Economic Analysis Method for Overvoltage of Offshore Flexible DC System Installed with Controllable Lightning Arrester

Abstract

The present invention provides an overvoltage economic analysis method for installing a controllable lightning arrester in an offshore flexible direct current system, comprising the following steps: building a controllable lightning arrester model and obtaining the total cost of the controllable lightning arrester; replacing the lightning arrester model in an initial simulation model with the controllable lightning arrester model to obtain a maximum controllable ratio boundary and an overvoltage after installation; obtaining an initial electric net distance value and an electric net distance after installation to obtain a reduced volume; obtaining a profit after installation based on the total volume, total weight, total cost and reduced volume of an offshore platform; constructing an adaptive analysis model with the goal of maximizing the total profit based on the maximum controllable ratio boundary, the overvoltage after installation, the total cost of the controllable lightning arrester and the profit after installation, and using the model to select a controllable ratio value set to obtain a controllable lightning arrester for installation. The present invention can quantitatively analyze the overvoltage suppression effect, construction parameters and economic efficiency after replacement, and provide guidance for installing controllable lightning arresters in offshore flexible direct current systems.

Description

Technical Field

[0001] The present invention relates to the technical field of controllable lightning arresters installed in power systems, and in particular to an overvoltage economic analysis method for controllable lightning arresters installed in offshore flexible direct current systems. Background Art

[0002] Overvoltages in power systems not only damage electrical equipment but can also lead to significant economic losses. Lightning arresters are key devices for suppressing overvoltages, but their voltage-limiting effectiveness is limited. Although existing research has made some progress in increasing the operating charge factor to enhance the arrester's suppression capability, this approach often results in an increase in the size and weight of the arrester. Controllable lightning arresters are devices that can flexibly limit operational overvoltages. Compared to lightning arresters, controllable lightning arresters sacrifice some system reliability, but they offer superior effectiveness in suppressing overvoltages, conserving transmission corridors, and protecting transmission equipment. Controllable lightning arresters were first used in AC systems, primarily to eliminate the closing resistance of circuit breakers. In recent years, research on the parameter selection, control strategies, and potential distribution of UHV AC switch-type controllable lightning arresters, as well as exploration of the relevant theoretical technologies for DC controllable lightning arresters, has laid a solid theoretical foundation for their practical application in AC and DC systems. However, due to technical and economic limitations, controllable lightning arresters have not yet been widely adopted in power systems.

[0003] Offshore HVDC Flexible transmission technology is maturing. Compared to conventional AC / DC systems, offshore HVDC Flexible systems are more sensitive to overvoltage and have higher requirements for size and weight. On the one hand, overvoltage threatens the safe and stable operation of the entire offshore HVDC Flexible system, placing stringent demands on the insulation level of equipment and lines, and impacting the reliability of a large amount of power electronic equipment, further increasing construction costs. On the other hand, overvoltage can affect the electrical clearance between valve towers within the valve hall of an offshore platform, thereby affecting the size and weight of the offshore platform. To ensure the equipment insulation level and cost-effectiveness of offshore HVDC Flexible transmission projects, it is necessary to effectively limit the overvoltage level of the offshore HVDC Flexible system while keeping the size and weight of the offshore platform within reasonable limits. Controllable lightning arresters (SLAs) have excellent overvoltage suppression capabilities, but in AC / DC systems, the benefits of reducing overvoltage by sacrificing some system reliability are relatively small. Offshore HVDC Flexible systems not only have higher overvoltage requirements but also have stricter size and weight restrictions. Therefore, the benefits of reducing overvoltage in offshore HVDC Flexible systems are further amplified, providing an ideal scenario for the application of SLAs. At present, controllable lightning arresters have not been used in offshore flexible DC transmission systems, and the applicability of controllable lightning arresters in offshore flexible DC transmission systems needs further analysis. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides an overvoltage economic analysis method for installing controllable lightning arresters in offshore flexible DC systems, which is used to explore the applicability of controllable lightning arresters in offshore flexible DC systems and provide guidance for installing controllable lightning arresters in offshore flexible DC systems.

[0005] To achieve the above-mentioned object, the present invention adopts the following technical solution: a method for analyzing the economic benefits of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester, comprising the following steps:

[0006] According to the offshore flexible DC system, the total volume, total weight, total cost of the offshore platform and the rated voltage of the controllable lightning arrester are obtained;

[0007] Obtaining a controllable ratio set and physical quantity parameters of the controllable lightning arrester;

[0008] Obtaining construction parameters of the controllable lightning arrester according to the rated voltage and the physical quantity parameters;

[0009] Building a controllable lightning arrester model according to the construction parameters, the total volume of the offshore platform, the total weight of the offshore platform, and the total cost of the offshore platform and obtaining the total cost of the controllable lightning arrester;

[0010] Building an initial simulation model based on the offshore flexible DC system; the initial simulation model includes a lightning arrester model;

[0011] Obtaining an initial overvoltage value according to the initial simulation model; calculating an initial electric clearance value according to the initial overvoltage value;

[0012] Replacing the arrester model in the initial simulation model with the controllable arrester model to obtain a simulation model after installation;

[0013] Obtaining a maximum controllable ratio boundary and a post-installation overvoltage according to the post-installation simulation model;

[0014] Obtaining a post-installation clear distance according to the post-installation overvoltage;

[0015] Obtaining a reduced volume according to the initial electrical clearance value, the electrical clearance after installation, and the total volume of the offshore platform;

[0016] Obtaining a profit after installation according to the total volume of the offshore platform, the total weight of the offshore platform, the total cost of the offshore platform and the reduced volume;

[0017] Obtaining a total benefit based on the total cost of the controllable lightning arrester and the benefit after installation;

[0018] An adaptive analysis model of the controllable lightning arrester of the offshore flexible DC system is constructed based on the maximum limit of the controllable ratio, the overvoltage after installation, the total cost of the controllable lightning arrester, and the profit after installation; the adaptive analysis model takes maximizing the total profit as a goal;

[0019] The controllable ratio set is selected according to the adaptive analysis model to obtain a controllable lightning arrester for installation.

