Zero-testing device for porcelain insulators, and zero-testing method for small current and distributed voltage in high-voltage circuits.

Abstract

This invention discloses a zero-detection device for porcelain insulators and a method for zero-detection of small current and distributed voltage in high-voltage circuits. The zero-detection device for porcelain insulators includes: a low-voltage pulse generator for converting a received voltage signal into a voltage pulse signal of a set frequency; a step-up transformer for converting the voltage pulse signal generated by the low-voltage pulse generator into voltage signal one; a voltage multiplier circuit for converting voltage signal one output from the step-up transformer into voltage signal two; a detection circuit for converting voltage signal two output from the voltage multiplier circuit into a detection signal; and discharge terminals POUT+ and POUT- connected to the output terminal of the detection circuit for bonding to the steel caps at both ends of the porcelain insulator. This invention ensures that the insulator is not damaged during the measurement process and can comprehensively detect defects in the insulator.

Description

Technical Field

[0001] This invention belongs to the field of porcelain insulator testing technology, specifically relating to a porcelain insulator zero-testing device and a method for zero-testing small current and distributed voltage in high-voltage circuits. Background Technology

[0002] Due to factors such as manufacturing quality and operating environment, micro-cracks and defects inside porcelain insulators may continuously increase, leading to varying degrees of deterioration. When these defects grow to a certain extent, the insulator's withstand voltage will decrease; the standard specifies a value of 45-50 kV. When the applied voltage exceeds the insulator's own withstand level, a breakdown discharge will occur inside the insulator.

[0003] Insulators with internal defects may also exhibit resistive characteristics; insulators with external contaminants may also exhibit resistive characteristics or surface discharge phenomena.

[0004] Traditional portable insulator defect detection devices employ two methods: the high-voltage breakdown method and the megohmmeter method. The high-voltage breakdown method involves applying a standard pulse voltage (above 50kV) to the insulator and then measuring its withstand voltage over a period of 500-1000ms. If the voltage amplitude is low or the voltage waveform drops rapidly, it indicates an insulation defect; if the voltage drop is less than a set range within the set time, the insulator is considered to have good insulation. The megohmmeter method involves applying a DC voltage of 2500-5000V to the insulator and measuring the circuit current to calculate the insulator's resistance.

[0005] The advantage of the high-voltage breakdown method is that it can detect defects in insulators when their withstand voltage is lower than the standard or their resistance is lower than a specified value. The disadvantage is that this pressurized method is further destructive to insulators with varying degrees of defect and is not entirely suitable for live-line testing. If multiple insulators in a running line's porcelain insulator string have mild to moderate degradation, the porcelain insulators retain some insulation resistance because the microcracks have not formed a continuous channel, allowing the insulator string to continue operating. However, after measurement using the high-voltage breakdown method, the number of degraded insulators in the string may further increase, leading to a drop below the minimum number of insulators required for safe operation and potentially causing a flashover fault in the insulator string.

[0006] The advantage of the megohmmeter method is that it can safely measure insulation resistance; the disadvantage is that because the measurement voltage is too low, at 5000V, some high-tonnage or slightly deteriorated insulators may not show low resistance characteristics, making it impossible to fully detect insulator defects, thus causing zero-value missed detection.

[0007] One standard method for detecting zero values ​​in online insulators is the distributed voltage method. This involves measuring the actual operating voltage of each insulator disc in the online insulator string and judging deterioration based on whether the distributed voltage meets the standard requirements (distributed voltage exceeding 50% of the standard reference value and not lower than that of adjacent normal insulators). Zero-value insulators have low distributed voltage, so the level of this voltage is used to determine if the insulator is in a zero-value state. The disadvantage of this method is that in long strings of porcelain insulators, several deteriorated porcelain discs in the middle section originally share a lower voltage. When one or more insulators experience mild to moderate deterioration, the voltage distribution between adjacent insulators often does not differ significantly due to the remaining insulation resistance, making it easy to miss detections. Furthermore, the traditional distributed voltage method is difficult to use for measuring porcelain insulators on ultra-high voltage lines. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a zero-measurement device for porcelain insulators and a method for zero-measurement of small current and distributed voltage in high-voltage circuits, which can ensure that the insulators are not damaged during the measurement process and can comprehensively detect defects in the insulators.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] In a first aspect, a zero-detection device for a porcelain insulator is provided, comprising: a low-voltage pulse generator for converting a received voltage signal into a voltage pulse signal of a set frequency; a step-up transformer for converting the voltage pulse signal emitted by the low-voltage pulse generator into a voltage signal one; a voltage multiplier circuit for converting the voltage signal one output by the step-up transformer into a voltage signal two, wherein the voltage signal two is an integer multiple of the voltage signal one; a detection circuit for converting the voltage signal two output by the voltage multiplier circuit into a detection signal; and a discharge terminal POUT+ and a discharge terminal POUT- connected to the output terminal of the detection circuit for connecting to the steel caps at both ends of the porcelain insulator.

[0011] Furthermore, the step-up transformer is an audio step-up transformer.

[0012] Furthermore, the voltage multiplier circuit includes several voltage multiplier units connected in series. Each voltage multiplier unit includes a capacitor and a diode, with the cathode of the diode connected to one end of the capacitor. The anode of the diode in the preceding voltage multiplier unit is connected to the other end of the capacitor in the following voltage multiplier unit, and the cathode of the diode in the preceding voltage multiplier unit is connected to the anode of the diode in the following voltage multiplier unit. The other end of the capacitor in the first voltage multiplier unit is connected to the output point H0 of the step-up transformer, and the anode of the diode in the first voltage multiplier unit is connected to the output point L0 of the step-up transformer.

[0013] Furthermore, it also includes a preamplifier circuit, which is used to output a corresponding voltage signal to the low-voltage pulse generator according to the received set input signal.

[0014] Furthermore, the detection circuit includes a filtering circuit, which includes a high-voltage resistor U22 and a high-voltage resistor U23. One end of the high-voltage resistor U22 and one end of the high-voltage resistor U23 are respectively connected to the output terminal of the voltage multiplier circuit. The other ends of the high-voltage resistor U22 and the other ends of the high-voltage resistor U23 are respectively connected to one end of capacitor C3 and one end of capacitor C4. The other end of capacitor C3 is connected to the other end of capacitor C4.

[0015] Furthermore, the detection circuit also includes sampling resistors U18 and U46. One end of sampling resistor U18 is connected to one end of capacitor C3, and the other end of sampling resistor U18 is grounded and connected to the discharge terminal POUT- through sampling resistor U46, high-voltage resistor U38, and high-voltage resistor U37. The other end of sampling resistor U18 is also connected to the discharge terminal POUT+ through high-voltage resistors U34, U39, U11, and U12. Diodes U40, U41, U42, U43, U44, and U45 are connected in series in sequence, and the cathode of diode U40 is connected to the common terminal of high-voltage resistors U11 and U39, the anode of diode U45 is connected to one end of capacitor C3, and the anode of diode U42 is connected to one end of capacitor C4.

