Method and system for calculating maximum allowable ice melting current and maximum ice melting length of OPGW (Optical Fiber Composite Overhead Ground Wire)

Abstract

The invention discloses a method and a system for calculating the maximum allowable ice melting current and the maximum ice melting length of an OPGW (Optical Fiber Composite Overhead Ground Wire). At present, the maximum ice melting current of the OPGW needs to be determined by adopting a finite element to perform simulation modeling and multi-round iterative optimization analysis calculation, and on-site ice coating faults cannot be quickly and timely determined. According to the method, the maximum allowable ice melting current of the OPGW is calculated by obtaining the model and the structure type of a field OPGW line and the maximum values of the internal temperatures of the OPGW in two stages before and after deicing monitored by a field online monitoring device during icing; and the maximum ice melting length of the OPGW is calculated by comprehensively considering the output power and the output voltage of the OPGW direct current ice melting device and the insulation and voltage resistance level of the OPGW line. According to the method, on the premise of not depending on finite element software modeling simulation calculation, theoretical support is provided for the maximum allowable ice melting current of the OPGW, remote icing monitoring and fault response of the high-voltage transmission line are facilitated, and a reference basis is provided for setting of a subsequent OPGW direct-current ice melting device.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power grid transmission lines, and relates to the calculation of the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, in particular to a calculation method and system for determining the maximum allowed ice-melting current and the maximum ice-melting length of OPGW in field tests by combining the parameters of online monitoring devices of high-voltage transmission lines and comprehensively considering OPGW DC ice-melting devices. BACKGROUND

[0002] With the gradual densification of the channels of power grid transmission lines, icing fault events of the lines occur frequently. Icing leads to damage of line towers, fault tripping of transmission lines, and disconnection of optical cable channels, which seriously affects the safe operation of the lines.

[0003] In the current design of OPGW ice-melting schemes, the determination of the required ice-melting current of OPGW in the field needs to use finite elements to perform simulation modeling, multiple rounds of iterative optimization analysis and calculation, and a large amount of modeling and simulation time and manpower investment, which is low in efficiency and cannot respond in time to the icing fault in the field. Meanwhile, there is no clear calculation method for the maximum ice-melting length of the line that can be supported by the DC ice-melting device, which cannot reliably guarantee the safe operation of high-voltage transmission lines.

[0004] Therefore, a calculation scheme for the maximum allowed ice-melting current and the maximum ice-melting length of OPGW is needed. SUMMARY

[0005] The technical problem to be solved by the present application is to solve the defects of the prior art, and to provide a calculation method and system for the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, which can calculate the maximum allowed ice-melting current and the maximum ice-melting length of OPGW in real time by combining the monitoring parameters of online monitoring devices in the field and the parameters of DC ice-melting devices, without the need for finite element simulation calculation, to effectively support the field icing monitoring and timely response to faults of high-voltage transmission lines, and also to provide a reference for subsequent design of OPGW DC ice-melting schemes.

[0006] To this end, one technical solution adopted by the present application is as follows: a calculation method for the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, comprising the steps of: a) obtaining the model and structure type of OPGW and each parameter monitored by online monitoring devices in the field during icing; b) calculating the maximum internal temperature of OPGW before and after ice shedding according to the data obtained in step a); c) calculating the maximum allowed ice-melting current of OPGW before and after ice shedding according to the maximum internal temperature of OPGW before and after ice shedding, and taking the smaller value of the two as the maximum allowed ice-melting current of OPGW; d) Obtain the output power, output voltage of the DC ice melting device and the insulation withstand voltage level of the OPGW, combine the maximum allowed ice melting current of the OPGW, and calculate the corresponding three maximum ice melting lengths of the OPGW; e) Take the minimum value of the three maximum ice melting lengths of the OPGW obtained in step d) as the final maximum ice melting length of the OPGW.

