An offshore overhead transmission line based on partial insulation and its design method

Abstract

The present invention relates to the technical field of power transmission line design, and discloses a partially insulated offshore overhead power transmission line and design method. The method comprises: providing an insulating layer at the lowest point of sag of the bare conductor of the offshore overhead power transmission line, and providing stress cones at the joints at both ends of the insulating layer; connecting the insulating layer to the bare conductor via a wire crimping tube to form a partially insulated conductor of the offshore overhead power transmission line; and providing a fixed pulley device on each tower, with a weight suspended below the fixed pulley device, and connecting the insulated wire of the fixed pulley device to the insulated wire portion of the fixed pulley device to elevate the lowest point of sag of the partially insulated conductor. The present invention optimizes the conductor withstand voltage and mechanical stability of the offshore overhead power transmission line through the partial insulation layer, the fixed pulley and the insulated wire device, and the stress cone structure, thereby improving the performance of the offshore power transmission system and significantly reducing the risk of corrosion and discharge of the transmission line due to the offshore environment.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission lines, and in particular to an offshore overhead power transmission line based on partial insulation and a design method thereof. Background Art

[0002] Offshore overhead transmission lines are a crucial component connecting offshore wind farms to the onshore power grid, ensuring the stable and efficient transmission of wind-generated electricity to the grid. Due to the unique characteristics of the marine environment, offshore overhead transmission lines face distinct challenges compared to onshore transmission lines. They must not only withstand environmental stresses such as salt spray corrosion, humidity, and wind and wave impacts, but also maintain excellent electrical performance to ensure long-term stable operation.

[0003] In traditional transmission line design, conductors are typically installed bare above poles or towers, with the air providing natural insulation. However, this design model is no longer suitable for offshore overhead transmission lines, which are exposed to high humidity and salt spray for extended periods of time. Without adequate insulation protection, the humid environment and salt spray can cause surface corrosion, leading to electrical failures and compromising the stability of the entire power grid. Insulating the entire conductor can lead to problems such as the use of large amounts of insulation material, susceptibility of the insulation to external environmental influences and forces, and uneven stress distribution.

[0004] Therefore, in order to ensure the safe and stable operation of offshore overhead transmission lines, it is necessary to carry out targeted insulation protection design for the conductors of offshore overhead transmission lines. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides an offshore overhead transmission line based on partial insulation and a design method, so as to solve the problem of line surface corrosion caused by the external environment of existing offshore overhead transmission lines, thereby achieving the effect of improving the safety and stability of offshore overhead transmission lines.

[0006] In a first aspect, the present invention provides a design method for an offshore overhead transmission line based on partial insulation, the method comprising:

[0007] An insulating layer is provided at the lowest point of the sag of the bare conductor of an offshore overhead transmission line, and stress cones are provided at the joints at both ends of the insulating layer; wherein the electrical parameters of the insulating layer are determined by an insulation optimization model based on three-dimensional simulation modeling, and the electrical parameters include insulation length, insulation thickness, and dielectric constant of the insulating material;

[0008] The insulating layer is connected to the bare conductor via a wire crimping tube to form a portion of the insulated conductor of an offshore overhead power transmission line;

[0009] A fixed pulley device is provided on each tower, a weight is hung below the fixed pulley device, and the insulating pull wire of the fixed pulley device is connected to the part of the insulated wire to lift the lowest point of the sag of the part of the insulated wire.

[0010] Furthermore, the step of calculating the electrical parameters of the insulating layer includes:

[0011] An insulation optimization model is established with minimization of insulation cost as the objective function and the constraint that the surface field strength of the insulation layer under different voltage conditions is less than the field strength threshold;

[0012] Solving the insulation optimization model to obtain electrical parameters of the insulation layer;

[0013] The surface field strength is obtained by data fitting based on a three-dimensional simulation model of an offshore overhead transmission line. The insulation layer is centered at the lowest point of the sag and extends a single-side insulation length to both sides of the lowest point of the sag. The single-side insulation length is determined based on the span of the offshore overhead transmission line.

[0014] The single-side insulation length is expressed by the following formula:

[0015]

[0016] In the formula, s represents the insulation length on one side, β represents the proportional coefficient, and L represents the spacing. Indicates additional length.

[0017] Furthermore, the step of taking the surface field strength of the insulating layer under different voltage conditions as a constraint condition to be less than a field strength threshold comprises:

[0018] Establish a three-dimensional simulation model of partially insulated offshore overhead transmission lines;

[0019] According to the three-dimensional simulation model, under power frequency voltage conditions and operating overvoltage conditions, data fitting is performed on the insulation thickness of the insulation layer, the dielectric constant of the insulation material, and the surface field strength to obtain the power frequency surface field strength and the overvoltage surface field strength of the insulation layer;

[0020] The first constraint condition is that the power frequency surface field strength is less than or equal to the corona initiation field strength on the bare conductor surface, and the second constraint condition is that the overvoltage surface field strength is less than or equal to the surface field strength on the bare conductor surface.

[0021] Furthermore, the first constraint condition is expressed by the following formula:

[0022]

[0023]

[0024] Where, E1 represents the power frequency surface field strength, E0 represents the corona initiation field strength on the bare conductor surface, k represents the safety factor, A1, B1, C1 and D1 all represent the power frequency condition fitting coefficients, m represents the insulation thickness, The dielectric constant of the insulating material representing the insulating layer;

[0025] The second constraint condition is expressed as follows:

[0026]

[0027]

[0028] Where, represents the overvoltage surface field strength, represents the surface electric field strength of the bare conductor, and A2, B2, C2 and D2 represent the fitting coefficients of the overvoltage condition.

[0029] Furthermore, the step of solving the insulation optimization model to obtain the electrical parameters of the insulation layer includes:

[0030] Obtaining an insulation length of the insulation layer according to the span of the offshore overhead transmission line;

[0031] According to the insulation length, using a linear programming algorithm, the objective function is solved under the first constraint condition to obtain a first initial parameter group, and the objective function is solved under the second constraint condition to obtain a second initial parameter group, wherein the first initial parameter group and the second initial parameter group are both parameter groups based on insulation thickness and dielectric constant;

[0032] An intersection operation is performed on the first initial parameter group and the second initial parameter group to obtain electrical parameters of the insulating layer.