[0020] Furthermore, the construction parameters include the number of resistors in the fixed part and the number of arrester columns in the fixed part; the physical quantity parameters include a first voltage, a first energy value, and a second energy value, wherein the first voltage is the voltage that each resistor withstands when a unit current is passed through it, the first energy value is the energy value that each resistor can withstand, and the second energy value is the energy value that the fixed part withstands under a single-pole grounding condition;

[0021] The steps for obtaining the construction parameters are:

[0022] Obtaining the highest voltage level of the offshore flexible DC system;

[0023] Obtaining the rated voltage according to the highest voltage level;

[0024] Obtain the controllable ratio calculation formula;

[0025] Obtaining the number of resistors in the fixed part according to the rated voltage, the controllable ratio calculation formula, and the first voltage;

[0026] The number of lightning arrester columns in the fixed part is obtained according to the first energy value, the second energy value and the number of resistor plates in the fixed part.

[0027] Furthermore, the physical quantity parameters also include the volume of each arrester column, the weight of each arrester column, the volume of each resistor sheet, and the weight of each resistor sheet;

[0028] The steps for obtaining the total cost of the controllable lightning arrester are:

[0029] Obtaining the weight per square meter of the offshore platform according to the total weight of the offshore platform and the total volume of the offshore platform;

[0030] Obtaining a cost per ton of the offshore platform based on the total cost of the offshore platform and the total weight of the offshore platform;

[0031] Obtain the cost of each arrester column, the cost of each resistor, and the cost of the bypass switch;

[0032] Obtaining a first cost based on the volume of each arrester column, the number of arrester columns in the fixed portion, the weight per square meter of the offshore platform, the weight of each arrester column, and the cost per ton of the offshore platform, where the first cost is the cost caused by the volume and weight of the arrester column;

[0033] Obtaining a second cost based on the volume of each resistor, the number of resistors in the fixed portion, the weight per square meter of the offshore platform, the weight of each resistor, and the cost per ton of the offshore platform, where the second cost is the cost caused by the volume and weight of the resistors;

[0034] Obtaining the cost of the arrester column according to the number of arrester columns in the fixed part and the cost of each arrester column;

[0035] Obtaining the cost of the resistors according to the number of the fixed resistors and the cost of each resistor;

[0036] The total cost of the controllable lightning arrester is obtained according to the first cost, the second cost, the cost of the lightning arrester column, the cost of the resistor, and the cost of the bypass switch.

[0037] Furthermore, the step of obtaining the reduced volume is:

[0038] Obtain the length, width, and floor height of the offshore platform, the first number of intervals, and the second number of intervals. The first number of intervals refers to the number of valve hall intervals along the length of the offshore platform, and the second number of intervals refers to the number of valve hall intervals along the width of the offshore platform. The valve hall intervals include the intervals between adjacent valve halls and the intervals between a wall and an adjacent valve hall.

[0039] Obtaining the total volume of the offshore platform according to the length of the offshore platform, the width of the offshore platform and the floor height of the offshore platform;

[0040] Obtaining a reduction in the electric clearance distance according to the initial electric clearance distance value and the electric clearance distance after installation;

[0041] Obtaining a volume reduction amount according to the length of the offshore platform, the number of the first intervals, the reduction in the electrical clearance, the width of the offshore platform, and the number of the second intervals, where the volume reduction amount is the volume reduction of the offshore platform after the installation;

[0042] The reduced volume is obtained according to the total volume of the offshore platform and the volume reduction.

[0043] Furthermore, the steps for obtaining the profit after the installation are:

[0044] The profit after the installation is obtained according to the reduced volume, the weight per square meter of the offshore platform and the cost per ton of the offshore platform.

[0045] Furthermore, the conditions for obtaining the maximum limit of the controllable ratio include:

[0046] Condition 1: when a single-pole grounding fault occurs in the installed simulation model, the overvoltage peak value that can be limited by the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model;

[0047] Condition 2: When a single-pole grounding fault occurs in the installed simulation model, the operating voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model;

[0048] And condition three: when a single-pole grounding fault occurs in the simulation model after installation and before the single-pole grounding fault ends, there is a moment when the tail current of the controllable lightning arrester model is less than the holding current of the thyristor.

[0049] At this time, the controllable lightning arrester installed in the offshore flexible DC system is a traditional controllable lightning arrester.

[0050] Furthermore, the conditions for obtaining the maximum limit of the controllable ratio include:

[0051] Condition 1: when a single-pole grounding fault occurs in the installed simulation model, the overvoltage peak value that can be limited by the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model;

[0052] Condition 2: When a single-pole grounding fault occurs in the installed simulation model, the operating voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model;

[0053] And condition three: when a single-pole grounding fault occurs in the simulation model after installation, the overvoltage peak value that can be limited by the controllable lightning arrester model is not lower than the second peak voltage value that rises at the moment the bypass switch returns to its original state.

[0054] At this time, the controllable lightning arrester installed in the offshore flexible DC system is an active exit type controllable lightning arrester.

[0055] Furthermore, the initial electrical clearance value and the post-installation electrical clearance value are obtained using a g parameter algorithm.

[0056] Furthermore, the adaptive analysis model is:

[0057] maxR(x,c)=X(v)-C(α);

[0058] x=X(v);

[0059] v = V(α);

[0060] c=C(α);

[0061] α min ≤α≤α max ;

[0062] Where max is the maximization function, R is the total benefit, x is the benefit after installation, X is the function corresponding to the benefit after installation, c is the total cost of the controllable lightning arrester, C(α) is the function corresponding to the total cost of the controllable lightning arrester, v is the overvoltage after installation, V is the function corresponding to the overvoltage after installation, α is the controllable ratio, α min is the minimum boundary of the controllable ratio, α max is the maximum controllable ratio boundary.

