A method to eliminate the influence of stray capacitance on oil-immersed high-voltage bushing testing

Abstract

The invention discloses a method for eliminating the influence of stray capacitance on the test of oil-immersed high-voltage bushings, belonging to the technical field of power transformer operation. By establishing a loss factor correction model of the oil-immersed high-voltage bushing affected by stray capacitance, the influence of temperature and frequency on the loss factor correction amount affected by stray capacitance in the loss factor test is comprehensively considered and quantitatively analyzed; the universality of the model is enhanced; a voltage correction coefficient is proposed, and the influence of the test voltage on the loss factor correction amount in the loss factor test is quantitatively characterized; the proposed loss factor correction model for eliminating voltage influence can eliminate the influence of stray capacitance on the loss factor test of the high-voltage bushing, thereby providing a guarantee for accurate evaluation of the insulation state of the oil-immersed high-voltage bushing.

Description

Technical Field

[0001] The present invention belongs to the technical field of power transformer operation and maintenance, and in particular relates to a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing. Background Art

[0002] Oil-immersed high-voltage bushings, as an important accessory of oil-immersed power transformers, primarily serve the purpose of electrical isolation and power transmission. As a key structural component of the power system, their safe and reliable operation directly impacts the stability of the power system.

[0003] Oil-immersed high-voltage bushings have a capacitor screen in the capacitor core that extends below the ground flange. Consequently, stray capacitance exists between the bushing capacitor screen and the transformer windings. When testing the bushing on a transformer, the applied voltage generates leakage current in the transformer windings. This leakage current flows from the transformer windings and enters the bushing core through stray capacitance. Since this leakage current flows directly into the bushing capacitor core rather than into the protection circuit, the protection circuit cannot eliminate it from the test circuit, potentially leading to loss factor measurement errors. Because stray capacitance contributes additional loss factor, the overall test results are biased upward, leading to a misjudgment of the bushing insulation condition and compromising the safety and stability of the oil-immersed power transformer.

[0004] Therefore, a new technical solution is urgently needed in the existing technology to solve this problem. Summary of the Invention

[0005] In order to overcome the deficiencies in the prior art, the present invention provides a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing, which is used to solve the problem that stray capacitance causes the overall test results to be larger and misjudges the insulation status of the bushing.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing, comprising the following steps:

[0007] S1. Perform high-frequency and low-frequency tests on the loss factor of the undisassembled bushing on the transformer and the bushing after disassembly of the same level in the laboratory under set temperature and set voltage; the high-frequency region is a frequency range of 1 to 1000 Hz; the low-frequency region is a frequency range of 0.001 to 1 Hz;

[0008] S2. Fit the difference in loss factor between the undisassembled bushing on the transformer and the bushing after disassembly of the same level in the laboratory simulation in the high-frequency region and the low-frequency region, respectively, to obtain a loss factor correction model affected by stray capacitance;

[0009] S3, changing the set temperature described in S1, fitting the loss factor correction model at different temperatures, and obtaining an expression for the coefficient affected by temperature in the loss factor correction model;

[0010] S4. Changing the set voltage described in S1, fitting the loss factor curves of the disassembled bushing at different test voltages with approximate multiples of the loss factor curves of the disassembled bushing at the set voltage to obtain an expression for the voltage correction coefficient;

[0011] S5. Using the voltage correction coefficient obtained in S4 and the loss factor correction model described in S2, a loss factor correction model that eliminates voltage influence is obtained;

[0012] S6. Perform frequency domain dielectric response testing on the high-voltage bushing on the on-site oil-immersed power transformer. Utilize the loss factor correction model of S5 that eliminates voltage effects to obtain the loss factor spectrum curve of the oil-immersed high-voltage bushing that eliminates stray capacitance and voltage effects.

[0013] Through the above design scheme, the present invention can bring the following beneficial effects:

[0014] 1. A loss factor correction model for oil-immersed high-voltage bushings affected by stray capacitance was established. The effects of temperature and frequency on the loss factor correction affected by stray capacitance in loss factor testing were comprehensively considered and quantitatively analyzed, enhancing the universality of the model.

[0015] 2. The voltage correction coefficient is proposed to quantify the effect of test voltage on the loss factor correction in loss factor test;

[0016] 3. The proposed loss factor correction model that eliminates voltage influence can eliminate the influence of stray capacitance on the loss factor test of high-voltage bushing, providing a guarantee for the accurate evaluation of the insulation status of oil-immersed high-voltage bushing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flow chart of a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing.

[0018] Figure 2 A high-voltage bushing test circuit diagram of a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing according to the present invention.