[0016] Furthermore, the detection circuit also includes an operational amplifier chip U47. Pin IN1 of the operational amplifier chip U47 is connected to one end of resistor R1, one end of resistor R2, and the positive terminal of diode D1. The other end of resistor R1 is connected to the common terminal of sampling resistor U46 and high-voltage resistor U38. The other end of resistor R2 is connected to pin OUT1 of the operational amplifier chip U47, and the negative terminal of diode D1 is grounded. Pin IN2 of the operational amplifier chip U47 is connected to the positive terminal of diode D2, one end of resistor R3, and one end of resistor R4. The negative terminal of diode D2 is grounded. The other end of resistor R3 is connected to one end of capacitor C3, and the other end of resistor R4 is connected to pin OUT2 of the operational amplifier chip U47. Pin OUT1 of the operational amplifier chip U47 is connected to the output terminal ADC123-IN11 of the detection circuit, and pin OUT2 of the operational amplifier chip U47 is connected to the output terminal ADC123-IN12 of the detection circuit.

[0017] Secondly, a method for zero-current measurement of a high-voltage circuit in a porcelain insulator is provided. This method is based on the porcelain insulator zero-current measurement device described in the first aspect and includes: setting a voltage signal from an input low-voltage pulse generator, wherein the voltage signal is used by the porcelain insulator zero-current measurement device described in the first aspect to form a low-voltage circuit current acting on the porcelain insulator under test; collecting the value of the low-voltage circuit current flowing through the porcelain insulator under test within a set time period, thereby obtaining the insulation resistance of the porcelain insulator under test; and determining the state of the porcelain insulator under test based on the insulation resistance according to a set insulation resistance criterion.

[0018] Furthermore, the insulation resistance criterion includes: if the insulation resistance of the porcelain insulator under test is within the normal threshold range, then the porcelain insulator under test is a normal porcelain insulator; if the insulation resistance of the porcelain insulator under test is within the defect threshold range, then the porcelain insulator under test is a defective inferior porcelain insulator; if the insulation resistance of the porcelain insulator under test is within the zero threshold range, then the porcelain insulator under test is a zero-value porcelain insulator.

[0019] Furthermore, the voltage signals of the input low-voltage pulse generator are set in ascending order. Each input voltage signal corresponds to an insulation resistance of the porcelain insulator under test. When the insulation resistance of the porcelain insulator under test is less than or equal to the set insulation threshold under the current voltage signal, it is determined that the current porcelain insulator has a zero value under the current voltage signal, and the input voltage signal is no longer increased for the current porcelain insulator.

[0020] Thirdly, a method for online zero-voltage measurement of porcelain insulator distribution voltage, based on the low-current zero-voltage measurement method for high-voltage circuits of porcelain insulators described in the second aspect, includes: disconnecting the voltage multiplier circuit to make the outputs of the discharge terminals POUT+ and POUT- connected to the steel caps at both ends of the porcelain insulator zero, and inputting the distribution voltage on the porcelain insulator into the detection circuit through the discharge terminals POUT+ and POUT-; reading the voltage value detected by the detection circuit and correcting it to obtain the actual voltage value on the current porcelain insulator; sequentially detecting each porcelain insulator in the porcelain insulator string and comparing adjacent ones, and identifying the zero-value porcelain insulator according to the set porcelain insulator zero-value criterion.

[0021] Furthermore, the zero-value criterion for porcelain insulators includes: (1) if the distributed voltage of the current porcelain insulator is less than 50% of the distributed voltage of the adjacent porcelain insulator, then the current porcelain insulator is a zero-value porcelain insulator; (2) if the distributed voltage of the current porcelain insulator is less than 50% of the standard distributed voltage, then the current porcelain insulator is a zero-value porcelain insulator; (3) if the peak value of the distributed voltage of the current porcelain insulator is less than the set peak voltage: (A) using the small current zero-value measurement method of the high-voltage circuit of the porcelain insulator, the insulation resistance of the current porcelain insulator is measured under the first set voltage signal and the second set voltage signal respectively; (B) based on the insulation resistance of the current porcelain insulator, the state of the current porcelain insulator is determined according to the set insulation resistance criterion two. (4) If the peak value of the current distributed voltage of the porcelain insulator is greater than the set peak voltage: (a) Using the small current zero measurement method of the high voltage circuit of the porcelain insulator, the insulation resistance of the current porcelain insulator is measured under the third set voltage signal and the fourth set voltage signal respectively; wherein, the third set voltage signal is the superposition voltage of the current distributed voltage of the porcelain insulator and the voltage applied to the current porcelain insulator, and does not exceed the set upper limit voltage one; the fourth set voltage signal is the superposition voltage of the current distributed voltage of the porcelain insulator and the voltage applied to the current porcelain insulator, and does not exceed the set upper limit voltage two; (b) Based on the insulation resistance of the current porcelain insulator, the state of the current porcelain insulator is determined according to the set insulation resistance criterion two.

[0022] Furthermore, the second insulation resistance criterion includes: if the insulation resistance measured twice is within the set normal threshold range, then the current porcelain insulator is judged to be a normal porcelain insulator; if the insulation resistance measured at any time is within the suspected low threshold range, then the current porcelain insulator is judged to be a suspected low-value porcelain insulator; if the insulation resistance measured at any time is within the low threshold range, then the current porcelain insulator is judged to be a low-value porcelain insulator; if the insulation resistance measured at any time is within the suspected zero threshold range, then the current porcelain insulator is judged to be a suspected zero-value porcelain insulator; if the insulation resistance measured at any time is within the zero threshold range, then the current porcelain insulator is judged to be a zero-value porcelain insulator.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention uses a low-voltage pulse generator to convert the received voltage signal into a voltage pulse signal of a set frequency; a step-up transformer to convert the voltage pulse signal emitted by the low-voltage pulse generator into voltage signal one; a voltage multiplier circuit to convert voltage signal one output by the step-up transformer into voltage signal two; and a detection circuit to convert voltage signal two output by the voltage multiplier circuit into a detection signal. By combining distributed voltage measurement with the high-voltage loop small current method, the present invention retains the advantages of the high-voltage breakdown method, the megohmmeter method, and the distributed voltage method, while avoiding their respective disadvantages. This ensures that the insulator is not damaged during the measurement process and that defects in the insulator can be detected comprehensively. Attached Figure Description

[0024] Figure 1 This is a circuit block diagram of a porcelain insulator zero-detection device provided in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the circuit principle of the step-up transformer in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the voltage multiplier circuit in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the detection circuit in an embodiment of the present invention;

[0028] Figure 5 This is a discharge curve diagram of a normal insulator;

[0029] Figure 6 It is a discharge curve collected when the probe is suspended in the air;

[0030] Figure 7 The discharge curve was collected when a 1G high-voltage resistor was connected in parallel to a normal insulator.

[0031] Figure 8 This is a discharge curve diagram of a zero-value insulator;

[0032] Figure 9 This is a schematic diagram of the circuit principle of the pre-amplifier circuit in an embodiment of the present invention;

[0033] Figure 10 It shows the measured waveforms of the distributed voltage of the insulator and the high-voltage output. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0035] Example 1

[0036] like Figure 1 As shown, a zero-detection device for a porcelain insulator includes: a low-voltage pulse generator for converting a received voltage signal into a voltage pulse signal of a set frequency; a step-up transformer for converting the voltage pulse signal emitted by the low-voltage pulse generator into voltage signal one; a voltage multiplier circuit for converting voltage signal one output by the step-up transformer into voltage signal two, wherein voltage signal two is an integer multiple of voltage signal one; a detection circuit for converting voltage signal two output by the voltage multiplier circuit into a detection signal; and discharge terminals POUT+ and POUT- connected to the output terminal of the detection circuit for connecting to the steel caps at both ends of the porcelain insulator.

