Discrete electrode system based on additional coupling capacitor

Abstract

A traditional direct current partial discharge detection method is not suitable for measuring direct current micro discharge in the aspects of quantitative description of sensitivity and partial discharge quantity. The invention provides a discrete electrode system based on an additional coupling capacitor, which comprises a current generation unit, the current generation unit is connected with a current transmission unit, the current transmission unit is connected with a current measurement unit, and the current generation unit comprises a defect mounting electrode and a measurement electrode. A discharge current is generated between the defect mounting electrode and the measuring electrode after a direct-current high voltage is applied to the defect mounting electrode, the current transmission unit comprises a first electrode and a second electrode, the first electrode is connected with the defect mounting electrode, the second electrode is connected with the measuring electrode, and the measuring electrode is connected with the defect mounting electrode. The first electrode is connected with the second electrode, and the defect mounting electrode, the measuring electrode, the first electrode and the second electrode are all disc-shaped. Inductance in a loop and refraction and reflection of electromagnetic waves are reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of direct current partial discharge, and particularly relates to a discrete electrode system based on an additional coupling capacitor. BACKGROUND

[0002] Direct current gas insulated switchgear (GIS) and gas insulated transmission line (GIL) have advantages of compact structure, large transmission capacity, stable operation and environmental friendliness, and have broad application prospects in offshore wind power transmission, cross-regional large-capacity power transmission and special geographical environment power transmission. As a core component of DC GIS / GIL, the uneven accumulation of gas-solid interface charge on the surface of the DC basin insulator causes the surface insulation problem, which is a technical bottleneck in the research and development. For DC GIS / GIL, although the maximum partial discharge amount meets the existing standard of "not greater than 5pC", micro-discharge below 1pC may still pose a serious threat to the insulation system. This may be related to the micro-discharge caused by the serious electric field distortion of the micro-protrusions generated by the micro-defects in the GIS / GIL or even the conductor surface roughness in the limited gas space range.

[0003] There is no specific measurement method for the partial discharge of DC GIS / GIL, and the same detection means and evaluation standard as the alternating current equipment are temporarily recommended to detect the partial discharge signal that can significantly affect the insulation performance of the direct current equipment, which may have a big problem. The traditional partial discharge detection methods mainly include pulse current method, ultra-high frequency (UHF) method and optical method. The measurement bandwidth of the traditional pulse current method recommended by IEC 60270 is usually less than 1MHz, which limits its capture ability of small discharge signals, and the detection lower limit is about 0.7pC; the detection bandwidth of the UHF method is 300MHz-2GHz, which has strong anti-interference ability, and the detection lower limit is 0.3pC, but the signal strength and the apparent discharge quantity cannot be one-to-one corresponding; the optical method has very high sensitivity in theory, but the quantitative relationship between the luminous intensity and the apparent discharge quantity is not uniform; the wideband pulse current method improves the detection bandwidth of the pulse current method, to a certain extent, improves the sensitivity of the measurement system, and realizes the high time resolution measurement of the partial discharge signal, but the electrode system used by the wideband pulse current method usually uses the stray capacitance between the electrodes as the coupling capacitance, which is very limited for improving the sensitivity of the measurement system. SUMMARY

[0004] 1. Technical problem to be solved

[0005] Based on the problem that the detection method of the traditional direct current partial discharge is not suitable for the measurement of the direct current micro-discharge in terms of sensitivity and quantitative description of the partial discharge amount, the application provides a discrete electrode system based on an additional coupling capacitor.

[0006] 2. Technical solution

[0007] To achieve the above objectives, this application provides a discrete electrode system based on an additional coupling capacitor, including a current generating unit connected to a current transmission unit and a current measuring unit. The current generating unit includes a defect mounting electrode and a measuring electrode. After applying a high DC voltage to the defect mounting electrode, a discharge current is generated between the defect mounting electrode and the measuring electrode. The current transmission unit includes a first electrode and a second electrode. The first electrode is connected to the defect mounting electrode, and the second electrode is connected to the measuring electrode. The first electrode is connected to the second electrode, and the defect mounting electrode, the measuring electrode, the first electrode, and the second electrode are all disk-shaped.

[0008] Another embodiment provided in this application is: the first electrode, the coupling capacitor, and the second electrode are connected.

[0009] Another embodiment provided in this application is as follows: the first electrode, the first capacitor cover, the coupling capacitor, the second capacitor cover, and the second electrode are connected in sequence.