[0019] Figure 3 The present invention provides a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing, showing a test curve of the loss factor of a 220 kV oil-immersed high-voltage bushing located on a transformer and a graph of the calculated and corrected curve.

[0020] Figure 4The present invention provides a method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing, showing a test curve of the loss factor of a disassembled 220 kV oil-immersed high-voltage bushing and a graph of the calculated and corrected curve.

[0021] In the figure, 1-test power supply, 2-measurement circuit, 3-high-voltage bushing, 4-low-voltage bushing, 5-stray capacitance, 6-transformer core, 7-transformer winding. DETAILED DESCRIPTION

[0022] The following is a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings.

[0023] To more clearly illustrate the present invention, the present invention is further described below with reference to preferred embodiments. Those skilled in the art will appreciate that the detailed description below is illustrative and non-restrictive, and that the user may make various changes to the following parameters without departing from the mechanism and scope of the invention as set forth in the claims. To avoid obscuring the essence of the present invention, well-known methods and processes are not described in detail.

[0024] By the attached Figures 1 to 4 A method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing includes the following steps:

[0025] S1. Perform high-frequency and low-frequency tests on the loss factor of the undisassembled bushing on the transformer and the disassembled bushing of the same level simulated in the laboratory at a set temperature and a set voltage. The high-frequency range is 1 to 1000 Hz; the low-frequency range is 0.001 to 1 Hz. The term "undisassembled" means connected to the transformer, and "disassembled" means disconnected from the transformer.

[0026] S2. Fit the difference in loss factor between the undisassembled bushing on the transformer and the bushing after disassembly of the same level in the laboratory simulation in the high-frequency and low-frequency regions to obtain the loss factor correction model affected by stray capacitance; the expression is as follows:

[0027]

[0028] Among them, Δtanδ(ω,T) is the loss factor correction amount of the high-voltage bushing 3 affected by the stray capacitance 5, ω is the angular frequency of the test power supply 1, unit: radian / second, T is the temperature, unit: degrees Celsius, f is the frequency domain dielectric response test frequency, unit: Hertz, A1, A2, t, m, B1, B2, q1, B3, q2 are the unknown coefficients in the formula, which are related to temperature. The loss factor curves of the bushing before and after disassembly are calculated at 30°C to obtain the difference at different frequencies. According to the data, the formulas with the highest difference fit between the high-frequency region (frequency range 1 to 1000 Hz) and the low-frequency region (frequency range 0.001 to 1 Hz) are inconsistent. Therefore, this patent adopts a segmented form for fitting calculation.

[0029] S3, changing the set temperature described in S1, fitting the loss factor correction model at different temperatures, and obtaining an expression for the coefficient affected by temperature in the loss factor correction model;

[0030]

[0031] Among them, A1 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0032] A2=39.68369×1.00086 T

[0033] Among them, A2 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0034] t=37.05793×1.00205 T

[0035] Where t is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0036] m=-0.00194(T-1350.91975)

[0037] Where m is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0038] B1=3.95139×10 -6 e (T / 17.95337)

[0039] Wherein, B1 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0040] B2=0.06375ln(13.83961ln(T))

[0041] Among them, B2 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0042] q1=0.90338+0.15208e (-T / 29.69801)

[0043] Where q1 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0044] B3=0.00544ln(11.921421ln(T))

[0045] Among them, B3 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, T is the temperature in degrees Celsius,

[0046] q2=21.92096+13.57121e (-T / 22.71564)

[0047] Wherein, q2 is the unknown coefficient in the loss factor correction of the high-voltage bushing affected by stray capacitance, and T is the temperature in degrees Celsius.

[0048] S4. Changing the set voltage described in S1, fitting the loss factor curves of the disassembled bushing at different test voltages with approximate multiples of the loss factor curves of the disassembled bushing at the set voltage to obtain an expression for the voltage correction coefficient;

[0049]

[0050] Where k is the voltage correction factor and U is the test voltage of the frequency domain dielectric response, in volts.

[0051] S5. Using the voltage correction coefficient obtained in S4 and the loss factor correction model described in S2, a loss factor correction model that eliminates voltage influence is obtained;

[0052] Δtanδ0(ω,T)=kΔtanδ(ω,T)

[0053] Wherein, Δtanδ0(ω,T) is the loss factor correction to eliminate the influence of voltage, ω is the angular frequency of test power supply 1, unit: radian / second, T is the temperature, unit: degree Celsius, k is the voltage correction factor, and Δtanδ(ω,T) is the loss factor correction for the high-voltage bushing affected by stray capacitance.

