Method for evaluating the degree of deterioration of an oil-impregnated bushing insulation system

Abstract

The application provides a method for evaluating the deterioration degree of an oil-immersed bushing inner insulation system, which can effectively determine the deterioration degree of the oil-immersed bushing inner insulation system, and comprises the following steps: S1, obtaining the operation parameters of the oil-immersed bushing to be measured multiple times, including the capacitance and dielectric loss value of the oil-paper capacitor core, and the real part and imaginary part of the complex capacitance of the oil-paper capacitor core at different frequency points; S2, calculating the real part and imaginary part of the complex capacitance of the oil-paper capacitor core according to the capacitance and dielectric loss value of the oil-paper capacitor core obtained multiple times; S3, determining the parameters in the extended Debye dielectric relaxation model according to the real part and imaginary part of the complex capacitance of the oil-paper capacitor core at different frequency points obtained multiple times; and S4, calculating the deterioration degree Q of the oil-immersed bushing inner insulation system, and if the Q is greater than the set deterioration degree threshold value, a warning is given.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment insulation condition assessment technology, and in particular to a method for assessing the deterioration of an oil-immersed bushing internal insulation system. Background Technology

[0002] Oil-immersed bushings, as one of the main accessories of transformers, are the only channel connecting the transformer's internal leads to the external power network. Oil-immersed bushings are fully sealed structures; their external insulation mainly consists of an oil conservator, upper and lower porcelain bushings, and flanges, while the internal insulation is an oil-paper capacitor core wrapped with insulating paper and aluminum foil. During operation, bushings are subjected to long-term electrical, thermal, and mechanical stresses, making them a weak link in the power system.

[0003] Statistics show that bushing failures account for approximately 30% of all transformer failures. Once a bushing fails, it can easily explode, causing a fire in the main transformer, resulting in severe economic losses and significant social impact. Currently, the main diagnostic methods for bushings include oil chromatography, insulation resistance testing, and partial discharge testing. Oil chromatography requires sampling oil from the bushing; however, the amount of oil inside the bushing is small and sampling is difficult. Partial discharge testing is difficult to conduct on-site and cannot be distinguished from the transformer body. Because these detection methods are ineffective in detecting bushing defects, especially early-stage defects, this significantly impacts the assessment of insulation condition. Summary of the Invention

[0004] In view of this, the present invention provides a method for assessing the deterioration of the internal insulation system of an oil-immersed bushing, which can make up for the shortcomings of current on-site diagnostic assessment methods, promptly detect bushing defects, and assess the insulation status of the bushing.

[0005] A method for assessing the degradation degree of an oil-immersed bushing internal insulation system includes the following steps:

[0006] S1. Obtain the operating parameters of the oil-immersed bushing under test multiple times, including the capacitance and dielectric loss of the oil-paper capacitor core, as well as the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at different frequency points.

[0007] S2. Calculate the real and imaginary parts of the complex capacitance of the oil-paper capacitor core by obtaining the capacitance and dielectric loss values ​​of the oil-paper capacitor core multiple times;

[0008] S3. Determine the parameters in the extended Debye dielectric relaxation model by obtaining the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at different frequency points multiple times.

[0009] S4. Calculate the degradation degree Q of the internal insulation system of an oil-immersed bushing:

[0010]

[0011] Where f1, f2, and f3 are the selected frequency points, C′(2πf1), C′(2πf2), and C′(2πf3) are the real parts of the complex capacitance of the extended Debye dielectric relaxation model at the frequency points f1, f2, and f3, respectively; C″(2πf1), C″(2πf2), and C″(2πf3) are the imaginary parts of the complex capacitance of the extended Debye dielectric relaxation model at the frequency points f1, f2, and f3, respectively; C′ av (20) C″ av (20) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor core reduced to 20℃, respectively; C0 is the geometric capacitance of the geometric equivalent circuit in the extended Debye dielectric relaxation model;

[0012] If Q > ε, then the insulation system inside the oil-immersed bushing is deteriorated to an excessive degree, and an early warning is issued; where ε is the set deterioration threshold.

[0013] Further, step S2 includes the following steps:

[0014] S21. Average the capacitance and dielectric loss values ​​of the obtained oil-paper capacitor cores:

[0015]

[0016]

[0017] Where P is the number of times each running parameter is obtained, and C... i (T) and tanδ i (T) represents the capacitance and dielectric loss of the oil-paper capacitor core at the test environment temperature T, i = 1, 2, 3, ..., P;

[0018] S22. Place C av (T), tanδ av (T) reduced to C at 20°C av (20) tanδ av (20) value:

[0019] C av (20)=C av (T)·1.5 (20-T) / 10

[0020] tanδ av (20)=tanδ av (T)·1.5 (20-T) / 10

[0021] S23. Calculate the real and imaginary parts of the complex capacitance of an oil-paper capacitor core at 20℃:

[0022]

[0023] Furthermore, the expression for the extended Debye dielectric relaxation model is as follows:

[0024]

[0025] Where ω is the angular frequency, ω=2πf; C′(ω) and C″(ω) represent the real and imaginary parts of the complex capacitance, respectively; C0 and R0 are the geometric capacitance and insulation resistance of the geometric equivalent circuit in the extended Debye dielectric relaxation model, respectively; R j C j These are the resistance and capacitance values ​​of the j-th RC series branch in the model, respectively, where j = 1, 2, ..., k; and k is the number of RC series branches in the model.

