Non-power-outage direct-current ice melting method, medium and system for overhead ground wire

Abstract

The invention discloses an overhead ground wire non-outage direct current deicing method, medium and system, and the method comprises the steps: determining the length of an overhead ground wire section to be deiced according to the obtained overhead ground wire parameters, overhead ground wire icing conditions and meteorological environment parameters; according to the resistance corresponding to the length of the ground wire section, the overhead ground wire parameter, the icing condition and the meteorological environment parameter, obtaining an ice melting current; calculating a lightning current value according to the overhead ground wire parameters and the lightning current peak value; if the maximum ice-melting current is greater than or equal to the thunder current value, reducing the length of the ground wire section until the maximum ice-melting current is less than the thunder current value; if the maximum ice melting current is smaller than the lightning current value, insulation transformation is carried out on the ground wire; and connecting the transformed ground wire section with a direct-current ice melting device to form an ice melting loop, and carrying out direct-current ice melting without power failure. According to the invention, lightning protection and ice melting are taken into consideration, the ice melting work is completed while lightning protection is maintained, and the reliability and the safety of uninterrupted power supply ice melting of the overhead ground wire in severe weather of a power system are improved.

Description

TECHNICAL FIELD

[0001] The present application mainly relates to the technical field of power transmission line ice melting, and particularly relates to an overhead ground wire non-power-off direct current ice melting method, medium and system. BACKGROUND

[0002] In winter, ice and snow weather often occurs in some southern areas. Such extreme weather conditions often lead to ice and snow phenomena of power transmission lines and overhead ground wires, and further cause a series of safety accidents, such as overhead ground wire fracture and tower collapse. These accidents not only cause huge economic losses, but also seriously affect the safe and stable operation of the power system. Therefore, how to effectively solve the ice coating problem of overhead ground wires in ice and snow weather has become one of the current research hotspots.

[0003] At present, the ice melting technology applied to overhead ground wires generally adopts a full insulation scheme. The technical path is to implement full insulation treatment on the overhead ground wire to build a closed ice melting loop composed of power transmission conductors and overhead ground wires. However, the following problems are exposed in the actual application of this scheme: first, power transmission conductors need to be powered off during ice melting operation, which not only affects the normal load transmission of the power grid, but also causes the risk of daily power supply interruption; second, the existing ice melting method does not consider the lightning current carrying capacity of the overhead ground wire, which leads to the fact that the original lightning protection effect cannot be achieved during the ice melting process, and there is a safety hazard in the ice melting construction process; third, the existing technical scheme mostly adopts a single loop ice melting connection mode, which significantly increases the capacity demand of the system on the direct current ice melting device, and cannot perform long line ice melting. In actual engineering application, it is often restricted by the technical bottleneck and economy of large-capacity direct current ice melting devices, and has certain limitations.

[0004] In view of this, it is a technical problem to be solved by those skilled in the art to provide an overhead ground wire non-power-off direct current ice melting method that takes into account lightning protection ice melting. SUMMARY

[0005] In view of the technical problems existing in the prior art, the present application provides an overhead ground wire non-power-off direct current ice melting method, medium and system that enables the overhead ground wire to complete ice melting work while maintaining lightning protection in an environment with frequent lightning strikes, and improves the reliability and safety of overhead ground wire non-power-off ice melting of the power system in severe weather.

[0006] To solve the above technical problems, the technical solution provided by the present application is as follows: An overhead ground wire non-power-off direct current ice melting method, comprising the following steps: determining the length of the overhead ground wire section to be melted according to the obtained overhead ground wire parameters, overhead ground wire icing conditions and meteorological environment parameters; The ice melting current is calculated according to the resistance corresponding to the length of the overhead ground wire section to be melted, the overhead ground wire parameters, the ice coating condition of the overhead ground wire and the meteorological environment parameters; wherein, the ice melting current comprises a minimum ice melting current and a maximum ice melting current; The lightning current value is calculated according to the overhead ground wire parameters and the lightning current peak value; The maximum ice melting current is compared with the lightning current value; if the maximum ice melting current is greater than or equal to the lightning current value, the length of the overhead ground wire section to be melted is reduced according to a preset rule, and the updated maximum ice melting current is calculated according to the resistance corresponding to the length of the overhead ground wire section to be melted after the reduction, the overhead ground wire parameters and the ice coating condition of the overhead ground wire, until the updated maximum ice melting current is less than the lightning current value; if the maximum ice melting current is less than the lightning current value, the overhead ground wire to be melted is insulated and reconstructed; The overhead ground wire section to be melted after the insulation reconstruction is connected with the direct current ice melting device to form an ice melting loop for non-power-off direct current ice melting.