[0033] Furthermore, the cone surface of the stress cone adopts a straight cone surface, and the thickness of the winding insulation layer of the stress cone is determined by the surface field strength constraint;

[0034] The axial length of the stress cone is determined by the axial field strength constraint.

[0035] Furthermore, the thickness of the winding insulation layer is expressed by the following formula:

[0036]

[0037] Where △d represents the thickness of the winding insulation layer, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, represents the dielectric constant of the insulating material of the insulating layer, Indicates the dielectric constant of the insulating material of the added insulation layer, U1 indicates the power frequency voltage, En Indicates the maximum working field strength on the surface of the wound insulation layer;

[0038] The axial length is expressed by the following formula:

[0039]

[0040] Where, L k Indicates the axial length, E t represents the axial field strength, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, R n Indicates the outer radius of the added insulation layer.

[0041] Furthermore, after the step of obtaining the electrical parameters of the insulating layer, the method further includes:

[0042] Inputting electrical parameters of the insulating layer and parameters of the stress cone into the three-dimensional simulation model, wherein the parameters of the stress cone include a cone surface, a thickness of the winding insulating layer, and an axial length;

[0043] Under power frequency voltage conditions and operation overvoltage conditions, simulations are carried out respectively to obtain power frequency simulated surface field strength and overvoltage simulated surface field strength;

[0044] Determining whether the power frequency simulated surface field strength satisfies the first constraint condition, and whether the overvoltage simulated surface field strength satisfies the second constraint condition;

[0045] If any one of the conditions is not satisfied, the insulation optimization model is solved again until the power frequency simulated surface field strength satisfies the first constraint condition and the overvoltage simulated surface field strength satisfies the second constraint condition.

[0046] Furthermore, the bare wires on both sides of the insulation layer are covered with heat shrink tubes of a preset length.

[0047] In a second aspect, the present invention provides an offshore overhead power transmission line based on partial insulation, wherein the offshore overhead power transmission line is designed using the method described above.

[0048] The present invention provides an offshore overhead transmission line based on partial insulation and a design method. Based on the traditional bare conductor, the present invention adds an insulation layer of appropriate thickness and length to meet the special needs of the offshore transmission environment, thereby reducing electrical breakdown and insulation damage caused by environmental factors. While the conductor installation height remains unchanged, the withstand voltage and current capabilities of the offshore transmission conductor are effectively enhanced, thereby significantly improving the working stability of the conductor in a high voltage and high current environment and effectively reducing the occurrence rate of faults. The present invention optimizes the conductor withstand voltage performance and mechanical stability of the offshore overhead transmission line through a local insulation layer, a fixed pulley and an insulating wire pulling device, and a stress cone structure, thereby improving the performance of the offshore transmission system, significantly reducing the risk of corrosion and discharge of the transmission line due to the offshore environment, and laying a solid foundation for ensuring the reliability of offshore power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 1 is a flow chart of a design method for a partially insulated offshore overhead transmission line according to an embodiment of the present invention;

[0050] Figure 2 Schematic diagram of the layout of an offshore overhead transmission line based on partial insulation in an embodiment of the present invention;

[0051] Figure 3 yes Figure 1 Schematic diagram of the structure of the middle stress cone 4.

[0052] Reference numerals:

[0053] 1. Insulated conductor; 2. First heat shrink tubing; 3. Bare conductor; 4. Stress cone; 5. Wire crimping tube; 6. Insulation layer; 7. First bare conductor; 8. Insulated pulley; 9. Fixed pulley assembly; 10. Pole tower; 11. Heavy object.

[0054] 41. Shielding layer; 42. Stress cone conductor; 43. Winding insulation layer; 44. Second heat shrink tube; 45. Waterproof shell. DETAILED DESCRIPTION

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0056] Before describing the present invention in detail, the relevant terms used in the present invention are first explained:

[0057] (1) Insulation layer: refers to the insulating material layer between heating wires or between heating wires and ground shielding layer. It is mainly used to isolate wires to prevent people from electric shock and injury. The wire insulation layer is a non-conductive insulating material wrapped around the outer surface of the wire to enhance the insulation of the wire, such as resin, plastic, silicone rubber, PVC, etc., forming an insulating layer to prevent the conductor from contacting the outside world and causing leakage, short circuit, electric shock and other accidents.

[0058] (2) Conductor joint: A conductor joint is a structure or device that connects two sections of conductors or conductors to other equipment components in a power system. Its main function is to ensure the stability of conductive performance while providing sufficient mechanical strength and environmental protection to adapt to various operating conditions. In overhead transmission lines, conductor joints are usually crimped or mechanically clamped to cope with line vibration and tension changes. In cable systems, the design of conductor joints is more complex and must take into account both electric field balancing (such as the use of stress cones) and sealing performance.

[0059] (3) Fixed pulley cable: Fixed pulley cable refers to a rope or steel cable connected to a fixed pulley, which is a linear structure used to transmit force and realize mechanical operation. The fixed pulley itself is a simple machine that is fixed and motionless, and the cable plays a key role in this system. It is both a carrier of force and a medium for changing the direction of force. In the lifting system, the cable transmits the downward gravity and converts it into an upward pulling force through the pulley, thereby achieving vertical lifting of the object. In the construction of overhead lines, the cable adjusts the tension and sag of the conductor through the fixed pulley to ensure the stability of the line structure.

[0060] (4) Stress cone: Stress cone is a structural design or device used for high-voltage cable terminals and joints in power engineering. Its function is to alleviate the electric field stress concentration phenomenon in the high-voltage electric field, thereby improving the safety and reliability of the insulation system. The design of the stress cone prevents the insulation material from being broken down or aging prematurely due to excessive local stress by optimizing the electric field distribution. The main functions are to alleviate the electric field concentration phenomenon caused by the termination of the cable shield or the connection of the joint, avoiding local excessive electric field stress; prevent the electric field concentration from damaging the cable insulation material, thereby extending the service life of the insulation material; reduce the risk of local discharge or insulation breakdown in the cable terminal and joint area, and improve the safety of system operation.

