An OPGW maximum allowed ice-melting current and maximum ice-melting length calculation method and system

Abstract

The application discloses a kind of OPGW maximum allowed ice-melting current and the calculation method and system of maximum ice-melting length.Currently, the determination of OPGW maximum ice-melting current needs to be simulated modeling and multiple iteration optimization analysis and calculation by using finite element, and the response to on-site icing fault is not fast and timely enough.The application obtains the highest value of OPGW cable internal temperature before and after ice shedding during icing period monitored by on-site online monitoring device by obtaining the type and structure type of OPGW line, and calculates the maximum allowed ice-melting current of OPGW;And considering the output power, output voltage of OPGW DC ice-melting device and the insulation withstand voltage level of OPGW line, the maximum ice-melting length of OPGW is calculated.The application provides theoretical support for the maximum allowed ice-melting current of OPGW without relying on finite element software modeling simulation calculation, which is helpful for remote icing monitoring and fault response of high-voltage transmission line, and provides reference for the subsequent setting of OPGW DC ice-melting device.

Description

TECHNICAL FIELD

[0001] The 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, line icing failure events occur frequently. Icing leads to damage of line towers, tripping of transmission lines, and breakage of optical cable channels, which seriously affects the safe operation of lines.

[0003] In the current OPGW ice-melting scheme design, 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 occurrence of icing failure 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 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 failure of high-voltage transmission lines, and also to provide a reference for subsequent OPGW DC ice-melting scheme design.

[0006] To this end, the application adopts a technical scheme as follows: a calculation method for the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, comprising the steps of:

[0007] a) obtaining the model and structure type of OPGW and each parameter monitored by online monitoring devices in the field during icing;

[0008] b) calculating the maximum internal temperature of OPGW optical cables before and after ice shedding according to the data obtained in step a);

[0009] c) According to the highest internal temperature of OPGW before and after ice shedding, the maximum allowed ice melting current of OPGW before and after ice shedding is calculated, and the smaller one is taken as the maximum allowed ice melting current of OPGW;

[0010] d) Obtain the output power, output voltage of the DC 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;

[0011] e) Take the minimum value of the three maximum ice melting lengths of OPGW obtained in step d) as the final maximum ice melting length of OPGW.

[0012] Further, in step a), the parameters monitored by the on-site online monitoring device during icing are the temperature values of OPGW internal points along the line monitored by distributed temperature sensors during icing. When the points are distributed along the OPGW line, at least 3 temperature monitoring points are set per span.

[0013] Further, in step b), the specific process of calculating the highest internal temperature of OPGW before ice shedding includes:

[0014] Obtain the highest temperature of OPGW internal points along the line monitored by the distributed temperature sensor before ice shedding, and take the maximum value of all the highest temperatures as the highest internal temperature of OPGW before ice shedding.

[0015] Further, in step b), the specific process of calculating the highest internal temperature of OPGW after ice shedding includes:

[0016] Obtain the highest temperature of OPGW internal points along the line monitored by the distributed temperature sensor after ice shedding, and take the maximum value of all the highest temperatures as the highest internal temperature of OPGW after ice shedding.

[0017] Further, in step c), the formula for calculating the maximum allowed ice melting current of OPGW before ice shedding is as follows:

[0018] ,

[0019] In the formula, I m is the maximum allowed ice melting current of OPGW before ice shedding, A; T pm is the highest internal temperature of OPGW before ice shedding, ℃; R T0 is the unit length equivalent conduction thermal resistance of air gap at the moment of ice shedding, W -1 ·m·℃; R T2 is the unit length equivalent conduction thermal resistance between the optical fiber inside OPGW and the surface of OPGW, W-1 m·℃; r T For T the unit length resistance of OPGW ice-melting conductor at 0 / m; T represents the temperature of OPGW ice-melting conductor.

[0020] Further, in step c), the formula for calculating the maximum allowed ice-melting current of OPGW after ice shedding is as follows:

[0021] ,

[0022] In the formula, I n is the maximum allowed ice-melting 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 optical 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 For T the unit length resistance of OPGW ice-melting conductor at 0 / m; T represents the temperature of OPGW ice-melting conductor.

[0023] Further, in step d), the first maximum ice-melting length of OPGW is calculated according to the output power of the DC ice-melting device, and the formula is as follows:

[0024] ,

[0025] In the formula, is the first maximum ice-melting length of OPGW, km; P 0 is the output power of the DC ice-melting device, W; I max is the maximum allowed ice-melting current of OPGW, A; r 0 is the ice-melting resistance per unit length of OPGW, Ω / km.

