Casing flange position external insulation discharge measurement and analysis method

Abstract

The invention relates to the technical field of voltage measurement, in particular to a sleeve flange position external insulation discharge measurement and analysis method. The method comprises the following steps: firstly, constructing an external insulation discharge measuring device at the position of a sleeve flange, secondly, reconstructing and calculating the voltage of the sleeve through the current of a sleeve end screen measured by a coil in combination with a measurement result of a penicillin bridge, and then, establishing an electric field numerical model according to an electromagnetic field theory when the sleeve end screen is partially discharged or the flange is discharged along a surface, and calculating the charge induced voltage; finally, the corona discharge condition can be analyzed according to the charge induced voltage, and the problem that the safety risk exists when the equipment voltage is directly connected or measured in a close range through a CVT method and the like is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage measurement, in particular to a method for measuring and analyzing external insulation discharge at a bushing flange position. Background Art

[0002] Bushings are crucial electrical equipment in power systems. Transformer bushings, for example, are the current-carrying components of transformers, providing support and insulation, and are crucial for the safe and stable operation of transformers. Partial discharge (PD) on the outer end shield of 66-110 kV transformer bushings, as well as surface discharge at the flange-to-particle connection, are common. This is primarily due to uneven electric field distribution on the bushing end shield and porcelain sleeve surfaces. If not promptly addressed, these issues can escalate and cause accidents. Therefore, it is essential to detect and analyze PD on the transformer bushing end shield and surface discharge along the flange, enabling preventive measures and repairs to prevent these accidents.

[0003] Currently, the methods that can be used to measure partial discharge outside the bushing include corona current measurement method, pulse current method, ultraviolet detection method, ultrasonic detection method, etc.

[0004] The corona current measurement method connects the detection circuit directly to the high-voltage circuit, measuring the weak current generated by the corona discharge. The strength of the current is used to determine the activity of the discharge. However, due to the high safety risk of electric shock and the high number of interference factors associated with direct connection to the high-voltage line, this method is generally not used.

[0005] The pulse current method applies a high-amplitude, short-duration pulse current to the system under test (such as a cable, transformer, or motor) and measures the system's response to the pulse current, detecting changes in current or voltage. By analyzing the characteristics of the response signal (such as amplitude, waveform, and frequency), it can determine whether insulation defects or partial discharge (PD) are present in the system. While methods like the pulse current method can accurately quantify the amount of partial discharge, the discharge characteristics of the pulsed current differ significantly from those of corona discharge under continuous power-frequency voltage, making them unsuitable for continuous corona discharge measurement and analysis. Furthermore, the method requires power outages for wiring, which is complex and inconvenient for on-site operations.

[0006] The ultraviolet observation method determines whether the continuous corona discharge occurs by quantifying the number of photons. The ultraviolet detection system is composed of a lens system, a filter, a light sensor, a control analysis system and an image display system. The visible light lens takes a visible image of the corona target, the filter filters out the light wave outside the solar blind region, the ultraviolet light lens performs ultraviolet imaging on the light wave filtered by the filter, the light sensor performs photoelectric conversion on the corona image, the control analysis system analyzes the intensity of the light, controls the entire detection system, and the image display system fuses and displays the two kinds of image information. The specific situation of the target discharge is determined by analyzing the mixed imaging information. The ultraviolet imaging method is accurate, but the measurement accuracy depends on the accuracy of the special instrument, the structure is complex, the cost is high, and the accuracy is affected by the measurement distance, and the error of the measured continuous corona discharge voltage is large.

[0007] The ultrasonic detection method is composed of three parts of acoustic-electric conversion, electric signal amplification and signal display. The ultrasonic detection method is easily affected by electromagnetic interference, has low detection sensitivity, can only determine whether the corona discharge occurs, and cannot obtain the corona discharge position and discharge characteristics.

[0008] Other methods include ozone detection method, radio frequency detection method, etc., which can only determine whether the corona discharge occurs, and cannot obtain the corona discharge position, discharge degree and other information.

[0009] On the other hand, in order to analyze the corona discharge characteristics and formation reasons of the bushing end screen, the synchronous measurement of the bushing voltage waveform is required. The existing voltage measurement methods include the voltage transformer method, the external partial voltage method, the optical fiber voltage sensor method, etc.

[0010] The voltage transformer method takes the capacitor voltage transformer (CVT) as an example. As shown in Figure 4 is the electrical structure diagram of the CVT. The capacitor voltage divider is composed of a high-voltage arm capacitor CH and a low-voltage arm capacitor CL in series, the electromagnetic unit is composed of an intermediate transformer T, a compensation reactor L, a damper D and other parts, and Z is the secondary load. The line voltage Us is input into the electromagnetic unit after being reduced by the capacitor voltage divider, is input into the intermediate transformer after the “compensation effect” of the compensation reactor, and is output after the “secondary voltage reduction” of the intermediate transformer. The CVT measures the line voltage, and has problems such as poor transient characteristics. At the same time, near the transformer, there may be a situation that the CVT is far away, the electromagnetic environment is complex, and the voltage is difficult to obtain.