[0010] Another embodiment provided in this application is that the edges of the first electrode, the first capacitor cover, the second capacitor cover, the second electrode, the defect mounting electrode, and the measuring electrode are all arc-shaped.

[0011] Another embodiment provided in this application is: the capacitance of the coupling capacitor is 200pF, and there are two coupling capacitors.

[0012] Another embodiment provided in this application is as follows: the first electrode is an external electrode, the second electrode is a ground electrode, the measuring electrode, the sampling resistor, the ground electrode are connected to the signal transmission interface, and the sampling resistor and the signal transmission interface are connected to the current measuring unit.

[0013] Another embodiment provided in this application is that the sampling resistor is composed of four 200Ω non-inductive resistors symmetrically connected.

[0014] Another embodiment provided in this application is as follows: the voltage across the sampling resistor and the time constant of the measurement circuit are:

[0015]

[0016] Where V0 is the voltage across the sampling resistor, Z m It is R and C P2 The parallel impedance form, I d It is the equivalent current source of the discharge, C g It is the capacitance between the defective mounting electrode and the measuring electrode, C.p1 It is an additional coupling capacitor, τ is the time constant of the measurement circuit, R is the sampling resistor, and C is the capacitance. p2 It is the stray capacitance between the measuring electrode and the ground electrode, and t is time.

[0017] Another embodiment provided in this application is that the minimum measured discharge quantity of the discrete electrode system is 0.02pC.

[0018] Another embodiment provided in this application is: the defect mounting electrode is used to mount a model of a pinhead defect, or a model of insulating surface metal particles and insulating surface micro-defects.

[0019] 3. Beneficial effects

[0020] Compared with the prior art, the advantages of the discrete electrode system based on additional coupling capacitor provided in this application are as follows:

[0021] The discrete electrode system based on an additional coupling capacitor provided in this application enables high-sensitivity measurement of DC micro-discharge.

[0022] The discrete electrode system based on additional coupling capacitor provided in this application reduces the inductance and electromagnetic wave reflection in the circuit by adopting a disk-shaped electrode design. At the same time, corresponding voltage equalization design is carried out on all electrode components to avoid partial discharge.

[0023] The discrete electrode system based on an additional coupling capacitor provided in this application reduces the time constant of the measurement circuit and improves the signal-to-noise ratio of the measurement circuit by designing an additional coupling capacitor between the external electrode and the ground electrode, thereby improving the measurement sensitivity and realizing high-sensitivity measurement of DC micro-discharge. Simultaneously, the design of the additional coupling capacitor allows interference generated on the high-voltage power supply side to directly enter the ground electrode through the coupling capacitor. Only discharge signals generated by defects in the defective electrode installation can generate a detectable signal on the sampling resistor. Furthermore, the coupling capacitor provides a low-impedance path for the discharge current, reducing the amount of charge leaked through stray capacitance to ground.

[0024] The discrete electrode system based on an additional coupling capacitor provided in this application has capacitor covers on both sides of the additional coupling capacitor to prevent discharge from occurring in the air gap where the capacitor connects to the electrode and causing interference to the measurement signal.

[0025] The discrete electrode system based on additional coupling capacitance provided in this application reduces the capacitance between the defective mounting electrode and the measuring electrode, improving the signal-to-noise ratio of the measurement circuit and thus enhancing measurement sensitivity. Simultaneously, an additional recessed structure is incorporated at the connection between the measuring electrode and the ground electrode, reducing stray capacitance between them, further improving the signal-to-noise ratio of the measurement circuit, thereby increasing sensitivity, and also reducing the time constant of the measurement circuit.

[0026] The discrete electrode system based on additional coupling capacitor provided in this application has a sampling resistor consisting of four symmetrically arranged 200Ω non-inductive resistors connected together, which reduces the inductance of the measurement circuit. At the same time, the design of the small-sized sampling resistor reduces the stray inductance and stray capacitance introduced by the sampling resistor.

[0027] The discrete electrode system based on additional coupling capacitor provided in this application has a matched impedance design for the connection part of the sampling resistor, the measuring electrode and the ground electrode to avoid oscillation of the discharge signal due to impedance mismatch.