[0007] Preferably, the specific process of calculating the minimum ice melting current of the overhead ground wire is as follows: If the overhead ground wire to be melted is a steel strand or an aluminum-clad steel strand, the minimum ice melting current thereof is The calculation method is as follows:

[0008] In the formula, R0 is the resistance per unit length of the overhead ground wire at 0℃; ΔT is the difference between the temperature of the overhead ground wire and the temperature of the outside world; R is the equivalent thermal resistance of convection and radiation; Ri is the equivalent ice layer conduction thermal resistance, If the overhead ground wire to be melted is OPGW, the minimum ice melting current thereof is The calculation method is as follows:

[0009] In the formula, λ is the thermal conductivity of ice; r is the ice coating radius; h is the heat transfer coefficient between the ice coating outer surface and the environment; T is the temperature of the environment; r is the ice coating radius; R is the radius of the overhead ground wire.

[0010] Preferably, the specific process of calculating the maximum ice melting current of the overhead ground wire is as follows: When the wind speed is greater than 2 meters / second:

[0011] In the formula, ​R is the resistance of the overhead ground wire at a temperature of 90 °C; ε is the radiation coefficient; h is the ice thickness; 、 、 M is the mutual inductance impedance; R is the self-impedance of the overhead ground wire-ground loop; When the wind speed is ≤ 2 m / s:

[0012] If the ice-melting ground wire is OPGW, the maximum ice-melting current is calculated as follows: The maximum ice-melting current of OPGW before ice shedding can be expressed as:

[0013] In the formula: I0 is the maximum ice-melting current determined by the service temperature of the optical fiber before ice shedding; T is the maximum allowable temperature of the optical fiber; Rth is the equivalent thermal resistance between the optical fiber and the surface of OPGW; R is the resistance of the overhead ground wire at T °C; F is the correction factor of wind speed and humidity; The maximum ice-melting current of OPGW after ice shedding is expressed as:

[0014] In the formula: I0 is the maximum ice-melting current determined by the service temperature of the optical fiber after ice shedding; h is the heat exchange coefficient of the surface of OPGW; In summary, the maximum ice-melting current of OPGW is: .

[0015] Preferably, the specific process of calculating the lightning current is as follows: Calculate the ground wire wave impedance of the overhead ground wire section :

[0016] In the formula, h h is the average height of the overhead ground wire to the ground; r R is the equivalent radius of the overhead ground wire; Recalculate the lightning current value borne by each side of the overhead ground wire :

[0017] In the formula, I0 is the peak value of the lightning current, usually selected according to the overhead ground wire design standard; R w R is the tower impulse grounding resistance.

[0018] Preferably, the specific process of insulation modification is: A1. Calculate the ice-melting voltage according to the ice-melting current and the resistance of the ice-melting loop; wherein the ice-melting loop is formed by the ice-melting conductor and the overhead ground wire to be ice-melted in a segmented combination manner; the resistance of the ice-melting loop includes the resistance of the ice-melting conductor and the resistance of the overhead ground wire segment to be ice-melted; A2. Determine the discharge gap distance and the number of insulators of the overhead ground wire segment to be ice-melted according to the ice-melting voltage, the altitude and the tower height; A3. Insulate the overhead ground wire segment to be ice-melted according to the discharge gap distance and the number of insulators.

[0019] Preferably, before step A3 is executed, further comprising: judging the size of the DC discharge voltage of the insulator discharge gap and the DC flashover voltage of the insulator, if the DC discharge voltage of the insulator discharge gap is greater than or equal to the DC flashover voltage of the insulator, then reducing the discharge gap distance of the overhead ground wire insulator according to a preset rule to obtain an updated discharge gap distance of the insulator, and reducing the length of the overhead ground wire segment to be ice-melted, calculating an updated ice-melting voltage according to the resistance of the ice-melting loop corresponding to the reduced length of the overhead ground wire segment to be ice-melted and the ice-melting current, until the updated ice-melting voltage, the DC discharge voltage of the updated discharge gap distance of the insulator and the DC flashover voltage of the insulator satisfy the following target conditions: the DC flashover voltage of the insulator is greater than the updated ice-melting voltage; the DC discharge voltage of the updated discharge gap distance of the insulator is greater than the updated ice-melting voltage; the DC discharge voltage of the updated discharge gap distance of the insulator is less than the DC flashover voltage of the ground wire insulator.

[0020] Preferably, when forming the ice-melting loop, a multi-loop ice-melting loop capable of dynamic segmented switching is formed by the ice-melting conductor and the overhead ground wire to be ice-melted in a series or parallel connection combination manner according to the DC ice-melting device parameters, the length of the overhead ground wire segment to be ice-melted and the icing condition of the overhead ground wire.

[0021] Preferably, the overhead ground wire parameters include the overhead ground wire material, the overhead ground wire diameter and the overhead ground wire unit resistance; the overhead ground wire icing condition includes the overhead ground wire icing type and the overhead ground wire icing thickness; the overhead ground wire icing type includes the glaze and the rime; and the meteorological environment parameters include the wind speed, the temperature and the humidity.

[0022] The application also discloses a computer readable storage medium, which stores a computer program, wherein the computer program performs the steps of the method when run by a processor.