[0007] Further, in step a), the parameters monitored by the on-site online monitoring device during icing are the temperature values of each point along the OPGW inside monitored by the distributed temperature sensor during icing. When the points are arranged along the OPGW line, at least 3 temperature monitoring points are arranged per span.

[0008] Further, in step b), the specific process of calculating the maximum internal temperature of the OPGW optical cable before ice shedding includes: Obtain the maximum temperature of each point along the line inside the OPGW monitored by the distributed temperature sensor before ice shedding, and take the maximum value of all the maximum temperatures as the maximum internal temperature of the OPGW optical cable before ice shedding.

[0009] Further, in step b), the specific process of calculating the maximum internal temperature of the OPGW optical cable after ice shedding includes: Obtain the maximum temperature of each point along the line inside the OPGW monitored by the distributed temperature sensor after ice shedding, and take the maximum value of all the maximum temperatures as the maximum internal temperature of the OPGW optical cable after ice shedding.

[0010] Further, in step c), the formula for calculating the maximum allowed ice melting current of the OPGW before ice shedding is as follows: , In the formula, I m A is the maximum allowed ice melting current of the OPGW before ice shedding; T pm T is the maximum internal temperature of the OPGW optical cable before ice shedding, ℃; R T0 R is the unit length equivalent conduction thermal resistance of the air gap at the moment of ice shedding, W -1 ·m·℃; R T2 R is the unit length equivalent conduction thermal resistance between the optical fiber inside the OPGW and the surface of the OPGW, W -1 ·m·℃; r T R is the unit length resistance of the OPGW ice melting conductor at T ℃, / m; T R represents the temperature of the OPGW ice melting conductor.

[0011] Further, in step c), the formula for calculating the maximum allowed deicing current of OPGW after ice shedding is as follows: , wherein, I n is the maximum allowed deicing current of OPGW after ice shedding, A; h c is the heat exchange coefficient per unit surface of OPGW, W / (m 2 ·℃); R c is the radius of OPGW, m; T pn is the maximum internal temperature of OPGW cable after ice shedding, ℃; T a is the ambient temperature, ℃; R T2 is the equivalent conduction thermal resistance per unit length between the internal optical fiber of OPGW and the surface of OPGW, W -1 ·m·℃; r T is the unit length resistance of OPGW deicing conductor at T ℃, / m; T represents the temperature of OPGW deicing conductor.

[0012] Further, in step d), the first maximum deicing length of OPGW is calculated according to the output power of the DC deicing device, and the formula is as follows: , wherein, is the first maximum deicing length of OPGW, km; P 0 is the output power of the DC deicing device, W; I max is the maximum allowed deicing current of OPGW, A; r 0 is the deicing resistance per unit length of OPGW, Ω / km.

[0013] Further, in step d), the second maximum deicing length of OPGW is calculated according to the output voltage of the DC deicing device, and the formula is as follows: , wherein, is the second maximum deicing length of OPGW, km; U 0 is the output voltage of the DC deicing device, V.

[0014] Further, in step d), the third maximum deicing length of OPGW is calculated according to the insulation withstand voltage level of OPGW line, and the formula is as follows: , In the formula: is the third OPGW maximum ice-melting length, km; U f is the OPGW line insulation withstand voltage level, V.

[0015] Another technical solution adopted by the present application is as follows: an OPGW maximum allowable ice-melting current and maximum ice-melting length calculation system for implementing the above calculation method, comprising: a data acquisition unit for acquiring OPGW type, structure type and each parameter monitored by the on-site online monitoring device during icing; an optical cable temperature maximum value calculation unit for calculating the highest internal temperature of the OPGW optical cable before and after ice shedding according to the data acquired by the data acquisition unit; a maximum allowable ice-melting current acquisition unit for calculating the maximum allowable ice-melting current of the OPGW before and after ice shedding according to the highest internal temperature of the OPGW optical cable before and after ice shedding, and taking the smaller value as the maximum allowable ice-melting current of the OPGW; a maximum ice-melting length calculation unit for acquiring the output power, output voltage of the DC ice-melting device and the OPGW insulation withstand voltage level, combining the maximum allowable ice-melting current of the OPGW and calculating the corresponding three OPGW maximum ice-melting lengths; a maximum ice-melting length selection unit for selecting the minimum value of the three OPGW maximum ice-melting lengths obtained by the maximum ice-melting length calculation unit as the final OPGW maximum ice-melting length.