[0037] In this invention, the low-voltage pulse generator is a 10kHz low-voltage pulse generator, and the step-up transformer is an audio step-up transformer. For example... Figure 2 As shown, this invention employs a push-pull structure to drive a conventional audio step-up transformer, whose secondary voltage can reach over 6KV. In the actual circuit of this invention, the step-up drive uses a 10kHz frequency, and the transformer's step-up ratio is 200. Therefore, when the input low-voltage pulse generator voltage signal is VCC24V=30V, the output terminal HO-LO of the step-up transformer is ±6KV.

[0038] Due to the electrical isolation provided by the transformer, the output voltage and input voltage levels are isolated. Therefore, the high-voltage step-up section is electrically isolated from the transformer's input section, which is also electrically isolated from the main control section. This electrical isolation between the high-voltage section and the main control section prevents interference from the significant voltage level changes during the high-voltage multiplication process. Simultaneously, since the detection circuit is located in the high-voltage loop, it requires an isolation power transformer to supply power. Furthermore, the signal obtained by the detection circuit is transmitted to the main control circuit via an optical communication receiver and signal processing unit.

[0039] like Figure 2 As shown, the emitter of transistor Q17 (S9014) is grounded, the base is connected to terminal TIM5_CH1 (used to receive the voltage pulse signal output by the low-voltage pulse generator) through resistor R42 (1kΩ), and the collector is connected to power supply VCC12V through resistor R33 (10kΩ). The collector of transistor Q17 is also connected to pin IN of isolated gate driver U9 (IRS2104STRPBF) and one end of resistor R44 (1kΩ). The other end of resistor R44 is connected to the base of transistor Q18 (S9014). The emitter of transistor Q18 is grounded, and the collector is connected to power supply VCC12V through resistor R43 (10kΩ). The collector of transistor Q18 is also connected to pin IN of isolated gate driver U7 (IRS2104STRPBF).

[0040] The VCC pin of the isolated gate driver U9 is connected to the positive terminal of diode D5 (SS14L), the power supply VCC (12V), one end of capacitor C35 (10uF), and one end of resistor R30 (10kΩ). The COM pin of the isolated gate driver U9 is grounded, the other end of capacitor C35 is grounded, and the other end of resistor R30 is connected to the SD# pin of the isolated gate driver U9. The negative terminal of diode D5 is connected to the VB pin of the isolated gate driver U9 and one end of capacitor C36 (10uF). The HO pin of the isolated gate driver U9 is connected to one end of resistor R31 (30Ω), and the LO pin is connected to resistor R... One end of resistor R32 (30Ω) is connected to pin VS of isolated gate driver U9, the other end of capacitor C36, the source of MOSFET Q5 (20N06D), the drain of MOSFET Q6 (20N06D), the anode of diode D6 (SMF30A), the cathode of diode D7 (SMF30A), and the input terminal of transformer U10; the other end of resistor R31 is connected to the gate of MOSFET Q5, the other end of resistor R32 is connected to the gate of MOSFET Q6, the drain of MOSFET Q5 is connected to power supply VCC24V, the cathode of diode D6, the source of MOSFET Q6 is grounded, and the anode of diode D7 is grounded.

[0041] The VCC pin of isolated gate driver U7 is connected to the positive terminal of diode D8 (SS14L), the power supply VCC (12V), one end of capacitor C37 (10uF), and one end of resistor R34 (10kΩ). The COM pin of isolated gate driver U9 is grounded, the other end of capacitor C37 is grounded, and the other end of resistor R34 is connected to the SD# pin of isolated gate driver U7. The negative terminal of diode D8 is connected to the VB pin of isolated gate driver U7 and one end of capacitor C38 (10uF). The HO pin of isolated gate driver U9 is connected to one end of resistor R35 (30Ω), and the LO pin is connected to resistor R3. One end of resistor 7 (30Ω) is connected to pin VS of isolated gate driver U9, the other end of capacitor C38, the source of MOSFET Q7 (20N06D), the drain of MOSFET Q9 (20N06D), the anode of diode D9 (SMF30A), the cathode of diode D10 (SMF30A), and the input terminal of transformer U10. The other end of resistor R35 is connected to the gate of MOSFET Q9, the other end of resistor R37 is connected to the gate of MOSFET Q9, the drain of MOSFET Q7 is connected to power supply VCC24V, the cathode of diode D9, the source of MOSFET Q9 is grounded, and the anode of diode D10 is grounded.

[0042] The output terminals HO-LO (used for output voltage signal one) of transformer U10 are ±6KV.

[0043] The voltage multiplier circuit includes several voltage multiplier units connected in series. Each voltage multiplier unit includes a capacitor and a diode, with the cathode of the diode connected to one end of the capacitor. The anode of the diode in the preceding voltage multiplier unit is connected to the other end of the capacitor in the following voltage multiplier unit, and the cathode of the diode in the preceding voltage multiplier unit is connected to the anode of the diode in the following voltage multiplier unit. The other end of the capacitor in the first voltage multiplier unit is connected to the output point HO of the step-up transformer, and the anode of the diode in the first voltage multiplier unit is connected to the output point LO of the step-up transformer.

[0044] like Figure 3 As shown, in this invention, capacitor C5 (10nF) and diode U24 (2CL77) form the first-stage voltage multiplier unit, capacitor C10 (10nF) and diode U25 (2CL77) form the second-stage voltage multiplier unit, and so on, for a total of 10 stages of voltage multiplier units. Capacitors C6-C9 and C11-C14 are all identical, with a capacitance value of 10nF; diodes U26-U33 are identical, all of model 2CL77. When the input is 6KV DC, the voltage between the output terminals P_0K and P_60K (used for output voltage signal two) is 60KV.

[0045] This invention utilizes the alternating characteristics of transformer output to achieve multi-stage voltage boosting through a circuit network composed of diodes and capacitors, ultimately achieving a DC output of up to 60KV or higher. The invention employs a 10x boost circuit, thus utilizing 10 high-voltage silicon stacks (i.e., diodes U24~U33) and 10 high-voltage capacitors (capacitors C5~C14).

[0046] The high-voltage output terminal after voltage multiplication is P-60K / P-0K. To reduce the 10kHz high-frequency component in the high-voltage output, a symmetrical RC filter network consisting of high-voltage resistors U22 (2MΩ) and U23 (2MΩ) and capacitors C3 (10nF) and C4 (10nF) is added. The terminals of capacitors C3 and C4 are the final DC high-voltage terminals.

[0047] like Figure 4 As shown, the filter circuit includes high-voltage resistors U22 and U23. One end of high-voltage resistor U22 and one end of high-voltage resistor U23 are respectively connected to the output terminal of the voltage multiplier circuit. The other ends of high-voltage resistors U22 and U23 are respectively connected to one end of capacitor C3 and one end of capacitor C4. The other end of capacitor C3 is connected to the other end of capacitor C4.

[0048] One end of the sampling resistor U18 (14KΩ) is connected to one end of the capacitor C3, and the other end of the sampling resistor U18 is grounded and connected to the discharge terminal POUT- through the sampling resistor U46 (14KΩ), the high voltage resistor U38 (100MΩ) and the high voltage resistor U37 (100MΩ).