[0063] Furthermore, the construction parameters are obtained according to the adaptive analysis model selection.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The present invention constructs an initial simulation model, replaces the arrester model in the initial simulation model with a controllable arrester to obtain a simulation model after installation, and takes maximizing the total benefit as the goal. According to the maximum boundary of the controllable ratio, the overvoltage after installation, the total cost of the controllable arrester and the benefit after installation, an adaptive analysis model of the controllable arrester of the offshore flexible DC system is constructed. The replacement position of the controllable arrester can be clarified, and the overvoltage suppression effect after replacement, the construction parameters of the controllable arrester, the controllable ratio, the total cost of the controllable arrester, the benefit after installation and the total benefit can be quantitatively analyzed. The model can be used to explore the applicability of the controllable arrester in the offshore flexible DC system and provide guidance for the installation of the controllable arrester in the offshore flexible DC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 A flow chart of the method for analyzing the economic benefits of installing a controllable lightning arrester in an offshore flexible DC system according to the present invention;

[0067] Figure 2 (a) is a schematic diagram of the position of the initial simulation model and the controllable lightning arrester model replacing the lightning arrester model in the initial simulation model, (b) is a schematic diagram of the structure of the controllable lightning arrester model and a schematic diagram of the structure of the lightning arrester model replacing the initial simulation model, and the bottom is a schematic diagram of the overvoltage waveform of the initial simulation model and the simulation model after the controllable lightning arrester in Example 1 is installed;

[0068] Figure 3 1. A top view of the valve hall of the offshore platform in Examples 1 and 2 of the present invention;

[0069] Figure 4 Schematic diagram of the volt-ampere characteristic curve of the simulation model after installation in Example 1 of the present invention;

[0070] Figure 5The voltage limiting effect of the controllable lightning arrester under different controllable ratios in Example 2 of the present invention during a single-pole grounding fault and the energy consumption of the controllable lightning arrester itself;

[0071] Figure 6 The voltage limiting effect of the controllable lightning arrester under different controllable ratios in embodiments 1 and 2 of the present invention during a single-pole grounding fault and the total cost of the controllable lightning arrester;

[0072] Figure 7 Schematic diagram of the tail current of the controllable lightning arrester of the present invention, (a) is the tail current of the controllable lightning arrester in Example 2, and (b) is the tail current of the controllable lightning arrester in Example 1;

[0073] Figure 8 Schematic diagrams of overvoltage waveforms of the initial simulation model of the present invention and the simulation models after installation of the controllable lightning arresters in Examples 1 and 2, respectively. DETAILED DESCRIPTION

[0074] It is worth noting that the methods used in the present invention are all conventional methods unless otherwise specified; the raw materials and devices used are all conventional commercially available products, and their sources are not specifically limited unless otherwise specified.

[0075] Example 1

[0076] See also Figure 1 A method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system overvoltage includes the following steps:

[0077] According to the offshore flexible DC system, the total volume, total weight, total cost of the offshore platform and the rated voltage of the controllable lightning arrester are obtained;

[0078] In this embodiment, the offshore flexible DC system is a 500kV true bipolar offshore flexible DC system, that is, the maximum voltage level of the offshore flexible DC system is 500kV;

[0079] The total volume of the offshore platform is V = l*w*h = 67*52*32.5, where l is the length of the offshore platform, w is the width of the offshore platform, and h is the height of the offshore platform. The units of l, w, and h are all in meters. The total cost of the offshore platform is K, which is 1 billion yuan, and the total weight of the offshore platform is W, which is 23,000 tons.

[0080] Calculation standard for rated voltage of lightning arrester installed on DC line:

[0081]

[0082] Where, The calculated value of the rated voltage of the arrester installed on the DC line, U is the highest voltage level of the offshore flexible DC system;

[0083] It can be seen that the rated voltage of the controllable lightning arrester of the 500kV offshore flexible DC system should not be less than 550kV. Refer to the "Lightning Arrester" to determine the rated voltage U of the controllable lightning arrester. n It is 571kV.

[0084] Obtain the controllable ratio value set and physical quantity parameters of the controllable lightning arrester; the controllable ratio is an important parameter of the controllable lightning arrester. The definition of the controllable ratio, that is, the controllable ratio calculation formula, is:

[0085]

[0086] Where U kg is the rated voltage of the controllable part of the controllable arrester, U n is the rated voltage of the controllable lightning arrester;

[0087] See also Figure 2 (b), the controllable arrester model includes a fixed part and a controllable part, where the controllable part includes a bypass switch, and the controllability ratio determines the rated voltage of the controllable part and the rated voltage of the fixed part;

[0088] The operating principle of a controllable surge arrester is as follows: During normal operation, the bypass switch is inoperative, and the voltage is shared between the fixed and controllable sections, effectively adding a conventional surge arrester to an offshore flexible DC system. Following a fault, the controllable surge arrester's bypass switch operates, bypassing the controllable section, leaving the voltage solely on the fixed section, thereby reducing overvoltage. Replacing conventional surge arresters with controllable surge arresters in an offshore flexible DC system allows the arresters to switch to a lower rated voltage, effectively reducing overvoltage in the system.

[0089] The cost of a controllable lightning arrester mainly consists of two parts:

[0090] 1. The increase in volume, weight and cost of the controllable lightning arrester body due to the newly added bypass switch;

[0091] 2. Since the fixed part of the controllable lightning arrester absorbs more energy than the ordinary lightning arrester, the number of lightning arrester columns and the number of resistors in the fixed part of the controllable lightning arrester itself will also exceed those of the ordinary lightning arrester. This change will also lead to an increase in volume, weight and cost.