[0026] Further, in step d), the second maximum ice-melting length of OPGW is calculated according to the output voltage of the DC ice-melting device, and the formula is as follows:

[0027] ,

[0028] 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.

[0029] Further, in step d), the third OPGW maximum ice-melting length is calculated according to the OPGW line insulation withstand voltage level, and the formula is as follows:

[0030] ,

[0031] In the formula, is the third OPGW maximum ice-melting length, km; U f is the OPGW line insulation withstand voltage level, V.

[0032] 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 realizing the above calculation method, which comprises:

[0033] a data acquisition unit for acquiring the OPGW type, structure type, and each parameter monitored by the on-site online monitoring device during icing;

[0034] 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;

[0035] 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 OPGW maximum allowable ice-melting current;

[0036] a maximum ice-melting length calculation unit for acquiring the output power, output voltage and OPGW insulation withstand voltage level of the DC ice-melting device, combining the OPGW maximum allowable ice-melting current, and calculating the corresponding three OPGW maximum ice-melting lengths;

[0037] 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.

[0038] Compared with the prior art, the present application has the beneficial effects as follows: the present application does not need to carry out finite element simulation modeling for the iced line, after obtaining the OPGW model, structure type of the on-site high-voltage transmission line and the highest temperature inside the OPGW cable at each point along the line of the on-site online monitoring device, the maximum allowed ice-melting current of the OPGW is calculated; then the output power, output voltage of the DC ice-melting device and the insulation withstand voltage level of the OPGW line are obtained, and the maximum ice-melting length of the OPGW is calculated accordingly. The present application can quickly obtain the maximum allowed ice-melting current and the maximum ice-melting length of the OPGW, improve the calculation efficiency, effectively support the on-site icing monitoring and timely response of the high-voltage transmission line fault, and also provide a reference for subsequent OPGW DC ice-melting scheme design. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 The flowchart of the present application for calculating the maximum allowed ice-melting current and the maximum ice-melting length of OPGW;

[0041] Figure 2 The flowchart of the specific calculation method of the maximum allowed ice-melting current of OPGW in the present application;

[0042] Figure 3 The flowchart of the specific calculation method of the maximum ice-melting length of OPGW in the present application;

[0043] Figure 4 The on-site OPGW line cross-section diagram in the specific embodiment of the present application;

[0044] Figure 5 The detection result diagram of the highest temperature inside the OPGW along the line before and after ice removal in the specific embodiment of the present application;

[0045] Figure 6 The composition diagram of the present application for calculating the maximum allowed ice-melting current and the maximum ice-melting length of OPGW;

[0046] 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. DETAILED DESCRIPTION

[0047] The technical solutions of the present application will be described clearly and completely in connection with the drawings. Obviously, the described embodiments are part of the 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 scope of protection of the present application.

[0048] Embodiment 1

[0049] The present embodiment is a calculation method of the maximum allowed ice-melting current and the maximum ice-melting length of OPGW, as shown in Figure 1 , the steps are as follows:

[0050] a) Obtain the OPGW model, structure type and each parameter monitored by the on-site online monitoring device during icing.

[0051] b) According to the data obtained in step a), calculate the maximum internal temperature of OPGW before and after ice shedding.

[0052] c) According to the maximum internal temperature of OPGW before and after ice shedding, calculate the maximum allowed ice-melting current of OPGW before and after ice shedding, and take the smaller value as the maximum allowed ice-melting current of OPGW.

[0053] The specific process of steps a), b) and c) is shown in Figure 2 .

[0054] d) Obtain the output power, output voltage and OPGW insulation withstand voltage level of the DC ice-melting device, combine the maximum allowed ice-melting current of OPGW, and calculate the corresponding three maximum ice-melting lengths of OPGW.

[0055] e) Take the minimum value of the three maximum ice-melting lengths of OPGW obtained in step d) as the final maximum ice-melting length of OPGW.

[0056] The specific process of steps d) and e) is shown in Figure 3 .

[0057] 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 line inside OPGW during icing by using a distributed temperature sensor, as shown in T 1、 T 2、 T 3、 T 4… T i …, i = 1, 2, 3, 4…; When the points are arranged along the OPGW line, at least 3 temperature monitoring points are arranged per pitch.

[0058] Specifically, in step b), the specific process of calculating the maximum internal temperature of the OPGW before icing is as follows: obtaining the maximum internal temperature of the OPGW at each point along the line monitored by the distributed temperature sensor before icing, and taking the maximum value of all the maximum internal temperatures as the maximum internal temperature of the OPGW before icing.