[0049] The other end of the sampling resistor U18 is also connected to the discharge terminal POUT+ through high-voltage resistors U34 (1GΩ), U39 (1GΩ), U11 (100MΩ), and U12 (100MΩ).

[0050] Diodes U40 (2CL77), U41 (2CL77), U42 (2CL77), U43 (2CL77), U44 (2CL77), and U45 (2CL77) are connected in series. The cathode of diode U40 is connected to the common terminal of high-voltage resistors U11 and U39, the anode of diode U45 is connected to one end of capacitor C3, and the anode of diode U42 is connected to one end of capacitor C4. In this invention, diodes U40, U41, U42, U43, U44, and U45 are all high-voltage silicon stacks.

[0051] Pin IN1 of op-amp chip U47 (LM358BIDR) is connected to one end of resistor R1 (2MΩ), one end of resistor R2 (2MΩ), and the positive terminal of diode D1 (1N4148WT). The other end of resistor R1 is connected to the common terminal of sampling resistor U46 and high voltage resistor U38. The other end of resistor R2 (2MΩ) is connected to pin OUT1 of op-amp chip U47. The negative terminal of diode D1 is grounded.

[0052] Pin IN2 of op-amp chip U47 is connected to the positive terminal of diode D2 (1N4148WT), one end of resistor R3 (2MΩ), and one end of resistor R4 (2MΩ). The negative terminal of diode D2 is grounded. The other end of resistor R3 is connected to one end of capacitor C3, and the other end of resistor R4 is connected to pin OUT2 of op-amp chip U47. Pin OUT1 of op-amp chip U47 is connected to the output terminal ADC123-IN11 of the detection circuit, and pin OUT2 of op-amp chip U47 is connected to the output terminal ADC123-IN12 of the detection circuit.

[0053] The external measurement output terminals of this invention are POUT- and POUT+. These two terminals are connected in series with a 200MΩ high-voltage resistor before being connected to the DC high-voltage terminal. A total of 400MΩ resistors are connected in series in the measurement circuit, limiting the discharge current when the insulator experiences zero-value breakdown and minimizing further damage to defective insulators during the measurement process. The two 14kΩ resistors U46 and U18 in the circuit are signal sampling resistors. Compared to the total 400MΩ resistors U37, U38, U11, and U12, their resistance is less than one ten-thousandth, so their presence can be ignored when calculating the high-voltage circuit discharge current.

[0054] The discharge terminals POUT+ and POUT- are connected to the insulator being measured via metal push pins. Typically, the electrical characteristics of an insulator are equivalent to a capacitor C (10-15pF) in parallel with a resistor R. For a good insulator, R is close to infinity. Insulators with a resistance above 2GΩ are generally considered good, those below 500MΩ are considered zero-value insulators, and those below 2GΩ but above 500MΩ are considered defective and inferior.

[0055] In this invention, 14KΩ resistors U18 and U46 are the sampling resistors for the high-voltage circuit small current zero-measurement method and the distributed voltage online zero-measurement method, respectively. GND in the figure is the power supply reference zero point of the detection circuit. The detection circuit uses a dual operational amplifier to convert the voltage changes on the sampling resistors U18 and U46 into the voltage outputs ADC123-IN12 and ADC123-IN11 of the operational amplifier, respectively. When the current flowing through the sampling resistors U18 and U46 is 0, the operational amplifier output is 3.3V; when the current reaches 150μA, the output is 0.3V. The larger the current, the lower the voltage, until the current reaches 165μA, at which point the output is 0V, and the operational amplifier reaches saturation. Therefore, the maximum detection current is 165μA.

[0056] When testing the insulator withstand voltage, the high-voltage circuit outputs a specified high voltage (generally between 20KV and 60KV) according to the system's instructions. Capacitors C3 and C4 reach the specified DC high voltage (U) within 40ms. This high voltage first passes through resistors U39 and U34 (1GΩ), totaling 2GΩ, and then through the 14KΩ sampling resistor U18 to form an internal loop, generating a loop current of U / 2G. Simultaneously, this high voltage also passes through resistors U11 and U12, connecting in series from POUT+ to the insulator (C and R in parallel), and then through POUT- to... Resistors U37 and U38, along with sampling resistors U46 and U18, form an external loop. The op-amp output voltage ADC123-IN12 is equal to the sum of the currents in the two loops multiplied by the 14KΩ resistor. If the high-voltage circuit malfunctions and fails to generate high voltage U, neither the internal nor external loop will generate current. The control circuit can immediately determine that there is a high-voltage fault and stop the invalid detection. Therefore, this invention can ensure the effectiveness of high-voltage detection. When high voltage U is generated normally, the current in the internal loop is known: U / 2G ohms. The portion exceeding the current in the internal loop is the current in the external loop.

[0057] The current across resistor U18 includes the known internal circuit current: U / 2G ohms, and the external circuit current U / (R+U11+U12+U37+U38)=U / (R+400MΩ); the total current is (U / 2G+U / (R+400MΩ)). This current is amplified by the operational amplifier and converted into a voltage signal ADC123-IN12. Setting the current conversion efficiency of the operational amplifier to K, the resistance R = U / ((K×(3.3-ADC123-IN12)-U / 2G))-400MΩ). With a fixed value for K, the equivalent resistance R of the insulator can be directly calculated based on the value of ADC123-IN12. For ease of illustration, the software system has implemented the following processing.

[0058] (1) For a normal insulator, the output of AD123-IN12 is as follows: When a 60KV high voltage U is applied for 500ms, AD123-IN12 samples at 1KHZ. The ADC of the microcontroller is 12-bit, and the original sampled value is 0-4095, corresponding to the 0-3.3V of the op-amp; under the 60KV voltage, the current in the inner circuit is 60KV / 2G=30μA, and the voltage change on the 14K ohm sampling resistor is 30μA×14KΩ resistance=420MV. In order to conveniently reflect the external circuit current, the microcontroller software makes a transformation on the sampled data: 0-2.88V voltage corresponds to 0-255 data output.

[0059] When the external loop current is 0, the corresponding sampling voltage of the ADC is 3.3V - 420MV = 2.88V, and the sampling value is 255. Figure 5 As shown, under normal insulator measurement, the ADC sampling output stabilizes at a value of 239. The corresponding voltage across the sampling resistor is (239 / 255) × 2.88 = 2.7V, and the corresponding current across the sampling resistor is (3.3V - 2.7V) / 14kΩ = 43μA. This indicates that the external circuit current is 43 - 30 = 13μA. Therefore, the voltage drop across the 400MΩ resistor connected in series in the external circuit is 13μA × 400MΩ = 5200V. Thus, the voltage across the two ends of the insulator stabilizes at 60KV - 5.2KV = 54.8KV, and the insulation resistance is calculated as 54.8KV / 13μA = 4.2GΩ.

[0060] (2) When the insulator is not connected, the ADC sampling value output is stable at 231 when the probe is suspended. The voltage on the sampling resistor is (231 / 256)×2.88v=2.61V, and the current on the sampling resistor is (3.3v-2.61v) / 14k=49μA. Then the external circuit current is 49μA-30μA=19μA, the voltage drop across the 400M series resistor in the external circuit is 19μA*400M=7.6KV, and the withstand voltage of the air on both sides of the probe is 60KV-7.6KV=52.4KV. If converted to insulation resistance, the insulation resistance is 52.4KV / 19μA=2.7G ohms.

