Method for determining the range of a pressure sensor for an arcing test of a transformer bushing

Abstract

This invention discloses a method for determining the range of a pressure sensor in a transformer bushing arc test, relating to the field of high-voltage electrical testing and detection technology. The method first establishes a test platform for the bushing and riser seat, and builds a corresponding geometric model to determine the spatial relationship between the arc source and the pressure sensor. Then, combining the impedance of the test system and power supply parameters, the expected short-circuit current and arc energy are calculated. Based on fluid acoustics theory, the initial pressure of the arc shock wave is derived, and the reflection gain is determined through the acoustic impedance characteristics of the transformer oil and the riser seat wall. Finally, using an acoustic attenuation model, the estimated peak pressure at the sensor installation location is calculated, thereby scientifically defining the range of the pressure sensor. This method can scientifically and accurately predict the peak pressure in an arc test, providing a theoretical basis for sensor selection and effectively solving the problems of blindly selecting sensors leading to sensor damage due to an insufficient range or low measurement accuracy due to an excessively large range.

Description

Technical Field

[0001] This invention relates to the field of high-voltage electrical testing technology, specifically to a method for determining the range of a pressure sensor for transformer bushing arc testing. Background Technology

[0002] Power transformers are core equipment in power systems, and bushings, as crucial components, directly affect the safe operation of the entire system and power grid. When internal insulation breakdown occurs in a transformer bushing, a high-energy electric arc discharge is generated, causing the insulating oil to rapidly vaporize and expand, producing a violent pressure shock wave. To verify the explosion-proof capability and mechanical strength of the bushing and riser under fault conditions, an arcing test of the transformer bushing is required. Accurately measuring the dynamic pressure changes inside the bushing and riser during the arcing test is a key step in assessing its safety performance. This typically relies on pressure sensors installed on the riser or at specific locations. However, because the arcing test is a destructive test characterized by large energy release, short duration, and rapid pressure rise, the peak impact pressure during the test is difficult to predict using simple empirical judgment. Choosing a sensor range that is too small can directly damage the sensor's internal sensitive elements or physical structure, resulting in not only costly equipment losses but also the loss of critical experimental data. Conversely, choosing a sensor range that is too large will significantly reduce the signal-to-noise ratio of the measurement signal when the actual pressure is much lower than the sensor's range, leading to insufficient measurement accuracy and an inability to accurately reflect the true characteristics and subtle changes of the electric arc shock wave. Therefore, there is an urgent need for a method that can accurately calculate the expected arc energy and shock wave propagation attenuation based on the electrical parameters and spatial geometry of the experimental system, thereby determining the location of the pressure sensor and estimating the peak pressure. This method would provide a theoretical basis for the scientific selection of pressure sensors, ensuring the accuracy of experimental data and the safety of the equipment. Summary of the Invention

[0003] This invention aims to provide a method for determining the range of a pressure sensor used in transformer bushing arc testing. Through establishing a geometric model, calculating arc energy, and performing fluid acoustic analysis, it achieves accurate prediction of the test pressure. The specific implementation steps are as follows:

[0004] S1: An arc-starting buried wire is installed inside the tail end of the transformer bushing, a test platform for the bushing and the riser is built, and a test space geometric model is constructed.

[0005] S2: Obtain the impedance of the test system and its test power supply parameters, measure the loop resistance from the top of the guide rod to the end screen position after the arc is buried, calculate the expected arc voltage and current waveform, and then calculate the arc energy;

[0006] S3: Determine the initial pressure of the shock wave source based on fluid acoustics, calculate the acoustic impedance of the medium, and determine the reflection gain;

[0007] S4: Determine the estimated peak pressure at the sensor location and determine the pressure sensor's range.

[0008] Furthermore, in step S1, a copper wire of length L and radius r is passed through the main insulation at the tail end of the bushing to achieve a direct connection between the zero screen of the main insulation of the bushing and the ground potential, thereby constructing a through discharge channel inside the bushing; an experimental platform is built, and in constructing the experimental space geometric model, the geometric center of the arc-inducing copper wire inside the bushing is defined as the origin of the wave source coordinates. By obtaining the spatial coordinates of the reserved mounting hole of the pressure sensor, the straight-line propagation distance d from the wave source to the sensor is calculated;

[0009] Furthermore, in step S2, obtaining the test power supply parameters includes: applying a phase voltage value U. s Voltage frequency ω, voltage application time t, resistance R of the test system s Reactance X s After the arc is buried, measure the loop resistance R from the top of the guide rod to the end screen position, and calculate the expected effective value of the short-circuit current I. est :

[0010] ;

[0011] In the formula: I est U represents the expected effective value of the short-circuit current, in kiloamperes; s The applied phase voltage is expressed in kilovolts; R is the resistance of the test circuit after arc burial, expressed in ohms; R s X represents the resistance of the test system, in ohms. s The reactance of the test system is expressed in ohms.