[0059] The specific process of calculating the maximum internal temperature of the OPGW after icing is as follows: obtaining the maximum internal temperature of the OPGW at each point along the line monitored by the distributed temperature sensor after icing, and taking the maximum value of all the maximum internal temperatures as the maximum internal temperature of the OPGW after icing.

[0060] The corresponding calculation formula is shown in formula (1).

[0061] (1)

[0062] In the formula, T pm is the maximum internal temperature of the OPGW before icing, ℃; T 1m , T 2m , T 3m , T 4m is the maximum internal temperature of the OPGW at each point along the line monitored by the distributed temperature sensor before icing, ℃; T pn is the maximum internal temperature of the OPGW after icing, ℃; T 1n , T 2n , T 3n , T 4n is the maximum internal temperature of the OPGW at each point along the line monitored by the distributed temperature sensor after icing, ℃; t is time, s; t 0 is the icing time, s.

[0063] Step c) is to calculate the maximum allowed ice melting current of the OPGW before and after icing according to the maximum internal temperature of the OPGW before and after icing, and take the smaller value as the maximum allowed ice melting current of the OPGW. The specific steps are as follows:

[0064] c1) The formula for calculating the maximum allowed ice melting current of the OPGW before icing is as follows:

[0065] (2)

[0066] In the formula, I mis the maximum allowed ice-melting current of OPGW before icing-off, A; T pm is the maximum internal temperature of OPGW before icing-off, ℃; R T0 is the unit length equivalent conduction thermal resistance of air gap at icing-off moment, W -1 ·m·℃; R T2 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 is the unit length resistance of OPGW ice-melting conductor at T ℃, / m; T represents the temperature of OPGW ice-melting conductor.

[0067] c2) the formula for calculating the maximum allowed ice-melting current of OPGW after icing-off is as follows:

[0068] (3)

[0069] wherein, I n is the maximum allowed ice-melting current of OPGW after icing-off, A; h c is the heat exchange coefficient of unit surface of OPGW, W / (m 2 ·℃); R c is the radius of OPGW, m; T pn is the maximum internal temperature of OPGW after icing-off, ℃; T a is the ambient temperature, ℃.

[0070] c3) after obtaining the maximum allowed ice-melting current of OPGW before and after icing-off, comparison is made, and the smaller value of the two is taken as the maximum allowed ice-melting current of OPGW, the calculation is shown in formula (4).

[0071] (4)

[0072] wherein, I max is the maximum allowed ice-melting current of OPGW, A; I m is the maximum allowed ice-melting current of OPGW before icing-off, A; I n is the maximum allowed ice-melting current of OPGW after icing-off, A.

[0073] Step d), obtain the output power, output voltage of the DC ice melting device and the OPGW insulation withstand level, combine the maximum allowed ice melting current of the OPGW, and calculate the corresponding three maximum ice melting lengths of the OPGW. The specific steps are as follows:

[0074] d1) obtain the output power, output voltage of the DC ice melting device and the OPGW insulation withstand level;

[0075] d2) calculate the first maximum ice melting length of the OPGW according to the output power of the DC ice melting device, see formula (5).

[0076] (5)

[0077] In the formula: is the first maximum ice melting length of the OPGW, km; P 0 is the output power of the DC ice melting device, W; I max is the maximum allowed ice melting current of the OPGW, A; r 0 is the ice melting resistance per unit length of the OPGW, Ω / km.

[0078] d3) calculate the second maximum ice melting length of the OPGW according to the output voltage of the DC ice melting device, see formula (6).

[0079] (6)

[0080] In the formula: is the second maximum ice melting length of the OPGW, km; U 0 is the output voltage of the DC ice melting device, V.

[0081] d4) calculate the third maximum ice melting length of the OPGW according to the OPGW line insulation withstand level, see formula (7).

[0082] (7)

[0083] In the formula: is the third maximum ice melting length of the OPGW, km; U f is the OPGW line insulation withstand level, V.

[0084] Step 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. The specific steps are as follows:

[0085] e1) obtain the three maximum ice melting lengths of the OPGW obtained in step d) , , ;

[0086] e2) Take the minimum value of the three values obtained in e1), which is the maximum ice-melting length of OPGW, see equation (8).

[0087] (8)

[0088] In the formula: l max Lmax is the maximum ice-melting length of OPGW, km; L1max is the first maximum ice-melting length of OPGW, km; L2max is the second maximum ice-melting length of OPGW, km; L3max is the third maximum ice-melting length of OPGW, km.