[0028] The discrete electrode system based on an additional coupling capacitor provided in this application compactly integrates the coupling capacitor, the test sample, and the sampling resistor into a single electrode, reducing the area of ​​the measurement circuit and suppressing interference from the high-voltage side, thereby reducing the interference of external interference signals on the measurement of micro-discharge signals. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the electrode system structure of this application;

[0030] Figure 2 This is a schematic diagram of the circuit diagram of this application;

[0031] Figure 3 This is a schematic diagram of the sampling resistor in this application;

[0032] Figure 4 This is a schematic diagram of the experimental results of this application;

[0033] Figure 5 This is a schematic diagram of the overall structure of this application;

[0034] Figure 6 This is a schematic diagram of the defective electrode installation structure in this application;

[0035] Figure 7 This is a schematic diagram of the external electrode structure of this application;

[0036] Figure 8 This is a schematic diagram of the capacitor cover structure of this application;

[0037] Figure 9 This is a schematic diagram of the measuring electrode structure of this application;

[0038] Figure 10 This is a schematic diagram of the ground electrode structure of this application. Detailed Implementation

[0039] In the following, specific embodiments of this application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand and implement this application. Without departing from the principles of this application, features from various embodiments can be combined to obtain new implementations, or certain features from some embodiments can be substituted to obtain other preferred implementations.

[0040] The traditional pulse current method circuit recommended by IEC 60270 consists of a test power supply, the test sample, a coupling capacitor, a sensing impedance, and a signal acquisition system. Since the coupling capacitor and sampling resistor are both independent components, the measurement circuit area is relatively large, making it susceptible to external electromagnetic interference. To suppress high-frequency noise interference, the system's measurement bandwidth is limited to below 1MHz. Therefore, its ability to capture minute discharge signals is somewhat limited, as minute discharges may involve faster discharge processes, and interference signals smaller than 1MHz will still severely interfere with its signal measurement.

[0041] The UHF method detects partial discharge by measuring the high-frequency electromagnetic wave signal generated by the partial discharge. It has a measurement bandwidth of 300MHz-2GHz and strong anti-interference capability. However, because the propagation of the electromagnetic wave signal is affected by the surrounding structure, its signal strength cannot establish a one-to-one correspondence with the apparent charge of the partial discharge. Therefore, it cannot quantitatively describe the severity of the partial discharge.

[0042] Optical measurement detects partial discharge by measuring its luminescence behavior. Theoretically, it has very high detection sensitivity. However, the quantitative relationship between the luminescence intensity and the charge amount of the partial discharge is not consistent, and it cannot quantitatively describe micro-discharges below the detection threshold of the traditional pulse current method.

[0043] The broadband pulse current method achieves high time resolution measurement of partial discharge signals by increasing the measurement bandwidth of the traditional pulse current method, which improves the sensitivity of the measurement system to a certain extent. However, it uses stray capacitance between electrodes as coupling capacitance, which has a very limited effect on improving the measurement sensitivity of the measurement system.

[0044] Figure 2 HV: High voltage power supply; R d : Protective resistor; C P1 Additional coupling capacitance and stray capacitance; I d : Micro-discharge equivalent current source; L1: Stray inductance from the high-voltage electrode; C g: Defective installation capacitance between the electrode and the measuring electrode; C P2 : Stray capacitance between the measuring electrode and the ground electrode; R sampling resistor; C P3 L1: Stray capacitance introduced by the measurement circuit and sampling resistor; L2: Stray inductance introduced by the measurement circuit and sampling resistor.

[0045] Figure 3 This is a schematic diagram of the sampling resistor, which consists of a circular circuit board with a diameter of 16mm, a thickness of 1mm, and a central opening diameter of 5mm. One side of the circuit board is a full copper-clad layer, and the other side is a ring-shaped copper-clad layer. The inner ring copper-clad layer is 1.25mm wide and is connected to the full copper-clad layer on the other side of the circuit board through a copper-clad layer with a central opening. The outer ring copper-clad layer is 3.25mm wide. The gray areas in the diagram represent areas without copper cladding. The full copper-clad side is connected to measuring electrode 2 and is connected to the inner ring copper-clad layer on the other side through the copper-clad layer with a central opening. The inner ring copper-clad layer is connected to the outer ring copper-clad layer through four symmetrically arranged 200Ω (commercial, purchased) non-inductive resistors. The outer ring copper-clad layer is connected to the ground electrode.

