Low-frequency ice melting device and method for power transmission line of power distribution network

Abstract

The invention discloses a low-frequency ice melting device for a distribution network power transmission line. A power supply module receives electric energy from a transformer and processes the electric energy; the rectifying unit is used for converting power frequency alternating current into direct current; the inversion unit is used for converting direct current into low-frequency alternating current; the information acquisition unit is used for acquiring the line temperature and the icing thickness on the icing line and feeding back the line temperature and the icing thickness to the control unit; the control unit is used for receiving the electric energy, calculating output power and output current according to the parameter information, the line temperature and the icing thickness, generating an ice melting instruction, executing the ice melting instruction and adjusting the output power and the output current; and the cooperative ice-melting switch is controlled according to the ice-melting execution instruction, wherein the inversion unit outputs low-frequency alternating current to the ice-coated line. Low-frequency alternating current is applied to a power transmission line of a distribution network, the ice melting distance is increased, three-phase simultaneous symmetric ice melting is achieved, the asymmetric pole falling phenomenon is avoided, frequent switching is avoided, and the working efficiency is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ice melting in distribution networks, and specifically relates to a low-frequency ice melting device and method for power transmission lines in a distribution network. Background Art

[0002] Icing is one of the natural disasters that poses the greatest threat to the safe operation of power grids. At present, line icing monitoring and ice-melting devices are mainly concentrated in the main grid, and the distribution network still mainly relies on manual ice observation, manual ice knocking and transformer AC ice melting. The ability to support ice melting and de-icing technology is insufficient, and it is difficult to meet the urgent requirements of digital transformation of power grids and highly reliable power supply. The installation and operation efficiency of existing ice melting technology is low, and the safety, scientificity, ice melting distance and efficiency need to be improved.

[0003] Thermal ice melting uses an external heat source or the self-heating of the conductor to prevent ice and snow from accumulating on the conductor, or to melt the accumulated ice and snow. The representative solution in the main grid of the transmission line is the short-circuit current ice melting method. Short-circuit current ice melting is divided into AC short-circuit ice melting and DC short-circuit ice melting. The two methods respectively apply industrial frequency AC and DC to the line to heat the conductor to achieve the purpose of ice melting. Specifically, when DC ice melting is used, three-phase symmetrical ice melting cannot be achieved. During the ice melting process, the knife switch needs to be operated to switch the ice melting phase line, which is not only inconvenient to operate but may also cause asymmetric pole collapse. When AC industrial frequency ice melting is used, the ice melting distance is not long enough and the efficiency is low. Summary of the invention

[0004] In view of the defects and improvement needs of the prior art, the low-frequency ice-melting device and method for distribution network transmission lines disclosed in the present invention increases the capacity of the device by fixing the physical position of the device. By applying low-frequency alternating current with an electric energy of less than 30 Hz to the distribution network transmission line, the defects of DC and AC ice-melting in the prior art are solved. Compared with the traditional industrial frequency transformer solution, the low-frequency ice-melting solution increases the ice-melting distance when the total power is provided by the same front-end ice-covered transformer. Secondly, compared with DC ice-melting, low-frequency ice-melting achieves simultaneous symmetrical ice-melting of three phases, avoids the phenomenon of asymmetric pole collapse, and avoids switching like DC ice-melting, which greatly improves the operating efficiency. Then, according to the principle of equal voltage-frequency ratio, the secondary side voltage of the distribution transformer on the ice-covered line is always within the safe voltage, so it does not need to be disconnected, which greatly improves the ice-melting efficiency.

[0005] To achieve the above-mentioned object, according to one aspect of the present invention, a low-frequency ice-melting device for a distribution network transmission line is provided, comprising: a power module, a control unit, a rectifier unit, an inverter unit, an information acquisition unit, and a coordinated ice-melting switch;

[0006] The power module is connected to the transformer, and is used to receive electric energy from the transformer and process the electric energy;

[0007] The rectifier unit is connected to the power module and is used to convert the industrial frequency alternating current provided by the power module into direct current;

[0008] The inverter unit is connected to the rectifier unit and is used to convert the direct current output by the rectifier unit into low-frequency alternating current;

[0009] The information acquisition unit is used to collect the line temperature and ice thickness on the ice-covered line and feed them back to the control unit;

[0010] The control unit receives the electric energy provided by the power module, calculates the output current according to the parameter information, the line temperature and the ice thickness, generates an ice melting instruction, executes the ice melting instruction and adjusts the output current;

[0011] The coordinated ice-melting switch is connected to the control unit and the inverter unit, and is controlled by the ice-melting instruction sent by the control unit.