[0012] Furthermore, the instantaneous current i(t) and the instantaneous arc resistance R are calculated. arc (t):

[0013] ;

[0014] ;

[0015] In the formula: i(t) is the instantaneous current, in kiloamperes; I est R represents the expected short-circuit current RMS value, in kiloamperes; ω represents the voltage frequency, in hertz; t represents the applied voltage time, in seconds; R arc i(t) is the instantaneous arc resistance in ohms; i(t) is the instantaneous current in kiloamperes; L is the length of the buried arc copper wire in meters; K oil is the Warrington coefficient for electric arc in oil, and its value is determined empirically;

[0016] Furthermore, the instantaneous arc energy W is calculated. arc :

[0017] ;

[0018] ;

[0019] In the formula: W arc i(t) is the instantaneous arc energy, measured in kilojoules; i(t) is the instantaneous current, measured in kiloamperes; u arc (t) represents the instantaneous voltage, measured in kilovolts.

[0020] Furthermore, in step S3, the initial impact pressure P on the bubble surface is calculated using a commonly used empirical formula based on the volume of gas converted from arc energy. s :

[0021] ;

[0022] ;

[0023] ;

[0024] In the formula: P s The initial impact pressure on the bubble surface is expressed in Pascals (Pa). This refers to the density of transformer oil, expressed in kilograms per cubic meter. V is the sound velocity of transformer oil, in meters per second; v is the initial expansion velocity of the bubble, in meters per second; V is the initial vaporization channel volume, in cubic meters; W arc The instantaneous arc energy is expressed in kilojoules; β is the coefficient of thermal expansion of the transformer oil; C P The specific heat capacity at constant pressure of transformer oil;

[0025] Furthermore, the reflection gain K is obtained by calculating the acoustic impedance:

[0026] ;

[0027] ;

[0028] ;

[0029] In the formula: Z oil Transformer oil acoustic impedance, unit: Rayleigh; Z s To increase the acoustic impedance of the enclosure, the unit is Rayleigh; To increase the density of the seat wall, the unit is kilograms per cubic meter; To increase the sound velocity of the seat wall, the unit is meters per second;

[0030] Furthermore, in step S4, based on the fluid acoustic wave equation and reflection gain, the peak pressure P is estimated by determining the location of the pressure sensor.

[0031] ;

[0032] In the formula: P is the peak pressure at the pressure sensor location, in Pascals; s denoted as ρ, where ρ is the initial impact pressure on the bubble surface, in Pascals; r is the radius of the copper wire, in meters; d is the straight-line propagation distance from the wave source to the sensor, in meters; and K is the reflection gain, dimensionless.

[0033] Predicting peak pressure based on the location of the pressure sensor can provide a basis for selecting the pressure sensor's range. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method for determining the range of the pressure sensor in the transformer bushing arc test according to the present invention;

[0035] Figure 2 This is a schematic diagram of the transformer bushing arc test platform of the present invention. Detailed Implementation

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] This invention provides a method for determining the range of a pressure sensor used in a transformer bushing arc test, such as... Figure 1 As shown, it includes the following steps:

[0038] S1: An arc-starting buried wire is installed inside the tail end of the transformer bushing, a test platform for the bushing and the riser is built, and a test space geometric model is constructed.

[0039] S2: Obtain the impedance of the test system and its test power supply parameters, measure the loop resistance from the top of the guide rod to the end screen position after the arc is buried, calculate the expected arc voltage and current waveform, and then calculate the arc energy;

[0040] S3: Determine the initial pressure of the shock wave source based on fluid acoustics, calculate the acoustic impedance of the medium, and determine the reflection gain;

[0041] S4: Determine the estimated peak pressure at the sensor location and determine the pressure sensor's range.

[0042] In step S1, the arc-initiating wire inside the transformer bushing is a copper round wire of length L and radius r that runs through the main insulation at the bushing tail end, directly connecting the neutral screen of the bushing main insulation and the ground potential, thereby constructing a through-discharge channel inside the bushing. An experimental platform is built, and in constructing the experimental space geometric model, the geometric center of the arc-initiating copper round wire inside the bushing is defined as the origin of the wave source coordinates. The spatial coordinates of the reserved mounting hole for the pressure sensor are obtained, and the linear propagation distance d from the wave source to the sensor is calculated.