[0061] like Figure 6 As shown, the R of the insulator is almost infinite, having no effect on the loop current. The charging time constant of the loop for capacitor C is 400M × 15pF = 6ms. Simultaneously, the high-voltage circuit also requires 40ms-100ms to generate U, thus producing the aforementioned curve. In the normal insulator measurement curve, the downward and then upward pulse represents the loop current during the process of high voltage U increasing from 0 to the specified value U, and simultaneously charging capacitor C to voltage U. This capacitor charging process is absent when the probe is suspended. Although both measured resistances are greater than 2G ohms (measured value 220Ω), the resistance of the normal insulator (measured value 239Ω) is slightly higher than that of the probe with the probe suspended (measured value 231Ω). This indicates that the insulation of the insulator disc effectively increases the creepage distance, while the air insulation between the two probes is somewhat poor when the probe is suspended.

[0062] (3) The sampling curve obtained when a 1G high-voltage resistor is connected in parallel to a good insulator is as follows: Figure 7 As shown.

[0063] The ADC sampling value is 201, corresponding to a voltage across the sampling resistor of (201 / 256) × 2.88V = 2.27V, and a current across the sampling resistor of (3.3V - 2.27V) / 14kΩ = 74μA. Therefore, the external circuit current is 74 - 30 = 44μA. The voltage drop across the 400MΩ series resistor in the external circuit is 44μA × 400MΩ = 17.6kV. Thus, the voltage across the insulator is 60kV - 17.6kV = 42.4kV. If calculated as insulation resistance, the insulation resistance is 42.6kV / 44μA = 0.97GΩ.

[0064] Because of the addition of a 1G resistor in the high-voltage circuit, the circuit current caused by the 1G resistor is increased while the capacitor C is being charged, and eventually stabilizes at a relatively large circuit current; the equivalent resistance is approximately 1G ohms.

[0065] (4) Actual measurement of a known zero-value insulator.

[0066] The ADC sampling value is 155, corresponding to a voltage across the sampling resistor of (155 / 256) × 2.88V = 1.38V, and a current across the sampling resistor of (3.3V - 1.38V) / 14kΩ = 137μA. Therefore, the external circuit current is 137 - 30 = 107μA, and the voltage drop across the 400MΩ series resistor in the external circuit is 107μA × 400MΩ = 42.8kV. Thus, the voltage across the insulator is 60kV - 42.8kV = 17.2kV. If calculated as insulation resistance, the insulation resistance is 17.2kV / 107μA = 160MΩ.

[0067] This zero-value insulator maintained a relatively large current under high voltage. During the 200ms-500ms time period, the equivalent resistance in the external circuit was lower than the 500MΩ resistance specified in this invention, thus it was determined to be a zero-value insulator. Figure 8 As shown.

[0068] The present invention also includes a pre-amplifier circuit, which is part of the main control circuit and is used to output a corresponding voltage signal to the low-voltage pulse generator according to the received set input signal.

[0069] This invention precisely controls the voltage output of the high-voltage generator by controlling the voltage of the pre-amplifier low-voltage circuit VCC24V, due to the fixed boost and multiplier relationship. For example... Figure 9 As shown, in this invention, by controlling A0, A1, and A2 of analog switch U3 (CD4051BM / TR), the feedback resistor network of boost circuit LM3478 is changed, and the voltage of VCC24V is controlled to 5V, 10V, 15V, 20V, 22.5V, 25V, 27.5V, and 30V respectively; the corresponding high voltage output is divided into 8 levels (10KV, 20KV, 30KV, 40KV, 45KV, 50KV, 55KV, and 60KV).

[0070] The 24V power supply VCC is connected via resistor R16 (43kΩ) to one end of resistors R15 (1.88kΩ), R11 (2.06kΩ), R10 (2.28kΩ), R9 (2.55kΩ), R8 (2.89kΩ), R7 (3.94kΩ), R6 (6.2kΩ), and R5 (14.5kΩ). The other ends of resistors R15, R11, R10, R9, R8, R7, R6, and R5 are connected to pins Y7, Y6, Y5, Y4, Y3, Y2, Y1, and Y0 of analog switch U3 (CD4051BM / TR), respectively. The 24V power supply VCC is also connected via resistor R16 to pin FB of power supply chip U5 (LM3478MAX / NOPB). Pins Z, E#, VEE, and VSS of analog switch U3 are grounded. The analog switch U3's pin VDD is connected to the power supply VCC12V6 and one end of capacitor C24 (100nF), while the other end of capacitor C24 is grounded.

[0071] The anode of diode D11 (SS56F) and one end of capacitor C23 (100nF) are grounded; the cathode of diode D11 is connected to one end of power inductor L1 (10μH), the other end of capacitor C23, and the drain of MOSFET U4 (20P10); the other end of power inductor L1 is connected to the drain of MOSFET Q3 (NCE6080K) and the anode of diode D3 (SS56F); the gate of MOSFET U4 is connected to one end of resistor R17 (30kΩ) and the drain of MOSFET Q2 (AO3400); MOSFET... The source and gate of transistor Q2 are connected to pin DR of power supply chip U5 and the gate of field-effect transistor Q3; the other end of resistor R17 is connected to the source of field-effect transistor U4, power supply VCC12V6, one end of capacitor C25 (100μF), one end of capacitor C26 (100μF), one end of capacitor C27 (100μF), one end of capacitor C28 (100μF), and pin VIN of power supply chip U5; the other ends of capacitors C25, C26, C27, and C28 are grounded.

[0072] The ISEN pin of power chip U5 is connected to one end of capacitor C22 (10pF) and one end of resistor R12 (100Ω). The other end of capacitor C22 is grounded. The other end of resistor R12 is connected to one end of high voltage resistor U6 (20mΩ) and the source of field-effect transistor Q3. The other end of high voltage resistor U6 is grounded. The cathode of diode D3 is connected to one end of capacitor C15 (100μF), one end of capacitor C16 (100μF), one end of capacitor C21 (100μF), one end of capacitor C17 (100μF), one end of capacitor C18 (100nF), and the power supply VCC24V. The other ends of capacitors C15, C16, C21, C17, and C18 are grounded.

[0073] The COMP pin of power chip U5 is connected to one end of capacitor C19 (10nF) and one end of capacitor C20 (220nF). The other end of capacitor C19 is grounded, and the other end of capacitor C20 is grounded through resistor R13 (1.05kΩ). The AGND pin of power chip U5 is grounded. The FA / SD pin of power chip U5 is grounded through resistor R14 (82kΩ). The PGND pin of power chip U5 is grounded.

[0074] Measure the insulator using voltage levels from low to high. Once a zero value is found in the insulator, stop increasing the applied voltage to avoid further expansion of the defective insulator due to excessively high applied voltage.

[0075] Example 2

[0076] Based on the zero-detection device for porcelain insulators described in Embodiment 1, this embodiment provides a method for zero-detection of small currents in high-voltage circuits of porcelain insulators, including:

[0077] Set the voltage signal of the input low-voltage pulse generator. The voltage signal is used by the porcelain insulator zero-detection device described in Example 1 to form a small high-voltage loop current acting on the porcelain insulator to be tested.

[0078] The small current value of the high-voltage circuit flowing through the porcelain insulator under test is collected within a set time period, and then the insulation resistance of the porcelain insulator under test is obtained.

[0079] Based on the established insulation resistance criterion one, the state of the porcelain insulator under test is determined according to the insulation resistance.