[0092] Obtain construction parameters of controllable lightning arrester according to rated voltage and physical quantity parameters;

[0093] In this embodiment, the resistor sheet specification is Φ105*22.5 (units are all mm), and the construction parameters include the number of fixed resistor sheets S and the number of fixed arrester columns P; the physical quantity parameters include the first voltage U s, the first energy value E s and the second energy value E g The first voltage is the voltage that each resistor piece can withstand when passing a unit current. The first energy value is the energy value that each resistor piece can withstand. In this embodiment, the first energy value E s The second energy value is 36kJ, and the second energy value is the energy value that the fixed part bears under the single-pole grounding condition;

[0094] The steps to obtain the construction parameters are:

[0095] Obtain the highest voltage level U of the offshore flexible DC system;

[0096] Get the rated voltage U according to the highest voltage level n ;

[0097] Obtain the controllable ratio calculation formula;

[0098] According to the rated voltage, the controllable ratio calculation formula and the first voltage, the number of resistors S in the fixed part is obtained as follows:

[0099]

[0100] Where U g is the rated voltage of the fixed part of the controllable lightning arrester;

[0101] The number of arrester columns P in the fixed part is obtained according to the first energy value, the second energy value and the number of resistors in the fixed part:

[0102]

[0103] Build a controllable lightning arrester model and obtain the total cost of the controllable lightning arrester according to the construction parameters, the total volume of the offshore platform, the total weight of the offshore platform and the total cost of the offshore platform;

[0104] Before calculating the total cost of the controllable lightning arrester, it is necessary to determine the influence of the changes in the volume and weight of the controllable lightning arrester on the total cost of the offshore platform. According to the linear influence of volume on weight and the linear influence of weight on cost, it can be obtained;

[0105] The physical quantity parameters also include the volume V of each lightning arrester column C , the weight of each lightning arrester column W C 、The volume of each resistor V R And the weight of each resistor W R ;

[0106] The steps to obtain the total cost of a controllable lightning arrester are:

[0107] According to the total weight W and total volume V of the offshore platform, the weight W of the offshore platform per square meter is obtained. V for:

[0108]

[0109] The cost per ton of the offshore platform K is obtained based on the total cost K and the total weight W of the offshore platform. W for:

[0110]

[0111] Get the cost K of each lightning arrester column C 、The cost of each resistor K R and bypass switch cost K S ;

[0112] According to the volume V of each column of the arrester C , the number of lightning arrester columns in the fixed part P, the weight per square meter of the offshore platform W V , the weight of each lightning arrester column W C and the cost per ton of offshore platform K W Get the first cost K C2 ,The first cost is the cost caused by the volume and weight of the lightning arrester column;

[0113] K C2 =(V C *P*W V +W C *P)*K W ;

[0114] According to the volume V of each resistor R , the number of fixed resistors S, the weight per square meter of the offshore platform W V , the weight of each resistor W R and offshore platforms per ton K W The second cost K is obtained from the cost of R2 The second cost is the cost caused by the volume and weight of the resistor;

[0115] K R2 =(V R *S*W V +W R *S)*K W ;

[0116] According to the number of fixed arrester columns P and the cost of each arrester column K C Get the cost of the arrester column K C1 ;

[0117] K C1 =P*K C ;

[0118] According to the number of fixed resistors S and the cost of each resistor K R Get the cost K of the resistor R1 ;

[0119] K R1 =S*K R ;

[0120] According to the first cost K C2 , the second cost K R2 , the cost of the arrester column K C1 、The cost of the resistor K R1 and bypass switch cost K S Get the total cost K of the controllable lightning arrester A :

[0121] K A =K C1 +K R1 +K C2 +K R2 +K S .

[0122] Build an initial simulation model based on the offshore flexible DC system; the initial simulation model includes a lightning arrester model;

[0123] Obtain an initial overvoltage value according to the initial simulation model; calculate an initial electric clearance value according to the initial overvoltage value;

[0124] Ginseng Figure 2, the controllable lightning arrester model replaces the lightning arrester model in the initial simulation model to obtain the simulation model after installation; preferably, in terms of the installation location, it is prioritized to determine whether the controllable lightning arrester can be installed on the land side to suppress part of the overvoltage on the offshore side; under the single-pole grounding condition, the controllable lightning arrester installed on the land side and the controllable lightning arrester installed on the offshore side have an effect of suppressing the overvoltage on the offshore side that differs by about 50kV. Such a difference results in the fact that the benefits of installing a controllable lightning arrester at sea to the offshore platform are greater than those of installing a controllable lightning arrester on land. At the same time, since the controllable lightning arrester installed on the land side cannot limit the lightning overvoltage that may be generated on the offshore side, based on the above two reasons, we determined that the controllable lightning arrester needs to be installed at the offshore converter valve outlet of the offshore flexible DC system, that is, the original lightning arrester on the offshore converter valve outlet side is replaced with a controllable lightning arrester, and the controllable lightning arrester model replaces the lightning arrester model on the offshore side in the initial simulation model to obtain the simulation model after installation; the offshore platform has high restrictions on volume and weight. Since the controllable lightning arrester itself is large in volume and weight, there are more restrictions on installing a controllable lightning arrester on the offshore side; based on the 500kV true bipolar offshore flexible DC system, overvoltage simulation analysis was carried out for different working conditions. Among them, under the single-pole grounding condition of the DC line, that is, when a single-pole grounding fault occurs, the overvoltage value on the DC line is the largest, which can reach 1.9pu. Therefore, subsequent studies all adopt the single-pole grounding condition;

[0125] According to the simulation model after installation, the maximum boundary of the controllable ratio and the overvoltage after installation are obtained;

[0126] From the perspective of post-installation revenue, the rated voltage of the fixed part is an important factor affecting the overvoltage level limited by the controllable lightning arrester. From the perspective of the total cost of the controllable lightning arrester, the rated voltage of the controllable part determines the maximum voltage that the controllable part can withstand. The maximum voltage that the controllable part can withstand is a factor that affects the volume and weight of the bypass switch. Combined with the simulation model after installation, the conditions for obtaining the maximum limit of the controllable ratio include:

[0127] Condition 1: When a single-pole grounding fault occurs in the installed simulation model, the controllable lightning arrester model can limit the overvoltage peak to no less than the starting voltage of the installed simulation model. When the system starts, the voltage will briefly reach 1.22 pu, that is, the starting voltage of the installed simulation model is 1.22 pu;

[0128] Condition 2: When a single-pole ground fault occurs in the installed simulation model, the operating voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model;

[0129] And condition three: when a single-pole grounding fault occurs in the simulation model after installation and before the single-pole grounding fault ends, there is a moment when the tail current of the controllable lightning arrester model is less than the holding current of the thyristor. Otherwise, the bypass switch of the controllable lightning arrester will continue to be closed and cannot be exited, resulting in the continuous accumulation of energy in the controllable lightning arrester. This is a traditional controllable lightning arrester. In this embodiment, the holding current of the thyristor is not less than 200mA.

[0130] The energy consumption and switch branch current of the controllable lightning arrester in this embodiment during a single-pole grounding fault can be obtained through simulation analysis of the simulation model after installation and the volt-ampere characteristic curve of the lightning arrester. Due to the existence of the tail current, the energy borne by the fixed part of the controllable lightning arrester in this embodiment is still relatively large. At the same time, the energy of the controllable lightning arrester may continue to increase because the tail current does not fall below the holding current of the thyristor at any time.

[0131] The value of the tail current can be calculated from the arrester's volt-ampere characteristic curve: Figure 4 , the expression of the arrester's voltage characteristic curve is:

[0132]

[0133] Where, I is the arrester current, V is the arrester voltage, R MOA is the equivalent resistance of the arrester, k1, α1, α2 are coefficients, I MAX The maximum current that the arrester can withstand;

[0134] The post-installation clear distance is obtained based on the post-installation overvoltage. The benefits generated by installing a controllable lightning arrester in the offshore flexible DC system, namely the post-installation benefits, are mainly due to the fact that the controllable lightning arrester can deeply suppress overvoltage, which will reduce the clear distance of equipment such as the valve tower inside the valve hall of the offshore platform, namely the post-installation clear distance, thereby reducing the volume of the offshore platform and generating benefits. The value of the clear distance affected by the controllable lightning arrester's overvoltage suppression level is calculated using the g parameter algorithm, and the initial clear distance value is 5m.

[0135] The reduced volume is obtained according to the initial electric clearance value, the electric clearance value after installation and the total volume of the offshore platform;

[0136] The steps to obtain the reduced volume are:

[0137] Get the length l of the offshore platform, the width w of the offshore platform, the height h of the offshore platform, the first interval number n1 and the second interval number n2. The first interval number is the number of valve hall intervals in the length direction of the offshore platform. Figure 3 There are 7 first intervals in the middle horizontal direction. The number of first intervals is 7. The number of second intervals is the number of valve hall intervals in the width direction of the offshore platform. Figure 3There is a total of 1 second interval in the vertical direction, and the number of second intervals is 1. The valve hall interval includes the interval between adjacent valve halls and the interval between the wall and the adjacent valve hall;

[0138] The total volume of the offshore platform is obtained according to the length, width and floor height of the offshore platform. The total volume of the offshore platform is: V = l*w*h = 67*52*32.5;

[0139] Obtain the net distance reduction d based on the initial net distance value and the net distance after installation;

[0140] The volume reduction is obtained based on the length of the offshore platform, the number of first intervals, the reduction in electrical clearance, the width of the offshore platform, and the number of second intervals. The volume reduction is the volume V2 reduced by the offshore platform after the installation:

[0141] V2=(l-n1*d)*(w-n2d)*h;

[0142] The reduced volume V is obtained based on the total volume of the offshore platform and the volume reduction Z :

[0143] V Z =V-V2.

[0144] The profit after installation is obtained based on the total volume, total weight, total cost and reduced volume of the offshore platform. The steps to obtain the profit after installation are as follows:

[0145] The profit after installation p is obtained based on the reduced volume, the weight per square meter of the offshore platform, and the cost per ton of the offshore platform:

[0146] p=V Z *W V *K W .

[0147] Obtain the total benefit based on the total cost of the controllable lightning arrester and the benefit after installation;

[0148] An adaptive analysis model for controllable arresters in offshore flexible DC systems is constructed based on the maximum controllable ratio, overvoltage after installation, total cost of controllable arresters, and benefits after installation. The adaptive analysis model aims to maximize total benefits. The adaptive analysis model is:

[0149] maxR(x,c)=X(v)-C(α);

[0150] x=X(v);

[0151] v = V(α);

[0152] c=C(α);

[0153] α min ≤α≤αmax ;

[0154] Where max is the maximization function, R is the total benefit, x is the benefit after installation, X is the function corresponding to the benefit after installation, c is the total cost of the controllable lightning arrester, C(α) is the function corresponding to the total cost of the controllable lightning arrester, v is the overvoltage after installation, V is the function corresponding to the overvoltage after installation, α is the controllable ratio, α min is the minimum boundary of the controllable ratio. Usually, the minimum boundary of the controllable ratio tends to 0 (when the controllable ratio is 0, it is an arrester). max is the maximum controllable ratio boundary.

[0155] A controllable ratio set is selected according to the adaptive analysis model to obtain a controllable lightning arrester for installation.

[0156] Furthermore, construction parameters are obtained according to the adaptive analysis model selection.