[0012] The inverter unit outputs the low-frequency alternating current to the ice-covered circuit through the cooperative ice-melting switch.

[0013] Furthermore, the power supply module is used to filter and perform reactive power compensation on the electric energy.

[0014] Preferably, the control unit is further used to receive the parameter information from a host computer, wherein the parameter information includes the length of the ice-melting line, the type of the ice-melting line conductor, the geometric average distance between the ice-melting lines, and the ice-melting current protection value.

[0015] Preferably, the output voltage and output power calculation formula are as follows:

[0016]

[0017] Wherein, I is the current flowing through the ice-covered line, and its value is mainly related to the line temperature and the ice thickness; U1 is the effective value of the high-voltage side voltage of the transformer; and Z is the impedance of the ice-covered line, which is related to the line parameters.

[0018] Preferably, the relationship between the output voltage and frequency of the transformer is as follows:

[0019]

[0020] Wherein, f is the frequency of the output voltage, U1 is the effective value of the voltage on the high-voltage side of the transformer, W1 is the number of turns on the high-voltage side of the transformer, Φ m is the main magnetic flux of the transformer core, the frequency f of the output voltage U1 ranges from 5 to 30 Hz, and the output voltage U1 ranges from 400 to 1800 V.

[0021] Preferably, the ice-melting instruction includes preset ice-melting time information, and the preset ice-melting time is sent to the control module via a host computer.

[0022] The present invention discloses a working method of a low-frequency ice melting device for a distribution network transmission line, comprising:

[0023] S11: The power module receives electric energy from the transformer and processes the electric energy;

[0024] S12: The control unit receives the electric energy provided by the power module, calculates the output current according to the parameter information, the line temperature and the ice thickness, generates an ice melting instruction, executes the ice melting instruction and adjusts the output current;

[0025] S13: The rectifier unit converts the industrial frequency alternating current provided by the power module into direct current;

[0026] S14: The inverter unit converts the direct current output by the rectifier unit into low-frequency alternating current;

[0027] S15: The coordinated ice-melting switch is controlled by the ice-melting instruction sent by the control unit, and the inverter unit outputs the low-frequency alternating current to the ice-covered line through the coordinated ice-melting switch;

[0028] S16: The information acquisition unit collects the line temperature and the ice thickness on the ice-covered line in real time and feeds back the information to the control unit. The control unit adjusts the output current according to the line temperature and the ice thickness.

[0029] The present invention also discloses a method for low-frequency ice melting of distribution network transmission lines, comprising:

[0030] S21: taking the ice-covered line offline from the system;

[0031] S22: Connect the low-frequency ice melting device, separate the load at the rear end of the branch transformer, and operate the end switch to short-circuit the three phases of the line;

[0032] S23: starting the low-frequency ice melting device to melt ice;

[0033] S24: Observation of ice melting is completed.

[0034] S25: End ice melting, restore the ice-covered line connection, and restore the line switch.

[0035] Preferably, the method comprises monitoring the temperature of the end knife switch contact point.

[0036] In general, through the above technical scheme conceived by the present invention, by real-time adjustment of the output power and output current of low-frequency ice melting, the three-phase simultaneous ice melting avoids the asymmetric pole collapse phenomenon and also avoids frequent switching during DC ice melting, thereby greatly improving the ice melting efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A structural diagram of a low-frequency ice melting device for a distribution network transmission line according to an embodiment of the present invention;

[0038] Figure 2 This is a working diagram of a low-frequency ice melting device for a distribution network transmission line according to an embodiment of the present invention;

[0039] Figure 3 A flow chart of a method for low-frequency ice melting of a distribution network transmission line according to an embodiment of the present invention; and

[0040] Figure 4 The figure is a specific application circuit example diagram of a low-frequency ice melting device for a distribution network transmission line according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0043] The embodiment of the present application realizes the effective melting of ice on the distribution network transmission lines through a low-frequency ice melting scheme and device for the distribution network transmission lines, and solves the operational complexity and asymmetric pole collapse risk in the DC ice melting scheme.