[0080] Insulation resistance criterion one includes:

[0081] If the insulation resistance Rx of the porcelain insulator under test is within the normal threshold range (Rx > 2GΩ), then the porcelain insulator under test is a normal porcelain insulator.

[0082] If the insulation resistance Rx of the porcelain insulator to be tested is within the defect threshold range (500MΩ < Rx < 2GΩ), then the porcelain insulator to be tested is a defective and inferior porcelain insulator.

[0083] If the insulation resistance Rx of the porcelain insulator under test is within the zero threshold range (Rx < 500 MΩ), then the porcelain insulator under test is a zero-value porcelain insulator.

[0084] The high-voltage circuit low-current method for measuring the zero value of insulators in this invention differs from the traditional insulator withstand voltage method for zero measurement. The traditional insulator withstand voltage method for zero measurement is as follows:

[0085] A high-voltage pulse is applied to the insulator, and then the change in voltage across the insulator is detected.

[0086] (1) A normal insulator can reach the specified voltage and slowly reduce the voltage after the pulse high voltage disappears;

[0087] (2) Inferior insulators can basically reach the specified voltage, but the voltage drops quickly after the pulse high voltage disappears;

[0088] (3) The zero-value insulator cannot reach the specified voltage and the voltage drops quickly after the pulse high voltage disappears.

[0089] Problems with traditional methods: (1) Whether a specified voltage can be applied to an insulator depends not only on the performance of the insulator but also on the power (internal resistance) of the high-voltage pulse generator. Therefore, there are high requirements for the performance consistency of the high-voltage pulse generator; (2) When a high-voltage pulse is applied transiently to an insulator, a large current discharge may occur if the insulator is zero-valued or the measuring probe has poor contact. Even with a good insulator, a large current will be generated when the pulse voltage is applied transiently to the insulator capacitance. The electromagnetic interference generated by the large current can easily affect other circuits; (3) If a poor-quality insulator can no longer withstand the specified high voltage, a sudden application of high voltage may cause problems. This could very likely cause the insulator to break down physically and be completely damaged. This kind of damage will not have adverse consequences for insulators not installed on the line, but it is very dangerous when used for online measurement: For example, there are already many inferior insulators on an insulator string. However, due to the design margin, these inferior insulators can still withstand the withstand voltage and allow the line to work normally. But if a pulse high voltage is directly applied to such insulators during the measurement process, it may cause the measured inferior insulator to break down directly and become zero value. After multiple such inferior insulators become zero value, the withstand voltage of other insulators will inevitably rise. In the worst case, the insulators will not be able to withstand the withstand voltage and will short circuit!

[0090] The high-voltage circuit low-current method of the present invention is different from the traditional withstand voltage zero-test method.

[0091] The high voltage generated in this invention is a controllable, continuous DC high voltage, applied to the insulator through a 400MΩ resistor. During the high voltage application process, there is a current limiting of up to 150μA (150μA at a 60KV applied voltage; the current limiting current decreases proportionally as the applied voltage decreases). By detecting the loop current, it is determined whether the insulator has reached the specified high voltage. During the measurement process, there is no need to pay too much attention to the transient changes in the voltage on the insulator; it is only necessary to determine the final loop current of the insulator within 200ms-500ms after the high voltage is applied. Based on the final loop current and the corresponding applied voltage, the equivalent resistance of the insulator under a given high voltage can be calibrated using a resistor.

[0092] During testing, the voltage signals of the low-voltage pulse generator are set in ascending order. Each input voltage signal corresponds to an insulation resistance of the porcelain insulator under test. When the insulation resistance of the porcelain insulator under test is less than or equal to the set insulation threshold under the current voltage signal, it is determined that the current porcelain insulator has a zero value under the current voltage signal. The input voltage signal will not be increased for the current porcelain insulator to avoid the defective insulator from being further enlarged due to excessively high applied voltage.

[0093] Example 3

[0094] Based on the porcelain insulator zero-detection device described in Embodiment 1 and the porcelain insulator high-voltage circuit small current zero-detection method described in Embodiment 2, this embodiment provides an online zero-detection method for the distributed voltage of porcelain insulators, including:

[0095] Disconnect the voltage multiplier circuit to make the outputs of the discharge terminals POUT+ and POUT- on the steel caps at both ends of the porcelain insulator zero. The distributed voltage on the porcelain insulator is input to the detection circuit through the discharge terminals POUT+ and POUT-.

[0096] The voltage value detected by the detection circuit is read and corrected to obtain the actual voltage value on the current porcelain insulator;

[0097] Each porcelain insulator on the porcelain insulator string is tested sequentially, and adjacent insulators are compared. The zero-value porcelain insulator is identified according to the set zero-value criterion.

[0098] When detecting distributed voltage, the high-voltage boost circuit stops working, and the output of P-60K / P-0K is 0. When POUT+ / POUT- is connected to the steel cap of the insulator, the distributed voltage on the insulator is applied to these two points. When the distributed voltage is in the negative half-cycle, POUT+ is negative and POUT- is positive. The high-voltage silicon stacks U40, U41, U42, U43, U44, and U45 are turned on, and the equivalent resistance of the POUT+ / POUT- path is 400M ohms (the two 14K resistors are negligible). At this time, the output of the first op-amp remains unchanged at 3.3V. Because the connection resistance is relatively small, the measured distributed voltage differs significantly from the actual distributed voltage. Therefore, the op-amp in the measuring circuit maintains a 3.3V output, and the system does not accept the distributed voltage in the negative half-cycle. When the distributed voltage is in the positive half-cycle, POUT+ is positive and POUT- is negative. The high-voltage silicon stacks U40, U41, U42, U43, U44, and U45 are cut off, and POUT+... The equivalent resistance of the / POUT- path is 2400M ohms (the two 14K resistors are negligible). At this time, the output of the first op-amp decreases as the distributed voltage increases. The equivalent capacitance of a normal insulator is 10-15pF. Calculated based on 10pF, the AC impedance at 50Hz is: 1 / WC = 300M ohms. This invention uses a 2400M ohm connection resistor. Compared to the 300M AC impedance, the connection of the 2400M resistor is equivalent to reducing the original insulator connection impedance from 300M to 267M. Therefore, the measured distributed voltage is 89% of the actual distributed voltage (267 / 300). The measured distributed voltage can be corrected by adding an 11% connection error to make the detected distributed voltage closer to the actual value.

[0099] This invention integrates insulator voltage distribution measurement and high-voltage low-current loop measurement into one device. During power-off measurement, the distributed voltage measurement is not activated, and only the high-voltage measurement is performed. During live measurement, the distributed voltage on the insulator is measured first, and then the appropriate high-voltage setting is determined based on the existing distributed voltage on the insulator to perform high-voltage withstand voltage measurement, so as to avoid the total amount of distributed voltage superimposed on the high-voltage measurement exceeding the withstand voltage limit of the insulator.

[0100] The online method for measuring zero voltage distribution on porcelain insulators and the principle for judging zero and low values ​​are as follows:

[0101] (1) Connect the probe to both ends of the porcelain insulator under test, start the distributed voltage measurement, and transmit the obtained sampling data to the main MCU. The normal distributed voltage is a near sine wave of 50HZ. However, due to the circuit structure, the system impedance in half of the 50HZ period is 2.4G and the system impedance in the other half of the period is 400M. Considering that the larger the impedance, the more accurate the data will be, only the half-cycle graph corresponding to the 2.4G impedance is used. Based on the peak value in the graph, the distributed voltage value of this insulator is determined.