[0157] According to the above controllable ratio maximum boundary conditions (conditions 1, 2, and 3), the controllable ratio maximum boundary of the 571kV controllable lightning arrester is 12%. Substituting this into the adaptive analysis model, it can be obtained that the optimal controllable ratio of the controllable lightning arrester is 12% of the controllable ratio maximum boundary. Compared with the lightning arrester, the differences in the number of lightning arrester columns P in the fixed part, the volume of the controllable lightning arrester, the weight of the controllable lightning arrester, and the total cost of the controllable lightning arrester in this embodiment are shown in Table 1:

[0158] Table 1 Differences between controllable arresters with different controllable ratios and arresters in Example 1

[0159] Controllable ratio Number of bars P <![CDATA[Volume (m 3 )]]> Weight (t) Cost (10,000 yuan) 10％ 1 0.047 0.095 -63.406 12％ 2 0.517 0.575 -51.504

[0160] In this embodiment, the controllable lightning arrester is a traditional controllable lightning arrester. It can be seen from the above table that even if the controllable ratio of the traditional controllable lightning arrester reaches the maximum limit, the cost of the traditional controllable lightning arrester is still higher than the cost of the lightning arrester. This is because at a controllable ratio of 12%, the lightning arrester does not need to increase the number of fixed lightning arrester columns to achieve the overvoltage peak that the controllable lightning arrester can achieve. However, the fixed part of the traditional controllable lightning arrester has too much energy to bear, resulting in the number of fixed lightning arrester columns exceeding the lightning arrester. At the same time, the existence of the bypass switch in the traditional controllable lightning arrester further increases the cost. In general, the cost of the traditional controllable lightning arrester is higher than that of the lightning arrester. The fundamental reason is that the switch of the traditional controllable lightning arrester cannot actively exit, and it is necessary to ensure that the tail current is small enough to disconnect the bypass switch, resulting in its fixed part bearing a large amount of energy, affecting the volume, weight and cost of the device.

[0161] Example 2

[0162] Based on Example 1, other aspects are the same as Example 1, and the differences from Example 1 are:

[0163] The conditions for obtaining the maximum boundary of the controllable ratio include:

[0164] Condition 1: When a single-pole ground fault occurs in the installed simulation model, the overvoltage peak value that the controllable lightning arrester model can limit is not lower than the starting voltage of the installed simulation model;

[0165] Condition 2: When a single-pole ground fault occurs in the installed simulation model, the operating voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model;

[0166] And condition three: when a single-pole grounding fault occurs in the simulation model after installation, the overvoltage peak value that the controllable lightning arrester model can limit is not lower than the second peak voltage value that rises at the moment the bypass switch returns to its original state.

[0167] During the research process, it was found that if the controllable lightning arrester is actively restored to the initial state by the bypass switch part after a period of time of reducing the overvoltage spike, the overall energy consumption of the controllable lightning arrester can be reduced. This controllable lightning arrester is called an active exit type controllable lightning arrester, that is, the controllable lightning arrester mentioned in Example 2 is an active exit type controllable lightning arrester. Since the tail current of the controllable lightning arrester has a large restriction on the selection of its controllable ratio, if the bypass switch of the controllable lightning arrester can be actively exited after limiting the overvoltage peak, the controllable ratio parameter selection of the controllable lightning arrester will not be constrained by condition three of the conditions of the maximum boundary of the controllable ratio in Example 1, that is, an active exit type controllable lightning arrester. This embodiment explores the controllable ratio parameters of the active exit type controllable lightning arrester and conducts an overvoltage economic analysis of the installation of a controllable lightning arrester in an offshore flexible DC system.

[0168] After the active exit type controllable lightning arrester of this embodiment is installed, the overvoltage value of the DC side of the offshore flexible DC system in the simulation model after a single-pole grounding fault occurs is as follows: Figure 5 As shown in the middle curve, it can be seen that the active exit type controllable lightning arrester exits when a fault occurs and exits after the overvoltage peak. According to the above controllable ratio maximum boundary conditions, it can be obtained that the maximum controllable ratio of the 571kV active exit type controllable lightning arrester is 34%; combined with the adaptive analysis model, the optimal controllable ratio parameter of the controllable lightning arrester in this embodiment is 34%; at the same time, the energy consumption of the active exit type controllable lightning arrester itself in the simulation model is as follows Figure 5 Shown as the middle bar.

[0169] Under the condition that the arrester's limiting level on overvoltage is kept consistent, the costs of the arrester and the controllable arrester in Example 2 are compared. The number of columns, volume, weight, and cost of the arrester minus the number of columns, volume, weight, and cost of the controllable arrester are respectively subtracted, and the results are shown in Table 2:

[0170] Table 2 Differences between controllable arresters and arresters with different controllable ratios in Example 2

[0171] Controllable ratio Overvoltage (kV) Bar Difference <![CDATA[Volume difference (m 3 )]]> Weight difference (t) Cost difference (10,000 yuan) 10％ 779.541 1 0.047 0.095 -101.906 15％ 752.080 6 2.204 2.32 -94.127 17％ 735.763 16 6.827 7.05 4.201 20％ 720.059 60 27.392 28.065 496.853

[0172] The table above shows that the controllable arrester in Example 2 is smaller in size, weight, and cost than the controllable arrester when the controllability ratio exceeds 17%. The cost difference between the two arresters becomes more pronounced when the overvoltage level is better controlled. At lower overvoltage levels, the arrester costs approximately 2-3 times more than the controllable arrester. At higher overvoltage levels, the arrester costs less than the controllable arrester.

[0173] The energy consumption and switch branch current of the controllable lightning arrester in this embodiment during a single-pole grounding fault can be obtained through simulation analysis of the simulation model after installation and the volt-ampere characteristic curve of the lightning arrester. Due to the existence of tail current, the energy borne by the fixed part of the controllable lightning arrester in Example 1 is greater than that borne by the fixed part of the controllable lightning arrester in Example 2. Figure 7 This study compares the tail currents of two types of controllable arresters ((a) the arrester from Example 2, and (b) the arrester from Example 1) with a controllability ratio of 15% under an operational overvoltage condition, i.e., a single-pole ground fault. The tail current of the arrester from Example 2 decreases rapidly after the arrester actively exits, and the energy does not increase after the tail current reaches zero. Therefore, the active-exit arrester has lower requirements for the fixed components.