[0044] Figure 1 This is a module diagram of a low-frequency ice melting device for a distribution network transmission line according to an embodiment of the present invention. Figure 1As shown, the low-frequency ice melting device 10 includes a power module 1, a control unit 2, a rectifier unit 3, an inverter unit 4, an information acquisition unit 5 and a coordinated ice melting switch 6. The power module 1 is connected to the transformer 7 at the head end of the ice-covered line, and is used to receive electric energy from the transformer 7 and process the electric energy. The processing of the electric energy includes but is not limited to filtering and reactive power compensation; the rectifier unit 3 is connected to the power module 1, and is used to convert the industrial frequency AC power provided by the power module 1 into DC power; the inverter unit 4 is connected to the rectifier unit 3, and is used to convert the DC power output by the rectifier unit 3 into low-frequency AC power, and the voltage and frequency of the low-frequency AC power can be adjusted; the information acquisition unit 5 is connected to the ice-covered line 8 to be detected, and is used to collect the line temperature and ice thickness on the ice-covered line 8, and transmit the collected line temperature and ice thickness to the control unit 2 in real time. Here, the information acquisition unit 5 can transmit information between the control unit 2 through the built-in wireless communication module, but is not limited to this transmission method. The control unit 2 is connected to the power module 1, the rectifier unit 3, and the inverter unit 4, and is used to receive the electric energy provided by the power module, and calculate the output current according to the parameter information, the line temperature and the ice thickness, generate the ice melting instruction, execute the ice melting instruction and adjust the output current; the collaborative ice melting switch 6 is connected to the control unit 2 and the inverter unit 4, and is used to turn on / off the collaborative ice melting switch according to the execution ice melting instruction sent by the control unit 2, wherein the inverter unit 4 outputs low-frequency alternating current to the ice-covered line 8 through the collaborative ice melting switch.

[0045] Specifically, the control unit 2 calculates the output current using the following formula:

[0046]

[0047] Where I is the current flowing through the ice-covered line, and its value is mainly related to the line temperature and ice thickness, U1 is the effective value of the voltage on the high-voltage side of the transformer, and Z is the impedance of the ice-covered line, which is related to the line parameters. Secondly, the relationship between the output voltage U1 of the transformer 7 at the head end of the ice-covered line and the frequency is as follows:

[0048]

[0049] Among them, f is the frequency of the output voltage, U1 is the effective value of the voltage on the high-voltage side of the transformer, W1 is the number of turns on the high-voltage side of the transformer, Φ m is the main magnetic flux of the transformer core, the frequency f of the output voltage U1 ranges from 5 to 30 Hz, and the output voltage U1 ranges from 400 to 1800 V.

[0050] In one embodiment, the staff sends parameter information and instructions to the control unit 2 in the low-frequency ice melting device 10 through the host computer. The instructions sent by the host computer are the highest level. The staff intervenes in the execution of the low-frequency ice melting plan according to the real-time status of the site. Secondly, the staff understands the working status of the low-frequency ice melting device 10 in real time through the control unit 2. Specifically, the parameter information includes information such as the length of the ice melting line, the wire model of the ice melting line, the geometric average distance between the ice melting lines, the ambient temperature, the average ice thickness, the ice melting current protection value, but is not limited to the above information. When the ice-covered line 8 generates an ice-covered situation that needs to be handled, the ice-covered line 8 is disconnected from the system, connected to the low-frequency ice melting device 10, and the head end of the ice-covered line is connected to the load side of the low-frequency ice melting device 10, and the end switch is operated to short-circuit the three-phase circuit. The information acquisition unit 5 in the low-frequency ice melting device 10 obtains the line temperature and ice thickness from the ice-covered line. The staff sends parameter information and preset ice melting time to the low-frequency ice melting device 10 through the host computer. The control unit 2 calculates the output current required for ice melting based on the parameter information, line temperature and ice thickness. The control unit 2 instructs the inverter unit 4 to output an output current that meets the requirements, and the control unit 2 instructs the coordinated ice melting switch 6 to turn on. The low-frequency AC power is output to the ice melting line through the coordinated ice melting switch 6 to start the ice melting operation. The information acquisition unit 5 collects the line temperature and ice thickness in real time and feeds them back to the control unit 2. The staff can instruct the control unit to instruct the inverter unit 4 to adjust the output current in real time based on the real-time line temperature and ice thickness. When the user observes the ice melting falling on site, the control unit 2 is instructed to turn off the low-frequency ice melting device 10, and the low-frequency ice melting process ends. Those skilled in the art should understand that the ice falling situation of the line here can be judged based on the experience of the staff and is not limited to a specific value.