[0016] Compared with the prior art, the present application has the following beneficial effects: the present application does not need to perform finite element simulation modeling on the iced line, after obtaining the OPGW type, structure type of the on-site high-voltage transmission line and the highest internal temperature of the OPGW optical cable at each point along the line monitored by the on-site online monitoring device, the maximum allowable ice-melting current of the OPGW is calculated; then the output power, output voltage of the DC ice-melting device and the OPGW line insulation withstand voltage level are acquired, and the OPGW maximum ice-melting length is calculated accordingly. The present application can quickly obtain the OPGW maximum allowable ice-melting current and maximum ice-melting length value, improve the calculation efficiency, effectively support the on-site icing monitoring and timely response to faults of the high-voltage transmission line, and also provide a reference for subsequent OPGW DC ice-melting scheme design. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art of the present application, the drawings required to be used in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0018] Figure 1 Flow chart of the calculation method of the maximum allowed ice-melting current and the maximum ice-melting length of an OPGW according to the present application; Figure 2 Flow chart of the specific calculation method of the maximum allowed ice-melting current of an OPGW according to the present application; Figure 3 Flow chart of the specific calculation method of the maximum ice-melting length of an OPGW according to the present application; Figure 4 On-site OPGW line sectional view in the specific embodiments of the present application; Figure 5 Detection result chart of the highest internal temperature of the optical fiber along the OPGW before and after ice shedding in the specific embodiments of the present application; Figure 6 Composition chart of the calculation system of the maximum allowed ice-melting current and the maximum ice-melting length of an OPGW according to the present application; Figure 4 In the figure, 1 represents a 20.3% aluminum alloy wire (ice-melting conductor), and 2 represents a stainless steel tube optical fiber unit. Specific embodiments

[0019] The technical solutions of the present application will be described in detail below with reference to the drawings. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0020] Embodiment 1 This embodiment is a calculation method of the maximum allowed ice-melting current and the maximum ice-melting length of an OPGW, as shown in Figure 1 The steps are as follows: a) Obtain the OPGW model, structure type, and each parameter monitored during icing by the on-site online monitoring device.

[0021] b) Calculate the highest internal temperature of the OPGW optical cable before and after ice shedding according to the data obtained in step a).

[0022] c) According to the highest internal temperature of the OPGW optical cable before and after ice shedding, the maximum allowed ice melting current of the OPGW before and after ice shedding is calculated, and the smaller one is taken as the maximum allowed ice melting current of the OPGW.

[0023] The specific process of steps a), b) and c) is shown in Figure 2 .

[0024] d) Obtain the output power, output voltage of the DC ice melting device and the OPGW insulation withstand voltage level, combine the maximum allowed ice melting current of the OPGW, and calculate the corresponding three maximum ice melting lengths of the OPGW.

[0025] e) Take the minimum value of the three maximum ice melting lengths of the OPGW obtained in step d) as the final maximum ice melting length of the OPGW.

[0026] The specific process of steps d) and e) is shown in Figure 3 .

[0027] Specifically, in step a), the parameters monitored by the on-site online monitoring device during icing are the temperature values of each point along the OPGW internal line monitored by the distributed temperature sensor during icing, as shown in T 1, T 2, T 3, T 4… T i When the points are arranged along the OPGW line, at least 3 temperature monitoring points are arranged per span.

[0028] Specifically, in step b), the specific process of calculating the highest internal temperature of the OPGW optical cable before ice shedding is as follows: obtain the highest temperature of each point along the line monitored by the distributed temperature sensor inside the OPGW before ice shedding, and take the maximum value of all the highest temperatures as the highest internal temperature of the OPGW optical cable before ice shedding.