[0089] Taking a specific type of OPGW line with ice as an example, the maximum allowable ice-melting current and the maximum ice-melting length of OPGW are calculated by using the optimization calculation method of the present application, and the specific steps are as follows:

[0090] a) Obtain the type, structure type and monitoring parameters of the on-line monitoring device during icing of the OPGW of the high-voltage transmission line. The type of the OPGW line 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 cross-sectional view of the OPGW line is shown in FIG. 1. The maximum temperature of the OPGW along the line before and after ice shedding during icing of the on-line monitoring device is shown in Table 1. The monitoring parameters of the on-line monitoring device during icing are shown in Table 2. Figure 4 Figure 5

[0091] Table 1 Maximum temperature of OPGW along the line before and after ice shedding during icing / ℃

[0092]

[0093] b) Obtain the maximum temperature of the OPGW cable before and after ice shedding in the two stages before and after ice shedding monitored by the on-line monitoring device. As shown in Table 1, the maximum temperature of the OPGW cable before ice shedding is 12.6 ℃, and the maximum temperature of the OPGW cable after ice shedding is 8 ℃.

[0094] c) Obtain the maximum temperature of the OPGW cable before ice shedding 12.6 ℃ and the maximum temperature of the OPGW cable after ice shedding 8 ℃ in step b). Among them, the line R T0 = 0.03 W -1 · m · ℃; R T2 = 0.095 W -1 · m · ℃; r T = 0.9954​​ / m, the maximum ice-melting current of OPGW before ice shedding ; R c = 0.0419 m; h c = 35 W / (m 2 ·℃); T pn = 8℃; T a = 5℃; r T = 0.9954 , the maximum ice-melting current of OPGW after ice shedding ; comparison is made, and the smaller value is taken, , as the maximum ice-melting current of OPGW.

[0095] d) obtaining the output power of the direct-current ice-melting device P 0 = 48 kW; the output voltage U 0 = 35 kV, the insulation withstand voltage level of OPGW line U f = 70 kV, the first maximum ice-melting length of OPGW is calculated ; the second maximum ice-melting length of OPGW is calculated ; the third maximum ice-melting length of OPGW is calculated .

[0096] e) comparison is made among the three maximum ice-melting lengths of OPGW calculated in step d), and the smallest value is taken, , as the maximum ice-melting length of OPGW.

[0097] In summary, the entire process of the calculation method for the maximum ice-melting current and the maximum ice-melting length of OPGW on site is completed.

[0098] Embodiment 2

[0099] The embodiment provides a calculation system for the maximum ice-melting current and the maximum ice-melting length of OPGW, which is used to implement the calculation method in Embodiment 1 and is composed of a data acquisition unit, an optical cable temperature maximum value calculation unit, a maximum ice-melting current acquisition unit, a maximum ice-melting length calculation unit and a maximum ice-melting length selection unit, as shown in Figure 6 .

[0100] 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 implement step a) in Embodiment 1, which is not described herein again.

[0101] The optical cable temperature maximum value calculation unit calculates the highest internal temperature of the OPGW before and after ice shedding according to the data obtained by the data acquisition unit, and is used to implement step b) in Embodiment 1, which will not be repeated here.

[0102] The maximum allowed ice melting current acquisition unit calculates the maximum allowed ice melting current of the OPGW before and after ice shedding according to the highest internal temperature of the OPGW before and after ice shedding, and takes the smaller value of the two as the maximum allowed ice melting current of the OPGW; and is used to implement step c) in Embodiment 1, which will not be repeated here.

[0103] The maximum ice melting length calculation unit is used to obtain the output power, output voltage and OPGW insulation withstand voltage level of the DC ice melting device, combine the maximum allowed ice melting current of the OPGW, and calculate the corresponding three maximum ice melting lengths of the OPGW; and is used to implement step d) in Embodiment 1, which will not be repeated here.

[0104] The maximum ice melting length selection unit selects the minimum value of the three maximum ice melting lengths of the OPGW obtained in the maximum ice melting length calculation unit as the final maximum ice melting length of the OPGW; and is used to implement step e) in Embodiment 1, which will not be repeated here.

[0105] It should be noted that each module in the above-mentioned OPGW maximum allowed ice melting current and maximum ice melting length calculation system can be realized by software, hardware and their combinations, in whole or in part. Each module can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the 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 the specific limitations of the OPGW maximum allowed ice melting current and maximum ice melting length calculation system, refer to the limitations of the OPGW maximum allowed ice melting current and maximum ice melting length calculation method in the above, which have the same functions and effects, and will not be repeated here.

[0106] The above description of the embodiments is for the purpose of facilitating 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 the improvements and modifications made by those skilled in the art to the present application according to the disclosure of the present application should be within the scope of protection of the present application.