[0051] Figure 2 This is a working diagram of a low-frequency ice melting device for a distribution network transmission line according to an embodiment of the present invention. Figure 2 Will combine Figure 1 To describe, the working process of the low-frequency ice melting device 10 is as follows:

[0052] S11: The power module 1 receives electric energy from the transformer and processes the electric energy. Specifically, the transformer is Figure 1 In the ice-covered line head-end transformer 7, the power module 1 processes the received electric energy including but not limited to filtering and reactive power compensation processing.

[0053] S12: The control unit 2 receives the electric energy provided by the power module 1, and calculates the output current according to the parameter information, the line temperature and the ice thickness, generates an ice melting instruction, executes the ice melting instruction and adjusts the output current. Specifically, the parameter information here is sent to the control unit 2 by the staff through the host computer, wherein the parameter information includes but is not limited to the length of the ice melting line, the model of the conductor of the ice melting line, the geometric average distance between the ice melting lines, the ambient temperature, the average thickness of the ice, the ice melting current protection value and other information, and the information acquisition unit 5 collects the line temperature and ice thickness information.

[0054] S13: The rectifier unit 3 converts the industrial frequency AC power provided by the power module 1 into DC power.

[0055] S14: The inverter unit 4 converts the DC power outputted by the rectifier unit 3 into low-frequency AC power. Specifically, the control unit 2 adjusts the switching frequency of the switch tubes in the rectifier unit 3 and the inverter unit 4 to output low-frequency AC power that meets the output frequency and output current requirements.

[0056] S15: The coordinated ice-melting switch 6 is controlled by the execution ice-melting instruction sent by the control unit 2, and the inverter unit 4 outputs low-frequency AC power to the ice-covered line 8 through the coordinated ice-melting switch 6. Specifically, the output current of the low-frequency AC power and the corresponding output voltage and output power are values ​​calculated by the control unit 2.

[0057] S16: The information acquisition unit 5 collects the line temperature and ice thickness on the ice-covered line in real time and feeds back to the control unit 2. The staff adjusts the output current through the control unit 2 according to the line temperature and ice thickness.

[0058] In one embodiment, the instruction sent by the host computer is the highest level, and the staff can intervene in the execution of the low-frequency ice melting plan according to the real-time status on site. Secondly, the staff can understand the working status of the low-frequency ice melting device 10 in real time through the control unit 2.

[0059] Figure 3 The present invention is a flow chart of a method for low-frequency ice melting of distribution network transmission lines according to an embodiment of the present invention. Figure 3 Will combine Figure 1 and Figure 2 Describe, such as Figure 3 As shown, the low-frequency ice melting method includes the following steps:

[0060] S21: Take the ice-coating line 8 offline from the system.

[0061] S22: Connect the low-frequency ice-melting device 10, separate the rear-end load of the branch transformer, operate the terminal switch, short-circuit the three phases of the line, and melt the ice on the lines after the three phases are short-circuited at the same time. The conditions and schemes for the ice-melting treatment are the same.

[0062] S23: Start the low-frequency ice melting device 10 to melt ice, wherein the working process of the low-frequency ice melting device 10 is as follows: Figure 1 and Figure 2 .

