Over-voltage economical efficiency analysis method for adding controllable lightning arrester to offshore flexible direct current system

Abstract

The invention provides an over-voltage economy analysis method for a controllable lightning arrester added to an offshore flexible direct current system. The method comprises 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 the initial simulation model with the controllable lightning arrester model to obtain a controllable ratio maximum 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; 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 revenue after installation; according to the maximum boundary of the controllable ratio, the overvoltage after installation, the total cost of the controllable lightning arrester and the income after installation, an adaptive analysis model with the maximum total income as the target is constructed, and the adaptive analysis model is used for selecting a controllable ratio set to obtain the controllable lightning arrester for installation. And a guiding effect is provided for the installation of the controllable lightning arrester on the offshore flexible direct current system.

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] Overvoltage in power systems not only damages electrical equipment, but may also cause significant economic losses. Lightning arresters are key devices for suppressing overvoltage, but they are insufficient in voltage limiting effects. Although existing research has made some progress in improving the operating charge rate to enhance the arrester's suppression capability, this approach often leads to an increase in the size and weight of the arrester. Controllable lightning arresters are equipment that can achieve flexible limitation of operating overvoltages. Compared with lightning arresters, controllable lightning arresters sacrifice part of the system's reliability, but they have better effects in suppressing overvoltages, saving transmission corridors, and protecting transmission equipment. Controllable lightning arresters were first used in AC systems, mainly to replace the closing resistance of circuit breakers. In recent years, the research on parameter selection, control strategy, and potential distribution of UHV AC switch-type controllable lightning arresters and the exploration of related theoretical technologies of DC controllable lightning arresters have laid a solid theoretical foundation for the practical application of controllable lightning arresters in AC and DC systems. However, due to technical and economic limitations, controllable lightning arresters have not yet been widely used in power systems.

[0003] Offshore flexible DC transmission technology is becoming more and more mature. Compared with conventional AC and DC systems, offshore flexible DC transmission systems are more sensitive to overvoltage and have higher requirements for volume and weight. On the one hand, overvoltage will threaten the safe and stable operation of the entire offshore flexible DC system, put forward high requirements for the insulation level of equipment and lines, and affect the reliability of a large number of power electronic equipment, further increasing the cost of engineering construction. On the other hand, overvoltage will affect the electrical clearance between the valve towers in the valve hall of the offshore platform, thereby affecting the volume and weight of the offshore platform. In order to make the equipment insulation level and cost of the offshore flexible DC transmission project economical and reasonable, it is necessary to effectively limit the overvoltage level of the offshore flexible DC transmission system and ensure that the volume and weight of the offshore platform are within a reasonable range. Controllable lightning arresters have good overvoltage suppression capabilities, but in AC and DC systems, the benefits of controlled lightning arresters reducing overvoltage by sacrificing part of the system reliability are small. The offshore flexible DC transmission system not only has higher requirements for overvoltage, but also has stricter restrictions on volume and weight. Therefore, the benefits of reducing overvoltage in the offshore flexible DC transmission system are further magnified, which provides an ideal scenario for the application of controllable lightning arresters. 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 view of 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 object, the technical solution adopted by the present invention is as follows: an overvoltage economic analysis method for installing a controllable lightning arrester in an offshore flexible DC system, comprising the following steps:

[0006] According to the offshore flexible DC system, the total volume of the offshore platform, the total weight of the offshore platform, the 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 and obtaining 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;

[0010] Building an initial simulation model according to 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 distance value according to the initial overvoltage value;

[0012] The controllable arrester model replaces the arrester model in the initial simulation 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 electric clearance distance according to the post-installation overvoltage;

[0015] Obtaining a reduced volume according to the initial electric clearance distance value, the electric clearance distance 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 a controllable lightning arrester of an offshore flexible DC system is constructed according to the maximum boundary of the controllable ratio, the overvoltage after installation, the total cost of the controllable lightning arrester and the benefit after installation; the adaptive analysis model takes the maximum total benefit 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 bears when a unit strength current passes through it, the first energy value is the energy value that each resistor can bear, and the second energy value is the energy value that the fixed part bears under a single-pole grounding condition;