[0046] Figure 5 The diagram shows the overall structure of the electrode system, comprising a disc-shaped external electrode 3, a defect-mounted electrode 1, four capacitor covers 6 or 7, two high-voltage ceramic capacitors (red parts in the diagram, commercially available, TDK) serving as coupling capacitors, a measuring electrode 2, a sampling resistor 8 (green parts in the diagram), a ground electrode 4, and an L29 (characteristic impedance 50Ω, commercially available) signal transmission interface 9. Connection method: The external electrode 3 and the defect-mounted electrode 1 are connected by threads on the defect-mounted electrode 1; the external electrode 3, capacitor covers, and coupling capacitors are connected by bolts; the ground electrode 4, capacitor covers, and coupling capacitors are connected by bolts; the signal transmission interface 9 and the ground electrode 4 are connected by bolts; the measuring electrode 2 and the signal transmission interface 9 are connected by a threaded metal conductor integrated into the signal transmission interface (the protruding part of the signal transmission interface), and the sampling resistor 8 is pressed between the measuring electrode 2 and the ground electrode 4.

[0047] Figure 6 A schematic diagram of the structure for mounting electrode 1 for defects. The bottom disc has a diameter of 50mm, a corner radius of 3mm on both sides, and a height of 10mm; the bottom opening has a diameter of 2mm and a depth of 8mm for mounting needle-tip defects. No opening is made when mounting other defects. The sample with defects is pressed together by adjusting the distance between it and the measuring electrode 2; the upper cylinder has a height of 25mm and a diameter of 8mm, with an M8 male thread machined on the outside for connecting to the outer electrode 3 and adjusting the distance between it and the measuring electrode 2; the upper cylinder opening has a diameter of 3.5mm and a height of 20mm for connecting to the high-voltage power line.

[0048] Figure 7This is a schematic diagram of the external electrode 3 structure. The disc has a diameter of 120mm, a thickness of 8mm, and a corner radius of 4mm on both sides. The central opening is an M8 female thread for installing the defect mounting electrode; the openings on both sides are M4 female thread holes for installing the capacitor cover and coupling capacitor with bolts.

[0049] Figure 8 This is a schematic diagram of capacitor cover 6 or 7. The overall structure has a diameter of 39mm, a thickness of 14mm, and a bottom corner radius of 2mm on both sides; the top opening has a diameter of 31mm, a depth of 4mm, a top corner radius of 2mm, and a bottom corner radius of 1mm; there is an M4 female threaded hole in the middle for connecting to the external electrode and coupling capacitor via bolts, or to the ground electrode and coupling capacitor.

[0050] Figure 9 This is a schematic diagram of the measuring electrode 2. The top disc has a diameter of 50mm, a thickness of 4mm, and a corner radius of 2mm; the bottom cylinder has a diameter of 20mm, a height of 17mm, a bottom corner radius of 2mm, and a corner radius of 1mm at the connection point with the upper disc; the bottom cylinder has an M5 female threaded hole with a depth of 10mm, which is used to connect to the signal transmission interface and press the sampling resistor between the ground electrode and the measuring electrode.

[0051] Figure 10 This is a schematic diagram of the ground electrode 4 structure. The upper disc has a diameter of 120mm, a thickness of 8mm, and a corner radius of 4mm. Two M4 female threaded holes are symmetrically opened on the disc, 50mm from the center axis of symmetry, for connecting the capacitor cover and coupling capacitor via bolts. The center of the disc is recessed, with a diameter of 60mm, a depth of 11mm, and a bottom thickness of 6mm. The corner radius at the connection point between the recessed area and the disc is 1mm, and the outer corner radius of the recessed area's bottom is 4mm. A 12mm diameter through hole is opened in the center of the recessed area. Four M3 female threaded holes, 4mm deep, are symmetrically distributed around the bottom opening of the recessed area, with a distance of 24.7mm between each pair, for installing the signal transmission interface.

[0052] See Figures 1-10 This application provides a discrete electrode system based on an additional coupling capacitor, including a current generating unit connected to a current transmission unit and a current measuring unit. The current generating unit includes a defect mounting electrode 1 and a measuring electrode 2. After applying a high DC voltage to the defect mounting electrode 1, a discharge current is generated between the defect mounting electrode 1 and the measuring electrode 2. The current transmission unit includes a first electrode, i.e., an external electrode 3, and a second electrode, i.e., a ground electrode 4. The first electrode is connected to the defect mounting electrode 1, and the second electrode is connected to the measuring electrode 2. The defect mounting electrode 1, the measuring electrode 2, the first electrode, and the second electrode are all disk-shaped.

