Design method of economical capacitor bank for direct-current power transmission project

Abstract

The invention belongs to the technical field of converter stations, and discloses an economical capacitor bank design method for a direct current transmission project, which comprises the following steps: S1, determining target design parameters of a high-voltage capacitor bank as the height of an interlayer post insulator and the height of a flange post of a frame; s2, performing Fourier analysis on the standard lightning waveform, and determining that the main influence factor of the lightning wave amplitude is frequency; s3, optimizing the value of the lightning tolerance distribution nonuniform coefficient; s4, adjusting the height of the interlayer post insulator; the method has the following beneficial effects: through Fourier expansion calculation and analysis of lightning waveforms, distribution cooperation of lightning tolerance and operation tolerance in the capacitor bank can be carried out according to capacitance deviation k between string segments of the capacitor bank, and the height of the flange pillar is used for replacing partial height of an interlayer pillar insulator, so that the reliability of the capacitor bank is improved, and the reliability of the capacitor bank is improved. And the complete set cost of the capacitor bank can be reduced on the premise of ensuring the reliability.

Description

Technical Field

[0001] This invention relates to the field of converter station technology, and more specifically to a design method for an economical capacitor bank used in DC transmission projects. Background Technology

[0002] With the demands of building a global energy internet and the large-scale development and utilization of renewable energy, DC transmission technology has developed rapidly. Converter stations are the core facilities of DC transmission projects. Their main function is to convert AC power into DC power for transmission (rectification), or to convert DC power back into AC power (inversion). Converter stations contain key equipment such as converter transformers, converter valves, and filters. Filters are used to eliminate harmonics generated during the conversion process, and these filters require a large number of capacitor banks. Through technology introduction and assimilation, the localization rate of capacitor banks used in DC transmission projects has gradually increased to 80% or more, leading to increasingly fierce market competition. Each ultra-high voltage DC transmission project is a vital artery for national energy transmission and a key national project, requiring extremely high operational safety standards. While existing capacitor banks have high reliability, their economic efficiency needs improvement. Therefore, researching and developing a capacitor bank that can meet the high reliability requirements of DC transmission projects while also possessing good economic efficiency would have significant engineering value. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a design method for an economical capacitor bank used in DC transmission projects. This invention is achieved through the following technical solutions.

[0004] A design method for an economical capacitor bank for DC transmission projects includes the following steps: S1, Determine the target design parameter for the high-voltage capacitor bank as the height of the interlayer support insulator. and the height of the flange supports of the frame ; S2. Perform Fourier analysis on the standard lightning waveform to determine that the main influencing factor on the amplitude of the lightning wave is frequency; S3, optimize the value of the uneven distribution coefficient of lightning tolerance; S4. Based on the optimized lightning withstand voltage distribution non-uniformity coefficient, the standard lightning impulse withstand voltage and standard switching impulse withstand voltage of the capacitor unit are calculated, and the height of the interlayer post insulator is adjusted. ; S5, the height variation of the interlayer support insulator is compensated by adjusting the height of the flange support, and the height of the flange support is determined through stability calculation. .

[0005] As a further embodiment of the present invention, in step S1, the high-voltage capacitor bank includes a high-voltage tower and a low-voltage tower arranged side by side. The high-voltage tower and the low-voltage tower are connected by a two-tower connecting busbar. Both the high-voltage tower and the low-voltage tower are provided with ground support insulators at their bottoms. Both the high-voltage tower and the low-voltage tower include several layers of frames arranged at intervals, and the number of frame layers of the high-voltage tower and the low-voltage tower is the same. The bottom frame of the high-voltage tower is higher than the bottom frame of the low-voltage tower. The frame includes a frame body welded from channel steel and flange supports at the four corners of the frame body. The flange supports are hollow inside. Capacitor units are connected in series on each layer of the frame. Two vertically adjacent frames are connected by interlayer support insulators.

[0006] As a further aspect of the present invention, in step S2, the wavefront time and half-peak time of the standard lightning waveform are 1.2 μs and 50 μs, respectively.