[0021] The steps of 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 resistors 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 of 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 according to 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 according to the volume of each arrester column, the number of arrester columns of the fixed part, the weight corresponding to each square meter of the offshore platform, the weight of each arrester column and the cost per ton of the offshore platform, wherein the first cost is the cost caused by the volume and weight of the arrester column;

[0033] Obtaining a second cost according to the volume of each resistor, the number of resistors in the fixed part, the weight of each square meter of the offshore platform, the weight of each resistor and the cost per ton of the offshore platform, wherein the second cost is the cost caused by the volume and weight of the resistor;

[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 resistor according to the number of the resistors in the fixed part 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 of the offshore platform, the width of the offshore platform, the height of the offshore platform, the first interval number, and the second interval number, wherein the first interval number is the number of valve hall intervals in the length direction of the offshore platform, and the second interval number is the number of valve hall intervals in the width direction of the offshore platform, and the valve hall interval includes the interval between adjacent valve halls and the interval between the wall and the 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 amount of the electrical clearance, the width of the offshore platform and the number of the second intervals, wherein the volume reduction amount is the volume reduced by 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 of 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 boundary 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 simulation model after installation, the action voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the simulation model after installation;

[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 boundary 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 simulation model after installation, the action voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the simulation model after installation;

[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 is raised at the moment when 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 actively exiting controllable lightning arrester.

[0055] Furthermore, a g parameter algorithm is used to obtain the initial electric clearance distance value and the electric clearance distance after installation.

[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] In the formula, 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 controllable ratio boundary, α max is the maximum controllable ratio boundary.

[0063] Further, 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 the maximum 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 an overvoltage economic analysis method for installing a controllable lightning arrester in an offshore flexible DC system of 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 It is a top view of the valve hall of the offshore platform in Examples 1 and 2 of the present invention;

[0069] Figure 4 It is a 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 when a single-pole grounding fault occurs 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 when a single-pole grounding fault occurs 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, (b) is the tail current of the controllable lightning arrester in Example 1;

[0073] Figure 8 Schematic diagram of overvoltage waveforms of the initial simulation model of the present invention and the simulation model 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 , an overvoltage economic analysis method for installing a controllable lightning arrester in an offshore flexible DC system, comprising the following steps:

[0077] According to the offshore flexible DC system, the total volume of the offshore platform, the total weight of the offshore platform, the 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 highest 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, l is the length of the offshore platform, w is the width of the offshore platform, h is the height of the offshore platform, the units of l, w, and h are all m, 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] According to the calculation standard of the rated voltage of the lightning arrester installed on the DC line:

[0081]

[0082] In the formula, It is the calculated value of the rated voltage of the arrester installed on the DC line, and 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 "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, wherein 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 working principle of the controllable arrester is as follows: in normal operation, the bypass switch does not operate, and the fixed part and the controllable part jointly bear the voltage, which is equivalent to installing a conventional arrester in the offshore flexible DC system. After a fault occurs, the bypass switch of the controllable arrester operates, bypassing the controllable part, and the fixed part alone bears the voltage, thereby reducing the overvoltage. If a controllable arrester is used to replace a conventional arrester in an offshore flexible DC system, the controllable arrester in the offshore flexible DC system will have the ability to switch to a smaller rated voltage, which can effectively reduce the overvoltage of the offshore flexible DC system.