[0011] The external partial voltage method constructs a voltage dividing circuit based on the existing equipment structure of the power system, and then measures the voltage. For example, the capacitor voltage divider based on the current transformer is shown in Figure 5, using the existing current transformer (CT) in the power system, the stray capacitance C1 of the high-voltage conductor to the CT is used as the high-voltage arm, and the external capacitor is used as the low-voltage arm to form a capacitive voltage divider. Using the existing CT as a voltage divider avoids a series of problems caused by the long-term parallel connection of the traditional high-voltage voltage divider to the high-voltage grid. However, the main disadvantage is that the capacitor C1 is unstable and has large measurement errors. Another example is the external voltage divider of the capacitive device (bushing), such as Figure 6 As shown in Figure 1, a capacitive sensor is added to the exterior of an existing capacitive device (bushing). The principle is similar to that of a high-voltage voltage divider: the geometric capacitance of the capacitive device acts as an equivalent high-voltage capacitor, while the external capacitor acts as a low-voltage capacitor. The two are connected in series to form a capacitive voltage divider. The voltage of the additional impedance of the capacitive device is measured and the line voltage is inversely calculated. The addition of capacitance to the ground loop increases the potential at the bushing's end screen, making partial discharge more likely. Furthermore, the capacitive device itself has a certain resistance, so this method introduces a certain voltage phase difference.

[0012] The fiber-optic voltage sensor method utilizes a fiber-optic sensor. Based on the voltage applied to a specific crystal by a laser, the refractive index of the crystal is altered. This refractive index change causes a shift in the phase or polarization direction of the light. This shift in light is then converted into a voltage value using an interferometer or polarization detector. However, the disadvantages of fiber-optic voltage sensors include the need for a transformer or voltage divider to obtain signals from the high-voltage power grid. This leads to poor electrical safety when obtaining signals from high-voltage lines or guide poles. Furthermore, optical components require high precision and are susceptible to interference, which can cause errors. This leads to high costs and the signal transmission process is also susceptible to electromagnetic interference. Summary of the Invention

[0013] In response to the above-mentioned problem of safety risks in measuring the device voltage by direct connection or close-range acquisition, the present invention proposes a method for measuring and analyzing insulation discharge outside the bushing flange position. First, the bushing voltage is calculated by reconstructing the bushing end screen current obtained by coil measurement in combination with the Xilin bridge measurement results. Then, when local discharge occurs at the bushing end screen or discharges along the flange surface, an electric field numerical model is established according to electromagnetic field theory to calculate the charge induced voltage. Finally, the corona discharge situation can be analyzed based on the charge induced voltage, which solves the problem of safety risks in measuring the device voltage by direct connection or close-range acquisition using the CVT method.

[0014] The specific implementation contents of the present invention are as follows: A method for measuring and analyzing external insulation discharge at a bushing flange position specifically comprises the following steps: Step S1: a metal induction plate is arranged to surround the lower end of the bushing, a shielding box is arranged at one end of the opening of the metal induction plate, and a detection circuit is arranged inside the shielding box and connected to a signal acquisition device and a current coil to obtain an external insulation discharge measurement device at the bushing flange position; Step S2: Before measuring partial discharge and creeping discharge, connect one end of the Xilin bridge to the bushing conductive rod and the other end to the bushing end screen lead wire, and reconstruct and calculate the bushing voltage using the bushing end screen current measured by the current coil; Step S3: When partial discharge occurs at the bushing end screen or discharge occurs along the flange surface, an electric field numerical model is established based on electromagnetic field theory to calculate the charge induced voltage; Step S4: Analyze the discharge condition according to the bushing voltage, the charge induced voltage, and the discharge pulse signal.

[0015] In order to better implement the present invention, further, step S1 specifically includes the following steps: Step S21: Before measuring partial discharge and creeping discharge, the bushing is powered off, and one end of the Xilin bridge is connected to the bushing conductive rod, and the other end is connected to the bushing end screen lead wire; Step S22: adjusting the resistor R4 and the capacitor C4 to adjust the Schilling bridge to a balanced state, and calculating the bridge arm impedance ratio; Step S23: Calculating the resistance value of the insulation resistor Rx and the capacitance value of the capacitor Cx in the casing according to the bridge arm impedance ratio; Step S24: measuring the current I applied to the insulation resistance Rx and capacitance Cx in the bushing using a current sensor connected to the grounding wire of the bushing end screen; Step S25: Calculate the bushing voltage U0 according to the resistance value of the resistor Rx, the capacitance value of the capacitor Cx, and the current I.

[0016] In order to better implement the present invention, further, the specific operations of step S12 are: Where j represents the imaginary unit and ω represents the angular frequency.

[0017] In order to better implement the present invention, further, the specific operations of step S23 are: Where ω is the angular frequency.

[0018] In order to better implement the present invention, further, the specific operations of step S24 are: Where I is the current applied to the insulation resistance Rx and capacitance Cx in the bushing, j represents the imaginary unit, and ω represents the angular frequency.