[0053] The measuring electrode 2 and the ground electrode 4 are set separately, so they are called discrete electrodes. Traditional partial discharge measuring electrodes use the entire ground electrode as the measuring electrode and then ground it through a sampling resistor.

[0054] A recessed structure, slightly larger in diameter than the upper disk of measuring electrode 2, is installed at the center of ground electrode 4. This increases the distance between measuring electrode 2 and ground electrode 4, except at the connection point, thus reducing the capacitance between them. The recessed structure has a diameter of 60mm and a height of 11mm. Excessive size would increase the measurement loop area, making it more susceptible to external interference. (There are no strict size limitations.)

[0055] The sample to be tested is mounted between the defect mounting electrode 1 and the measuring electrode 2. A high DC voltage is applied to the defect mounting electrode 1. Once the electric field strength at the needle tip exceeds the critical field strength for electron avalanche formation, the gas begins to ionize, forming an electron avalanche or streamer discharge. The space charge generated by the discharge begins to move towards the needle tip and the measuring electrode 2 in the electric field. The movement of charged particles in the space generates a current in the defect mounting electrode 1 and the measuring electrode 2 (this current includes the current generated by the movement of charged particles and the displacement current). The current generated by the electrodes forms a loop through the current transmission unit. The discharge current is measured by measuring the voltage of the current transmission unit through the current measuring unit.

[0056] The design of the disc-shaped first electrode and the defect mounting electrode 1 reduces the reflection and refraction of L1 and electromagnetic waves in the measurement circuit (reducing inductance: the symmetry and uniform current distribution of the disc electrode help reduce inductance, and the short current path of the disc-shaped electrode helps reduce edge effects, which can lead to uneven magnetic field distribution and thus increase inductance; reducing the reflection and refraction of electromagnetic waves: compared with other shapes of electrodes, the disc-shaped electrode makes the electromagnetic waves more uniformly distributed on the electrode surface, reducing the local reflection phenomenon generated by the electrode edge, that is, the symmetry of the disc makes the reflection and refraction of electromagnetic waves more uniform; and its circular edge produces less edge effect than the right-angled edge of the electrode).

[0057] The current generating unit includes a defect mounting electrode 1, a measuring electrode 2, and a defect between the two electrodes (e.g., the air gap between the two electrodes when mounting a needle tip, or a sample containing metal particles when mounting a metal particle defect).

[0058] The current transmission unit includes an external electrode 3, a capacitor cover, a coupling capacitor 5, and a ground electrode 4.

[0059] Furthermore, the first electrode, coupling capacitor 5, and the second electrode are connected. The use of the additional coupling capacitor 5 increases C. P1 And make it much larger than C gIncreasing the voltage V0 of the sampling resistor improves the signal-to-noise ratio of the measurement circuit and reduces the time constant of the circuit. Furthermore, interference from the high-voltage side can directly enter the ground electrode through this low-impedance circuit, reducing interference to the discharge signal measurement. More importantly, it provides a high-pass circuit for discharge, reducing the amount of charge leaked through stray capacitance to ground.

[0060] Furthermore, the first electrode, the first capacitor cover 6, the coupling capacitor 5, the second capacitor cover 7, and the second electrode are connected sequentially. The design of the capacitor cover 6 or 7 will incorporate an additional coupling capacitor 5 (reference value 200pF for needle tip defects; for other defects, ensure it is at least 10 times the capacitance between the measuring electrode 2 and the defect mounting electrode 1). P1 The air gap at the connection between the external electrode 3 and the ground electrode 4 is completely shielded within it to prevent discharge during the measurement process and avoid affecting the measurement.

[0061] Furthermore, the edges of the first electrode, the first capacitor cover 6, the second capacitor cover 7, the second electrode, the defect mounting electrode 1, and the measuring electrode 2 are all arc-shaped. The outer electrode 3, capacitor cover 6 or 7, defect mounting electrode 1, measuring electrode 2, and ground electrode 4 all have corresponding voltage equalization structure designs (arc-shaped edges) to avoid self-discharge during measurement from affecting the measurement.

[0062] Furthermore, the capacitance of the coupling capacitor 5 is 200pF, and there are two coupling capacitors 5.