[0007] As a further aspect of the present invention, the specific steps of the Fourier analysis in step S2 are as follows: Expressed in exponential form Standard lightning strike at any moment The formula is as follows:

[0008] in, It is the peak value of the impulse voltage. It is a time constant. , ; By performing a Fourier series expansion, we can obtain the spectrum function:

[0009] in, Angular frequency; After integration, we get:

[0010] The amplitude spectrum function is obtained as follows:

[0011] Phase spectrum function:

[0012] right Find a common denominator for the numerator inside the square root, and substitute it into the formula. get: .

[0013] As a further aspect of the present invention, in step S3, it is assumed that the required value of the lightning withstand distribution non-uniformity coefficient of the high-voltage capacitor bank is k0. Since the lightning wave amplitude is affected by the angular frequency, and the angular frequency is not affected by the target design parameters, the lightning withstand distribution of the capacitor unit is only affected by the capacitor unit itself. Therefore, the lightning withstand distribution non-uniformity coefficient of the high-voltage capacitor bank can be adjusted to be consistent with the requirements of the capacitor bank used in DC transmission projects. After adjustment, it is k, where k is 1.01 and k < k0. The lightning withstand distribution non-uniformity coefficient is the ratio of the maximum capacitance to the minimum capacitance of each series segment of the capacitor bank.

[0014] As a further aspect of the present invention, in step S4, when designing the capacitor bank, the required values ​​for lightning impulse withstand voltage and switching impulse withstand voltage of the interlayer post insulators are respectively... and The lightning impulse withstand voltage and switching impulse withstand voltage of capacitor banks used in DC transmission projects are respectively and Then we have:

[0015]

[0016] Where n is the number of layers in the capacitor bank; Since k decreases relative to k0, therefore and Decrease; and Height of interlayer post insulator Positive correlation Decrease.

[0017] As a further aspect of the present invention, in step S5, the height of the flange support is increased. To compensate for the height of interlayer post insulators The decrease; The criteria for stability assessment are as follows: ,in,

[0018] The meanings of each term in the formula are as follows: It is the critical force of the flange support; E is the working pressure of the flange support; E is the elastic modulus of the flange support; I is the moment of inertia of the section. ,in and These are the inner and outer diameters of the flange support, respectively; μ is the length coefficient of the flange support, taken as μ=2.0; It is the specified stability safety factor, taken as... .

[0019] As a further aspect of the present invention, the... The diameter is 140mm to 360mm. The diameter ranges from 160mm to 380mm. The diameter is 200mm to 600mm. The value is 100mm to 500mm, where h is the height of the channel steel.

[0020] The beneficial effects of this invention are as follows: 1. The Fourier decomposition method is introduced into the insulation design calculation of high-voltage capacitor banks used in DC transmission projects to improve the accuracy of the calculation. By calculating and analyzing the Fourier expansion of the lightning waveform, it is found that the lightning withstand and switching withstand of the capacitor bank can be allocated and coordinated according to the capacitance deviation k between the series segments of the capacitor bank. This allows for the accurate calculation of the lightning withstand requirements of the interlayer insulators, thereby reducing the height of the interlayer post insulators. The reduced height of the interlayer post insulators can lower the cost of the interlayer post insulators.

[0021] 2. The height of the flange support is 100mm to 500mm higher than the height h of the channel steel. Through precise electrical and mechanical calculations, the height of the flange support is used to replace part of the height of the interlayer support insulator, which can reduce the overall cost of the capacitor bank while ensuring reliability. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 Schematic diagram of the structure of the capacitor bank; Figure 2 Schematic diagram of a capacitor unit; Figure 3 : A schematic diagram of the framework; Figure 4 : Schematic diagram of the structure of interlayer post insulator.

[0024] The attached figures are labeled as follows: 1-High voltage tower, 2-Low voltage tower, 3-Connecting busbar between the two towers, 4-Ground support insulator, 5-Frame, 51-Channel steel, 52-Flange support, 6-Capacitor unit, 7-Interlayer support insulator. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] A design method for an economical capacitor bank for DC transmission projects includes the following steps: S1, Determine the target design parameter for the high-voltage capacitor bank as the height of the interlayer support insulator 7. and the height of the flange support 52 of frame 5. .