[0029] The specific process of calculating the highest internal temperature of the OPGW optical cable after ice shedding is as follows: obtain the highest temperature of each point along the line monitored by the distributed temperature sensor inside the OPGW after ice shedding, and take the maximum value of all the highest temperatures as the highest internal temperature of the OPGW optical cable after ice shedding.

[0030] The corresponding calculation formula is shown in formula (1).

[0031] (1) In the formula: T pm is the highest internal temperature of the OPGW optical cable before ice shedding, ℃; T 1m , T2m 、 T 3m 、 T 4m Tmax,pre-icing is the maximum temperature of OPGW internal points along the line monitored by the distributed temperature sensor before icing, ℃; T pn Tmax,post-icing is the maximum temperature of OPGW internal points after icing, ℃; T 1n 、 T 2n 、 T 3n 、 T 4n Tmax,post-icing is the maximum temperature of OPGW internal points after icing, ℃; t t is time, s; t 0 is the moment of icing, s.

[0032] Step c), according to the maximum temperature of OPGW internal points before and after icing, calculate the maximum allowable ice-melting current of OPGW before and after icing, take the smaller value as the maximum allowable ice-melting current of OPGW. The specific steps are as follows: c1) The formula for calculating the maximum allowable ice-melting current of OPGW before icing is as follows: (2) In the formula, I m Ipre-icing is the maximum allowable ice-melting current of OPGW before icing, A; T pm Tmax,pre-icing is the maximum temperature of OPGW internal points along the line monitored by the distributed temperature sensor before icing, ℃; R T0 R0 is the unit length equivalent conduction thermal resistance of air gap at the moment of icing, W -1 ·m·℃; R T2 R1 is the unit length equivalent conduction thermal resistance between the internal optical fiber of OPGW and the surface of OPGW, W -1 ·m·℃; r T R0 is the unit length equivalent conduction thermal resistance of air gap at the moment of icing, W T / m; T is the temperature of OPGW ice-melting conductor. T

[0033] c2) The formula for calculating the maximum allowable ice-melting current of OPGW after icing is as follows: (3) In the formula, I n Ipost-icing is the maximum allowable ice-melting current of OPGW after icing, A;​h c h is the heat exchange coefficient of OPGW unit surface, W / (m 2 ·℃); R c r is the radius of OPGW, m; T pn Tmax is the maximum internal temperature of OPGW after ice shedding, ℃; T a T is the ambient temperature, ℃.

[0034] c3) After obtaining the maximum allowable ice melting current of OPGW before and after ice shedding, comparison is made, and the smaller one is taken as the maximum allowable ice melting current of OPGW. The calculation is shown in formula (4).

[0035] (4) In the formula: I max I is the maximum allowable ice melting current of OPGW, A; I m I1 is the maximum allowable ice melting current of OPGW before ice shedding, A; I n I2 is the maximum allowable ice melting current of OPGW after ice shedding, A.

[0036] Step d), obtain the output power, output voltage of the DC ice melting device and the insulation withstand level of OPGW, combine the maximum allowable ice melting current of OPGW, and calculate the corresponding three maximum ice melting lengths of OPGW. The specific steps are as follows: d1) Obtain the output power, output voltage of the DC ice melting device and the insulation withstand level of OPGW; d2) Calculate the first maximum ice melting length of OPGW according to the output power of the DC ice melting device, as shown in formula (5).

[0037] (5) In the formula: L1 is the first maximum ice melting length of OPGW, km; P P0 is the output power of the DC ice melting device, W; I max I is the maximum allowable ice melting current of OPGW, A; r R0 is the ice melting resistance per unit length of OPGW, Ω / km.

[0038] d3) Calculate the second maximum ice melting length of OPGW according to the output voltage of the DC ice melting device, as shown in formula (6).

[0039] (6) In the formula: is the second OPGW maximum ice-melting length, km. U 0 is the output voltage of the DC ice-melting device, V.