[0174] Figure 8 The green curve (MOA) is the overvoltage waveform of the original offshore flexible DC system including the arrester. When the offshore flexible DC system is equipped with the controllable arrester in Example 1, the overvoltage waveform diagram is as follows: Figure 8 As shown in the red curve (Controllable MOA), the controllable arrester bypass switch operates before the overvoltage reaches its peak, and the fixed part works alone to reduce the overvoltage peak. When the controllable arrester in Example 2 is installed in the offshore flexible DC system, the overvoltage waveform diagram is as follows: Figure 8 As shown in the purple curve (Active-exit Type Controllable MOA), some time after the overvoltage reaches its peak, the bypass switch of the active-exit type controllable arrester actively restores its initial state, changing from a fixed partial working state to an overall working state to reduce the energy of the arrester.

[0175] In the process of comparing the costs of the two controllable lightning arresters in Example 1 and Example 2, the controllable ratios of the two controllable lightning arresters are kept consistent, thereby obtaining the cost difference between the controllable lightning arrester and the active exit type controllable lightning arrester, see Figure 6 and Table 3:

[0176] Table 3 Cost comparison of the controllable lightning arrester in Example 2 and the controllable lightning arrester in Example 1

[0177] Controllable ratio Fixed fraction energy (mJ) Cost difference (10,000 yuan) 10％ 41.03 41.03 11％ 43.03 43.03 12％ 45.02 45.02

[0178] It can be seen from the data in Table 3 that the active exit type controllable lightning arrester has a higher limit due to its controllability ratio parameter. Therefore, the benefits brought by the active exit type controllable lightning arrester to the offshore flexible DC system are more substantial than those of the controllable lightning arrester.

[0179] Combining the total cost and profit after installation of the controllable lightning arrester in Example 2, the total profit of the active exit type controllable lightning arrester under different controllability ratio parameters is shown in Table 4.

[0180] Table 4 Total benefits brought by controllable lightning arrester to offshore flexible DC system in Example 2

[0181]

[0182]

[0183] The data in Table 4 shows that as the controllability ratio increases, the total revenue generated by active-exit controllable surge arresters for the offshore flexible DC system generally increases. Among them, the active-exit controllable surge arresters with a 34% controllability ratio have the highest total revenue of 232 million yuan, accounting for 23.2% of the total cost of the offshore platform.

[0184] In summary, Example 1 and Example 2:

[0185] 1. Controllable lightning arresters have advantages in suppressing overvoltage. In the 500kV offshore flexible DC system, they can reliably suppress overvoltage under different system operating conditions.

[0186] 2. The cost of installing a controllable lightning arrester in an offshore flexible DC system is determined by the bypass switch of the controllable lightning arrester itself, the number of lightning arrester columns in the fixed part, and the number of resistors in the fixed part. The maximum cost increase brought by the controllable lightning arrester shall not exceed RMB 3.5 million.

[0187] 3. The benefits of installing controllable lightning arresters in offshore flexible DC systems are that after the controllable lightning arresters suppress overvoltages, they reduce the electrical clearance distance between various devices in the valve hall of the offshore platform, thereby reducing the size of the offshore platform. Controllable lightning arresters can reduce the cost of the offshore platform by up to 119 million yuan, which is approximately 12% of the total platform cost.

[0188] 4. Compared with the lightning arrester, the controllable lightning arrester in Example 1 has no advantages in terms of volume, weight and cost due to the upper limit of the controllable ratio parameter.

[0189] 5. Compared with conventional controllable arresters, the controllable arrester in Example 2 has a higher cost within the controllable ratio limit of the controllable arrester in Example 1. However, because the controllable arrester in Example 2 has a higher controllable ratio limit than the controllable arrester in Example 1, the total benefit of an offshore flexible DC system equipped with the controllable arrester in Example 2 is greater.

[0190] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for analyzing the economic benefits of overvoltage in an offshore flexible DC system equipped with a controllable lightning arrester, characterized by: The following steps are involved: According to the offshore flexible DC system, the total volume, total weight, total cost of the offshore platform and the rated voltage of the controllable lightning arrester are obtained; Obtaining a controllable ratio set and physical quantity parameters of the controllable lightning arrester; Obtaining construction parameters of the controllable lightning arrester according to the rated voltage and the physical quantity parameters; Building a controllable lightning arrester model according to the construction parameters, the total volume of the offshore platform, the total weight of the offshore platform, and the total cost of the offshore platform and obtaining the total cost of the controllable lightning arrester; Building an initial simulation model based on the offshore flexible DC system; the initial simulation model includes a lightning arrester model; obtaining an initial overvoltage value according to the initial simulation model; Calculating an initial electric clearance value according to the initial overvoltage value; Replacing the arrester model in the initial simulation model with the controllable arrester model to obtain a simulation model after installation; Obtaining a maximum controllable ratio boundary and a post-installation overvoltage according to the post-installation simulation model; Obtaining a post-installation clear distance according to the post-installation overvoltage; Obtaining a reduced volume according to the initial electrical clearance value, the electrical clearance after installation, and the total volume of the offshore platform; Obtaining a profit after installation according to the total volume of the offshore platform, the total weight of the offshore platform, the total cost of the offshore platform and the reduced volume; Obtaining a total benefit based on the total cost of the controllable lightning arrester and the benefit after installation; An adaptive analysis model of the controllable lightning arrester of the offshore flexible DC system is constructed based on the maximum limit of the controllable ratio, the overvoltage after installation, the total cost of the controllable lightning arrester, and the profit after installation; the adaptive analysis model takes maximizing the total profit as a goal; The controllable ratio set is selected according to the adaptive analysis model to obtain a controllable lightning arrester for installation.