[0023] The application further discloses an overhead ground wire non-power-off direct current ice melting system, which comprises a memory and a processor connected with each other, the memory stores a computer program, and the computer program performs steps of the method as described above when the processor runs.

[0024] Compared with the prior art, the application has the following advantages: The compatible lightning overhead ground wire segmented non-power-off direct current ice melting method of the application determines the current and voltage parameters required for direct current ice melting of the overhead ground wire, and synchronously checks the lightning current bearing capacity of the ground wire; by comparing the ice melting current and the lightning current threshold, the maximum safe length of the ground wire ice melting section is determined; insulation transformation is implemented on the target section, and adaptive insulators and discharge gaps are configured; the insulation section is subjected to segmented live ice melting by the direct current ice melting device. The application can realize precise ice melting of the ground wire in a live state, effectively reduces the risk of overhead ground wire icing failure through the collaborative design of lightning protection and ice melting parameters, and maintains the safe operation of the power grid; the dynamic segmentation strategy adopted by the application can effectively reduce the capacity requirement of the ice melting device and save the transformation cost; the insulation transformation of the application does not affect the normal power transmission function of the line. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The flowchart of the direct current ice melting method of the application in the embodiment.

[0026] Figure 2 The line icing and ice melting state schematic diagram in the application; (a) is the icing ground wire; (b) is the ice melting state.

[0027] Figure 3 The segmented ice melting principle schematic diagram in the application; (a) is two overhead ground wires connected in series; (b) is two overhead ground wires connected in parallel.

[0028] Figure 4 The wiring schematic of the insulation transformation of a specific example of a 110kV overhead ground wire in the embodiment of the application Figure 1 .

[0029] Figure 5 The wiring schematic of the insulation transformation of a specific example of a 110kV overhead ground wire in the embodiment of the application Figure 2 . DETAILED DESCRIPTION

[0030] The application will be further described below in combination with the drawings and specific embodiments of the specification.

[0031] In order to better understand the above technical solutions, the above technical solutions will be described in detail in combination with the drawings and specific embodiments of the specification.

[0032] As Figure 1As shown, the overhead ground wire non-power-off DC ice melting method provided by the embodiment of the application comprises the following steps: S1. Determine the length of the overhead ground wire section to be melted according to the obtained overhead ground wire parameters, overhead ground wire icing conditions and meteorological environment parameters. Specifically, the overhead ground wire parameters comprise overhead ground wire material, overhead ground wire diameter and overhead ground wire unit resistance. The overhead ground wire icing conditions comprise overhead ground wire icing type and overhead ground wire icing thickness. The overhead ground wire icing type comprises glaze and rime. The meteorological environment parameters comprise wind speed, temperature and humidity.

[0033] In actual application, the overhead ground wire parameters and overhead ground wire icing conditions can be real-time collected by using sensors, high-precision cameras, video monitoring devices and unmanned aerial vehicles and the like. In addition, the overhead ground wire icing conditions can be predicted by establishing an overhead ground wire icing growth model through system analysis of historical data such as overhead ground wire icing thickness, temperature, humidity and wind speed.

[0034] It should be noted that the length of the overhead ground wire section to be melted is determined in step S1, so as to determine the resistance corresponding to the overhead ground wire section, and to prepare for subsequent calculation of the ice melting current. In actual application, the length of the overhead ground wire section to be melted is the length of the ground wire icing prone section, which can be obtained according to actual measurement of the overhead ground wire parameters and overhead ground wire icing conditions, or inferred according to the overhead ground wire icing growth model constructed based on historical data of the overhead ground wire parameters and overhead ground wire icing conditions.

[0035] S2. Calculate the ice melting current according to the resistance corresponding to the length of the overhead ground wire section to be melted, the overhead ground wire parameters, the overhead ground wire icing conditions and the meteorological environment parameters. The ice melting current comprises minimum ice melting current and maximum ice melting current. Specifically, the minimum ice melting current and the maximum ice melting current are calculated according to the overhead ground wire material, the overhead ground wire diameter, the meteorological environment parameters and the overhead ground wire icing conditions.

[0036] It should be noted that the ice melting process is as shown in the following figure: Figure 2 Before the ice melting starts, the Joule heat generated by the current passing through the conductor is transferred outward through the interface between the conductor and the inner surface of the ice After passing through the ice layer, the current flows to the external environment, and the heat is exchanged with the air through convection and radiation at the interface between the outer surface of the ice and the external environment. At this time, the temperatures of the conductor and the ice , the outer surface temperature of the ice and the environmental temperature reach equilibrium. When the ice melting starts, the current in the conductor gradually increases, and the Joule heat makes the temperature of the conductor gradually increase, and the temperature of the ice The temperature gradually rises and the ice coating begins to melt. At this time, due to the melting of the ice coating, an air gap is formed between the conductor and the ice coating, and part of the Joule heat is transferred from the conductor. The ice melting process mainly occurs in the part of the conductor in contact with the ice coating above the conductor. As the ice gradually melts, the thickness of the ice coating above the conductor gradually decreases, until the thickness of the ice coating is zero, the ice coating falls off, and the ice melting process ends.