[0026] Furthermore, step S3 includes the following steps:

[0027] S31. Average the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at different frequency points:

[0028]

[0029] Among them, C′ i (f l ,T)C″ i (f l T and T are the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at temperature T and the l-th frequency point, respectively.

[0030] S32. Place C′ av (f l ,T)C″ av (f l T) reduced to C′ at 20℃ av (f l ,20)C″ av (f l ,20) value:

[0031]

[0032] S33. Establish the optimization objective function:

[0033]

[0034] Wherein, C′(f l ,20)C″(f l ,20) represents the fitted value at the l-th frequency point obtained by the extended Debye dielectric relaxation model, C′ av (f l ,20)C″ av (f l,20) represents the measured value at the l-th frequency point, and n is the total number of frequency points tested, l = 1, 2, 3, ..., n;

[0035] S34. Minimize the established optimization objective function H, and calculate C′. av (f l ,T) and C″ av (f l ,T), calculate the parameters in the extended Debye dielectric relaxation model: C0, R0, R j C j .

[0036] The present invention has the following beneficial effects:

[0037] The degradation assessment method for the internal insulation system of oil-immersed bushings provided by this invention can overcome the shortcomings of current on-site diagnostic assessment methods. Operating parameters can be measured and obtained separately. In addition, the method for obtaining the capacitance, dielectric loss value, and real and imaginary parts of the complex capacitance of the oil-paper capacitor core is simple and easy to operate on-site. Moreover, the process of calculating the degradation degree is simple, which can effectively determine the degradation degree of the internal insulation system of oil-immersed bushings, detect bushing defects in a timely manner, assess the insulation status of the bushing, and take early action. Attached Figure Description

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0039] Figure 1 A flowchart for assessing the degradation of internal insulation systems in oil-immersed bushings;

[0040] Figure 2 This is a schematic diagram of a test platform for assessing the degradation of the internal insulation system of an oil-immersed bushing. Detailed Implementation

[0041] The present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments.

[0042] This invention provides a method for assessing the degradation degree of an oil-immersed bushing internal insulation system, comprising the following steps:

[0043] S1. Obtain the operating parameters of the oil-immersed bushing under test multiple times, including the capacitance and dielectric loss of the oil-paper capacitor core, as well as the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at different frequency points.

[0044] S2. Calculate the real and imaginary parts of the complex capacitance of the oil-paper capacitor core by obtaining the capacitance and dielectric loss values ​​of the oil-paper capacitor core multiple times;

[0045] S3. Determine the parameters in the extended Debye dielectric relaxation model by obtaining the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at different frequency points multiple times.

[0046] S4. Calculate the degradation degree Q of the internal insulation system of an oil-immersed bushing:

[0047]

[0048] Where f1, f2, and f3 are the selected frequency points, C′(2πf1), C′(2πf2), and C′(2πf3) are the real parts of the complex capacitance of the extended Debye dielectric relaxation model at the frequency points f1, f2, and f3, respectively; C″(2πf1), C″(2πf2), and C″(2πf3) are the imaginary parts of the complex capacitance of the extended Debye dielectric relaxation model at the frequency points f1, f2, and f3, respectively; C′ av (20) C″ av (20) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor core reduced to 20℃, respectively; C0 is the geometric capacitance of the geometric equivalent circuit in the extended Debye dielectric relaxation model;

[0049] If Q > ε, then the insulation system inside the oil-immersed bushing is deteriorated to an excessive degree, and an early warning is issued; where ε is the set deterioration threshold.

[0050] In this embodiment, the method for repeatedly obtaining the operating parameters of the oil-immersed bushing under test in step S1 is as follows:

[0051] S11. For example Figure 2 Set up a test platform:

[0052] A test platform for the internal insulation system of an oil-immersed bushing is constructed, mainly including an oil-immersed bushing 1, a frequency domain dielectric response tester 2, a dielectric loss meter 3, and a computer 4. The cap 5 of the oil-immersed bushing 1 is connected to the high-voltage end Hv of the frequency domain dielectric response tester 2, the flange 6 of the oil-immersed bushing 1 is connected to the low-voltage end Lv of the frequency domain dielectric response tester 2, the frequency domain dielectric response tester 2 is connected to the computer 4, the high-voltage end of the dielectric loss meter 3 is connected to the cap 5 of the oil-immersed bushing 1, and the shielded end Cx of the dielectric loss meter 3 is connected to the flange 6 of the oil-immersed bushing 1.