[0061] See also Figure 1 The first embodiment of the present invention provides a design method for a partially insulated offshore overhead transmission line, which includes steps S10 to S30:

[0062] Step S10: providing an insulation layer at the lowest point of the sag of the bare conductor of the offshore overhead transmission line, and providing stress cones at the joints at both ends of the insulation layer; wherein the electrical parameters of the insulation layer are determined by an insulation optimization model based on three-dimensional simulation modeling, and the electrical parameters include insulation length, insulation thickness, and dielectric constant of the insulation material;

[0063] Step S20, connecting the insulating layer and the bare wire through a wire crimping tube to form a partially insulated wire of an offshore overhead transmission line;

[0064] Step S30: installing a fixed pulley device on each tower, hanging a load-bearing object below the fixed pulley device, and connecting the insulating pulley wire of the fixed pulley device to the partially insulated conductors to lift the lowest sag section of the partially insulated conductors.

[0065] The present invention addresses the high humidity and high salt spray environments of offshore overhead transmission lines. By adding insulated conductors to the bare conductors, these conductors must not only exhibit excellent electrical insulation properties but also possess high voltage withstand capability and mechanical strength to withstand erosion and damage from marine salt spray, moisture, and high-intensity winds and waves. Offshore transmission lines commonly operate at medium to high voltages, placing very high demands on the insulation material's withstand voltage. If the insulation of the conductor is distributed over the entire length of the conductor, without centralized insulation at a specific location, problems such as high insulation material usage, susceptibility of the insulation to the external environment and forces, and uneven stress on the insulation can easily arise. To address these issues, the present invention proposes a novel design method for offshore overhead transmission lines, concentrating the insulation of the conductor at the lowest point of the bare conductor's sag. Sag refers to the natural curve of the conductor between two towers. In offshore transmission lines, the lowest point of the sag is where the conductor is closest to the sea level and has the greatest impact.

[0066] A key challenge for offshore overhead transmission lines compared to fixed-land overhead transmission lines is the periodic fluctuations in sea level caused by wave motion. As sea levels rise, the safe distance between conductors and the sea surface decreases, making them more susceptible to the effects of the humid seawater environment. Consequently, stricter requirements are placed on the conductor's electrical insulation strength. The lowest point of the line, where the conductor sag reaches its lowest point, is particularly susceptible to environmental influences.

[0067] Therefore, the insulation part of the conductor is set at the lowest point of the sag to ensure that the suspension height and insulation performance of the conductor can be effectively guaranteed under harsh marine conditions, thereby maximizing the safety and reliability of the line.

[0068] In this embodiment, the bare conductor at the lowest point of the sag between the two towers is covered with an insulating layer to achieve insulation protection for the bare conductor at the sag. Figure 2 An insulation layer is installed at the lowest point of the sag of the bare conductor 3 between the two towers 10. This insulation layer and the first bare conductor it encases together form the insulated conductor 1. Specifically, the insulated conductor comprises the insulation layer 6 and the first bare conductor 7, with the first bare conductor 7 being part of the bare conductor 3. This arrangement not only conforms to the laws of gravity and stress distribution but also significantly reduces the adverse effects of line sag on offshore operations. This optimized design ensures smoother operation of the transmission line, demonstrating enhanced reliability, particularly in complex environments such as wind loads and offshore conditions.

[0069] The insulating layer 6 and the bare conductor 3, or rather, the insulated conductor 1 and the bare conductor 3, are connected via a wire crimping tube 5. The wire crimping tube 5 is L-shaped. As a key transition component, its unique shape and material ensure excellent electrical conductivity while preventing loosening or oxidation at the contact points, further enhancing the reliability of the entire line. In other words, in this embodiment, by adding an insulating layer to the bare conductor of a conventional offshore overhead transmission line, the offshore overhead transmission line becomes partially insulated.

[0070] Optionally, to comprehensively enhance the safety of the bare conductors, a first heat-shrink tubing 2 of a predetermined length is applied to the bare conductors 3 on both sides of the insulated conductor 1. The specific length can be adjusted adaptively based on the offshore transmission line's environmental conditions and installation costs. This heat-shrink tubing, securely wrapped around the line surface through a heat-shrinking process, effectively improves insulation and prevents environmental corrosion such as rain, dust, and salt spray. It also provides mechanical protection for the bare conductors, extending the line's service life.

[0071] In order to effectively balance the internal electric field distribution at the joint between the insulated wire 1 and the bare wire 3, this embodiment provides a stress cone 4 at the two end joints of the insulated wire 1. The main function of the stress cone is to strictly control the electric field strength inside the joint within the design range by increasing the shielding diameter, thereby achieving effective balance of the electric field distribution inside the joint.

[0072] Furthermore, to further optimize the conductor sag height and enhance the overall safety of the line, in this embodiment, a fixed pulley assembly 9 is installed on each tower 10. Since the tower is erected offshore, in this embodiment, the tower 10 comprises the tower itself and a floating platform beneath it. Specifically, the fixed pulley assembly 9 is installed near the three-phase conductors of the tower 10. Through its rational mechanical structure, the fixed pulley assembly 9 provides a stable support platform capable of accommodating the insulating cable 8 and ensuring the accuracy of the force applied to it. One end of the insulating cable 8 is securely connected to the fixed pulley assembly 9, while the other end is connected to a point on a portion of the insulating cable. A weight 11 of appropriate weight is suspended below the fixed pulley assembly 9. The weight 11 provides a continuous and uniform force to the insulating cable 8, enabling it to exert an upward pull on the conductor. This design allows the lowest sag point of the three-phase conductor to be appropriately raised while maintaining the height of the tower 10. This adjustment greatly optimizes the sag distribution of the conductors, effectively reducing the relative distance between the lowest point of the line and the sea level, thereby significantly reducing the risk of discharge due to the conductors being too low.