[0037] In actual application, the calculation of the ice melting current size in step S2 specifically includes the following steps: S2.1 Calculate the minimum ice melting current of the overhead ground wire: S2.1.1 If the overhead ground wire to be melted is a steel strand or an aluminum-clad steel strand, the minimum ice melting current is calculated as follows:

[0038] In the formula, R is the resistance per unit length of the overhead ground wire at 0℃; ΔT is the difference between the temperature of the overhead ground wire and the outside temperature; is the equivalent thermal resistance of convection and radiation; is the equivalent ice layer conduction thermal resistance, which is calculated as follows:

[0039] In the formula, D is the outer diameter of the overhead ground wire after icing, and s is the diameter of the overhead ground wire; is the thermal conductivity, which is taken as follows according to different types of ice coating: Graupel: ; Rime: .

[0040] The equivalent thermal resistance of convection and radiation is calculated as follows: Graupel: ; Rime: ; In the formula, is the wind speed.

[0041] S2.1.2 If the overhead ground wire to be melted is OPGW, the minimum ice melting current is calculated as follows: Under the condition of critical ice melting, the heat balance equation of the overhead ground wire can be expressed as:

[0042] In the formula, is the minimum ice melting current of OPGW at critical ice melting; is the resistance of the overhead ground wire at T℃.​ T is the temperature between the overhead ground wire and the ice; T is the temperature at the interface T is the temperature; R is the thermal resistance of the ice. R = f(θ) where θ is the angle of the ice location from the horizontal. The thermal resistance of the ice may be expressed as:

[0043] where R is the thermal resistance of the ice; k is the thermal conductivity of the ice.

[0044] Under the critical ice-melting condition, the heat exchange of the ice on the overhead ground wire can be expressed as:

[0045] where R is the radius of the overhead ground wire; h is the thickness of the ice; h is the heat transfer coefficient between the outer surface of the ice and the environment; T is the temperature of the environment. It can be obtained that:

[0046] where T is the temperature of the environment.

[0047] It can be obtained that: The expression of R is:

[0048] Therefore, the minimum ice-melting current of the OPGW is expressed as:

[0049] S2.2 Calculation of the maximum ice-melting current of the overhead ground wire: S2.2.1 If the overhead ground wire to be melted is a steel strand or an aluminum-clad steel strand, the maximum ice-melting current thereof is calculated as follows: (1) When the wind speed is greater than 2 meters / second:

[0050] where R is the resistance of the overhead ground wire when the temperature is 90°C; ε is the radiation coefficient.

[0051] (2) When the wind speed is less than or equal to 2 meters / second:

[0052] In addition, when the transmission line passes through the alternating current, the surrounding will produce alternating magnetic field. According to Faraday's law of electromagnetic induction, the overhead ground wire will produce a larger induced electromotive force due to the change of magnetic field. If the ground wire forms a closed loop, it will form an induced current, which is calculated as follows: The self-impedance of the "overhead ground wire-ground" loop can be expressed as:

[0053] 、 、 M is the mutual inductance impedance, which can be expressed as:

[0054]

[0055] In the formula: is the equivalent depth of the current in the ground; is the current frequency; is the ground resistivity; is the resistance of the overhead ground wire; is the effective radius of the overhead ground wire; is the distance between the lines. Therefore, for a single-circuit line, the induced current on the overhead ground wire is:

[0056] In summary, the maximum ice-melting current of the overhead ground wire can be expressed as: (1) When the wind speed is > 2 meters / second:

[0057] (2) When the wind speed is ≤ 2 meters / second:

[0058] S2.2.2 If the ground wire to be melted is OPGW, the maximum ice-melting current is calculated as follows: The maximum ice-melting current of OPGW before ice shedding can be expressed as:

[0059] In the formula: is the maximum ice-melting current determined by the use temperature of the optical fiber before ice shedding; is the maximum allowable temperature of the optical fiber; is the equivalent thermal resistance of the optical fiber and the surface of OPGW; is the resistance of the overhead ground wire at T°C; is a correction factor for wind speed and humidity, which describes the influence of environmental parameters on the ice-melting current.

[0060] The maximum ice-melting current of OPGW after ice shedding can be expressed as:

[0061] wherein, is the maximum ice-melting current obtained from the temperature of the optical fiber after ice shedding; is the heat exchange coefficient of the surface of OPGW. In summary, the maximum ice-melting current of OPGW is: .

[0062] S3. Calculate the lightning current value according to the parameters of the overhead ground wire and the peak value of the lightning current; Specifically, the lightning current value is calculated according to the tower impulse grounding resistance of the overhead ground wire section, the ground wave impedance of the overhead ground wire section, and the peak value of the lightning current.

[0063] In actual application, the calculation of the lightning current value of the overhead ground wire in step S3 specifically includes the following steps: Calculate the ground wave impedance of the overhead ground wire section:

[0064] wherein, h is the average height of the overhead ground wire to the ground; r is the equivalent radius of the overhead ground wire.