[0040] d4) the third OPGW maximum ice-melting length is calculated according to the OPGW line insulation withstand voltage level, see formula (7).

[0041] (7) In the formula, is the third OPGW maximum ice-melting length, km. U f is the OPGW line insulation withstand voltage level, V.

[0042] Step e), take the minimum value of the three OPGW maximum ice-melting lengths obtained in step d) as the final OPGW maximum ice-melting length. The specific steps are as follows: e1) obtain the three OPGW maximum ice-melting length values obtained in step d) 、 、 ; e2) compare the three values obtained in e1), take the minimum value among the three, that is, the OPGW maximum ice-melting length, see formula (8).

[0043] (8) In the formula, l max is the OPGW maximum ice-melting length, km. is the first OPGW maximum ice-melting length, km. is the second OPGW maximum ice-melting length, km. is the third OPGW maximum ice-melting length, km.

[0044] Taking a specific type of iced OPGW line in the field as an example, the following application of the optimization calculation method of the application is used to calculate the OPGW maximum allowable ice-melting current and the maximum ice-melting length, and the specific steps are as follows: a) obtain the OPGW type, structure type and on-line monitoring device monitoring parameters during icing of the field high-voltage transmission line. The OPGW line type is OPGW-12B1+2A1a-68, the structure type is OPGW diameter: 11.4 mm, and the ice-melting conductor is 23% aluminum-clad steel wire. The OPGW line sectional view is shown in Figure 4 . The OPGW line fiber highest temperature before and after ice shedding during icing of the on-line monitoring device in the field is shown in Table 1. The on-line monitoring device monitoring parameters during icing in the field are shown in Figure 5 .

[0045] Table 1 OPGW line fiber highest temperature before and after ice shedding / ℃

[0046] b) Obtain the maximum temperature of OPGW cable before and after deicing, which is monitored by the online monitoring device. As shown in Table 1, the maximum temperature of OPGW cable before deicing is 12.6℃, and the maximum temperature of OPGW cable after deicing is 8℃.

[0047] c) In step b), the maximum temperature of OPGW cable before deicing is 12.6℃, and the maximum temperature of OPGW cable after deicing is 8℃. Among them, the line R T0 =0.03W -1 ·m·℃; R T2 =0.095W -1 ·m·℃; r T =0.9954 / m, the maximum allowable ice melting current of OPGW before deicing ; R c =0.0419m; h c =35W / (m 2 ·℃); T pn =8℃; T a =5℃; r T =0.9954 , the maximum allowable ice melting current of OPGW after deicing ; comparison, take the smaller value of the two, , as the maximum allowable ice melting current of OPGW.

[0048] d) Obtain the output power of DC ice melting device P 0=48kW; output voltage U 0=35kV, the insulation withstand voltage level of OPGW line U f =70kV, calculate the first maximum ice melting length of OPGW ; the second maximum ice melting length of OPGW ; the third maximum ice melting length of OPGW .

[0049] e) comparison in step d), calculate the three maximum ice melting lengths of OPGW, take the minimum value of the three, , that is, the maximum ice melting length of OPGW.

[0050] In summary, the entire process of the calculation method for the maximum allowed ice-melting current and the maximum ice-melting length of OPGW on site is completed.

[0051] Embodiment 2 The embodiment provides a calculation system for the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, which is used to realize the calculation method in embodiment 1 and is composed of a data acquisition unit, an optical cable temperature maximum value calculation unit, a maximum allowed ice-melting current acquisition unit, a maximum ice-melting length calculation unit and a maximum ice-melting length selection unit, as shown in the figure. Figure 6

[0052] The data acquisition unit is used to acquire the OPGW type, the structure type and each parameter monitored by the on-site online monitoring device during icing, and is used to realize step a) in embodiment 1, which will not be repeated here.

[0053] The optical cable temperature maximum value calculation unit is used to calculate the highest internal temperature of OPGW before and after ice shedding according to the data acquired by the data acquisition unit, and is used to realize step b) in embodiment 1, which will not be repeated here.