[0043] In step S2, obtaining the test power supply parameters includes: applying the phase voltage value U. s Voltage frequency ω, voltage application time t, resistance R of the test system s Reactance X s After the arc is buried, measure the loop resistance R from the top of the guide rod to the end screen position, and calculate the expected effective value of the short-circuit current I. est :

[0044] ;

[0045] In the formula: I est U represents the expected effective value of the short-circuit current, in kiloamperes; s The applied phase voltage is expressed in kilovolts; R is the resistance of the test circuit after arc burial, expressed in ohms; R s X represents the resistance of the test system, in ohms. s The reactance of the test system is expressed in ohms.

[0046] In this embodiment of the invention, the instantaneous current i(t) and the instantaneous arc resistance R are calculated. arc (t):

[0047] ;

[0048] In the formula: i(t) is the instantaneous current, in kiloamperes; I est ω is the expected effective value of the short-circuit current, in kiloamperes; ω is the voltage frequency, in hertz; t is the applied voltage time, in seconds.

[0049] ;

[0050] In the formula: R arc i(t) is the instantaneous arc resistance in ohms; i(t) is the instantaneous current in kiloamperes; L is the length of the buried arc copper wire in meters; K oil is the Warrington coefficient for electric arc in oil, and its value is determined empirically;

[0051] In the Warrington model, the arc discharge coefficient in air is 8750 in imperial units, which is approximately 28700 in SI units. Converting to kiloamperes, it is 28.7. The Warrington coefficient is related to the arc gradient E. Under high current conditions in the kiloampere range, the average arc gradient E in air... air The average arc gradient E in transformer oil is 10-15 V / cm. oil Given a voltage of 50-100V / cm, calculate the correction ratio for the medium:

[0052] ;

[0053] To avoid overestimating the voltage and selecting an excessively large measurement range that results in a loss of sensitivity, a lower limit of the ratio range of 3.0 is selected. Therefore, the arc coefficient K in Warrington oil is... oil It is 86.1;

[0054] In this embodiment of the invention, the instantaneous arc energy W is calculated. arc :

[0055] ;

[0056] ;

[0057] In step S3, the gas production from arc discharge in oil is calculated based on a commonly used empirical formula for the volume of gas converted from arc energy:

[0058] ;

[0059] In the formula: V is the initial gasification channel volume in cubic meters; r is the radius of the copper wire in meters; L is the length of the copper wire in meters.

[0060] The initial impact pressure P on the bubble surface is calculated using the acoustic wave equation. s :

[0061] ;

[0062] ;

[0063] In the formula: P s The initial impact pressure on the bubble surface is expressed in Pascals (Pa). The density of transformer oil is expressed in kilograms per cubic meter, and is taken as 885 kg / m³. 3 ; ρ is the sound velocity of transformer oil, in meters per second, taken as 1450 m / s; v is the initial expansion velocity of the bubble, in meters per second; V is the initial vaporization channel volume, in cubic meters; W arcThe instantaneous arc energy is expressed in kilojoules; β is the coefficient of thermal expansion of the transformer oil; C P The specific heat capacity of transformer oil at constant pressure is taken as 1950 J / (kg•K);

[0064] In this embodiment of the invention, the acoustic impedance of the transformer oil and the riser wall is calculated:

[0065] ;

[0066] ;

[0067] In the formula: Z oil Transformer oil acoustic impedance, unit: Rayleigh; Z s To increase the acoustic impedance of the enclosure, the unit is Rayleigh; To increase the density of the seat wall, the unit is kilograms per cubic meter, and the value is taken as 7900 kg / m³. 3 ; To increase the sound velocity on the seat wall, the unit is meters per second, and the value is taken as 5900 m / s;

[0068] In this embodiment of the invention, the reflection gain K is obtained as follows:

[0069] ;

[0070] In step S4, based on the fluid acoustic wave equation and reflection gain, the peak pressure P is estimated by determining the location of the pressure sensor.

[0071] ;

[0072] In the formula: P is the peak pressure at the pressure sensor location, in Pascals; s denoted as ρ, where ρ is the initial impact pressure on the bubble surface, in Pascals; r is the radius of the copper wire, in meters; d is the straight-line propagation distance from the wave source to the sensor, in meters; and K is the reflection gain, dimensionless.

[0073] Predicting peak pressure based on the location of the pressure sensor can provide a basis for selecting the pressure sensor's range.