[0073] In this embodiment, the fixed pulley assembly 9 is constructed of materials and structures that are highly strong, corrosion-resistant, and durable, ensuring that it will not fail during long-term operation due to wind vibration, temperature differences, or tension fluctuations. The insulating pull wire 8 is selected to balance insulation performance and mechanical strength. Its exterior material offers excellent resistance to electric shock and weathering, maintaining stable performance even in harsh environments. The mass of the suspended weight 11 is rigorously calculated to ensure sufficient tension to elevate the lowest point of the sag while also preventing excessive weight from causing localized stress on the wire or damage to the pulley structure.

[0074] For the above structure, the electrical parameters of the insulation layer in this embodiment include insulation length, insulation thickness, and the dielectric constant of the insulation material. Insulation length refers to the length of the insulation layer, and insulation thickness refers to its thickness. Since different insulation materials have different dielectric constants, determining the dielectric constant effectively determines the insulation material used for the insulation layer. The stress cone parameters include the cone surface, the thickness of the insulation layer, and the axial length.

[0075] In this embodiment, the electrical parameters of the insulation layer can be determined by performing a three-dimensional simulation model of an existing offshore overhead transmission line. The electrical field strength of the conductors under different electrical parameters is simulated to determine whether it meets the design requirements. The stress cone parameters can be conventional stress cone parameters used in existing cable joints, or simulation can be performed within the aforementioned three-dimensional simulation model to determine stress cone parameters that optimize transmission performance.

[0076] In a preferred embodiment, the present invention calculates the electrical parameters of the insulation layer by establishing an insulation optimization model based on a three-dimensional simulation model, and the specific steps include:

[0077] An insulation optimization model is established with minimization of insulation cost as the objective function and the constraint that the surface field strength of the insulation layer under different voltage conditions is less than the field strength threshold;

[0078] Solving the insulation optimization model to obtain electrical parameters of the insulation layer;

[0079] The surface field strength is obtained by data fitting based on a three-dimensional simulation model of an offshore overhead transmission line. The insulation layer takes the lowest point of the sag as the center point and extends a single-side insulation length to both sides of the lowest point of the sag. The single-side insulation length is determined based on the span of the offshore overhead transmission line.

[0080] In this embodiment, the objective function F is to minimize the insulation cost:

[0081]

[0082] Where m represents the insulation thickness, S represents the insulation length, represents the dielectric constant of the insulating material of the insulating layer, Represents the comprehensive cost function related to insulation thickness, insulation length, and dielectric constant.

[0083] The constraint condition of the model is that the surface field strength of the insulating layer under different voltage conditions is less than the field strength threshold. In a preferred embodiment, the voltage condition includes a power frequency voltage condition and an operating overvoltage condition. The steps of constructing the constraint condition include:

[0084] Establish a three-dimensional simulation model of partially insulated offshore overhead transmission lines;

[0085] According to the three-dimensional simulation model, under power frequency voltage conditions and operating overvoltage conditions, data fitting is performed on the insulation thickness of the insulation layer, the dielectric constant of the insulation material, and the surface field strength to obtain the power frequency surface field strength and the overvoltage surface field strength of the insulation layer;

[0086] The first constraint condition is that the power frequency surface field strength is less than or equal to the corona initiation field strength on the bare conductor surface, and the second constraint condition is that the overvoltage surface field strength is less than or equal to the surface field strength on the bare conductor surface.

[0087] In this example, a three-dimensional simulation model of a partially insulated offshore overhead transmission line was first established. The model assumed the offshore overhead transmission line used double-split LGJ-400 / 35 steel-core aluminum stranded conductors. Phases A, B, and C were arranged horizontally, with a subconductor radius of 13.4 mm and a split spacing of 0.45 m. The horizontal phase spacing between adjacent phases at the pollution level was 5.11 m. The conductor sag, represented by a catenary curve, was 8.54 m. The height of the lowest point of the sag relative to sea level was set at 14 m. A three-span model was established, with each span being 350 m, for a total length of 1050 m.

[0088] In the above three-dimensional simulation model, under power frequency voltage conditions, the insulation thickness of different insulation layers, the dielectric constant of the insulation material, and the surface field strength are simulated. For example, when power frequency voltage is applied to the conductor, the thickness of the insulation layer is increased from 1 mm to 10 mm, and the insulation material of some insulated conductors is changed. Finally, the obtained insulation thickness of the insulation layer, the dielectric constant of the insulation material, and the surface field strength are fitted to obtain the fitting relationship expression between the surface field strength of the insulation layer and the insulation thickness of the insulation layer and the dielectric constant of the insulation material under power frequency voltage conditions:

[0089]

[0090] Where, E1 represents the surface field strength of the insulation layer under power frequency conditions, that is, the power frequency surface field strength; A1, B1, C1, and D1 all represent the power frequency condition fitting coefficients; m represents the insulation thickness. Indicates the dielectric constant of the insulating material of the insulation layer.

[0091] To ensure that the maximum electric field strength on the conductor surface remains within a safe range after adding insulated conductors, the power frequency surface field strength of the insulation layer should not be greater than the corona inception field strength on the bare conductor surface. Considering that in marine environments, the surface of the conductor may increase humidity due to the adhesion of water droplets, thereby affecting the surface field strength, the coefficient k is introduced to provide a certain safety margin. In other words, the power frequency surface field strength also needs to meet the following requirements:

[0092]

[0093] Where E0 represents the corona initiation field strength on the bare conductor surface, and k represents the safety factor. The value of k is optional and ranges from 1 to 4.

[0094] Because power frequency voltage is a continuous AC voltage, its electric field distribution is relatively stable and varies periodically. By analyzing the electrical parameters of the insulation layer under power frequency voltage, we can ensure that the electric field strength does not exceed the material's tolerance limit during long-term operation. Furthermore, due to the inevitable extreme conditions encountered in offshore overhead transmission lines, such as transient high-voltage pulses caused by switching operations, these pulses are characterized by amplitudes up to 2-3 times the power frequency voltage and short durations. Transient high electric fields can cause partial discharge or breakdown. Therefore, the electrical parameters of the insulation layer also need to be verified for the safety of the insulation design under extreme conditions to ensure that the transient electric field peak is below the breakdown threshold.