[0019] In order to better implement the present invention, further, step S3 specifically includes the following steps: Step S31: When partial discharge occurs at the bushing end screen or discharge occurs along the flange surface, the relationship between the electric field intensity E and the charge density ρ is established according to Gauss's law; Step S32: according to the relationship between the electric field intensity E and the charge density p, the relationship between the electric field intensity E and the electric potential φ is obtained; Step S33: according to the vacuum dielectric constant, the relationship between the electric field intensity E and the charge density p, the relationship between the electric field intensity E and the electric potential φ, the Poisson equation is obtained; Step S34: taking the Poisson equation as the control equation, a finite element simulation model is established; Step S35: according to the simulation model, the partial discharge or surface discharge space charge is set, the charge density p on the metal induction plate is obtained, and the induced charge amount is calculated according to the area of the metal induction plate; Step S36: according to the induced charge amount, the charge induction voltage is calculated.

[0020] Step S37: according to the discharge space charge value set in the simulation and the calculated charge induction voltage value, the proportional relationship between the discharge space charge and the charge induction voltage of the metal induction plate is obtained; during measurement, the charge induction voltage is measured, the discharge space charge amount is analyzed, and the partial discharge condition is obtained.

[0021] In order to better realize the present application, further, the specific operation of step S4 is: analyzing the discharge condition according to the induced voltage waveform, if the charge induction voltage rises in the 0~60° and 180°~240° of the sine period of the sleeve voltage, obvious corona discharge occurs, and the absolute value of the space charge amount increases; if the charge induction voltage drops in the 60°~180° and 240°~270° of the sine period of the sleeve voltage, the discharge stops and the space charge dissipates, and the absolute value of the space charge amount decreases; other phases are basically coincided with the horizontal zero value line, at this time, there is no obvious net space charge accumulation in space; the maximum absolute value of the charge induction voltage is large, which is judged as strong surface discharge, which may develop to the stage of glow discharge.

[0022] In order to better realize the present application, further, the discharge condition is analyzed according to the discharge pulse waveform, if there is a discharge pulse in the 0~90° of the positive half cycle of the sleeve voltage, strong surface discharge occurs, that is, there is uneven distribution of surface electric field at the connection position of the flange and the sleeve, the discharge is obvious, and corresponding measures need to be taken.

[0023] The present application has the following beneficial effects: (1) The present application combines the measurement results of Xilin bridge, reconstructs and calculates the sleeve voltage by the sleeve end screen current measured by the coil, adopts a non-contact measurement method, does not change the grounding structure, and measures the sleeve voltage; solves the problems of CVT method, mutual inductor method and the like that are not convenient for directly measuring the sleeve voltage, and the problems of sleeve end screen voltage increasing, partial discharge being easy to occur and voltage phase error, solves the problems of CVT method and the like that directly connect or take the device voltage at a short distance, and there is a safety risk in measuring the device voltage.

[0024] (2) The present invention can analyze the corona discharge situation based on the charge induced voltage; solve the problems of low safety of direct measurement of corona current measurement method, power outage measurement of pulse current method, limited detection distance of ultraviolet detection method, obvious influence of electromagnetic interference on ultrasonic detection method, and limitation in measuring corona discharge of casing flange; solve the problem that ultraviolet imaging method, which is a relatively accurate measurement technology, relies on the precision of special instruments and is expensive; solve the problem that the signal processing and application of detection technologies such as ultraviolet detection method and ultrasonic detection method are complex; combine the casing voltage and charge induced voltage to analyze the local discharge of the end screen and the characteristics of discharge intensity and discharge phase, and solve the problem that the existing technology cannot analyze and judge the degree of corona discharge, discharge phase, etc.

[0025] (3) The charge-induced voltage metal induction plate of the annular structure of the present invention can measure the induced charge of local discharge in all directions of the circumference of the bushing flange; the analysis method of local discharge of the bushing end screen and discharge along the flange surface based on the charge-induced voltage, and the method of analyzing the degree of discharge, discharge phase and discharge cause by combining the bushing voltage and the charge-induced voltage; the sensor and the measuring device are both passive devices and do not require power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the pulse current method detection flow chart.

[0027] Figure 2 This is the principle diagram of the UV detection method.

[0028] Figure 3 This is the ultrasonic testing flow chart.

[0029] Figure 4 This is the CVT electrical structure diagram.

[0030] Figure 5 Schematic diagram of the capacitor voltage divider of the current transformer.

[0031] Figure 6 Schematic diagram of the bushing end screen voltage sensor.

[0032] Figure 7 This is the overall structure diagram of the external insulation discharge measurement device at the bushing flange position.

[0033] Figure 8 This is a cross-sectional structural diagram of the external insulation discharge measuring device at the bushing flange position.

[0034] Figure 9 This is the structural diagram of the shielding box for the external insulation discharge measurement device at the bushing flange position.

[0035] Figure 10 This is the structural diagram of the through-type current sensor of the external insulation discharge measurement device at the bushing flange position.

[0036] Figure 11 This is the schematic diagram of the detection circuit of the external insulation discharge measurement device at the bushing flange position.