Claims

1. A method for determining the range of a pressure sensor used in a transformer bushing arc test, characterized in that, The method and steps include: S1: An arc-starting buried wire is installed inside the tail end of the transformer bushing, a test platform for the bushing and the riser is built, and a test space geometric model is constructed. S2: Obtain the impedance of the test system and its test power supply parameters, measure the loop resistance from the top of the guide rod to the end screen position after the arc is buried, calculate the expected arc voltage and current waveform, and then calculate the arc energy; S3: Determine the initial pressure of the shock wave source based on fluid acoustics, calculate the acoustic impedance of the medium, and determine the reflection gain; S4: Determine the estimated peak pressure at the sensor location and determine the pressure sensor's range.

2. The method for determining the range of a pressure sensor for a transformer bushing arc test according to claim 1, characterized in that, A copper circular wire of length L and radius r is passed through the main insulation at the tail end of the bushing to achieve a direct connection between the zero screen of the main insulation of the bushing and the ground potential, thereby constructing a through discharge channel inside the bushing; an experimental platform is built, and in the construction of the experimental space geometric model, the geometric center of the arc-inducing copper circular wire inside the bushing is defined as the origin of the wave source coordinates, the spatial coordinates of the reserved mounting hole of the pressure sensor are obtained, and the straight-line propagation distance d from the wave source to the sensor is calculated.

3. The method for determining the range of a transformer bushing arc test pressure sensor according to claim 1, characterized in that, By obtaining the test power supply parameters, including: the applied phase voltage value U s Voltage frequency ω, voltage application time t, resistance R of the test system s Reactance X s After the arc is buried, measure the loop resistance R from the top of the guide rod to the end screen position, and calculate the expected effective value of the short-circuit current I. est : ； In the formula: I est U represents the expected effective value of the short-circuit current, in kiloamperes; s The applied phase voltage is expressed in kilovolts; R is the resistance of the test circuit after arc burial, expressed in ohms; R s X represents the resistance of the test system, in ohms; s The reactance of the test system is expressed in ohms. Then the instantaneous current i(t): ； In the formula: i(t) is the instantaneous current, in kiloamperes; I est ω is the expected effective value of the short-circuit current, in kiloamperes; ω is the voltage frequency, in hertz; t is the applied voltage time, in seconds. Instantaneous arc resistance: ； In the formula: R arc i(t) is the instantaneous arc resistance in ohms; i(t) is the instantaneous current in kiloamperes; L is the length of the buried arc copper wire in meters; K oil is the Warrington coefficient for electric arc in oil, and its value is determined empirically; Instantaneous arc voltage u arc (t): ； Instantaneous arc energy W arc : ； In the formula: W arc i(t) is the instantaneous arc energy, measured in kilojoules; i(t) is the instantaneous current, measured in kiloamperes; u arc (t) represents the instantaneous voltage, measured in kilovolts.

4. The method for determining the range of a transformer bushing arc test pressure sensor according to claim 1, characterized in that, The gas production rate of arc discharge in oil is: ； In the formula: V is the initial gasification channel volume in cubic meters; r is the radius of the copper wire in meters; L is the length of the copper wire in meters. The initial impact pressure P on the bubble surface is calculated using the acoustic wave equation. s : ； ； In the formula: P s The initial impact pressure on the bubble surface is expressed in Pascals (Pa). This refers to the density of transformer oil, expressed in kilograms per cubic meter. V is the sound velocity of transformer oil, in meters per second; v is the initial expansion velocity of the bubble, in meters per second; V is the initial vaporization channel volume, in cubic meters; W arc The instantaneous arc energy is expressed in kilojoules; β is the coefficient of thermal expansion of the transformer oil; C P The specific heat capacity at constant pressure of transformer oil; Calculate the acoustic impedance of the transformer oil and the raised mounting wall: ； ； In the formula: Z oil Transformer oil acoustic impedance, unit: Rayleigh; Z s To increase the acoustic impedance of the enclosure, the unit is Rayleigh; To increase the density of the seat wall, the unit is kilograms per cubic meter; To increase the sound velocity in the seat wall, the unit is meters per second; Calculate the reflection gain K: 。 5. The method for determining the range of a transformer bushing arc test pressure sensor according to claim 1, characterized in that, Based on the fluid acoustic wave equation and reflection gain, the peak pressure P is predicted by the location of the pressure sensor. ； In the formula: P is the peak pressure at the pressure sensor location, in Pascals; s denoted as ρ, where ρ is the initial impact pressure on the bubble surface, in Pascals; r is the radius of the copper wire, in meters; d is the straight-line propagation distance from the wave source to the sensor, in meters; and K is the reflection gain, dimensionless. Predicting peak pressure based on the location of the pressure sensor can provide a basis for selecting the pressure sensor's range.

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