[0053] S12. Parameter Measurement:

[0054] Record the test temperature T;

[0055] The frequency domain dielectric response tester 2 is activated, and the oil-immersed bushing 1 is tested P times at n different frequency points f under temperature T. l The real part C of the complex capacitor core of the oil-paper capacitor i ′(f l (T) and imaginary part C i "(f l (,T), and recorded to computer 4, the C i′(f l ,T)C i "(f l T) represent the frequency point f at temperature T, respectively. l The real part and imaginary part of the complex capacitance of the oil-paper capacitor core measured in the i-th time, i = 1, 2, 3, ..., P, l = 1, 2, 3, ..., n;

[0056] In this embodiment, the number of frequency points tested is n = 13, and the 13 frequency points are f l = 0.001Hz, 0.005Hz, 0.01Hz, 0.05Hz, 0.1Hz, 0.5Hz, 1Hz, 5Hz, 10Hz, 50Hz, 100Hz, 500Hz and 1000Hz;

[0057] The dielectric loss measuring instrument 3 is activated to test the dielectric loss and capacitance P times of the oil-immersed bushing 1 at temperature T, denoted as C. i (T), tanδ i (T), i = 1, 2, 3, ..., P.

[0058] In this embodiment, step S2 includes the following steps:

[0059] S21. Average the capacitance and dielectric loss values ​​of the obtained oil-paper capacitor cores:

[0060]

[0061]

[0062] Where P is the number of times each running parameter is obtained, and C... i (T) and tanδ i (T) represents the capacitance and dielectric loss of the oil-paper capacitor core at the test environment temperature T, i = 1, 2, 3, ..., P;

[0063] S22. Place C av (T), tanδ av (T) reduced to C at 20°C av (20) tanδ av (20) value:

[0064] C av (20)=C av (T)·1.5 (20-T) / 10

[0065] tanδ av (20)=tanδ av (T)·1.5 (20-T) / 10

[0066] S23. Calculate the real and imaginary parts of the complex capacitance of an oil-paper capacitor core at 20℃:

[0067]

[0068] In this embodiment, the extended Debye dielectric relaxation model equates the oil-paper capacitor core to an equivalent circuit consisting of a geometric equivalent circuit and multiple RC series branches connected in parallel; the geometric equivalent circuit consists of a capacitor and a resistor connected in parallel; the expressions for the real and imaginary parts of the complex capacitance of the equivalent circuit are:

[0069]

[0070] Where ω is the angular frequency, ω=2πf; C′(ω) and C″(ω) represent the real and imaginary parts of the complex capacitance, respectively; C0 and R0 are the geometric capacitance and insulation resistance of the geometric equivalent circuit in the extended Debye dielectric relaxation model, respectively; R j C j These are the resistance and capacitance values ​​of the j-th RC series branch in the model, respectively, where j = 1, 2, ..., k; and k is the number of RC series branches in the model.

[0071] In this embodiment, the number of RC series branches k is 5.

[0072] In this embodiment, step S3 includes the following steps:

[0073] S31. Average the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at different frequency points:

[0074]

[0075] Among them, C′ i (f l ,T)C″ i (f l T and T are the real and imaginary parts of the complex capacitance of the oil-paper capacitor core at temperature T and the l-th frequency point, respectively.

[0076] S32. Place C′ av (f l ,T)C″ av (f l T) reduced to C′ at 20℃ av (f l ,20)C″ av (f l ,20) value:

[0077]

[0078] S33. Establish the optimization objective function:

[0079]

[0080] Wherein, C′(f l ,20)C″(f l ,20) represents the fitted value at the l-th frequency point obtained by the extended Debye dielectric relaxation model, C′ av (f l ,20)C″ av (f l ,20) represents the measured value at the l-th frequency point, and n is the total number of frequency points tested, l = 1, 2, 3, ..., n; in this embodiment, n = 13;

[0081] S34. Minimize the established optimization objective function H, and calculate C′. av (f l ,T) and C″ av (f l ,T), calculate the parameters in the extended Debye dielectric relaxation model: C0, R0, R j C j .