[0037] Figure 12 This is the wiring diagram of the Xilin bridge principle.

[0038] Figure 13 Schematic diagram of the simulation modeling model structure.

[0039] Figure 14 Schematic diagram of finite element mesh division for simulation modeling.

[0040] Figure 15 Schematic diagram of simulation results of electric potential intensity at different points.

[0041] Figure 16 Schematic diagram of the simulation results of electric field strength at different points.

[0042] Figure 17 Schematic diagram of the average surface charge density calculation results.

[0043] Figure 18 Schematic diagram of induced voltage measurement results.

[0044] Figure 19 Schematic diagram of discharge pulse signal measurement results. DETAILED DESCRIPTION

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. It should be understood that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, and therefore should not be regarded as limiting the scope of protection. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technical personnel in this field without making creative work are within the scope of protection of the present invention.

[0046] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0047] Example 1: This embodiment provides a method for measuring and analyzing insulation discharge outside the bushing flange, which specifically includes the following steps: Step S1: a metal induction plate is arranged to surround the lower end of the bushing, a shielding box is arranged at one end of the opening of the metal induction plate, and a detection circuit is arranged inside the shielding box and connected to a signal acquisition device and a current coil to obtain an external insulation discharge measurement device at the bushing flange position; Step S2: Before measuring partial discharge and creeping discharge, connect one end of the Xilin bridge to the bushing conductive rod and the other end to the bushing end screen lead wire, and reconstruct and calculate the bushing voltage using the bushing end screen current measured by the current coil; The step S1 specifically includes the following steps: Step S21: Before measuring partial discharge and creeping discharge, the bushing is powered off, and one end of the Xilin bridge is connected to the bushing conductive rod, and the other end is connected to the bushing end screen lead wire; Step S22: adjusting the resistor R4 and the capacitor C4 to adjust the Schilling bridge to a balanced state, and calculating the bridge arm impedance ratio; The specific operations of step S22 are: Where j represents the imaginary unit and ω represents the angular frequency.

[0048] Step S23: Calculating the resistance value of the insulation resistor Rx and the capacitance value of the capacitor Cx in the casing according to the bridge arm impedance ratio; The specific operations of step S23 are: Here, ω represents the angular frequency.

[0049] Step S24: measuring the current I applied to the insulation resistance Rx and capacitance Cx in the bushing using a current sensor connected to the grounding wire of the bushing end screen; The specific operations of step S24 are: Where I is the current applied to the insulation resistance Rx and capacitance Cx in the bushing, j represents the imaginary unit, and ω represents the angular frequency.

[0050] Step S25: Calculate the bushing voltage U0 according to the resistance value of the resistor Rx, the capacitance value of the capacitor Cx, and the current I.

[0051] Step S3: When partial discharge occurs at the bushing end screen or discharge occurs along the flange surface, an electric field numerical model is established based on electromagnetic field theory to calculate the charge induced voltage; The step S3 specifically includes the following steps: Step S31: When partial discharge occurs at the bushing end screen or discharge occurs along the flange surface, the relationship between the electric field intensity E and the charge density ρ is established according to Gauss's law; Step S32: Obtaining the relationship between the electric field intensity E and the electric potential φ based on the relationship between the electric field intensity E and the charge density ρ; Step S33: Obtaining the Poisson equation based on the vacuum dielectric constant, the relationship between the electric field intensity E and the charge density ρ, and the relationship between the electric field intensity E and the electric potential φ; Step S34: Using the Poisson equation as the control equation, a finite element simulation model is established; Step S35: according to the simulation model, set the local discharge or surface discharge space charge, obtain the charge density ρ on the metal sensing plate, and calculate the induced charge amount according to the area of ​​the metal sensing plate; Step S36: Calculate the charge induced voltage according to the induced charge amount.

[0052] Step S37: Based on the discharge space charge value set in the simulation and the calculated charge induced voltage value, the proportional relationship between the discharge space charge and the charge induced voltage of the metal induction plate is obtained; during actual measurement, the discharge space charge is analyzed based on the measured charge induced voltage to obtain the partial discharge situation.

[0053] Step S4: Analyze the discharge condition according to the bushing voltage, the charge induced voltage, and the discharge pulse signal.

[0054] The specific operation of step S4 is as follows: analyzing the discharge situation according to the induced voltage waveform; if the charge induced voltage rises at 0° to 60° and 180° to 240° of the sinusoidal period of the sinusoidal bushing voltage, obvious corona discharge occurs and the absolute value of the space charge increases; if the charge induced voltage drops at 60° to 180° and 240° to 270° of the sinusoidal period of the sinusoidal bushing voltage, the discharge stops, the space charge dissipates, and the absolute value of the space charge decreases; the other phases basically coincide with the horizontal zero value line, and at this time there is no obvious net space charge accumulation in the space; the maximum absolute value of the charge induced voltage is large, which is judged to be a strong surface discharge, which may develop into a glow discharge stage.