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

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

[0091] 2. Since the fixed part of the controllable arrester absorbs more energy than the ordinary arrester, the number of arrester columns and resistors in the fixed part of the controllable arrester itself will also exceed that of the ordinary arrester. This change will also increase the 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 millimeters), and the construction parameters include the number of resistor sheets in the fixed part S and the number of lightning arrester columns in the fixed part 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 bears when passing a current of unit strength, and the first energy value is the energy value that each resistor piece can bear. In this embodiment, the first energy value E s The second energy value is 36 kJ, 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 S of the fixed part resistors 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 arrester, it is necessary to determine the influence of the changes in the volume and weight of the controllable arrester on the total cost of the offshore platform. It can be obtained that the volume linearly affects the weight and the weight linearly affects the cost;

[0105] The physical quantity parameters also include the volume V of each arrester column C 、The weight of each 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 arrester are:

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

[0108]

[0109] According to the total cost K of the offshore platform and the total weight W of the offshore platform, the cost per ton of the offshore platform K is obtained. W for:

[0110]

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

[0112] According to the volume V of each arrester column C , the number of lightning arrester columns in the fixed part P, the weight of the offshore platform per square meter W V 、The weight of each 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 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 of the offshore platform per square meter W V , the weight of each resistor W R and offshore platforms per ton K W The second cost K is obtained by 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 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] An initial simulation model is built based on the offshore flexible DC system; the initial simulation model includes a lightning arrester model;

[0123] Obtain an initial overvoltage value according to an initial simulation model; calculate an initial electric clearance distance 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 sea side; under the single-pole grounding condition, the controllable lightning arrester installed on the land side and the controllable lightning arrester installed on the sea side have a difference of about 50kV in suppressing the overvoltage on the sea side. Such a difference leads to the fact that the benefits of installing controllable lightning arresters at sea to offshore platforms are greater than those of installing controllable lightning arresters on land. At the same time, since the controllable lightning arresters installed on the land side cannot limit the lightning overvoltage that may be generated on the offshore side, we determine from the above two reasons: the controllable lightning arrester needs to be installed at the outlet of the offshore converter valve of the offshore flexible DC system, that is, the original lightning arrester on the outlet side of the offshore converter valve 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 has a large volume and weight, there are more restrictions on installing controllable lightning arresters 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 benefits, the rated voltage of the fixed part is an important factor affecting the overvoltage level of the controllable arrester. From the perspective of the total cost of the controllable 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 boundary of the controllable ratio include:

[0127] Condition 1: 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 starting voltage of the simulation model after installation. When the system starts, the voltage will briefly reach 1.22pu, that is, the starting voltage of the simulation model after installation is 1.22pu;

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

[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 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 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 arrester. Due to the existence of the tail current, the energy borne by the fixed part of the controllable arrester in this embodiment is still relatively large. At the same time, the energy of the controllable arrester may continue to grow because the tail current does not have a moment lower than the thyristor holding current.

[0131] The value of the tail current can be calculated from the volt-ampere characteristic curve of the arrester: 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 net distance after installation is obtained according to the overvoltage after installation; the benefits generated by installing controllable lightning arresters in the offshore flexible DC system, i.e., the benefits after installation, are mainly due to the fact that the controllable lightning arrester can deeply suppress overvoltage, which will reduce the net distance of equipment such as the valve tower inside the valve hall of the offshore platform, i.e., the net distance after installation, thereby reducing the volume of the offshore platform and generating benefits. The value of the net distance affected by the controllable lightning arrester's suppression of overvoltage level is calculated by the g parameter algorithm, and the initial net distance value is 5m.

[0135] The reduced volume is obtained according to the initial electric clearance value, the electric clearance 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 middle vertical direction, the number of second intervals is 1, and 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 layer height of the offshore platform. The total volume of the offshore platform is: V = l*w*h = 67*52*32.5;

[0139] Obtain the reduction amount d of the electric clearance distance according to the initial electric clearance distance value and the electric clearance distance after installation;

[0140] The volume reduction is obtained according to the length of the offshore platform, the number of first intervals, the reduction in the 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 of the offshore platform, the total weight of the offshore platform, the total cost of the offshore platform and the reduced volume; the steps to obtain the profit after installation are:

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

[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] According to the maximum boundary of controllable ratio, overvoltage after installation, total cost of controllable arrester and benefit after installation, an adaptive analysis model of controllable arrester of offshore flexible DC system is constructed; the adaptive analysis model takes the maximum total benefit as the goal; 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] In the formula, 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 a lightning 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] Further, 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 arrester is 12%. Substituting it into the adaptive analysis model, the optimal controllable ratio of the controllable arrester can be obtained as the controllable ratio maximum boundary is 12%; compared with the arrester, the differences in the number of arrester columns P in the fixed part, the volume of the controllable arrester, the weight of the controllable arrester and the total cost of the controllable arrester in the controllable 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 (ten thousand yuan) 10％ 1 0.047 0.095 -63.406 12％ 2 0.517 0.575 -51.504

[0160] The controllable lightning arrester in this embodiment 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-part 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 bears too much energy, resulting in the number of fixed-part lightning arrester columns exceeding the lightning arrester. At the same time, the existence of the bypass switch in the traditional controllable lightning arrester additionally 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 be actively exited, and the tail current needs to be small enough to disconnect the bypass switch, resulting in the fixed part of the arrester bearing a large amount of energy, which affects the volume, weight and cost of the device.

[0161] Example 2

[0162] On the basis of Example 1, the rest is the same as Example 1, and the difference from Example 1 is:

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

[0164] Condition 1: When a single-pole grounding 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 grounding fault occurs in the simulation model after installation, the action voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the simulation model after installation;

[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 arrester can be 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 arrester can be reduced. This controllable arrester is called an active exit type controllable arrester, that is, the controllable arrester mentioned in Example 2 is an active exit type controllable arrester. Since the tail current of the controllable arrester has a large restriction on the selection of its controllable ratio, if the bypass switch of the controllable arrester can be actively exited after limiting the overvoltage peak, the controllable ratio parameter selection of the controllable 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 arrester. This embodiment explores the controllable ratio parameters of the active exit type controllable arrester, and conducts an overvoltage economic analysis of the installation of a controllable arrester in an offshore flexible DC system.

[0168] After the active exit type controllable lightning arrester in 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 middle bar.

[0169] Under the condition of keeping the arrester's limiting level of overvoltage the same, the cost of the arrester is compared with that of the controllable arrester in Example 2. The number of columns, volume, weight, and cost of the arrester are respectively subtracted from the number of columns, volume, weight, and cost of the controllable arrester, and the values ​​are shown in Table 2:

[0170] Table 2 Differences between controllable arresters with different controllable ratios and arresters 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] It can be seen from the above table that the controllable lightning arrester in Example 2 is smaller than the lightning arrester in terms of volume, weight and cost when the controllable ratio exceeds 17%. The better the overvoltage level is limited, the more obvious the difference in cost between the two lightning arresters. When the overvoltage level is low, the cost of the lightning arrester is about 2-3 times the cost of the present device. When the overvoltage level is high, the cost of the lightning arrester is lower than the cost of the controllable lightning 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 the tail current, the energy borne by the fixed part of the controllable lightning arrester in Example 1 is greater than the energy borne by the fixed part of the controllable lightning arrester in Example 2; Figure 7 The tail current of two types of controllable lightning arresters ((a) is the controllable lightning arrester in Example 2, (b) is the controllable lightning arrester in Example 1) with a controllable ratio of 15% under the operating overvoltage condition, i.e., a single-pole grounding fault, is compared. The tail current of the controllable lightning arrester in Example 2 decreases rapidly after the controllable lightning arrester actively exits, and the energy no longer increases after the tail current is reduced to 0, so the active exit type controllable lightning arrester has lower requirements for the fixed part.

[0174] Figure 8 The green curve (MOA) in the middle 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 bypass switch of the controllable arrester is actuated before the overvoltage reaches the peak value, and the fixed part works alone to reduce the overvoltage peak value. 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 part 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, because the active exit type controllable lightning arrester has a higher boundary due to its controllability ratio parameter, the benefits brought by the active exit type controllable lightning arrester to the offshore flexible DC system are more considerable than those of the controllable lightning arrester.

[0179] Combining the total cost and the 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] From the data in Table 4, we can see that with the increase of controllable ratio, the total revenue brought by active exit type controllable arrester to the offshore flexible DC system is generally on the rise. Among them, the total revenue of active exit type controllable arrester with 34% controllable ratio is the highest, which is 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 and can reliably suppress overvoltage under different operating conditions in the 500kV offshore flexible DC system.