[0082] In this embodiment, step S4 specifically includes:

[0083] S41. Take f1 = 49.8Hz, f2 = 50.0Hz, f3 = 50.2Hz, substitute ω1 = 2πf1, ω2 = 2πf2, ω3 = 2πf3 into the extended Debye dielectric relaxation model with determined parameters, and obtain the real part C′(2πf1), C′(2πf2), C′(2πf3) and the imaginary part C″(2πf1), C″(2πf2), C″(2πf3) of the complex capacitance at frequencies f1, f2, f3;

[0084] S42. Calculate the degree of degradation of the internal insulation system of an oil-immersed bushing:

[0085]

[0086] S43. If Q > 5%, the insulation system inside the oil-immersed bushing is deteriorated to an excessive degree, and an early warning should be issued, requiring timely replacement of the bushing.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of assessing the degree of degradation of an oil- immersed bushing internal insulation system, characterized in that: The method comprises the steps of: S1. obtaining the operating parameters of the oil-impregnated bushing to be tested multiple times, including the capacitance and dielectric loss of the oil-paper capacitor core, and the real part and imaginary part of the complex capacitance of the oil-paper capacitor core at different frequency points; S2. calculating the real part and imaginary part of the complex capacitance of the oil-paper capacitor core according to the capacitance and dielectric loss of the oil-paper capacitor core obtained multiple times; S3. determining the parameters in the extended Debye dielectric relaxation model according to the real part and imaginary part of the complex capacitance of the oil-paper capacitor core at different frequency points obtained multiple times; S4. calculating the degradation degree Q of the internal insulation system of the oil-impregnated bushing: wherein f1, f2, f3 are the frequency points taken, C'(2pf1), C'(2pf2), C'(2pf3) are the real parts of the complex capacitance of the extended Debye dielectric relaxation model at the frequency points f1, f2, f3, respectively; C"(2pf1), C"(2pf2), C"(2pf3) are the imaginary parts of the complex capacitance of the extended Debye dielectric relaxation model at the frequency points f1, f2, f3, respectively; C' (20), C" (20) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor core, respectively, reduced to 20°C; C0 is the geometric capacitance of the geometric equivalent circuit in the extended Debye dielectric relaxation model. av (20), C" av (20) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor core, respectively, reduced to 20°C; C0 is the geometric capacitance of the geometric equivalent circuit in the extended Debye dielectric relaxation model. If Q > ε, the degradation degree of the internal insulation system of the oil-impregnated bushing is too high, and a warning is given; wherein ε is a set threshold value of the degradation degree; The step S2 comprises the steps of: S21. averaging the capacitance and dielectric loss of the oil-paper capacitor core obtained: wherein P is the number of times each operating parameter is acquired, C i (T) and tan δ i (T) are the capacitance and dielectric loss value of the oil-paper capacitor core at the temperature T of the test environment, respectively, i = 1, 2, 3, …, P. S22. C av (T), tan δ av (T) to C av (20), tan δ av (20) values: C av (20) = C av (T) · 1.5 (20-T) / 10 tan δ av (20) = tan δ av (T) · 1.5 (20-T) / 10 S23. calculating the real part and imaginary part of the complex capacitance of the oil-paper capacitor core at a temperature of 20 DEG C:

2. The method of assessing the degree of deterioration of the oil- immersed bushing inner insulation system according to claim 1, characterized in that: The expression of the extended Debye dielectric relaxation model is: wherein ω is the angular frequency, ω = 2πf; C'(ω), C"(ω) represent the real part and the imaginary part of the complex capacitance, respectively; C0, R0 are the geometric capacitance and the insulation resistance of the equivalent geometric circuit in the extended Debye dielectric relaxation model; R j , C j are the resistance and the capacitance of the jth RC series branch in the model, respectively, j = 1, 2, …, k; k is the number of RC series branches in the model.

3. The method of assessing the degree of deterioration of the oil- immersed bushing inner insulation system according to claim 2, characterized in that: The step S3 comprises the steps of: S31. averaging the real part and imaginary part of the complex capacitance of the oil-paper capacitor core at different frequency points obtained: wherein C' (T) and C" (T) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor at temperature T and the lth frequency point, respectively. i (f l wherein C' (T) and C" (T) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor at temperature T and the lth frequency point, respectively. i (f l wherein C' (T) and C" (T) are the real and imaginary parts of the complex capacitance of the oil-paper capacitor at S32. C' av (f l , T) is reduced to C' av (f l , 20) at a temperature of 20 °C av (f l , 20) is reduced to C" av (f l , 20) S33. establishing an optimization objective function: Wherein, C′(f l ,20)C″(f l ,20) represents the fitted value at the l-th frequency point obtained by the extended Debye dielectric relaxation model, C′ av (f l ,20)C″ av (f l ,20) represents the measured value at the l-th frequency point, and n is the total number of frequency points tested, l=1,2,3,…,n; S34. Another optimization objective function H is established and minimized by calculating C' av (f l ,T) and C" av (f l ,T), the parameters in the extended Debye dielectric relaxation model: C0, R0, R j , C j are calculated.

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