[0027] like Figure 1 As shown, the high-voltage capacitor bank includes a high-voltage tower 1 and a low-voltage tower 2 arranged side by side. The high-voltage tower 1 and the low-voltage tower 2 are connected by a two-tower connecting busbar 3. Both the high-voltage tower 1 and the low-voltage tower 2 are equipped with ground support insulators 4 at their bottoms. Both the high-voltage tower 1 and the low-voltage tower 2 include several layers of frames 5 arranged at intervals, and the number of layers of frames 5 in the high-voltage tower 1 and the low-voltage tower 2 is the same. The bottom frame 5 of the high-voltage tower 1 is higher than the bottom frame 5 of the low-voltage tower 2. The frame 5 includes a frame body welded from channel steel 51 and flange supports 52 at the four corners of the frame body. The flange supports 52 are hollow inside. Capacitor units 6 are connected in series on each layer of frame 5. Two vertically adjacent frames 5 are connected by interlayer support insulators 7.

[0028] The capacitors in capacitor unit 6 are as follows Figure 2 As shown, capacitor unit 6 serves to filter system harmonics, compensate for inductive reactive power, and improve the power factor. Capacitor unit 6 is made of polypropylene film, benzyl toluene, aluminum foil, stainless steel plate, and sleeve, and its weight is between 60kg and 120kg.

[0029] The structure of frame 5 is as follows Figure 3 As shown, each layer of frame 5 can accommodate 12 to 24 capacitor units 6.

[0030] The insulation between the interlayer post insulators 7 and the frame 5, with 4 interlayer post insulators 7 per layer, and the structure of the interlayer post insulators 7 is as follows. Figure 4 As shown.

[0031] The frame 5 and interlayer post insulator 7 account for approximately 45% of the total cost of a high-voltage capacitor bank (excluding capacitor unit 6). Therefore, reducing the cost of the frame 5 and interlayer post insulator 7 is the key to the design of an economical capacitor bank. In other words, the key to this application is the parametric structural design of the interlayer post insulator 7 and the frame 5. The more accurate the parameter calculation, the more materials can be saved while ensuring safety.

[0032] S2. Fourier analysis was performed on the standard lightning waveform to determine that the main influencing factor on the amplitude of the lightning wave was frequency.

[0033] The wavefront time and half-peak time of a standard lightning waveform are 1.2 μs and 50 μs, respectively.

[0034] The specific steps of Fourier analysis are as follows: Expressed in exponential form Standard lightning strike at any moment The formula is as follows:

[0035] in, It is the peak value of the impulse voltage. It is a time constant. , ; By performing a Fourier series expansion, we can obtain the spectrum function:

[0036] in, Angular frequency; After integration, we get:

[0037] The amplitude spectrum function is obtained as follows:

[0038] Phase spectrum function:

[0039] right Find a common denominator for the numerator inside the square root, and substitute it into the formula. get: .

[0040] In the frequency range of ≤1000Hz compared to , Smaller, at this time , ,but Within this frequency band, as the frequency gradually increases from a lower value to 1000Hz, Gradually increase, making The presence of a certain numerical distribution indicates that the amplitude accounts for a certain proportion within this frequency band. In the frequency range >1000Hz, Much larger , ,at this time , ,but ,along with As the frequency f increases (i.e., the frequency f continues to increase), the denominator... The growth rate is much faster than that of molecules. The growth rate led to The value decreases rapidly. The same method can also be used to obtain... The variation characteristics across different frequency ranges. Therefore, 1.2 / 50 Standard lightning amplitude It is mainly concentrated in the frequency range of ≤1000Hz, and as the frequency continues to increase, the amplitude decreases rapidly.

[0041] Since the amplitude of lightning waves is significantly affected by frequency, when designing the lightning withstand distribution within a high-voltage capacitor bank, it is only necessary to calculate the impact of the capacitor on the lightning withstand distribution, and the calculation should mainly focus on frequencies within the 1000Hz range.

[0042] S3, optimize the value of the uneven distribution coefficient of lightning tolerance.

[0043] Assuming the required value of the uneven distribution coefficient of lightning withstand voltage in the high-voltage capacitor bank is k0, since the amplitude of lightning waves is affected by the angular frequency, and the angular frequency is not affected by the target design parameters, the lightning withstand voltage distribution of capacitor unit 6 is only affected by capacitor unit 6 itself. Therefore, the uneven distribution coefficient of lightning withstand voltage in the high-voltage capacitor bank can be adjusted to be consistent with the requirements of capacitor banks used in DC transmission projects. After adjustment, it is k, where k is 1.01 and k < k0. The uneven distribution coefficient of lightning withstand voltage is the ratio of the maximum capacitance to the minimum capacitance of each series segment of the capacitor bank.