[0054] S6. Perform frequency domain dielectric response testing on the high-voltage bushing on the on-site oil-immersed power transformer. Utilize the loss factor correction model of S5 that eliminates voltage effects to obtain the loss factor spectrum curve of the oil-immersed high-voltage bushing that eliminates stray capacitance and voltage effects.

[0055] tanδ k =tanδ s -Δtanδ0

[0056] Among them, tanδ k To eliminate the loss factor of oil-immersed high-voltage bushing affected by stray capacitance and voltage, tanδ s It is the measured loss factor of oil-immersed power transformer on site, and Δtanδ0 is the loss factor correction value to eliminate the influence of voltage.

[0057] The fitting described in S2 and S3 was performed by applying the least squares method using Origin software.

[0058] Furthermore, the set temperature in S1 is 30° C.; the set voltage is 100 volts.

[0059] Furthermore, the different temperatures described in S3 are 30° C., 50° C., and 70° C. The different test voltages described in S4 are 500 volts, 1000 volts, and 2000 volts.

[0060] In the specific implementation, the dielectric loss factor curve of the 220 kV oil-paper capacitor bushing on the transformer was tested. The on-site test temperature was 31°C and the test voltage was 2000 volts. The test curve is as follows: Figure 3 The dielectric loss factor curve of the disassembled 220 kV oil-paper capacitor bushing was tested at a field test temperature of 31°C and a test voltage of 2000 volts. The test curve is shown in the figure below. Figure 4 shown.

[0061] At the current test voltage, the voltage correction factor is 1.3877. Table 1 shows the calculated dissipation factor corrections at various frequencies to eliminate voltage effects at the current test temperature.

[0062] Table 1 Calculation results of loss factor correction to eliminate voltage influence

[0063]

[0064]

[0065] The loss factor curve after eliminating the influence of stray capacitance and the loss factor test curve after the bushing is disassembled are as follows: Figure 4 As shown, the fit between the two is 97.6%.

[0066] Obviously, the embodiments described above are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0067] The above mainly introduces the solution of the embodiment of the present application from the perspective of the execution process of the method side. It is understandable that in order to implement the above functions, the network device includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should easily realize that, in combination with the units and algorithm steps of each example described in the embodiment provided herein,

[0068] This application can be implemented in hardware or a combination of hardware and computer software. Whether a function is implemented in hardware or by computer software driving hardware depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing, characterized in that: The steps include: S1. Perform high-frequency and low-frequency tests on the loss factor of the undisassembled bushing on the transformer and the bushing after disassembly of the same level in the laboratory under set temperature and set voltage; the high-frequency region is a frequency range of 1 to 1000 Hz; the low-frequency region is a frequency range of 0.001 to 1 Hz; S2. Fit the difference in loss factor between the undisassembled bushing on the transformer and the bushing after disassembly of the same level in the laboratory simulation in the high-frequency and low-frequency regions to obtain the loss factor correction model affected by stray capacitance; the expression is as follows: Wherein, Δtanδ(ω,T) is the loss factor correction of the high-voltage bushing affected by stray capacitance, ω is the angular frequency of the test power supply, T is the temperature, f is the frequency domain dielectric response test frequency, A1, A2, t, m, B1, B2, q1, B3, q2 are the unknown coefficients in the formula, which are related to temperature; S3. Changing the set temperature described in S1, fitting the loss factor correction model at different temperatures, and obtaining expressions for the undetermined coefficients A1, A2, t, m, B1, B2, q1, B3, and q2 in the loss factor correction model for the high-voltage bushing affected by stray capacitance; S4. Changing the set voltage described in S1, fitting the loss factor curves of the disassembled bushing at different test voltages with approximate multiples of the loss factor curves of the disassembled bushing at the set voltage to obtain an expression for the voltage correction coefficient; S5. Using the voltage correction coefficient obtained in S4 and the loss factor correction model, obtain a loss factor correction model that eliminates voltage influence; S6. Perform frequency domain dielectric response testing on the high-voltage bushing on the on-site oil-immersed power transformer. Utilize the loss factor correction model of S5 that eliminates voltage effects to obtain the loss factor spectrum curve of the oil-immersed high-voltage bushing that eliminates stray capacitance and voltage effects.

2. The method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing according to claim 1, characterized in that: The fitting described in S2 and S3 was performed using the least squares method using Origin software.

3. The method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing according to claim 1, characterized in that: The set temperature in S1 is 30° C.; the set voltage is 100 volts.

4. The method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing according to claim 1, characterized in that: The different temperatures described in S3 are 30°C, 50°C and 70°C.

5. The method for eliminating the influence of stray capacitance on oil-immersed high-voltage bushing testing according to claim 1, characterized in that: The different test voltages described in S4 are 500 volts, 1000 volts and 2000 volts.

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