[0065] Calculate the lightning current value borne by each side of the overhead ground wire:

[0066] wherein, I0 is the peak value of the lightning current, which is usually selected according to the design standard of the overhead ground wire; Rw is the tower impulse grounding resistance.

[0067] S4. Compare the maximum ice-melting current with the lightning current value; if the maximum ice-melting current is greater than or equal to the lightning current value, then the length of the overhead ground wire section to be deiced should be reduced in combination with the output voltage of the ice-melting device and the difference between the maximum ice-melting current and the lightning current, and the updated maximum ice-melting current is calculated according to the resistance corresponding to the reduced length of the overhead ground wire section to be deiced, the parameters of the overhead ground wire, and the icing condition of the overhead ground wire, until the updated maximum ice-melting current is less than the lightning current value; In practical applications, the required direct current ice melting current is usually less than the peak value of lightning current. Therefore, when the ice melting current is less than the lightning current, the overhead ground wire can not only complete effective ice melting, but also ensure that the lightning protection function of the ground wire is not affected. This feature enables the method to ensure the safety of overhead ground wires while ensuring lightning protection, and to melt ice through appropriate direct current, thereby improving the safety and reliability of overhead ground wires in severe weather conditions. Compared with the prior art, the core advantage of the present application is that by accurately calculating the relationship between the ice melting current and the lightning current value, the overhead ground wire can maintain its electrical protection performance while successfully completing the ice melting work in an environment with frequent lightning strikes, thereby improving the reliability and safety of the power system after ice melting modification.

[0068] S5. If the maximum ice melting current is less than the lightning current value, insulate the overhead ground wire to be melted; It should be noted that, since the overhead ground wire is directly connected to the power transmission tower and is distributed along the ground, it cannot directly bear the ice melting current. Therefore, before ice melting, it must be insulated and modified as necessary to achieve electrical isolation between the power transmission tower and the overhead ground wire. The modification method is to install insulators between the ground wire and the power transmission tower, thereby effectively blocking the electrical connection between the two.

[0069] Specifically, the insulating modification of the overhead ground wire to be melted in step S5 includes the following steps: A1. Calculate the ice melting voltage according to the ice melting current and the resistance of the ice melting circuit; wherein the ice melting circuit is composed of the ice melting conductor and the overhead ground wire to be melted by segment combination; the resistance of the ice melting circuit includes the resistance of the ice melting conductor and the resistance of the overhead ground wire segment to be melted; In practical applications, step A1 calculates the ice melting voltage according to the ice melting current and the resistance of the ice melting circuit, which complies with Ohm's law, and the calculation formula is as follows:

[0070] In the formula, R is the direct current resistance of the ice melting circuit, is the actual ice melting current, which is in the range of minimum ice melting current - maximum ice melting current.

[0071] A2. Determine the overhead ground wire segment insulator discharge gap distance and the number of insulator pieces to be melted according to the ice melting voltage, the altitude and the tower height; In the actual application process, the selection of insulators is crucial in the insulation transformation of overhead ground wires. According to the 110kV-750kV Overhead Transmission Line Design Specification (GB 50545-2010), the minimum number of insulators of the suspension insulator string required by the operating overvoltage and lightning overvoltage should meet the requirements of Table 1 in the area below an altitude of 1000m. The number of insulator pieces of the tension insulator string should be increased based on Table 1, by 1 piece for 110kV-330kV transmission lines, by 2 pieces for 500kV transmission lines, and no increase for 750kV transmission lines.

[0072] Table 1 Minimum number of insulator pieces of suspension insulator string required by operating overvoltage and lightning overvoltage

[0073] In addition, for the towers with overhead ground wires whose total height exceeds 40m, 1 piece of insulator corresponding to a height of 146mm should be added for each 10m increase in height compared to Table 1. For the towers whose total height exceeds 100m, the number of insulator pieces should be determined according to the operating experience combined with calculation. When the number of insulator pieces is increased due to high towers, the minimum gap of lightning overvoltage should also be increased accordingly. For 750kV towers whose total height exceeds 40m, whether the number of insulator pieces and the gap need to be increased can be determined according to the actual situation through calculation.

[0074] In step A2, the discharge gap distance of the overhead ground wire insulator is determined, specifically: the ground wire insulator protection gap distance is determined according to the ice-melting voltage. In the actual application process, when the gap is adjusted to 30mm, the discharge voltage is stable in the range of 7-9kV; when the gap is increased to 40mm, the discharge voltage is increased to 10kV; when the gap is further expanded to 50mm, the discharge voltage reaches the critical value of 12kV. It is worth noting that when the gap is expanded to 60mm, the insulator body will flashover, resulting in complete failure of the protection gap. This phenomenon verifies that the conventional ground wire insulation device has reliable 12kV DC voltage resistance characteristics in the icing environment, and also defines the parameter boundary in the application of overhead ground wire ice-melting. Based on the above electrical characteristics, under the premise of meeting the insulation performance requirements in the icing area, for the lines with DC ice-melting voltage below 10kV, 40mm protection gap is preferred; when the ice-melting voltage reaches 12kV, the gap distance should be adjusted to 50mm. This grading configuration strategy can not only ensure the effectiveness of the ice-melting process, but also maintain the protection function of the insulation device.