[0055] The discharge situation is analyzed based on the discharge pulse waveform. If the discharge signal exists in the positive half cycle of the bushing divided voltage 0~90°, a discharge pulse indicates that a strong surface discharge has occurred, that is, there is an uneven distribution of the surface electric field at the connection position between the flange and the bushing, and the discharge is more obvious, and corresponding measures need to be taken.

[0056] Working principle: This embodiment combines the measurement results of the Xilin bridge, reconstructs and calculates the bushing voltage through the bushing end screen current obtained by coil measurement, and adopts a non-contact measurement method to measure the bushing voltage without changing the grounding structure. It solves the problem that the CVT method and the mutual inductor method are inconvenient to directly measure the bushing voltage, and the bushing end screen voltage divider method increases the bushing end screen potential and is prone to partial discharge and voltage phase error. It also solves the problem that the CVT method and other methods directly connect or take the device voltage at close range, and there are safety risks in measuring the device voltage.

[0057] Example 2: This embodiment is based on the above embodiment 1. Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 As shown, the structure of the external insulation discharge measuring device at the bushing flange position is described with a specific embodiment.

[0058] like Figure 7 As shown, the device for measuring insulation discharge outside the bushing flange includes a metal sensing plate, a support device, a shielding box, detection circuitry within the shielding box, a signal transmission line (cable), and a signal acquisition device. The sensing plate is embedded in the shielding box and wired to a detection circuit board. The entire detection circuit is located within the shielding box. The lower plate of the shielding box has an opening for outputting electrical signals via the cable.

[0059] like Figure 8 As shown, the metal sensing plate can be replaced according to different bushing models and accommodates bushings of varying sizes, enabling measurement of partial discharge at the end shield and discharge along the flange surface. The sensing plate is made of aluminum alloy, approximately 75 cm wide, approximately 1 m from the flange, and 0.5 cm thick. It is curved and flexible, allowing for a certain degree of opening to enclose the flange, end shield, and the porcelain sleeve connected to the flange. The sensing plate is supported by a fixed insulating support structure that can be attached to the flange.

[0060] like Figure 9 As shown, the metal sensor board is partially embedded in the shielding box and connected to the circuit board. The shielding box is a split aluminum shell with a thickness of 2mm. The front and rear U-shaped plates have two large holes for connecting the sensor board, while the rear U-shaped plate has four small holes for securing the detection circuit board. A hole is punched in the center of the bottom for routing cables. The front and rear U-shaped plates fit together to seal the enclosure. The center gap of the upper cover is used to insert and secure the sensor board.

[0061] like Figure 10 As shown in the figure, the through-type current sensor can measure μA-level industrial frequency AC current.

[0062] like Figure 11 As shown, the detection circuit is mainly composed of protection capacitors and matching resistors. The circuit principle is as follows Figure 11 As shown, the entire detection circuit is installed in the shielding box in the form of a circuit board.

[0063] The measured voltage signals U1 and U2 are led out by a shielded cable. The cable leads the signal from the detection circuit board, passes through the lower cover of the shielding box, and then transmits U1 / U2 to the signal acquisition unit for collection; the current signal I collected by the microcurrent coil is also collected by the acquisition device.

[0064] The signal acquisition unit collects signals U1 and U2. The induced voltage signal U1 is a low-frequency signal, acquired at a sampling rate of at least 100 Msa / s. The discharge signal U2, containing discharge pulses, is a high-frequency signal, acquired at a sampling rate of at least 1 Gsa / s. The induced voltage waveform and discharge pulse signal waveform are obtained on the signal acquisition unit (using an oscilloscope as an example).

[0065] The device of this embodiment has a simple structure, low cost, short detection time, does not require complex signal processing, and is easy to operate and use.

[0066] The sensing board, detection circuit and shielding structure of this embodiment adopt a lightweight design while ensuring the working effect; the sensing board is embedded in the integrated structure of the shielding box, and the detection circuit is fully shielded in the shielding box and is not affected by external electromagnetic signals.

[0067] The rest of this embodiment is the same as that of the above-mentioned embodiment 1, and therefore will not be described in detail.

[0068] Example 3: This embodiment is based on any one of the above embodiments 1 to 2. Figure 12 、 Figure 13 、 Figure 14 、 Figure 15 、 Figure 16 、 Figure 17 、 Figure 18 、 Figure 19 As shown, a specific embodiment is used to describe in detail the bushing voltage, charge induced voltage and discharge pulse measurement method, and the corona discharge analysis method.

[0069] like Figure 12 The following figure shows the bushing voltage measurement method. Combined with the Schilling bridge measurement results, the bushing voltage is reconstructed and calculated using the bushing end screen current measured by the coil. Before partial discharge and creeping discharge measurements, Schilling bridge measurements are performed first.

[0070] The bushing is powered off, one end of the Xilin bridge is connected to the bushing conductive rod, and the other end is connected to the bushing end screen lead wire. R x 、 C x Parallel circuit representation. R3 is an adjustable non-inductive resistor C N The capacitance C4 of the high-voltage standard capacitor is an adjustable capacitor; R4 is a fixed-value non-inductive resistor; and P is an AC ammeter.