[0063] S24: Observe the melting and falling of ice. After the ice melting is completed, the host computer sends an ice melting end instruction to the control unit 2 to determine that the ice melting is completed.

[0064] S25: end ice melting, restore the connection of ice-covered line 8, and restore the line switch.

[0065] Figure 4 The figure is a specific application circuit example diagram of a low-frequency ice melting device for a distribution network transmission line according to an embodiment of the present invention. Figure 4 Will combine Figure 1 , Figure 2 as well as Figure 3 The following is a description of the process of melting ice using the low-frequency ice-melting device disclosed in the present invention, taking a 10kV busbar ice-covered line as an example. First, disconnect the circuit breaker or knife switch behind the front-end transformer on the main line to cut off the power supply of the ice-covered line, and then disconnect the substation load from the main line. The specific operation is to disconnect the low-voltage side of the 10kV / 400V substation transformer of all branches at the rear end of this line, such as branch line 1 and branch line 2, and then short-circuit the ice-melting short-circuit switch K4 at the end of the ice-covered line, short-circuit the three phases of the ice-covered line together, and replace the circuit breaker or knife switch behind the front-end transformer with a low-frequency ice-melting device 10 to connect to the main line. When the low-frequency ice-melting device 10 is connected to the cooperative ice-melting switch 6 used at the rear end, the front end connects the transformer 7 at the head end of the ice-covered line to the power module 1 of the low-frequency ice-melting device, and installs multiple information acquisition modules 5 with wireless functions on the ice-covered line. The information acquisition module 5 can collect the line temperature and ice thickness, and the wiring preparation work before ice melting is completed.

[0066] Furthermore, when the power system standard inspection wiring is completed, the staff sends the length of the ice melting line, the type of the ice melting line conductor, the geometric average distance between the ice melting lines, the ambient temperature, the approximate average thickness of ice, the ice melting current protection value and other parameter information to the control unit 2 in the low-frequency ice melting device through the host computer, and the control unit 2 calculates the output current required for ice melting. After the staff confirms that it is correct, the control unit 2 sends an ice melting instruction to the control unit 2, and the control unit 2 outputs the calculated low-frequency alternating current by adjusting the switching frequency of the switch tubes in the rectifier unit 3 and the inverter unit 4. The control unit 2 controls the relay device in the coordinated ice melting switch 6 to turn on the coordinated ice melting switch 6, and the inverter unit 4 outputs the low-frequency ice melting current to the ice-covered line.

[0067] Furthermore, when the staff determines that the ice melting is completed, the host computer sends an instruction to end the ice melting to the control unit 2, and the control unit 2 then instructs the coordinated ice melting switch 6 to disconnect and end the ice melting work. When the control unit 2 detects abnormal ice melting, it will automatically control the rectifier unit 3 and the inverter unit 4 to reduce the ice melting output current according to the alarm level, or control the coordinated ice melting switch 6 to disconnect and end the ice melting work in advance. In one embodiment, it can be set to feedback alarm information to the staff every 1s. If the staff determines that the ice melting status of the line needs to be adjusted, the rectifier unit 3 and the inverter unit 4 can be controlled according to the control unit 2 to increase or decrease the ice melting output current or frequency. For example, the ice melting output current can be appropriately reduced when the ice coverage is greatly reduced, and when the line temperature is low, the ice melting output current can be appropriately increased. During the entire working process, the intervention instructions from the staff have the highest priority. At the same time, monitor the contact point of the terminal knife switch to ensure that the contact point temperature is within a safe range to avoid safety hazards.

[0068] The low-frequency ice-melting device and method for distribution network transmission lines disclosed in the present invention increase the capacity of the device by fixing the physical position of the device. By applying low-frequency alternating current with an electric energy of less than 25 Hz to the line, the defects of DC and AC ice-melting in the prior art are solved. Compared with the traditional industrial frequency transformer solution, the low-frequency ice-melting solution can increase the ice-melting distance when the total power supply is provided by the same front-end ice-coating transformer. Secondly, compared with DC ice-melting, low-frequency ice-melting can achieve simultaneous and symmetrical ice-melting of three phases, avoiding the phenomenon of asymmetric pole collapse, and avoiding the need for switching like DC ice-melting, which greatly improves the operating efficiency. Then, according to the principle of equal voltage-frequency ratio, the secondary side voltage of the distribution transformer on the ice-coated line is always within the safe voltage, so it does not need to be disconnected, which greatly improves the ice-melting efficiency.