[0095] In this embodiment, the second constraint condition is a constraint on the surface field strength of the insulating layer under an operating overvoltage condition. The calculation steps are similar to those for the first constraint condition. In a three-dimensional simulation model, an operating overvoltage at a high voltage level is applied to the conductor, the thickness of the insulating layer is increased from 1 mm to 10 mm, and the material of some insulated conductors is changed. Finally, the obtained insulation thickness of the insulating layer, the dielectric constant of the insulating material, and the surface field strength are fitted to obtain a fitting relationship expression between the surface field strength of the insulating layer and the insulation thickness of the insulating layer and the dielectric constant of the insulating material under the operating overvoltage condition:

[0096]

[0097] Where, It represents the surface field strength of the insulating layer under the operating overvoltage condition, that is, the overvoltage surface field strength. A2, B2, C2 and D2 all represent the overvoltage condition fitting coefficients.

[0098] By applying a switching overvoltage at the corresponding voltage level on the surface of the conductor, the electric field strength on the surface of the bare conductor can be obtained. To ensure the safety of the line, the surface field strength of the insulation layer should be less than or equal to the electric field strength on the surface of the bare conductor. Therefore, under the switching overvoltage condition, the overvoltage surface field strength also needs to meet the following requirements:

[0099]

[0100] Where, Indicates the surface electric field strength of the bare conductor.

[0101] By solving the above two constraints, multiple sets of parameters based on insulation thickness and dielectric constant can be obtained. With respect to insulation length, since the length of the insulation layer has little effect on the electric field on the surface of the insulation layer of the conductor, and in order to ensure the insulation performance of the lowest point of the sag and its surrounding areas, the length of the insulated conductor needs to cover a certain range on both sides of the lowest point of the sag. Therefore, in this embodiment, the single-sided insulation length on one side of the lowest point of the sag is calculated based on the span and sag height of the transmission line, and the entire insulation length of the insulation layer can be obtained by multiplying the single-sided insulation length by 2.

[0102] In this embodiment, the single-side insulation length s is expressed by the following formula:

[0103]

[0104] In the formula, β represents the proportional coefficient, L represents the gear distance, Indicates additional length.

[0105] The span of an offshore overhead transmission line refers to the horizontal distance L between two adjacent towers of the conductor. The span determines the geometry and maximum sag of the conductor. The lowest point of the conductor sag is the center point of the span, which is at L / 2. According to the catenary approximation formula, the sag can be expressed as:

[0106]

[0107] Where, f c represents sag, L represents span, w represents weight per unit length of conductor, and T represents horizontal tension of conductor.

[0108] Therefore, in actual scenarios, the greater the sag, the closer the lowest point of the conductor is to the sea level, and the higher the insulation requirement. Therefore, the insulation length can be determined by analyzing the sag. According to the above formula, the relationship between the sag and the square of the span is positively correlated. In order to simplify the calculation, in this embodiment, the span is used as an input parameter to determine the single-sided insulation length of the insulation layer.

[0109] In the above single-side insulation length formula, β represents the proportional coefficient, which is used to compensate for the span calculation error or dynamic load influence. The range of β is optional and is between 5% and 10%. It is an additional length used to cover local environmental differences (such as areas with sudden changes in salt spray concentration) or mechanical stress concentration points. These two values can be adjusted for applicability based on the specific weather environment of the offshore overhead transmission line.

[0110] After determining the single-side insulation length according to the span of the offshore overhead transmission line, the single-side insulation length is multiplied by 2 to obtain the insulation length S of the entire insulation layer, that is, S=2*s.

[0111] In this embodiment, a linear programming algorithm is used to calculate the objective function, and the specific steps include:

[0112] Obtaining an insulation length of the insulation layer according to the span of the offshore overhead transmission line;

[0113] According to the insulation length, using a linear programming algorithm, the objective function is solved under the first constraint condition to obtain a first initial parameter group, and the objective function is solved under the second constraint condition to obtain a second initial parameter group, wherein the first initial parameter group and the second initial parameter group are both parameter groups based on insulation thickness and dielectric constant;

[0114] An intersection operation is performed on the first initial parameter group and the second initial parameter group to obtain electrical parameters of the insulating layer.

[0115] In this embodiment, the length of the insulation layer is first determined based on the insulation length formula. Since the insulation length has been determined, It can be equivalent to a function based on the insulation thickness and dielectric constant , for this objective function In this embodiment, the simplex method is preferably used to solve the objective function under different constraints. Taking the first constraint as an example, the calculation steps are as follows:

[0116] Insulation thickness m and dielectric constant As the independent variable, according to the actual situation, set , To convert the inequality constraints into equality constraints, for the first constraint:

[0117]

[0118] Introduce the slack variable t so that:

[0119]

[0120] Therefore, for the objective function , its first constraint is converted from inequality to equality constraint and non-negativity constraint.

[0121] The simplex method can be used to solve the converted objective function and constraints. The simplex method is a standard algorithm for solving linear programming problems. Its steps include:

[0122] Normalization problem: Inequality constraints are transformed into equality by introducing slack variables.

[0123] Construct an initial simplex table: including the objective function coefficients, the constraint equation coefficient matrix, and the constant term on the right side.

[0124] Select variables to be included in the basis: Determine the variables to be included in the basis through the maximum number of positive tests.

[0125] Select variables to be removed from the basis: Determine the variables to be removed from the basis through the minimum ratio test.

[0126] Update basis variables and simplex tables: Generate new basis feasible solutions through row transformation.

[0127] Iteration termination condition: all test numbers are non-positive (maximization problem) or non-negative (minimization problem).

[0128] It can be seen that this embodiment achieves problem standardization by converting the objective function and the constraints into equations. Based on the standardized problem, the conventional steps of the simplex method can be used to solve it, thereby obtaining the first initial parameter group, that is, the parameter group consisting of the insulation thickness and the dielectric constant.

[0129] Similarly, under the second constraint condition, the objective function and the second constraint condition are standardized by introducing slack variables, and a linear solution is performed using the simplex method to obtain the second initial parameter group.