[0071] Adjust R3 and C4 to make the bridge balanced, that is, the current passing through is zero. At this time, U CA / U AD =U CB / U BD Since the currents through the bridge arms CA and AD, CB and BD are I1 and I2 respectively, the ratio of the bridge arm voltages, i.e. the ratio of the corresponding bridge arm impedances, is: Z1 / Z4 = Z2 / Z3 or Z1Z4 = Z2Z3 (1) That is: (2) (3) The micro-current sensor connected to the ground wire of the bushing end shield can measure the current I applied to the bushing inner insulation R x , C x The bushing voltage U 0 is equal to: (4) According to the values of C x , R x , the voltage-current phase angle difference can be calculated and derived.

[0072] The charge-induced voltage detection and discharge characteristic analysis method is shown in Figure 13 , Figure 14 , Figure 15 , Figure 16 ; When the bushing end shield has partial discharge or flange surface discharge, space charges generate induced voltage on the induction plate. According to electromagnetic field theory, an electric field numerical model is established, and the electric potential is related to the electric charge.

[0073] The relationship between the electric field strength E and the charge density ρ is governed by Gauss's law: (5) where is the vacuum permittivity, is the differential operator.

[0074] The relationship between the electric field strength E and the electric potential φ is: (6) By combining equation (5) and equation (6), the Poisson equation is obtained: (7) (8) Taking the above equation as the control equation, a finite element simulation model is established. Through finite element simulation calculation in the real structure size line-plate-ground geometry model, the electric potential, electric field strength, and charge density at each place can be obtained.

[0075] Calculate the charge density on the sensing plate ρ , further based on ρ Calculate the magnitude of the induced charge: (9) Where S is the area of ​​the induction plate. Then, the induction plate is connected to the conditioning circuit. The conditioning circuit under the power frequency voltage is mainly C 2( R 1 relative C 2 is extremely small), then the charge induced voltage U 1 is: (10) According to the charge density simulation results and formula, the charge induced voltage can be obtained U 1 and discharge space charge Q 1 is in direct proportion.

[0076] The calculated proportional relationship is U 1 / Q 1. The charge induced voltage is measured in the field test. U 1 ， When , the corresponding discharge space charge can be obtained Q 1 ， = U 1 ， Q 1 / U 1.

[0077] If corona discharge further develops into glow discharge, during a single discharge process, the amount of space charge changes rapidly in a short period of time, and induced charge is generated on the surface of the metal electrode by induction, which in turn forms a pulse current in the detection circuit.

[0078] The frequency range of the discharge pulse signal is about 3 MHz to 30 MHz. Take the lowest frequency f =3 MHz, calculated C 2The maximum value of the capacitive reactance is about several ohms (take C 2=10nF, X C2 =5.3Ω). Take R 1=100Ω, then measure the resistance of the circuit R 1 is much greater than C 2 capacitive reactance, in R Discharge pulse signal on 1 U There is a discharge pulse in 2. Based on this, we can analyze whether glow discharge occurs and the corresponding discharge characteristics.

[0079] Working principle: This embodiment combines the Xilin bridge measurement results to reconstruct and calculate the bushing voltage through the bushing end screen current measured by the coil. Figure 15 Bushing voltage U 1.

[0080] That is, a non-contact measurement method is adopted to measure the bushing voltage without changing the grounding structure.

[0081] The above-mentioned CVT method, mutual inductor method, etc. are not convenient for directly measuring the bushing voltage. The bushing end screen voltage divider method increases the bushing end screen potential, easily produces partial discharge and voltage phase error, and solves the problem that the CVT method, etc. directly connects or takes the device voltage at close range, and there are safety risks in measuring the device voltage.

[0082] This embodiment proposes a method for analyzing end-screen partial discharge and bushing flange surface discharge based on charge induced voltage, and proposes a method for further analyzing the intensity, discharge phase, and space charge characteristics of the partial discharge or surface discharge around the discharge position.

[0083] The actual measurement of partial discharge of the end screen and discharge along the flange surface has achieved the desired effect, as shown by the charge induced voltage. U 1 and discharge pulse signal U 2, etc. The corona discharge situation can be analyzed based on the charge induced voltage, such as Figure 15 , charge induced voltage U 1 (red curve) The rise / fall corresponds to the increase and dissipation of the accumulated space charge within a single cycle. U 1 in sinusoidal bushing voltage U 0 (black curve) The absolute value of the space charge increases when the 0-60° and 180-240° phases of the sine cycle rise; the absolute value of the space charge decreases when the 60-180° and 240-270° phases fall. The other phases basically coincide with the horizontal zero value line, that is, there is no obvious space charge. The maximum absolute value of the charge induced voltage reflects the strength of the discharge. At the same time, according to whether the average value of the charge induced voltage is higher or lower than the zero value horizontal line, it can be judged whether the space charge around the circuit is continuously accumulated. According to the discharge pulse signal U 2, to determine whether there is a discharge pulse and whether partial discharge or creeping discharge occurs. Figure 15 , U 2. Bushing voltage U In the positive half cycle from 0° to 90°, there is a discharge pulse, indicating that partial discharge has occurred. At the same time, the discharge characteristics can be analyzed. For example, the discharge pulse is more obvious in the positive half cycle, and there is basically no discharge pulse in the negative half cycle, indicating that the discharge first occurs in the positive half cycle.