[0044] from Figure 1 It can be seen that the high-voltage capacitor bank adopts a series and multi-layer arrangement. In the existing technology, according to GB311.2-2013, k0 is generally taken as 1.05, while DL / T604-2020 requires that the ratio of the maximum capacitance to the minimum capacitance of each series section of the capacitor bank, k, should not exceed 1.02.

[0045] However, the above analysis shows that since the amplitude of lightning waves is affected by the angular frequency, and the angular frequency is not affected by the target design parameters, the high-voltage capacitor bank can refer to the project specification requirements for capacitor banks used in power transmission projects, that is, the lightning withstand distribution non-uniformity coefficient should not be greater than 1.01. In this application, k is taken as 1.01, which is greatly reduced compared to the original 1.05.

[0046] S4. Based on the optimized lightning withstand voltage distribution non-uniformity coefficient, the standard lightning impulse withstand voltage and standard switching impulse withstand voltage of capacitor unit 6 are calculated, and the height of the interlayer post insulator 7 is adjusted. .

[0047] When designing capacitor banks, the required lightning impulse withstand voltage and switching impulse withstand voltage for interlayer post insulator 7 are respectively... and The lightning impulse withstand voltage and switching impulse withstand voltage of capacitor banks used in DC transmission projects are respectively and Then we have:

[0048]

[0049] Where n is the number of layers in the capacitor bank; Since k decreases relative to k0, therefore and Decrease; and Height of interlayer post insulator 7 Positive correlation Decrease.

[0050] In this application, both high-voltage tower 1 and low-voltage tower 2 have nine stories, therefore n=18. Through Fourier expansion calculation and analysis of lightning impulse waves, the value of k is reduced from 1.05 as specified in GB311.2-2013 to 1.01, thus reducing the impact on the interlayer support insulator 7. and The required value is approximately 4%.

[0051] After reducing the height of the interlayer post insulator 7, a physical model was made and subjected to 50% wet flashover voltage tests for positive and negative polarity lightning impulses and positive and negative polarity switching impulses according to GB / T 16927.1–2011 and the corresponding standard name "High Voltage Testing Techniques Part 1: General Definitions and Test Requirements". The results showed that even with a smaller value of k, the safety requirements were still met.

[0052] By analyzing and calculating, reducing the possible values ​​of k can... Decrease Reducing the size can lower the cost of the interlayer post insulator 7, and further improve the economics of the capacitor bank.

[0053] S5, the height variation of the interlayer support insulator 7 is compensated by adjusting the height of the flange support 52, and the height of the flange support 52 is determined by stability calculation. .

[0054] Increase the height of the flange support by 52. To compensate for the height of the interlayer post insulator 7 The decrease; The criteria for stability assessment are as follows: ,in,

[0055] The meanings of each term in the formula are as follows: It is the critical force of flange support 52; The working pressure of flange support 52 is E; E is the elastic modulus of flange support 52. In this application, flange support 52 is made of structural steel, and its elastic modulus is... I is the moment of inertia of the cross section. ,in and These are the inner and outer diameters of flange support 52, respectively; μ is the length coefficient of flange support 52, taken as μ=2.0; It is the specified stability safety factor, taken as... .

[0056] The diameter is 140mm to 360mm. The diameter ranges from 160mm to 380mm. The diameter is 200mm to 600mm. The diameter is 100mm to 500mm, and h is the height of the channel steel 51.

[0057] Since the flange support 52 is made of structural steel, its cost is much lower than that of the interlayer support insulator 7. Therefore, the cost can be reduced by lowering the interlayer support insulator 7 and increasing the height of the flange support 52.