[0075] A3. According to the discharge gap distance of the insulator and the number of insulator pieces, the overhead ground wire section to be ice-melted is insulated. The insulation transformation includes permanent insulation transformation and temporary insulation transformation.

[0076] Before step A3 is performed, it also includes: The size of the DC discharge voltage of the insulator discharge gap and the DC flashover voltage of the insulator is determined, and if the DC discharge voltage of the insulator discharge gap is greater than or equal to the DC flashover voltage of the insulator, the length of the overhead ground wire for DC ice melting can be reduced or the wiring combination mode can be changed, the ice melting voltage is recalculated to reduce the overhead ground wire insulator discharge gap distance, the updated insulator discharge gap is obtained, and the length of the overhead ground wire section to be melted is reduced, and the updated ice melting voltage is calculated according to the resistance and ice melting current of the ice melting circuit corresponding to the reduced length of the overhead ground wire section to be melted, until the updated ice melting voltage, the DC discharge voltage of the updated insulator discharge gap and the DC flashover voltage of the insulator satisfy the following target conditions: The DC flashover voltage of the insulator is greater than the updated ice melting voltage. The DC discharge voltage of the updated insulator discharge gap is greater than the updated ice melting voltage. The DC discharge voltage of the updated insulator discharge gap is less than the DC flashover voltage of the ground wire insulator.

[0077] S6. The overhead ground wire section to be melted after insulation reconstruction is connected with the DC ice melting device to form an ice melting circuit, and non-power-off DC ice melting is performed.

[0078] Specifically, according to the DC ice melting device parameters, the length of the overhead ground wire section to be melted and the icing condition of the overhead ground wire, the ice melting conductor and the overhead ground wire to be melted are connected in series or parallel to form a multi-loop ice melting circuit which can be dynamically switched and segmented.

[0079] In actual application, in order to reduce the capacity required by the DC ice melting device, reduce the ice melting cost and take into account the flexibility of ice melting wiring, a multi-loop ice melting circuit which can be dynamically switched and segmented is formed by series or parallel wiring combination, as shown in Figure 3 , by connecting the two ends of each section of the ground wire through the grounding knife switch. As shown in Figure 3 , the series mode is suitable for the scene where the total resistance of multiple sections is high and the voltage needs to be boosted. For the ground wire with single-point grounding of segmented insulation, the series mode needs to connect each section through a jumper wire; for the full-line insulation ground wire, the jumper wire is not needed and the series circuit is directly formed. The parallel mode is suitable for the scene where the resistance of a single section is low and a large current is needed.

[0080] Implementation steps: 1. According to the icing monitoring data, the ice melting section is determined. 2. The ice melting section is insulated. 3. The required ice melting current, voltage and capacity are calculated. 4. The series / parallel mode is determined. If it is series: disconnect the target section grounding knife switch → connect the adjacent sections with parallel groove clamps → connect the two ends of the series circuit to the ice melting power supply → adjust the voltage to the ice melting voltage. If it is parallel: disconnect the single-section grounding knife switch → directly connect the two ends of the section to the power supply → adjust the current to the ice melting current.

[0081] It needs to be explained that the icing of the power transmission line is closely related to the topographic conditions of the line, the meteorological conditions of the microtopography along the line are quite different, and the serious icing section generally accounts for only 10%-20% of the total length of the line. The traditional full-line ice melting mode cannot distinguish between light and heavy icing sections, needs to configure an ultra-large capacity system, and forces the non-icing section to bear overcurrent, which not only causes resource redundancy and economic loss, but also accelerates the thermal stress damage of the ice melting conductor. Compared with the prior art, the segment prediction mode of the multi-loop ice melting loop based on the series / parallel connection combination mode and capable of dynamically switching segmentation of the present scheme can quantitatively locate the high-risk microtopography area, provide the key decision basis for the access point site selection, ice melting power on-demand matching and induced voltage suppression strategy of the segmented ice melting system, so as to ensure the safety of the power grid while significantly reducing the ice melting system capacity and avoiding the current overload of the non-icing section.

[0082] The compatible lightning overhead ground wire segmented non-power-off direct current ice melting method of the application determines the current and voltage parameters required for overhead ground wire direct current ice melting, synchronously checks the lightning current carrying capacity of the ground wire, determines the maximum safe length of the ground wire ice melting section by comparing the ice melting current and the lightning current threshold, implements insulation modification on the target section and configures adaptive insulators and discharge gaps, and implements segmented live ice melting on the insulated section by the direct current ice melting device. The application can realize precise ice melting of the ground wire in a live state, effectively reduces the risk of overhead ground wire icing failure through the collaborative design of lightning protection and ice melting parameters, and maintains the safe operation of the power grid. The dynamic segmentation strategy adopted by the application can effectively reduce the capacity demand of the ice melting device and save the modification cost. The insulation modification of the application will not affect the normal power transmission function of the line.