[0084] Under actual working conditions, measurements can be achieved at a horizontal distance of 1m from the casing. The charge induced voltage and discharge pulse measurement sensitivities are high and the anti-interference performance is good. According to the technical solution description, the sensor is mainly composed of an induction plate, a shielding box and a relatively simple passive detection circuit, and has low cost. The detection time is short, and the signal can be used to analyze the corona discharge characteristics after simple processing.

[0085] The method solves the problems of low safety of direct measurement by the aforementioned corona current measurement method, the need for power outage for measurement by the pulse current method, the limitation of detection distance by the ultraviolet detection method, and the obvious influence of electromagnetic interference on the ultrasonic detection method, which are limited when measuring corona discharge of the casing flange; solves the problem that the ultraviolet imaging method, which is a more accurate existing measurement technology, relies on the accuracy of special instruments and is expensive; solves the problem of complex signal processing and complex application of detection technologies such as the ultraviolet detection method and the ultrasonic detection method.

[0086] The local discharge, discharge intensity, discharge phase and other characteristics of the end screen are analyzed by combining the bushing voltage and charge induced voltage, solving the problem that the existing technology cannot analyze and determine the corona discharge degree, discharge phase and so on.

[0087] The rest of this embodiment is the same as any of the above-mentioned embodiments 1 and 2, and thus will not be described in detail.

[0088] Example 4: This embodiment is based on any one of the above embodiments 1 to 3. Figure 18 As shown, a specific test result is used to illustrate.

[0089] 1) Discharge space charge / charge induced voltage ratio and calculation of actual space charge; Taking the case of partial discharge at the end screen of the bushing generating a space charge of 0.01μC and the distance between the induction plate and the bushing flange being 1m as an example, the finite element simulation is used to analyze the induction and carry out electromagnetic field simulation. The simulation results of electric potential and electric field strength are shown in the figure below. Figure 15 、 Figure 16 shown.

[0090] Based on the simulation results of the average surface charge density, such as Figure 17 shown.

[0091] Combining equations (9) and (10), the induced charge of the metal induction plate is calculated as Q 2=16.33pC, charge induced voltage U 1=1.633mV. Then U 1 / Q 1=1.633×10 11 .

[0092] Furthermore, if the charge induced voltage is measured U 1 ， =10mV, then the actual space charge Q 1 ， =0.062μC.

[0093] 2) Detection and analysis Install the induction plate at the transformer bushing flange and the current sensor at the end screen grounding wire. The signal acquisition unit collects the voltage signal. U 1. U 2 and current I Signal, taking the oscilloscope as an example. Discharge signal U 2. The sampling rate is 1 Gsa / s and the sampling resolution is 12 bits. The induced voltage and discharge pulse signals are combined to analyze the characteristics of partial discharge or creeping discharge.

[0094] The detected charge induced voltage signal (red, U 1), and the bushing voltage after adjusting the amplitude U 0 (black, sine wave); the discharge pulse signal (blue) is filtered and processed.

[0095] According to the analysis of the induced voltage waveform: charge induced voltage U 1. In the sinusoidal bushing voltage U The black curve shows a rise in the 0-60° and 180-240° ranges of the sinusoidal cycle, indicating a significant corona discharge and an increase in the absolute value of the space charge. A decrease in the 60-180° and 240-270° ranges indicates the cessation of discharge, the dissipation of space charge, and a decrease in the absolute value of the space charge. The other phases essentially coincide with the horizontal zero-value line, indicating no significant net space charge accumulation. The large maximum absolute value of the charge-induced voltage indicates a strong surface discharge, potentially progressing to the glow discharge stage.

[0096] According to the discharge pulse waveform analysis: U 2. Voltage divider in bushing U In the positive half cycle of 0~90°, there are discharge pulses, which proves that strong surface discharge has occurred, that is, there may be uneven distribution of surface electric field at the connection position between flange and bushing, and the discharge is more obvious, so corresponding measures need to be taken.

[0097] Working Principle: This embodiment forms a non-contact bushing voltage measurement method, which reconstructs the bushing voltage based on the bushing end screen grounding current and the bushing resistance and capacitance parameters obtained by Schilling bridge measurement.

[0098] The charge-induced voltage metal sensing plate of the ring structure of this embodiment can measure the induced charge of partial discharge in all directions around the bushing flange; a method for analyzing partial discharge at the bushing end screen and discharge along the flange surface based on charge-induced voltage is used, and a method for analyzing the degree of discharge, discharge phase, and cause of discharge is combined with bushing voltage and charge-induced voltage; both the sensor and the measuring device are passive devices and do not require power supply.

[0099] This embodiment combines the bushing voltage, charge induced voltage and discharge pulse to analyze the characteristics of the end screen partial discharge and the surface discharge at the flange position.

[0100] The rest of this embodiment is the same as any one of the above-mentioned embodiments 1 to 3, and thus will not be described in detail.