2. The method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system according to claim 1 is characterized by: The construction parameters include the number of resistors in the fixed part and the number of lightning arrester columns in the fixed part; the physical quantity parameters include a first voltage, a first energy value, and a second energy value. The first voltage is the voltage that each resistor bears when a unit current is passed through it, the first energy value is the energy value that each resistor can withstand, and the second energy value is the energy value that the fixed part can withstand under a single-pole grounding condition. The steps for obtaining the construction parameters are: Obtaining the highest voltage level of the offshore flexible DC system; Obtaining the rated voltage according to the highest voltage level; Obtain the controllable ratio calculation formula; Obtaining the number of resistors in the fixed part according to the rated voltage, the controllable ratio calculation formula, and the first voltage; The number of lightning arrester columns in the fixed part is obtained according to the first energy value, the second energy value and the number of resistor plates in the fixed part.

3. The method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system according to claim 2 is characterized by: The physical quantity parameters also include the volume of each lightning arrester column, the weight of each lightning arrester column, the volume of each resistor sheet, and the weight of each resistor sheet; The steps for obtaining the total cost of the controllable lightning arrester are: Obtaining the weight per square meter of the offshore platform according to the total weight of the offshore platform and the total volume of the offshore platform; Obtaining a cost per ton of the offshore platform based on the total cost of the offshore platform and the total weight of the offshore platform; Obtain the cost of each arrester column, the cost of each resistor, and the cost of the bypass switch; Obtaining a first cost based on the volume of each arrester column, the number of arrester columns in the fixed portion, the weight per square meter of the offshore platform, the weight of each arrester column, and the cost per ton of the offshore platform, where the first cost is the cost caused by the volume and weight of the arrester column; Obtaining a second cost based on the volume of each resistor, the number of resistors in the fixed portion, the weight per square meter of the offshore platform, the weight of each resistor, and the cost per ton of the offshore platform, where the second cost is the cost caused by the volume and weight of the resistors; Obtaining the cost of the arrester column according to the number of arrester columns in the fixed part and the cost of each arrester column; Obtaining the cost of the resistors according to the number of the fixed resistors and the cost of each resistor; The total cost of the controllable lightning arrester is obtained according to the first cost, the second cost, the cost of the lightning arrester column, the cost of the resistor, and the cost of the bypass switch.

4. The method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system according to claim 3 is characterized by: The steps of obtaining the reduced volume are: Obtain the length, width, and floor height of the offshore platform, the first number of intervals, and the second number of intervals. The first number of intervals refers to the number of valve hall intervals along the length of the offshore platform, and the second number of intervals refers to the number of valve hall intervals along the width of the offshore platform. The valve hall intervals include the intervals between adjacent valve halls and the intervals between a wall and an adjacent valve hall. Obtaining the total volume of the offshore platform according to the length of the offshore platform, the width of the offshore platform and the floor height of the offshore platform; Obtaining a reduction in the electric clearance distance according to the initial electric clearance distance value and the electric clearance distance after installation; Obtaining a volume reduction amount according to the length of the offshore platform, the number of the first intervals, the reduction in the electrical clearance, the width of the offshore platform, and the number of the second intervals, where the volume reduction amount is the volume reduction of the offshore platform after the installation; The reduced volume is obtained according to the total volume of the offshore platform and the volume reduction.

5. The method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system according to claim 4 is characterized by: The steps to obtain the benefits after installation are as follows: The profit after the installation is obtained according to the reduced volume, the weight per square meter of the offshore platform and the cost per ton of the offshore platform.

6. The method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system according to claim 1 is characterized by: The conditions for obtaining the maximum limit of the controllable ratio include: Condition 1: when a single-pole grounding fault occurs in the installed simulation model, the overvoltage peak value that can be limited by the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model; Condition 2: When a single-pole grounding fault occurs in the installed simulation model, the operating voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model; And condition three: when a single-pole grounding fault occurs in the simulation model after installation and before the single-pole grounding fault ends, there is a moment when the tail current of the controllable lightning arrester model is less than the holding current of the thyristor.

7. The method for analyzing the economic benefits of overvoltage in an offshore HVDC system equipped with a controllable lightning arrester according to claim 1 is characterized by: The conditions for obtaining the maximum limit of the controllable ratio include: Condition 1: when a single-pole grounding fault occurs in the installed simulation model, the overvoltage peak value that can be limited by the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model; Condition 2: When a single-pole grounding fault occurs in the installed simulation model, the operating voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the installed simulation model; And condition three: when a single-pole grounding fault occurs in the simulation model after installation, the overvoltage peak value that can be limited by the controllable lightning arrester model is not lower than the second peak voltage value that rises at the moment the bypass switch returns to its original state.

8. The method for analyzing the economic benefits of installing a controllable lightning arrester on an offshore flexible DC system according to claim 1 is characterized by: The g parameter algorithm is used to obtain the initial electrical clearance distance value and the electrical clearance distance after installation.

9. The method for analyzing the economic benefits of overvoltage in an offshore HVDC system equipped with a controllable lightning arrester according to claim 1 is characterized by: The adaptive analysis model is: maxR(x,c)=X(v)-C(α); x=X(v); v = V(α); c=C(α); α min ≤α≤α max ； Where max is the maximization function, R is the total benefit, x is the benefit after installation, X is the function corresponding to the benefit after installation, c is the total cost of the controllable lightning arrester, C(α) is the function corresponding to the total cost of the controllable lightning arrester, v is the overvoltage after installation, V is the function corresponding to the overvoltage after installation, α is the controllable ratio, α min is the minimum boundary of the controllable ratio, α max is the maximum controllable ratio boundary.

10. The method for analyzing the economic benefits of installing a controllable lightning arrester in an offshore flexible DC system according to claim 1, characterized in that: The construction parameters are obtained according to the adaptive analysis model selection.

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