[0130] In this embodiment, the first initial parameter group and the second initial parameter group are the insulation thickness and dielectric constant under different voltage conditions. In order to make the insulation layer meet the power transmission safety requirements under both power frequency voltage and operating overvoltage conditions, the final insulation thickness and dielectric constant can be obtained by performing an intersection operation on the two parameter groups. Since the insulation length has been determined in the early stage, the final electrical parameters of the insulation layer can be obtained.

[0131] Since the stress cone needs to be designed based on the electrical parameters of the insulation layer, the stress cone part is not simulated in the above 3D simulation model. Instead, the stress cone parameters at the insulation layer joint are designed based on the insulation layer after the electrical parameters of the insulation layer are determined. Figure 3 The stress cone 4 is set at the joint of the insulated wire 1 (including the insulating layer 6 and the first bare wire 7). The outer side of the insulating layer 6 is covered with a shielding layer 41, a stress cone conductor 42 and a winding insulating layer 43. The parameters of the stress cone 4 mainly include the geometric configuration of the cone surface (such as Figure 3 AB segment shown), the thickness of the winding insulation layer △d and the axial length L x .

[0132] Specifically, the geometric configuration of the cone surface of the stress cone can be divided into ideal stress cone, single straight line cone and double straight line cone. Among them, the ideal stress cone refers to the cone surface designed according to the ideal electric field distribution curve (logarithmic curve), the single straight line cone refers to the ideal curve approximated by a single straight line, and the endpoint coincides with the ideal curve, and the double straight line cone refers to the ideal curve approximated by two straight lines with different slopes.

[0133] Since the wrapping process of a single straight cone is the simplest, the least amount of insulating material is used, and it has a better uniform field effect, in order to facilitate on-site construction and minimize the errors caused by workers in the manual wrapping process, this embodiment adopts a single straight cone, that is, the stress cone surface at the joint of some insulated wires is selected to be a straight cone surface with the same endpoint as the ideal stress cone curve, such as Figure 3 As shown, segment AB is a straight cone surface.

[0134] The stress cone 4 is a key component for uniform electric field distribution at the joint of some insulated wires. The thickness of the winding insulation layer of the stress cone 4 is determined by the electric field intensity constraint. The axial length L of the stress cone is x Determined by the axial field strength constraint, specifically, the thickness of the added insulation layer of the stress cone is determined by the difference between the outer radius of the added insulation layer of the stress cone and the outer radius of the insulation layer of the partially insulated conductor:

[0135]

[0136] Among them, △d represents the thickness of the winding insulation layer, R represents the outer radius of the insulation layer, R n Indicates the outer radius of the added insulation layer.

[0137] according to Figure 3 It can be seen that the insulation layer outer radius R is actually the conductor radius of the partially insulated conductor, that is, it is composed of the thickness of the insulation layer 6 and the radius of the first bare conductor 7. The additional insulation layer outer radius is the outer radius of the entire additional insulation layer with the additional insulation layer thickness added to the insulation layer outer radius.

[0138] Calculate the electric field of a cylinder with a radius r( ) is:

[0139]

[0140] Where U1 represents the power frequency voltage, U2 represents the voltage at the interface between the insulation layer and the winding insulation, r represents the radius of the insulation layer, and r represents the power frequency voltage. c It represents the outer radius of the bare conductor, and R represents the outer radius of the insulation layer.

[0141] The power frequency voltage in this embodiment is also the power frequency withstand voltage test voltage. According to industry standards, for a 220kV line, the test voltage is 127kV. The power frequency withstand voltage test voltage should be 2.5 times the test voltage, that is, 318kV, and the withstand time is 30 minutes. Therefore, when performing stress cone electrical structure calculations in this embodiment, the power frequency voltage is set to 318V.

[0142] Maximum working field strength E of the conductor max It can be expressed as:

[0143]

[0144] The thickness of the winding insulation layer can be calculated based on the maximum working field strength E of the winding insulation layer. n To determine, generally take the maximum working field strength E of the conductor max Therefore:

[0145]

[0146] Radius r of the added insulation layer n ( ) at the power frequency surface field strength for:

[0147]

[0148] Where R n Indicates the outer radius of the added insulation layer.

[0149] On the contact surface between the insulation layer and the additional winding insulation, the following conditions are met:

[0150]

[0151] Where, represents the dielectric constant of the insulating material of the insulating layer, The dielectric constant of the insulating material of the added insulation layer, Indicates the power frequency surface field strength at the maximum radius in the insulation layer, It indicates the power frequency surface field strength at the minimum radius in the added insulation layer.

[0152] From this we can solve:

[0153]

[0154] Where △d represents the thickness of the winding insulation layer, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, represents the dielectric constant of the insulating material of the insulating layer, Indicates the dielectric constant of the insulating material of the winding insulation layer, E n Indicates the maximum working field strength on the surface of the wound insulation layer.

[0155] According to the fact that the electric displacement remains constant at the interface between the inner and outer interfaces of the insulating layer, and based on the Gaussian formula, it can be known that the electric field strength is inversely proportional to the radius under cylindrical geometry, the thickness of the winding insulating layer can be calculated based on the maximum working field strength E on the surface of the winding insulating layer. nTo determine, preferably, the safety threshold is set according to 45% to 60% of the working field strength E1 of the insulated wire. Therefore, the maximum working field strength on the surface of the additional winding insulation layer should be less than or equal to the safety threshold. Under this condition, the thickness of the additional winding insulation layer can be expressed as:

[0156]

[0157] Where △d represents the thickness of the winding insulation layer, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, represents the dielectric constant of the insulating material of the insulating layer, Indicates the dielectric constant of the insulating material of the added insulation layer, U1 indicates the power frequency voltage, E n Indicates the maximum working field strength on the surface of the wound insulation layer.

[0158] The axial field strength of the stress cone 4 is set to be less than or equal to the maximum allowable axial field strength. Therefore, the axial field strength E at any point on the stress cone surface is t The radial field strength E at this point should have the following relationship:

[0159]

[0160] Where α represents the angle between the electric field direction and the normal direction of the stress cone surface.