[0186] 2. The cost of installing a controllable lightning arrester in the 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 the offshore flexible DC system are that after the controllable lightning arresters suppress overvoltage, the net electrical distance of each device in the valve hall of the offshore platform is reduced, thereby reducing the size of the offshore platform. The controllable lightning arresters can reduce the cost of the offshore platform by up to 119 million yuan, which is about 12% of the total cost of the platform;

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

[0189] 5. Compared with the traditional controllable lightning arrester, the controllable lightning arrester in Example 2 has a higher cost than the controllable lightning arrester in Example 1 within the controllable ratio limit of the controllable lightning arrester in Example 1. However, because the controllable ratio limit of the controllable lightning arrester in Example 2 is higher than that of the controllable lightning arrester in Example 1, the total benefit of the offshore flexible DC system equipped with the controllable lightning 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. An economic analysis method for overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester, characterized in that: The following steps are involved: According to the offshore flexible DC system, the total volume of the offshore platform, the total weight of the offshore platform, the 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 and obtaining 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; Building an initial simulation model according to 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 distance value according to the initial overvoltage value; The controllable arrester model replaces the arrester model in the initial simulation 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 electric clearance distance according to the post-installation overvoltage; Obtaining a reduced volume according to the initial electric clearance distance value, the electric clearance distance 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 a controllable lightning arrester of an offshore flexible DC system is constructed according to the maximum boundary of the controllable ratio, the overvoltage after installation, the total cost of the controllable lightning arrester and the benefit after installation; the adaptive analysis model takes the maximum total benefit 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 efficiency of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester according to claim 1 is characterized by: 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 bears when passing a current of unit strength, the first energy value is the energy value that each resistor can bear, and the second energy value is the energy value that the fixed part bears under a single-pole grounding condition; The steps of 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 resistors in the fixed part.

3. The method for analyzing the economic efficiency of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester according to claim 2 is characterized by: 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; The steps of 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 according to 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 according to the volume of each arrester column, the number of arrester columns of the fixed part, the weight corresponding to each square meter of the offshore platform, the weight of each arrester column and the cost per ton of the offshore platform, wherein the first cost is the cost caused by the volume and weight of the arrester column; Obtaining a second cost according to the volume of each resistor, the number of resistors in the fixed part, the weight of each square meter of the offshore platform, the weight of each resistor and the cost per ton of the offshore platform, wherein the second cost is the cost caused by the volume and weight of the resistor; 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 resistor according to the number of the resistors in the fixed part 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 efficiency of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester according to claim 3 is characterized by: The steps of obtaining the reduced volume are: Obtain the length of the offshore platform, the width of the offshore platform, the height of the offshore platform, the first interval number, and the second interval number, wherein the first interval number is the number of valve hall intervals in the length direction of the offshore platform, and the second interval number is the number of valve hall intervals in the width direction of the offshore platform, and the valve hall interval includes the interval between adjacent valve halls and the interval between the wall and the 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 amount of the electrical clearance, the width of the offshore platform and the number of the second intervals, wherein the volume reduction amount is the volume reduced by 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 efficiency of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester according to claim 4 is characterized by: The steps to obtain the benefits after the installation are: 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 efficiency of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester according to claim 1 is characterized by: The conditions for obtaining the maximum boundary 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 simulation model after installation, the action voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the simulation model after installation; 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 efficiency of overvoltage of an offshore flexible DC system equipped with a controllable lightning arrester according to claim 1 is characterized by: The conditions for obtaining the maximum boundary 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 simulation model after installation, the action voltage of the bypass switch in the controllable lightning arrester model is not lower than the starting voltage of the simulation model after installation; 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 is raised at the moment when the bypass switch returns to its original state.

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

9. The method for analyzing the economic efficiency of overvoltage of an offshore flexible DC 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 ； In the formula, 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 controllable ratio boundary, α max is the maximum controllable ratio boundary.

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

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