[0063] Furthermore, the first electrode is an external electrode 3, the second electrode is a ground electrode 4, the measuring electrode 2, the sampling resistor 8, and the ground electrode 4 are connected to the signal transmission interface 9, and the sampling resistor 8 and the signal transmission interface 9 are connected to the current measuring unit.

[0064] The connection between sampling resistor 8, measuring electrode 2, and ground electrode 4 involves the selection of sampling resistor 8 and the selection of the opening radius of ground electrode 4. Sampling resistor 8 is composed of four 200-ohm non-inductive resistors stacked together, with a characteristic impedance of 50 ohms. The opening of ground electrode 4 and the inner conductor of signal transmission interface 9 form a coaxial transmission line structure. When its characteristic impedance is 50 ohms, the opening diameter is 12mm.

[0065] The characteristic impedance of sampling resistor 8, the connection point, and signal transmission interface 9 is 50 ohms, achieving impedance matching.

[0066] The sample to be tested is mounted between the defect mounting electrode 1 and the measuring electrode 2. A high DC voltage is applied to the defect mounting electrode 1. Once the electric field strength at the needle tip exceeds the critical field strength for electron avalanche formation, the gas begins to ionize, forming an electron avalanche or streamer discharge. The space charge generated by the discharge begins to move towards the needle tip and the measuring electrode 2 in the electric field. The movement of charged particles in the space generates a current in the defect mounting electrode 1 and the measuring electrode 2 (this current includes the current generated by the movement of charged particles and the displacement current). The current generated by the electrodes forms a loop through the additional coupling capacitor 5 and the sampling resistor 8. The discharge current is measured by measuring the voltage across the sampling resistor 8.

[0067] The defect mounting electrode 1 is connected to the outer electrode 3 via threads. The defect mounting electrode 1 can be mounted using defect models such as pinpoint defects, insulating surface defects, and insulating surface metal particles. The measuring electrode 2 is connected to the ground electrode 4 and the signal transmission interface 9 via the sampling resistor 8. The outer electrode 3, the additional coupling capacitor 5, and the capacitor cover 6 or 7 are connected via threads.

[0068] Furthermore, the sampling resistor is composed of four 200Ω non-inductive resistors symmetrically connected.

[0069] Ignoring stray inductance and stray capacitance introduced by the measurement circuit, the voltage across the sampling resistor 8 and the time constant of the measurement circuit are:

[0070]

[0071] Where V0 is the voltage across the sampling resistor, Z m It is R and C P2 The parallel impedance form, I d It is the equivalent current source of micro-discharge, C g It is the capacitance between the defective mounting electrode and the measuring electrode, C. p1 It is an additional coupling capacitor, τ is the time constant of the measurement circuit, R is the sampling resistor, and C is the capacitance. p2 It is the stray capacitance between the measuring electrode and the ground electrode, and t is time.

[0072] The use of discrete measuring electrodes 2 reduces C g Increasing the voltage V0 of the sampling resistor improves the signal-to-noise ratio of the measurement loop and reduces the time constant of the loop.

[0073] The design of the recessed structure of ground electrode 4 reduces the stray capacitance C between measuring electrode 2 and ground electrode 4. P2 This reduces the time constant of the measurement loop.

[0074] The sampling resistor 8, installed using a symmetrical, disk-shaped design, reduces the stray inductances L2 and C introduced by the sampling resistor 8. P3 This is to avoid the measured discharge signal from oscillating.

[0075] The opening size of the ground electrode 4 was determined by matching impedance design based on the design of the inner conductor of the signal transmission interface 9.

[0076] Improving the signal-to-noise ratio (SNR) enhances the sensitivity of the measurement system. The design of the additional coupling capacitor 5 structure improves the SNR of the measurement circuit, reduces the time constant of the measurement circuit, and increases its sensitivity; it also suppresses the influence of high-voltage side interference signals on the measurement. The integrated design of the entire electrode improves the anti-interference capability of the measurement circuit. This enables high-sensitivity measurement of DC micro-discharges, with a minimum measurable discharge quantity of 0.02 pC.

[0077] Experimental verification was conducted, and the minimum measurement sensitivity was 0.02 pC by measuring the micro-discharge generated by the needle tip mounted on the defective electrode. The high sensitivity of the proposed electrode system was verified by joint measurement with a photon counting system and a UHF sensor (measured by the DC micro-discharge initiation voltage).