[0058] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A design method for an economical capacitor bank for DC transmission projects, characterized in that, Includes the following steps: S1, Determine the target design parameter for the high-voltage capacitor bank as the height of the interlayer support insulator. and the height of the flange supports of the frame ; S2. Perform Fourier analysis on the standard lightning waveform to determine that the main influencing factor on the amplitude of the lightning wave is frequency; S3, optimize the value of the uneven distribution coefficient of lightning tolerance; S4. Based on the optimized lightning withstand voltage distribution non-uniformity coefficient, the standard lightning impulse withstand voltage and standard switching impulse withstand voltage of the capacitor unit are calculated, and the height of the interlayer post insulator is adjusted. ; S5, the height variation of the interlayer support insulator is compensated by adjusting the height of the flange support, and the height of the flange support is determined through stability calculation. .

2. The design method for an economical capacitor bank for DC transmission projects according to claim 1, characterized in that, In step S1, the high-voltage capacitor bank includes a high-voltage tower and a low-voltage tower arranged side by side. The high-voltage tower and the low-voltage tower are connected by a connecting busbar. Both the high-voltage tower and the low-voltage tower are equipped with ground support insulators at their bottoms. Both the high-voltage tower and the low-voltage tower include several layers of frames arranged at intervals, and the number of frame layers in the high-voltage tower and the low-voltage tower is the same. The bottom frame of the high-voltage tower is higher than the bottom frame of the low-voltage tower. The frame includes a frame made of channel steel and flange supports at the four corners of the frame. The flange supports are hollow inside. Capacitor units are connected in series on each layer of the frame. Two vertically adjacent frames are connected by interlayer support insulators.

3. The design method for an economical capacitor bank for DC transmission projects according to claim 1, characterized in that, In step S2, the wavefront time and half-peak time of the standard lightning waveform are 1.2 μs and 50 μs, respectively.

4. The design method for an economical capacitor bank for DC transmission projects according to claim 2, characterized in that, In step S2, the specific steps of the Fourier analysis are as follows: Expressed in exponential form Standard lightning strike at any moment The formula is as follows: ； in, It is the peak value of the impulse voltage. It is a time constant. , ; By performing a Fourier series expansion, we can obtain the spectrum function: ； in, Angular frequency; After integration, we get: ； The amplitude spectrum function is obtained as follows: ； Phase spectrum function: ； right Find a common denominator for the numerator inside the square root, and substitute it into the formula. get: 。 5. The design method for an economical capacitor bank for DC transmission projects according to claim 3, characterized in that, In step S3, it is assumed that the required value of the lightning withstand distribution non-uniformity coefficient of the high-voltage capacitor bank is k0. Since the lightning wave amplitude is affected by the angular frequency, and the angular frequency is not affected by the target design parameters, the lightning withstand distribution of the capacitor unit is only affected by the capacitor unit itself. Therefore, the lightning withstand distribution non-uniformity coefficient of the high-voltage capacitor bank can be adjusted to be consistent with the requirements of the capacitor bank used in DC transmission projects. After adjustment, it is k, k is 1.01, and k < k0. The lightning withstand distribution non-uniformity coefficient is the ratio of the maximum capacitance to the minimum capacitance of each series segment of the capacitor bank.

6. The design method for an economical capacitor bank for DC transmission projects according to claim 1, characterized in that, In step S4, when designing the capacitor bank, the required values ​​for lightning impulse withstand voltage and switching impulse withstand voltage of the interlayer post insulators are respectively... and The lightning impulse withstand voltage and switching impulse withstand voltage of capacitor banks used in DC transmission projects are respectively and Then we have: ； ； Where n is the number of layers in the capacitor bank; Since k decreases relative to k0, therefore and Decrease; and Height of interlayer post insulator Positive correlation Decrease.

7. The design method for an economical capacitor bank for DC transmission projects according to claim 1, characterized in that, In step S5, the height of the flange support is increased. To compensate for the height of interlayer post insulators The decrease; The criteria for stability assessment are as follows: ,in, ; The meanings of each term in the formula are as follows: It is the critical force of the flange support; E is the working pressure of the flange support; E is the elastic modulus of the flange support; I is the moment of inertia of the section. ,in and These are the inner and outer diameters of the flange support, respectively; μ is the length coefficient of the flange support, taken as μ=2.0; It is the specified stability safety factor, taken as... .

8. The design method for an economical capacitor bank for DC transmission projects according to claim 6, characterized in that, The The diameter is 140mm to 360mm. The diameter ranges from 160mm to 380mm. The diameter is 200mm to 600mm. The value is 100mm to 500mm, where h is the height of the channel steel.

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