor are calculated based on the inherent inductance value Lx.

2. The apparatus according to claim 1, wherein the vacuum interrupter circuit comprises: The release device and energy storage circuit, wherein the energy storage circuit separates the contacts of the vacuum interrupter and raises them to the limit position by means of a spring to complete the opening process; When it is necessary to close the vacuum interrupter to generate an underdamped oscillating current in the discharge circuit of the power capacitor, the closing process is initiated, and the contacts of the interrupter are quickly pulled back to the tight contact position by the release device and spring.

3. The device according to claim 1, wherein the measurement circuit of the discharge device comprises a Rogowski coil and a high-speed current signal recording circuit of the host; the Rogowski coil is used to measure the voltage waveform flowing through the high-current copper busbar during the discharge process and output a voltage signal; the voltage signal enters the current signal current measurement shunt of the host.

4. The device according to claim 3, wherein when the main controller issues a start closing test command, a high-speed AD acquisition signal is synchronously started, and when the output voltage signal of the Rogowski coil is detected to exceed the minimum threshold, 10ms discharge waveform data is measured and acquired, and the waveform characteristic frequency is calculated through the discharge waveform data.

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