[0078] The measurement case described is a pin-tip micro-discharge, which represents only one case and does not mean that this electrode can only measure micro-discharges caused by this type of defect. It is applicable to DC micro-discharges caused by metal particles, micro-defects on insulating surfaces, and micro-protrusions on ground electrodes.

[0079] like Figure 4 The figure shows the PDIV of positive and negative polarity micro-discharges measured in 0.1 and 0.5 MPa SF6 gas environments, respectively. As can be seen from the figure, under negative polarity voltage, the PDIV measured by the photon counting system and the UHF sensor are 95.8–98.8% and 111.4%–112.5% ​​of the constructed system, respectively. This indicates that the constructed measurement system has similar sensitivity to the photon counting system, and both are higher than the UHF sensor. Under positive polarity voltage, the PDIV measured by the photon counting system and the UHF sensor are 105.9–118.1% and 104.8%–124.2% of the constructed system, respectively. This indicates that the UHF sensor and the photon counting system have similar measurement sensitivity, and both are lower than the constructed measurement system. (The lower the measured PDIV, the higher the sensitivity).

[0080] The defect mounting electrode 1 is not limited to setting needle tip defects, but is also applicable to mounting models of insulating surface metal particles and insulating surface micro-defects.

[0081] Although this application has been described above with reference to specific embodiments, those skilled in the art will understand that many modifications can be made to the configurations and details disclosed in this application within the principles and scope of the disclosure. The scope of protection of this application is determined by the appended claims, and the claims are intended to cover all modifications included in the literal meaning or scope of equivalents of the technical features in the claims.

Claims

1. A discrete electrode system based on an additional coupling capacitor, characterized in that: The device includes a current generating unit connected to a current transmission unit and a current measuring unit. The current generating unit includes a defect mounting electrode and a measuring electrode. After applying a high DC voltage to the defect mounting electrode, a discharge current is generated between the defect mounting electrode and the measuring electrode. The current transmission unit includes a first electrode and a second electrode. The first electrode is connected to the defect mounting electrode, and the second electrode is connected to the measuring electrode. The first electrode is connected to the second electrode. The defect mounting electrode, the measuring electrode, the first electrode, and the second electrode are all disc-shaped.

2. The discrete electrode system based on an additional coupling capacitor as described in claim 1, characterized in that: The first electrode, the coupling capacitor, and the second electrode are connected.

3. The discrete electrode system based on an additional coupling capacitor as described in claim 2, characterized in that: The first electrode, the first capacitor cover, the coupling capacitor, the second capacitor cover, and the second electrode are connected in sequence.

4. The discrete electrode system based on an additional coupling capacitor as described in claim 3, characterized in that: The edges of the first electrode, the first capacitor cover, the second capacitor cover, the second electrode, the defect mounting electrode, and the measuring electrode are all arc-shaped.

5. The discrete electrode system based on an additional coupling capacitor as described in claim 3, characterized in that: The capacitance of the coupling capacitor is 200pF, and there are two coupling capacitors.

6. The discrete electrode system based on an additional coupling capacitor as described in claim 5, characterized in that: The first electrode is an external electrode, the second electrode is a ground electrode, the measuring electrode, the sampling resistor, the ground electrode are connected to the signal transmission interface, and the sampling resistor and the signal transmission interface are connected to the current measuring unit.

7. The discrete electrode system based on an additional coupling capacitor as described in claim 6, characterized in that: The sampling resistor is composed of four 200Ω non-inductive resistors symmetrically connected.

8. The discrete electrode system based on an additional coupling capacitor as described in claim 7, characterized in that: The voltage across the sampling resistor and the time constant of the measurement circuit are: Where V0 is the voltage across the sampling resistor, Z m It is R and C P2 The parallel impedance form, I d It is the equivalent current source of the discharge, C g It is the capacitance between the defective mounting electrode and the measuring electrode, C. p1 It is an additional coupling capacitor, τ is the time constant of the measurement circuit, R is the sampling resistor, and C is the capacitance. p2 It is the stray capacitance between the measuring electrode and the ground electrode, and t is time.

9. The discrete electrode system based on an additional coupling capacitor as described in any one of claims 1 to 8, characterized in that: The minimum measurable discharge quantity of the discrete electrode system is 0.02 pC.

10. The discrete electrode system based on an additional coupling capacitor as described in claim 9, characterized in that: The defect mounting electrode is used to mount a model of a pinhead defect, or a model of metal particles and micro-defects on an insulating surface.

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