[0161] The radial field strength E is still calculated based on the cylindrical electric field. Figure 3 Draw an xy plane diagram with the lower left corner of the first bare conductor 7 as the origin. For the insulated cable, the following should be obtained:

[0162]

[0163]

[0164] Where y represents the ordinate, R represents the outer radius of the insulation layer, represents the dielectric constant of the insulating material of the insulating layer, Represents the dielectric constant of the insulating material of the winding insulation layer, r c Indicates the outer radius of the bare conductor.

[0165] After simplifying the above, we can get:

[0166]

[0167] Substitute E into the axial field strength formula and calculate E t integral:

[0168]

[0169] Where x represents the horizontal coordinate.

[0170] If E t is a constant, so that the axial electric field intensity along the surface is a constant, then the ideal stress cone AB surface equation can be obtained:

[0171]

[0172] Thus we get:

[0173]

[0174] When y=R n When x=L k This is the ideal stress cone axial length. If the insulation layer and the additional winding insulation layer are made of the same material, that is, Since the straight cone surface and the curved cone surface share the same endpoint, the axial length of the stress cone of the straight cone surface is:

[0175]

[0176] Where, L k Indicates the axial length, E t represents the axial field strength, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, R n Indicates the outer radius of the added insulation layer.

[0177] From the above formula, we can see that E t The smaller the value, the k The longer the length, the longer the length of the connection box. Therefore, when designing the connection box for cable connection, E is generally used. t The maximum permissible axial field strength of the insulation layer of the connection box is used to shorten the size of the connection box. t The value is generally taken as 1 / 10~1 / 20 of the maximum working field strength of the cable body.

[0178] To further ensure the safety of the transmission line, the stress cone 4 is encapsulated and protected by a second heat-shrink tubing 44 and a waterproof outer shell 45, supplemented by a water-absorbent insulating material (such as superabsorbent polymer / SAP or silicone) to form a composite protective system. The second heat-shrink tubing 44, a thermoplastic polymer, shrinks radially upon heating, tightly wrapping the joint and creating a uniform insulation barrier that blocks the intrusion of moisture, dust, and contaminants, reducing the risk of electrochemical corrosion and short circuits. Its high dielectric strength enhances the electrical safety of the joint while also providing mechanical reinforcement for tensile, compressive, and impact resistance. The water-absorbent material actively captures and holds ambient moisture through physical adsorption or chemical bonding, suppressing humidity buildup within the joint and slowing down insulation aging and electrochemical corrosion. When combined with the second heat shrink tube 44, the two form a double-layer protective structure: the outer second heat shrink tube 44 provides physical isolation and mechanical protection, and the inner layer of water-absorbing material realizes dynamic humidity control, significantly improving the long-term reliability and environmental adaptability of the joint, thereby extending the service life of the cable system and improving its operational stability, and has broad application prospects. The stress cone design of this embodiment not only shows a high degree of stability and safety in the mechanical structure, but also has significant advantages in optimizing electrical performance. Key components such as heat shrinkable sealing tubes, flanges, sealing rings and stress cones complement each other and together constitute a set of complex and efficient connection solutions. This design fully takes into account the various complex working conditions in the actual operating environment, thereby providing a solid guarantee for the reliable operation of overhead transmission lines.

[0179] In a preferred embodiment, the present invention simulates the above parameters through a three-dimensional simulation model to determine whether some insulated wires under the parameters meet the constraint conditions. The specific steps include:

[0180] Inputting electrical parameters of the insulating layer and parameters of the stress cone into the three-dimensional simulation model, wherein the parameters of the stress cone include a cone surface, a thickness of the winding insulating layer, and an axial length;

[0181] Under power frequency voltage conditions and operation overvoltage conditions, simulations are carried out respectively to obtain power frequency simulated surface field strength and overvoltage simulated surface field strength;

[0182] Determining whether the power frequency simulated surface field strength satisfies the first constraint condition, and whether the overvoltage simulated surface field strength satisfies the second constraint condition;

[0183] If any one of the conditions is not satisfied, the insulation optimization model is solved again until the power frequency simulated surface field strength satisfies the first constraint condition and the overvoltage simulated surface field strength satisfies the second constraint condition.

[0184] In this embodiment, the stress cone is added to the three-dimensional simulation model, and the design parameters are simulated through the three-dimensional simulation model to determine whether some insulated conductors meet the constraints of the surface field strength. If not, the design parameters need to be corrected, thereby further ensuring the transmission safety of the offshore overhead transmission line.

[0185] This embodiment provides a design method for partially insulated offshore overhead transmission lines. Based on traditional bare conductors, the present invention adds an insulation layer of appropriate thickness and length to meet the special needs of the offshore transmission environment. This reduces electrical breakdown and insulation damage caused by environmental factors. While maintaining the conductor installation height, the method effectively enhances the offshore transmission conductor's withstand voltage and current capabilities, significantly improving the conductor's operating stability in high-voltage and high-current environments and effectively reducing the incidence of failures. The present invention optimizes the conductor's withstand voltage and mechanical stability of the offshore overhead transmission line through a partial insulation layer, fixed pulleys, an insulation pulley device, and a stress cone structure. This improves the performance of the offshore transmission system and significantly reduces the risk of corrosion and discharge caused by the offshore environment, laying a solid foundation for ensuring the reliability of offshore power supply.

[0186] Based on the same inventive concept, a second embodiment of the present invention proposes an offshore overhead transmission line based on partial insulation, and the offshore overhead transmission line is designed using the method described above.

[0187] In summary, an embodiment of the present invention proposes a partially insulated offshore overhead transmission line and design method, wherein the method provides an insulating layer at the lowest point of the sag of the bare conductor of the offshore overhead transmission line and provides stress cones at the joints at both ends of the insulating layer; wherein the electrical parameters of the insulating layer are determined by an insulation optimization model based on three-dimensional simulation modeling, and the electrical parameters include insulation length, insulation thickness, and dielectric constant of the insulating material; the insulating layer is connected to the bare conductor through a wire tube to form a partially insulated conductor of the offshore overhead transmission line; a fixed pulley device is provided on each tower, a weight is suspended below the fixed pulley device, and the insulation cable of the fixed pulley device is connected to the partially insulated conductor to raise the lowest point of the sag of the partially insulated conductor. The present invention optimizes the conductor withstand voltage performance and mechanical stability of the offshore overhead transmission line through the local insulation layer, the fixed pulley and the insulation cable device, and the stress cone structure, thereby improving the performance of the offshore transmission system and significantly reducing the risk of corrosion and discharge of the transmission line due to the offshore environment, laying a solid foundation for ensuring the reliability of offshore power supply.