[0083] The following will be described in detail in combination with a specific embodiment: As Figure 4 and Figure 5As shown, the icing section of the certain 110kV overhead ground wire is located at #071-#072 section, with a length of 149.87m, and the overhead ground wire type is GJ-80 / OPGW-48B1-150. The ice melting current range is 166A-272A, and the lightning current value is 46.35kA, which is much larger than the maximum ice melting current, so the ice melting length can be determined as 149.87m, and the required ice melting voltage is 130V. The ground wire of the section is melted by the ice melting method of the application, so that the insulation length of the OPGW and the steel strand is the same, and then the OPGW, the steel strand, the tower cross arm and the ice melting device form an ice melting loop to achieve the ice melting purpose. The #71-#72 tower is located on the mountain, and the ice melting device can be placed under the #72 tower, as shown in Figure 4. After the insulation modification of the #71-#72 tower, the ground wire and the OPGW optical cable are short-circuited at the #71 tower, and the ground wire of the #71-#72 section is connected in series to form an ice melting loop. Since the altitude of the line is 200m, the heights of the #71 and #72 towers are both 40m, and the insulator type can be selected as U70CN, and the discharge gap distance is 30mm. Then, the ground wire is introduced to the tower bottom through the support composite insulator at the #72 tower, and is connected to the single-ground output knife switch in the ice melting device container through the cable. When ice melting is needed, the output knife switch is closed to connect the ice melting power supply for ice melting.

[0084] The application can accurately melt the overhead ground wire under uninterrupted power supply, and effectively reduces the risk of lightning failure of the overhead ground wire after insulation modification through the cooperative design of lightning protection and ice melting current, so as to maintain the safe operation of the power grid. The overhead ground wire uninterrupted power supply direct current ice melting method of the application considers lightning protection and ice melting, accurately calculates the relationship between the ice melting current and the lightning current, so that the overhead ground wire can complete the ice melting work while maintaining lightning protection in the environment with frequent lightning strikes, thereby improving the reliability and safety of the power system in performing the overhead ground wire uninterrupted power supply ice melting in bad weather.

[0085] The application further discloses a computer readable storage medium, which stores a computer program, and the computer program executes the steps of the above method when being run by a processor. The application further discloses an overhead ground wire uninterrupted power supply direct current ice melting system, which comprises a memory and a processor connected with each other, and the memory stores a computer program, and the computer program executes the steps of the above method when being run by the processor. The medium and the system of the application correspond to the above method, and also have the advantages of the above method.

[0086] The present application can realize all or part of the processes in the above-mentioned embodiment methods, and can also be completed by computer program instruction related hardware. The computer program can be stored in a computer readable storage medium. When the computer program is executed by a processor, the steps of the above-mentioned method embodiment can be realized. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms, etc. The computer readable storage medium includes any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. The memory is used to store computer programs and / or modules. The processor realizes various functions by running or executing the computer programs and / or modules stored in the memory, and calling the data stored in the memory. The memory can include high-speed random access memory, and can also include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage device, etc.

[0087] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiment. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that some improvements and refinements made by ordinary skilled in the art without departing from the principles of the present application shall be considered as the protection scope of the present application.

Claims

1. A method for melting ice on overhead ground wires without power outages, characterized in that: The following steps are involved: Determine the length of the overhead ground wire section to be de-iced based on the acquired overhead ground wire parameters, the icing condition of the overhead ground wire, and the meteorological environment parameters; The ice melting current is calculated based on the resistance corresponding to the length of the overhead ground wire section to be de-iced, the overhead ground wire parameters, the ice coverage of the overhead ground wire, and the meteorological environment parameters; wherein the ice melting current includes the minimum ice melting current and the maximum ice melting current; Calculate the lightning current value based on the overhead ground wire parameters and lightning current peak value; Compare the maximum ice-melting current with the lightning current value; if the maximum ice-melting current is greater than or equal to the lightning current value, reduce the length of the overhead ground wire section to be melted according to preset rules, and calculate an updated maximum ice-melting current based on the resistance corresponding to the reduced length of the overhead ground wire section to be melted, the overhead ground wire parameters, and the icing condition of the overhead ground wire, until the updated maximum ice-melting current is less than the lightning current value; if the maximum ice-melting current is less than the lightning current value, perform insulation modification on the overhead ground wire to be melted; The overhead ground wire section to be de-iced after insulation transformation is connected to the DC de-icing device to form an de-icing circuit, and DC de-icing is performed without power outage.