[0054] The maximum allowed ice-melting current acquisition unit is used to calculate the maximum allowed ice-melting current of OPGW before and after ice shedding according to the highest internal temperature of OPGW before and after ice shedding, and take the smaller value as the maximum allowed ice-melting current of OPGW, and is used to realize step c) in embodiment 1, which will not be repeated here.

[0055] The maximum ice-melting length calculation unit is used to acquire the output power, the output voltage of the direct-current ice-melting device and the insulation withstand voltage level of OPGW, combine the maximum allowed ice-melting current of OPGW and calculate the corresponding three maximum ice-melting lengths of OPGW, and is used to realize step d) in embodiment 1, which will not be repeated here.

[0056] The maximum ice-melting length selection unit is used to select the minimum value of the three maximum ice-melting lengths of OPGW in the maximum ice-melting length calculation unit as the final maximum ice-melting length of OPGW, and is used to realize step e) in embodiment 1, which will not be repeated here.

[0057] ​It should be noted that each module in the above-mentioned system for calculating the maximum allowed ice-melting current and the maximum ice-melting length of OPGW can be realized by software, hardware, or a combination thereof, in whole or in part. Each module can be embedded in or independent of a processor in a computer device in hardware form, or stored in a memory in the computer device in software form, so as to be called and executed by the processor to perform the operations corresponding to each module. For specific limitations of the system for calculating the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, refer to the limitations of the method for calculating the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, which have the same functions and effects, and will not be described here.

[0058] The above description of the embodiments is to facilitate those skilled in the art to understand and apply the present application. Those skilled in the art can easily make various modifications to the above embodiments, and apply the general principles described herein to other embodiments without creative labor. Therefore, the present application is not limited to the above embodiments, and any improvements and modifications made to the present application by those skilled in the art based on the disclosure of the present application shall be within the scope of protection of the present application.

Claims

1. A method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW, characterized in that: Including steps: a) Obtain the OPGW model, structural type, and various parameters monitored by the on-site online monitoring device during icing; b) calculating the maximum internal temperature of the OPGW optical cable before and after de-icing based on the data obtained in step a); c) Calculate the maximum allowable ice-melting current of the OPGW before and after de-icing based on the maximum internal temperature of the OPGW optical cable before and after de-icing, and take the smaller value as the maximum allowable ice-melting current of the OPGW; d) Obtain the output power and output voltage of the DC ice-melting device and the insulation withstand voltage level of the OPGW, and calculate the corresponding maximum ice-melting lengths of the three OPGWs based on the maximum allowable ice-melting current of the OPGW; e) taking the minimum value of the three OPGW maximum ice melting lengths obtained in step d) as the final OPGW maximum ice melting length.

2. The calculation method of the maximum allowable ice melting current and the maximum ice melting length of the OPGW according to claim 1 is characterized in that: In step a), the parameters monitored by the on-site online monitoring device during icing are the temperature values ​​of various points along the OPGW interior during icing using distributed temperature sensors. When the points are distributed along the OPGW line, at least three temperature monitoring points are set per span.

3. The calculation method of the maximum allowable ice melting current and the maximum ice melting length of the OPGW according to claim 1 is characterized in that: In step b), the specific process of calculating the maximum internal temperature of the OPGW optical cable before de-icing includes: Obtain the maximum temperature value of each point along the OPGW cable monitored by the distributed temperature sensor before de-icing, and take the maximum value of all the maximum temperature values ​​as the maximum temperature value inside the OPGW optical cable before de-icing.

4. The method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW according to claim 1, characterized in that: In step b), the specific process of calculating the maximum internal temperature of the OPGW optical cable after de-icing includes: Obtain the maximum temperature value of each point along the OPGW cable monitored by the distributed temperature sensor after de-icing, and take the maximum value of all the maximum temperature values ​​as the maximum temperature value inside the OPGW cable after de-icing.