[0188] Each embodiment in this specification is described in a progressive manner, and the same or similar parts of each embodiment can be directly referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. It should be noted that the various technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0189] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. A design method for partially insulated offshore overhead transmission lines, characterized in that: include: An insulating layer is provided at the lowest point of the sag of the bare conductor of an offshore overhead transmission line, and stress cones are provided at the joints at both ends of the insulating layer; wherein the electrical parameters of the insulating layer are determined by an insulation optimization model based on three-dimensional simulation modeling, and the electrical parameters include insulation length, insulation thickness, and dielectric constant of the insulating material; The insulating layer is connected to the bare conductor via a wire crimping tube to form a portion of the insulated conductor of an offshore overhead power transmission line; A fixed pulley device is provided on each tower, a weight is suspended below the fixed pulley device, and an insulating pull wire of the fixed pulley device is connected to the part of the insulated wire to raise the lowest point of the sag of the part of the insulated wire; The step of calculating the electrical parameters of the insulating layer includes: An insulation optimization model is established with minimization of insulation cost as the objective function and the constraint that the surface field strength of the insulation layer under different voltage conditions is less than the field strength threshold; Solving the insulation optimization model to obtain electrical parameters of the insulation layer; The surface field strength is obtained by data fitting based on a three-dimensional simulation model of an offshore overhead transmission line. The insulation layer is centered at the lowest point of the sag and extends a single-side insulation length to both sides of the lowest point of the sag. The single-side insulation length is determined based on the span of the offshore overhead transmission line. The single-side insulation length is expressed by the following formula: In the formula, s represents the insulation length on one side, β represents the proportional coefficient, and L represents the spacing. Indicates additional length; The step of taking the surface field strength of the insulating layer under different voltage conditions as a constraint condition to be less than the field strength threshold comprises: Establish a three-dimensional simulation model of partially insulated offshore overhead transmission lines; According to the three-dimensional simulation model, under power frequency voltage conditions and operating overvoltage conditions, data fitting is performed on the insulation thickness of the insulation layer, the dielectric constant of the insulation material, and the surface field strength to obtain the power frequency surface field strength and the overvoltage surface field strength of the insulation layer; The first constraint condition is that the power frequency surface field strength is less than or equal to the corona initiation field strength on the bare conductor surface, and the second constraint condition is that the overvoltage surface field strength is less than or equal to the surface field strength on the bare conductor surface.

2. The design method of partially insulated offshore overhead transmission lines according to claim 1, characterized in that: The first constraint condition is expressed as follows: Where, E1 represents the power frequency surface field strength, E0 represents the corona initiation field strength on the bare conductor surface, k represents the safety factor, A1, B1, C1 and D1 all represent the power frequency condition fitting coefficients, m represents the insulation thickness, The dielectric constant of the insulating material representing the insulating layer; The second constraint condition is expressed as follows: Where, represents the overvoltage surface field strength, represents the surface electric field strength of the bare conductor, and A2, B2, C2 and D2 represent the fitting coefficients of the overvoltage condition.

3. The design method of partially insulated offshore overhead transmission lines according to claim 1, characterized in that: The step of solving the insulation optimization model to obtain the electrical parameters of the insulation layer includes: Obtaining an insulation length of the insulation layer according to the span of the offshore overhead transmission line; According to the insulation length, using a linear programming algorithm, the objective function is solved under the first constraint condition to obtain a first initial parameter group, and the objective function is solved under the second constraint condition to obtain a second initial parameter group, wherein the first initial parameter group and the second initial parameter group are both parameter groups based on insulation thickness and dielectric constant; An intersection operation is performed on the first initial parameter group and the second initial parameter group to obtain electrical parameters of the insulating layer.

4. The design method of partially insulated offshore overhead transmission lines according to claim 1, characterized in that: The cone surface of the stress cone adopts a straight cone surface, and the thickness of the winding insulation layer of the stress cone is determined by the surface field strength constraint; The axial length of the stress cone is determined by the axial field strength constraint.

5. The design method of partially insulated offshore overhead transmission lines according to claim 4, characterized in that: The thickness of the added winding insulation layer is expressed by the following formula: Where △d represents the thickness of the winding insulation layer, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, represents the dielectric constant of the insulating material of the insulating layer, Indicates the dielectric constant of the insulating material of the added insulation layer, U1 indicates the power frequency voltage, E n Indicates the maximum working field strength on the surface of the wound insulation layer; The axial length is expressed by the following formula: Where, L k Indicates the axial length, E t represents the axial field strength, R represents the outer radius of the insulation layer, r c Indicates the outer radius of the bare conductor, R n Indicates the outer radius of the added insulation layer.

6. The design method of partially insulated offshore overhead transmission line according to claim 5, characterized in that: After the step of obtaining the electrical parameters of the insulating layer, the method further includes: Inputting electrical parameters of the insulating layer and parameters of the stress cone into the three-dimensional simulation model, wherein the parameters of the stress cone include a cone surface, a thickness of the winding insulating layer, and an axial length; Under power frequency voltage conditions and operation overvoltage conditions, simulations are carried out respectively to obtain power frequency simulated surface field strength and overvoltage simulated surface field strength; Determining whether the power frequency simulated surface field strength satisfies the first constraint condition, and whether the overvoltage simulated surface field strength satisfies the second constraint condition; If any one of the conditions is not satisfied, the insulation optimization model is solved again until the power frequency simulated surface field strength satisfies the first constraint condition and the overvoltage simulated surface field strength satisfies the second constraint condition.

7. The design method of partially insulated offshore overhead transmission lines according to claim 1, characterized in that: The bare wires on both sides of the insulation layer are also covered with heat shrink tubes of a preset length.

8. An offshore overhead transmission line based on partial insulation, characterized in that: The offshore overhead power transmission line is designed using the method according to any one of claims 1 to 7.

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