[0101] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for measuring and analyzing external insulation discharge at the bushing flange position, characterized in that: The specific steps include: Step S1: a metal induction plate is arranged to surround the lower end of the bushing, a shielding box is arranged at one end of the opening of the metal induction plate, and a detection circuit is arranged inside the shielding box and connected to a signal acquisition device and a current coil to obtain an external insulation discharge measurement device at the bushing flange position; Step S2: Before measuring partial discharge and creeping discharge, connect one end of the Xilin bridge to the bushing conductive rod and the other end to the bushing end screen lead wire, and reconstruct and calculate the bushing voltage using the bushing end screen current measured by the current coil; Step S3: When partial discharge occurs at the bushing end screen or discharge occurs along the flange surface, an electric field numerical model is established based on electromagnetic field theory to calculate the charge induced voltage; Step S4: Analyze the discharge condition according to the bushing voltage, the charge induced voltage, and the discharge pulse signal.

2. The method for measuring and analyzing insulation discharge outside the bushing flange according to claim 1, characterized in that: The step S2 specifically includes the following steps: Step S21: Before measuring partial discharge and creeping discharge, the bushing is powered off, and one end of the Xilin bridge is connected to the bushing conductive rod, and the other end is connected to the bushing end screen lead wire; Step S22: adjusting the resistor R4 and the capacitor C4 to adjust the Schilling bridge to a balanced state, and calculating the bridge arm impedance ratio; Step S23: Calculating the resistance value of the insulation resistor Rx and the capacitance value of the capacitor Cx in the casing according to the bridge arm impedance ratio; Step S24: measuring the current I applied to the insulation resistance Rx and capacitance Cx in the bushing using a current sensor connected to the grounding wire of the bushing end screen; Step S25: Calculate the bushing voltage U0 according to the resistance value of the resistor Rx, the capacitance value of the capacitor Cx, and the current I.

3. The method for measuring and analyzing insulation discharge outside the bushing flange according to claim 2, characterized in that: The specific operations of step S22 are: Where j represents the imaginary unit and ω represents the angular frequency.

4. The method for measuring and analyzing insulation discharge outside the bushing flange according to claim 3, characterized in that: The specific operations of step S23 are: Where w is the angular frequency.

5. The method for measuring and analyzing external insulation discharge at the bushing flange position according to claim 4, characterized in that: The specific operations of step S24 are: Among them, I is the insulation resistance Rx applied to the bushing, and the capacitance C x The current, j represents the imaginary unit, and ω represents the angular frequency.

6. The method for measuring and analyzing external insulation discharge at the bushing flange position according to claim 1, characterized in that: The step S3 specifically includes the following steps: Step S31: When partial discharge occurs at the bushing end screen or discharge occurs along the flange surface, the relationship between the electric field intensity E and the charge density ρ is established according to Gauss's law; Step S32: Obtaining the relationship between the electric field intensity E and the electric potential φ based on the relationship between the electric field intensity E and the charge density ρ; Step S33: Obtaining the Poisson equation based on the vacuum dielectric constant, the relationship between the electric field intensity E and the charge density ρ, and the relationship between the electric field intensity E and the electric potential φ; Step S34: Using the Poisson equation as the control equation, a finite element simulation model is established; Step S35: according to the simulation model, set the partial discharge or surface discharge space charge, obtain the charge density ρ on the metal sensing plate, and calculate the induced charge according to the area of ​​the metal sensing plate; Step S36: Calculating the charge induced voltage value according to the induced charge amount; Step S37: Based on the discharge space charge value set in the simulation and the calculated charge induced voltage value, the proportional relationship between the discharge space charge and the charge induced voltage of the metal induction plate is obtained; during actual measurement, the discharge space charge is analyzed based on the measured charge induced voltage to obtain the partial discharge situation.

7. The method for measuring and analyzing external insulation discharge at the bushing flange position according to claim 1, characterized in that: The specific operation of step S4 is as follows: analyzing the discharge situation according to the induced voltage waveform; if the charge induced voltage rises at 0° to 60° and 180° to 240° of the sinusoidal period of the sinusoidal bushing voltage, obvious corona discharge occurs and the absolute value of the space charge increases; if the charge induced voltage drops at 60° to 180° and 240° to 270° of the sinusoidal period of the sinusoidal bushing voltage, the discharge stops, the space charge dissipates, and the absolute value of the space charge decreases; the other phases basically coincide with the horizontal zero value line, and at this time there is no obvious net space charge accumulation in the space; the maximum absolute value of the charge induced voltage is large, which is judged to be a strong surface discharge, which may develop into a glow discharge stage.

8. The method for measuring and analyzing external insulation discharge at the bushing flange position according to claim 1, characterized in that: The discharge situation is analyzed based on the discharge pulse waveform. If the discharge signal exists in the positive half cycle of the bushing divided voltage 0~90°, a discharge pulse indicates that a strong surface discharge has occurred, that is, there is an uneven distribution of the surface electric field at the connection position between the flange and the bushing, and the discharge is more obvious, and corresponding measures need to be taken.

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