[0102] (2) Corresponding to the physical arrangement of porcelain insulators, the distributed voltage values ​​of a string of porcelain insulators are compared with adjacent values. Insulators that are significantly less than 50% of the adjacent values ​​are insulators that are already operating in a zero-value state; insulators that are significantly lower than 50% of the standard distributed voltage are also judged as zero-value insulators. Insulators with very low distributed voltages definitely have zero-value problems, but insulators with very high distributed voltages are not necessarily without zero-value or low-value problems, because the equivalent AC impedance of the insulator capacitance is about 400M ohms, and inferior insulators with a resistance of about 1000M ohms will also share a relatively large distributed voltage in the circuit.

[0103] (3) For insulators with a distributed voltage (peak value) of less than 15KV, (A) first apply a high voltage of 30KV (first set voltage signal) to measure the high voltage loop current. When the impedance corresponding to the high voltage loop current is greater than 2G, apply a high voltage of 50KV (second set voltage signal) to measure the high voltage loop current again, and then determine the impedance corresponding to the high voltage loop current. When the measured impedances are both greater than 2G, it is judged as a normal insulator; when the measured impedance under the specified high voltage is between 1.5G and 2G, it is judged as a suspected low-value insulator; when the measured impedance under the specified high voltage is between 1.5G and 1G, it is judged as a low value; when the measured impedance under the specified high voltage is between 1G and 0.5G, it is judged as a suspected zero value; when the measured impedance under the specified high voltage is less than 500MΩ, it is judged as a zero value.

[0104] (4) For insulators with a distributed voltage greater than 15KV, it is necessary to estimate the value of the applied high voltage; the first applied high voltage (third set voltage signal) plus the distributed voltage value should not exceed 40KV (set upper limit voltage one), and the second applied high voltage (fourth set voltage signal) plus the distributed voltage value should not exceed 60KV (set upper limit voltage two); the judgment basis is the same as above.

[0105] (5) Figure 10 These are data measured in actual online operating lines. Figure 10 The green curve in the figure represents the distributed voltage measurement data.

[0106] The distributed voltage (AD123-IN11, sampled at 2kHz) only shows a value for half a cycle in 50Hz, and the measured peak voltage of the distributed voltage is 20kV; therefore, the high voltage U is selected for measurement at 40kV. The effect of the distributed voltage superposition can be seen in the high voltage measurement curve (AD123-IN12, sampled at 1kHz) (red curve). At the same time, the equivalent resistance of this insulator under high voltage is above 2G ohms, so it is judged to be a normal insulator.

[0107] In summary, the criteria for determining the zero value of porcelain insulators include:

[0108] (1) If the current porcelain insulator's distributed voltage is less than 50% of the distributed voltage of the adjacent porcelain insulator, then the current porcelain insulator is a zero-value porcelain insulator;

[0109] (2) If the current distributed voltage of the porcelain insulator is lower than 50% of the standard distributed voltage, then the current porcelain insulator is a zero-value porcelain insulator;

[0110] (3) If the peak value of the distributed voltage of the current porcelain insulator is less than the set peak voltage: (A) Use the porcelain insulator zero-measurement method described in Example 2 to measure the insulation resistance of the current porcelain insulator under the first set voltage signal and the second set voltage signal respectively; (B) Based on the insulation resistance of the current porcelain insulator, determine the state of the current porcelain insulator according to the set insulation resistance criterion 2.

[0111] (4) If the peak value of the current distributed voltage of the porcelain insulator is greater than the set peak voltage: (a) Using the porcelain insulator zero-measurement method described in Example 2, the insulation resistance of the current porcelain insulator is measured under the third set voltage signal and the fourth set voltage signal respectively; wherein, the third set voltage signal is the superposition voltage of the current distributed voltage of the porcelain insulator and the voltage applied to the current porcelain insulator, and does not exceed the set upper limit voltage one; the fourth set voltage signal is the superposition voltage of the current distributed voltage of the porcelain insulator and the voltage applied to the current porcelain insulator, and does not exceed the set upper limit voltage two; (b) Based on the insulation resistance of the current porcelain insulator, the state of the current porcelain insulator is determined according to the set insulation resistance criterion two.

[0112] Insulation resistance criterion two includes:

[0113] If the insulation resistance measured twice is within the set normal threshold range (Rx > 2GΩ), then the current porcelain insulator is determined to be a normal porcelain insulator.

[0114] If any measured insulation resistance falls within the suspected low-value threshold range (1.5GΩ < Rx < 2GΩ), then the current porcelain insulator is judged to be a suspected low-value porcelain insulator.

[0115] If any measured insulation resistance falls within the low threshold range (1GΩ < Rx < 1.5GΩ), then the current porcelain insulator is determined to be a low-value porcelain insulator.

[0116] If any measured insulation resistance falls within the suspected zero-value threshold range (0.5GΩ < Rx < 1GΩ), then the current porcelain insulator is determined to be a suspected zero-value porcelain insulator.

[0117] If any measured insulation resistance is within the zero threshold range (Rx < 500MΩ), then the current porcelain insulator is determined to be a zero-value porcelain insulator.

[0118] This invention integrates insulator voltage distribution measurement and high-voltage low-current loop measurement into one device. During power outage measurement, the voltage distribution measurement is not activated, and only the high-voltage measurement is performed.

[0119] When performing zero-value measurements on insulators operating online, first measure the distributed voltage of the insulator under test. Then, based on the existing distributed voltage on the porcelain insulator, determine an appropriate high-voltage range for small-current measurement of the high-voltage circuit. This avoids the total voltage measured due to the superposition of the distributed voltage and the applied high voltage exceeding the insulator's withstand voltage limit. The superposition of the distributed voltage and the applied high voltage should be close to 60kV but not exceed 60kV. This ensures that potential zero-value defects in the insulator can be measured while preventing overvoltage or overcurrent damage to the insulator during the measurement process.