5. The method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW according to claim 1, characterized in that: In step c), the formula for calculating the maximum allowable ice-melting current of the OPGW before de-icing is as follows: ， Where, I m is the maximum allowable ice-melting current of OPGW before de-icing, A; T pm is the maximum internal temperature of the OPGW optical cable before de-icing, °C; R T0 W is the equivalent thermal conduction resistance per unit length of the air gap at the time of deicing. -1 m℃; R T2 W is the equivalent thermal resistance per unit length between the optical fiber inside the OPGW and the surface of the OPGW, -1 m℃; r T for T The unit length resistance of OPGW ice melting conductor at ℃, / m; T Indicates the temperature of the OPGW ice-melting conductor.

6. The method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW according to claim 1, characterized in that: In step c), the formula for calculating the maximum allowable ice-melting current of the OPGW after de-icing is as follows: ， Where, I n is the maximum allowable ice-melting current of OPGW after de-icing, A; h c is the heat exchange coefficient per unit surface of OPGW, W / (m 2 ℃); R c is the radius of OPGW, m; T pn is the maximum internal temperature of the OPGW optical cable after de-icing, °C; T a is the ambient temperature, °C; R T2 W is the equivalent thermal resistance per unit length between the optical fiber inside the OPGW and the surface of the OPGW, -1 m℃; r T for T The unit length resistance of OPGW ice melting conductor at ℃, / m; T Indicates the temperature of the OPGW ice-melting conductor.

7. The method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW according to claim 1, characterized in that: In step d), the maximum ice-melting length of the first OPGW is calculated based on the output power of the DC ice-melting device, and the formula is as follows: ， Where, is the maximum ice melting length of the first OPGW, km; P 0 is the output power of the DC ice melting device, W; I max is the maximum allowable ice melting current of OPGW, A; r 0 is the ice melting resistance per unit length of OPGW, Ω / km.

8. The method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW according to claim 1, characterized in that: In step d), the maximum ice-melting length of the second OPGW is calculated based on the output voltage of the DC ice-melting device, and the formula is as follows: ， Where, is the maximum ice melting length of the second OPGW, km; U 0 is the output voltage of the DC ice melting device, V; I max is the maximum allowable ice melting current of OPGW, A; r 0 is the ice melting resistance per unit length of OPGW, Ω / km.

9. The method for calculating the maximum allowable ice melting current and maximum ice melting length of an OPGW according to claim 1, characterized in that: In step d), the maximum ice melting length of the third OPGW is calculated based on the insulation withstand voltage level of the OPGW line, and the formula is as follows: ， Where: is the maximum ice melting length of the third OPGW, km; U f is the insulation withstand voltage level of the OPGW line, V; I max is the maximum allowable ice melting current of OPGW, A; r 0 is the ice melting resistance per unit length of OPGW, Ω / km.

10. A calculation system for the maximum allowable ice melting current and maximum ice melting length of an OPGW, used to implement the calculation method according to any one of claims 1 to 9, characterized in that: include: Data acquisition unit: used to obtain the OPGW model, structural type and various parameters monitored by the on-site online monitoring device during icing; Optical cable temperature maximum value calculation unit: calculates the maximum internal temperature of the OPGW optical cable before and after de-icing based on the data obtained by the data acquisition unit; Maximum allowable ice-melting current acquisition unit: Calculates the maximum allowable ice-melting current of the OPGW before and after ice-shedding based on the maximum internal temperature of the OPGW optical cable before and after ice-shedding, and takes the smaller value as the maximum allowable ice-melting current of the OPGW; Maximum ice melting length calculation unit: used to obtain the output power, output voltage and insulation withstand voltage level of the DC ice melting device, combined with the maximum allowable ice melting current of the OPGW, and calculate the corresponding maximum ice melting lengths of the three OPGWs; Maximum ice melting length selection unit: selects the minimum value of the three OPGW maximum ice melting lengths obtained in the maximum ice melting length calculation unit as the final OPGW maximum ice melting length.

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