2. The method for melting ice on overhead ground wires without power outage according to claim 1, characterized in that: The specific process of calculating the minimum ice melting current of overhead ground wire is as follows: If the overhead ground wire to be de-iced is a steel stranded wire or an aluminum-clad steel stranded wire, the minimum de-icing current is The calculation is as follows: Where: The resistance per unit length of the overhead ground wire at 0°C; is the difference between the overhead ground wire temperature and the outside temperature; is the equivalent thermal resistance of convection and radiation; is the equivalent ice layer conduction thermal resistance, If the overhead ground wire to be de-iced is an OPGW, then its minimum de-icing current is The calculation is as follows: in is the thermal conductivity of ice; is the ice radius; h is the heat transfer coefficient between the ice surface and the environment; is the ambient temperature; is the ice cover radius; is the radius of the overhead ground wire.

3. The method for melting ice on overhead ground wires without power outage according to claim 2, characterized in that: Calculating the Maximum Ice Melting Current of Overhead Ground Wires The specific process is: When wind speed is greater than 2 m / s: Where: is the resistance of the overhead ground wire at a temperature of 90°C; is the emissivity; is the ice cover thickness; 、 、 is the mutual inductance impedance; is the self-impedance of the overhead ground wire-ground loop; When wind speed ≤ 2 m / s: If the ground wire to be melted is an OPGW, the maximum ice-melting current is calculated as follows: The maximum ice-melting current before OPGW de-icing can be expressed as: Where: It is the maximum ice-melting current determined by the operating temperature of the optical fiber before de-icing; is the maximum allowable temperature of the optical fiber; is the equivalent thermal resistance between the optical fiber and the OPGW surface; is the resistance of the overhead ground wire at T℃; is the correction factor for wind speed and humidity; The maximum ice melting current after OPGW de-icing is expressed as: Where: is the maximum ice-melting current obtained from the optical fiber temperature after de-icing; is the heat exchange coefficient of the OPGW surface; In summary, the maximum ice melting current of OPGW is: .

4. The method for melting ice on overhead ground wires without power outage according to claim 1, 2 or 3, characterized in that: The specific process of calculating lightning current is: Calculate the ground wave impedance of the overhead ground wire section : Where, h is the average height of the overhead ground wire above the ground; r is the equivalent radius of the overhead ground wire; Then calculate the lightning current value on each side of the overhead ground wire : Where I0 is the peak value of lightning current, which is usually selected according to the design standard of overhead ground wire; R w is the tower impact grounding resistance.

5. The method for melting ice on overhead ground wires without power outage according to claim 1, 2 or 3, characterized in that: The specific process of insulation transformation is as follows: A1. Calculate the ice-melting voltage based on the ice-melting current and the resistance of the ice-melting circuit. The ice-melting circuit is composed of a segmented combination of the ice-melting conductor and the overhead ground wire to be melted. The resistance of the ice-melting circuit includes the resistance of the ice-melting conductor and the resistance of the overhead ground wire segment to be melted. A2. Determine the insulator discharge gap distance and number of insulators in the overhead ground wire section to be de-iced based on the de-icing voltage, altitude, and tower height. A3. According to the insulator discharge gap distance and the number of insulators, insulation modification shall be carried out on the overhead ground wire section to be de-iced.

6. The method for melting ice on overhead ground wires without power outage according to claim 5, characterized in that: Before executing step A3, the following steps are also included: Determine the magnitude of the DC discharge voltage of the insulator discharge gap and the DC flashover voltage of the insulator. If the DC discharge voltage of the insulator discharge gap is greater than or equal to the DC flashover voltage of the insulator, reduce the distance of the overhead ground wire insulator discharge gap according to a preset rule to obtain an updated insulator discharge gap, and reduce the length of the overhead ground wire section to be de-iced. Calculate an updated de-icing voltage based on the resistance and de-icing current of the de-icing circuit corresponding to the reduced length of the overhead ground wire section to be de-iced, until the updated de-icing voltage, the updated DC discharge voltage of the insulator discharge gap, and the insulator DC flashover voltage meet the following target conditions: The insulator DC flashover voltage is greater than the updated ice melting voltage; The updated DC discharge voltage of the insulator discharge gap is greater than the updated ice melting voltage; The DC discharge voltage of the updated insulator discharge gap is less than the DC flashover voltage of the ground wire insulator.

7. The method for melting ice on overhead ground wires without power outage according to claim 1, 2 or 3, characterized in that: When forming an ice-melting circuit, based on the parameters of the DC ice-melting device, the length of the overhead ground wire section to be melted, and the icing condition of the overhead ground wire, a multi-circuit ice-melting circuit that can be dynamically switched into segments is formed by connecting the ice-melting conductors and the overhead ground wire to be melted in series or in parallel.

8. The method for melting ice on overhead ground wires without power outage according to claim 1, 2 or 3, characterized in that: Overhead ground wire parameters include overhead ground wire material, overhead ground wire diameter and overhead ground wire unit resistance; The icing conditions of overhead ground wires include: the type of icing on the overhead ground wires and the thickness of icing on the overhead ground wires; the types of icing on the overhead ground wires include: rime and hoarfrost; the meteorological environment parameters include: wind speed, temperature and humidity.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 8.

10. An overhead ground wire non-stop DC ice melting system, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 8.

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