[0120] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A zero-detection device for porcelain insulators, characterized in that, include: A low-voltage pulse generator used to convert a received voltage signal into a voltage pulse signal of a set frequency; A step-up transformer used to convert voltage pulse signals generated by a low-voltage pulse generator into voltage signal 1; A voltage multiplier circuit is used to convert voltage signal one output from a step-up transformer into voltage signal two, wherein voltage signal two is an integer multiple of voltage signal one; A detection circuit used to convert the voltage signal output by the voltage multiplier circuit into a detection signal; Connected to the output of the detection circuit, it is used to connect the discharge terminals POUT+ and POUT- on the steel caps at both ends of the porcelain insulator. The detection circuit includes a filter circuit, which includes a high-voltage resistor U22 and a high-voltage resistor U23. One end of the high-voltage resistor U22 and one end of the high-voltage resistor U23 are respectively connected to the output terminal of the voltage multiplier circuit. The other end of the high-voltage resistor U22 and the other end of the high-voltage resistor U23 are respectively connected to one end of capacitor C3 and one end of capacitor C4. The other end of capacitor C3 is connected to the other end of capacitor C4. One end of the sampling resistor U18 is connected to one end of the capacitor C3, and the other end of the sampling resistor U18 is grounded and connected to the discharge terminal POUT- through the sampling resistor U46, high voltage resistor U38 and high voltage resistor U37. The other end of the sampling resistor U18 is also connected to the discharge terminal POUT+ through high-voltage resistors U34, U39, U11, and U12; Diodes U40, U41, U42, U43, U44, and U45 are connected in series in sequence. The cathode of diode U40 is connected to the common terminal of high-voltage resistors U11 and U39, the anode of diode U45 is connected to one end of capacitor C3, and the anode of diode U42 is connected to one end of capacitor C4. Pin IN1 of op-amp chip U47 is connected to one end of resistor R1, one end of resistor R2, and the positive terminal of diode D1. The other end of resistor R1 is connected to the common terminal of sampling resistor U46 and high voltage resistor U38. The other end of resistor R2 is connected to pin OUT1 of op-amp chip U47. The negative terminal of diode D1 is grounded. Pin IN2 of op-amp chip U47 is connected to the positive terminal of diode D2, one end of resistor R3, and one end of resistor R4. The negative terminal of diode D2 is grounded. The other end of resistor R3 is connected to one end of capacitor C3, and the other end of resistor R4 is connected to pin OUT2 of op-amp chip U47. Pin OUT1 of op-amp chip U47 is connected to the output terminal ADC123-IN11 of the detection circuit, and pin OUT2 of op-amp chip U47 is connected to the output terminal ADC123-IN12 of the detection circuit.

2. The zero-detection device for porcelain insulators according to claim 1, characterized in that, The step-up transformer is an audio step-up transformer.

3. The zero-detection device for porcelain insulators according to claim 1, characterized in that, The voltage multiplier circuit includes several voltage multiplier units connected in series. Each voltage multiplier unit includes a capacitor and a diode, and the negative terminal of the diode is connected to one end of the capacitor. In this system, the positive terminal of the diode in the pre-stage voltage multiplier unit is connected to the other end of the capacitor in the post-stage voltage multiplier unit, and the negative terminal of the diode in the pre-stage voltage multiplier unit is connected to the positive terminal of the diode in the post-stage voltage multiplier unit. The other end of the capacitor in the first-stage voltage multiplier unit is connected to the output point HO of the step-up transformer, and the positive terminal of the diode in the first-stage voltage multiplier unit is connected to the output point LO of the step-up transformer.

4. The zero-detection device for porcelain insulators according to claim 1, characterized in that, It also includes a preamplifier circuit, which is used to output a corresponding voltage signal to the low-voltage pulse generator according to the received set input signal.

5. A method for zero-current measurement in a high-voltage circuit of a porcelain insulator, characterized in that, This method is based on the porcelain insulator zero-detection device according to any one of claims 1 to 4, and includes: The voltage signal of the input low-voltage pulse generator is set, and the voltage signal is used by the porcelain insulator zero-detection device according to any one of claims 1 to 4 to form a high-voltage loop small current acting on the porcelain insulator to be tested; The small current value of the high-voltage circuit flowing through the porcelain insulator under test is collected within a set time period, and then the insulation resistance of the porcelain insulator under test is obtained. Based on the established insulation resistance criterion one, the state of the porcelain insulator under test is determined according to the insulation resistance.

6. The method for zero-current measurement in a high-voltage circuit of a porcelain insulator according to claim 5, characterized in that, Insulation resistance criterion one includes: If the insulation resistance of the porcelain insulator under test is within the normal threshold range, then the porcelain insulator under test is a normal porcelain insulator. If the insulation resistance of the porcelain insulator to be tested is within the defect threshold range, then the porcelain insulator to be tested is a defective and inferior porcelain insulator. If the insulation resistance of the porcelain insulator under test is within the zero threshold range, then the porcelain insulator under test is a zero-value porcelain insulator.

7. The method for zero-current measurement in a high-voltage circuit of a porcelain insulator according to claim 5, characterized in that, The voltage signals of the low-voltage pulse generator are set in ascending order. Each input voltage signal corresponds to an insulation resistance of the porcelain insulator under test. When the insulation resistance of the porcelain insulator under test is less than or equal to the set insulation threshold under the current voltage signal, it is determined that the current porcelain insulator has a zero value under the current voltage signal, and the input voltage signal will not be increased for the current porcelain insulator.

8. A method for online zero-measurement of distributed voltage on porcelain insulators, characterized in that, This method is based on the method for zero-current measurement of high-voltage circuits for porcelain insulators as described in any one of claims 5 to 7, and includes: Disconnect the voltage multiplier circuit to make the outputs of the discharge terminals POUT+ and POUT- on the steel caps at both ends of the porcelain insulator zero. The distributed voltage on the porcelain insulator is input to the detection circuit through the discharge terminals POUT+ and POUT-. The voltage value detected by the detection circuit is read and corrected to obtain the actual voltage value on the current porcelain insulator; Each porcelain insulator on the porcelain insulator string is tested sequentially, and adjacent insulators are compared. The zero-value porcelain insulator is identified according to the set zero-value criterion.

9. The method for online zero-measurement of distributed voltage of porcelain insulators according to claim 8, characterized in that, Criteria for determining the zero value of porcelain insulators include: (1) If the current porcelain insulator's distributed voltage is less than 50% of the distributed voltage of the adjacent porcelain insulator, then the current porcelain insulator is a zero-value porcelain insulator; (2) If the current distributed voltage of the porcelain insulator is lower than 50% of the standard distributed voltage, then the current porcelain insulator is a zero-value porcelain insulator; (3) If the peak value of the distributed voltage of the current porcelain insulator is less than the set peak voltage: (A) Use the small current zero measurement method of the high voltage circuit of the porcelain insulator to measure the insulation resistance of the current porcelain insulator under the first set voltage signal and the second set voltage signal respectively; (B) Based on the insulation resistance of the current porcelain insulator, determine the state of the current porcelain insulator according to the set insulation resistance criterion two. (4) If the peak value of the current distributed voltage of the porcelain insulator is greater than the set peak voltage: (a) Using the small current zero-measurement method of the high voltage circuit of the porcelain insulator, the insulation resistance of the current porcelain insulator is measured under the third set voltage signal and the fourth set voltage signal respectively; wherein, the third set voltage signal is the superposition voltage of the current distributed voltage of the porcelain insulator and the voltage applied to the current porcelain insulator, and does not exceed the set upper limit voltage one; the fourth set voltage signal is the superposition voltage of the current distributed voltage of the porcelain insulator and the voltage applied to the current porcelain insulator, and does not exceed the set upper limit voltage two; (b) Based on the insulation resistance of the current porcelain insulator, the state of the current porcelain insulator is determined according to the set insulation resistance criterion two.

10. The method for online zero-measurement of distributed voltage of porcelain insulators according to claim 9, characterized in that, Insulation resistance criterion two includes: If both measured insulation resistance values ​​are within the set normal threshold range, then the current porcelain insulator is determined to be a normal porcelain insulator. If any measured insulation resistance falls within the suspected low-value threshold range, then the current porcelain insulator is determined to be a suspected low-value porcelain insulator. If any measured insulation resistance falls within the low threshold range, then the current porcelain insulator is determined to be a low-value porcelain insulator. If any measured insulation resistance falls within the suspected zero threshold range, then the current porcelain insulator is determined to be a suspected zero-value porcelain insulator. If any measured insulation resistance is within the zero threshold range, then the current porcelain insulator is determined to be a zero-value porcelain insulator.

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