Claims

1. A method for calculating the maximum allowable de-icing current and maximum de-icing length of an OPGW, characterized in that, Including the following steps: a) Obtain the OPGW model, structural type, and various parameters monitored by the on-site online monitoring device during icing; b) Based on the data obtained in step a), calculate the maximum internal temperature of the OPGW optical cable before and after de-icing; c) Based on the highest internal temperature of the OPGW optical cable before and after de-icing, calculate the maximum allowable de-icing current of the OPGW before and after de-icing, and take the smaller value of the two as the maximum allowable de-icing current of the OPGW. d) Obtain the output power, output voltage, and OPGW insulation withstand voltage level of the DC de-icing device, combine them with the maximum allowable de-icing current of the OPGW, and calculate the corresponding maximum de-icing length of the three OPGWs. e) Take the minimum of the three maximum OPGW melting lengths obtained in step d) as the final maximum OPGW melting length; 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, using the following formula: ， In the formula, The maximum melting length of the first OPGW, in km; P 0 represents the output power of the DC ice-melting device, in W; I max The maximum allowable de-icing current for OPGW is in A; r 0 represents the de-icing resistance per unit length of OPGW, in Ω / km; The maximum ice-melting length of the second OPGW is calculated based on the output voltage of the DC ice-melting device, using the following formula: ， In the formula, The maximum melting length of the second OPGW, in km; U 0 represents the output voltage of the DC ice-melting device, in V; 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: ， In the formula: The maximum melting length of the third OPGW, in km; U f The insulation withstand voltage level of the OPGW line is V.

2. The method for calculating the maximum allowable melting current and maximum melting length of OPGW according to claim 1, characterized in that, 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 the line monitored by distributed temperature sensors during icing. When setting up the monitoring points along the OPGW line, at least 3 temperature monitoring points are set up at each span.

3. The method for calculating the maximum allowable melting current and maximum melting length of OPGW according to claim 1, characterized in that, Step b) involves calculating the maximum internal temperature of the OPGW optical cable before de-icing, including the following steps: Before de-icing, obtain the highest temperature values ​​at various points along the OPGW interior monitored by distributed temperature sensors, and take the maximum value among all the highest temperature values ​​as the highest internal temperature value of the OPGW optical cable before de-icing.

4. The method for calculating the maximum allowable melting current and maximum melting length of OPGW according to claim 1, characterized in that, Step b) involves calculating the maximum internal temperature of the OPGW optical cable after de-icing, including the following steps: After de-icing, the highest temperature values ​​at various points along the OPGW are obtained from the distributed temperature sensors. The maximum value among all the highest temperature values ​​is taken as the highest internal temperature value of the OPGW optical cable after de-icing.

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

6. The method for calculating the maximum allowable melting current and maximum melting length of OPGW according to claim 1, characterized in that, In step c), the formula for calculating the maximum allowable de-icing current of the OPGW after de-icing is as follows: ， In the formula, I n The maximum allowable de-icing current of the OPGW after de-icing is expressed in A. h c The heat transfer coefficient per unit surface area of ​​OPGW is W / (m²). 2 ·℃); R c Let be the radius of the OPGW, in meters. T pn This represents the highest internal temperature of the OPGW optical cable after de-icing, in °C. T a The ambient temperature is in °C. R T2 W is the equivalent thermal resistance per unit length between the internal optical fiber and the surface of the OPGW. -1 ·m·℃; r T for T Resistance per unit length of the OPGW ice-melting conductor at ℃ / m; T This indicates the temperature of the OPGW de-icing conductor.

7. A calculation system for the maximum allowable melting current and maximum melting length of an OPGW, used to implement the calculation method according to any one of claims 1-6, characterized in that, include: Data acquisition unit: used to acquire the OPGW model, structural type, and various parameters monitored by the on-site online monitoring device during icing; Maximum temperature calculation unit for optical cable: 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 de-icing current acquisition unit: Based on the highest internal temperature of the OPGW optical cable before and after de-icing, calculate the maximum allowable de-icing current of the OPGW before and after de-icing, and take the smaller value of the two as the maximum allowable de-icing current of the OPGW. Maximum ice melting length calculation unit: used to obtain the output power, output voltage and OPGW insulation withstand voltage level of DC ice melting device, combined with the maximum allowable ice melting current of OPGW, and calculate the corresponding maximum ice melting length of the three OPGWs accordingly; Maximum melting length selection unit: Select the minimum value of the three OPGW maximum melting lengths obtained in the maximum melting length calculation unit as the final OPGW maximum melting length.

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