[0069] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-frequency ice melting device for a distribution network transmission line, characterized in that: include: Power module, control unit, rectifier unit, inverter unit, information acquisition unit, collaborative ice-melting switch; The power module is connected to the transformer, and is used to receive electric energy from the transformer and process the electric energy; The rectifier unit is connected to the power module and is used to convert the industrial frequency alternating current provided by the power module into direct current; The inverter unit is connected to the rectifier unit and is used to convert the direct current output by the rectifier unit into low-frequency alternating current; The information acquisition unit is used to collect the line temperature and ice thickness on the ice-covered line and feed them back to the control unit; The control unit is connected to the power module and the information acquisition unit, and is used to receive the electric energy provided by the power module, calculate the output current according to the parameter information, the line temperature and the ice thickness, generate an ice melting instruction, execute the ice melting instruction and adjust the output current; as well as The coordinated ice-melting switch is connected to the control unit and the inverter unit, and is controlled by the execution ice-melting instruction sent by the control unit; The inverter unit outputs the low-frequency alternating current to the ice-covered circuit through the cooperative ice-melting switch.

2. The low-frequency ice melting device for power distribution network transmission lines according to claim 1, characterized in that: The power supply module is used for filtering and performing reactive power compensation on the electric energy.

3. The low-frequency ice melting device for power distribution network transmission lines according to claim 1, characterized in that: The control unit is also used to receive the parameter information from the host computer, and the parameter information includes the length of the ice-melting line, the type of the ice-melting line conductor, the geometric average distance between the ice-melting lines, and the ice-melting current protection value.

4. The low-frequency ice melting device for power distribution network transmission lines according to claim 1, characterized in that: The output current calculation formula is as follows: Wherein, I is the current flowing through the ice-covered line, and its value is mainly related to the line temperature and the ice thickness; U1 is the effective value of the high-voltage side voltage of the transformer; and Z is the impedance of the ice-covered line, which is related to the line parameters.

5. The low-frequency ice melting device for power distribution network transmission lines according to claim 4, characterized in that: The relationship between the output voltage and frequency of the transformer is as follows: Wherein, f is the frequency of the output voltage, U1 is the effective value of the voltage on the high-voltage side of the transformer, W1 is the number of turns on the high-voltage side of the transformer, Φ m is the main magnetic flux of the transformer core, the frequency f of the output voltage U1 ranges from 5 to 30 Hz, and the output voltage U1 ranges from 400 to 1800 V.

6. The low-frequency ice melting device for power distribution network transmission lines according to claim 1, characterized in that: The ice-melting instruction includes information about a preset ice-melting duration, and the preset ice-melting duration is sent to the control module via a host computer.

7. A working method of a low-frequency ice melting device for a distribution network transmission line, characterized in that: include: S11: The power module receives electric energy from the transformer and processes the electric energy; S12: The control unit receives the electric energy provided by the power module, calculates the output current according to the parameter information, the line temperature and the ice thickness, generates an ice melting instruction, executes the ice melting instruction and adjusts the output current; S13: The rectifier unit converts the industrial frequency alternating current provided by the power module into direct current; S14: The inverter unit converts the direct current output by the rectifier unit into low-frequency alternating current; S15: The coordinated ice-melting switch is controlled by the ice-melting instruction sent by the control unit, and the inverter unit outputs the low-frequency alternating current to the ice-covered line through the coordinated ice-melting switch; S16: The information acquisition unit collects the line temperature and the ice thickness on the ice-covered line in real time and feeds back the information to the control unit. The control unit adjusts the output current according to the line temperature and the ice thickness.

8. A method for low-frequency ice melting of distribution network transmission lines, characterized in that: include: S21: taking the ice-covered line offline from the system; S22: Connect the low-frequency ice melting device, separate the load at the rear end of the branch transformer, and operate the end switch to short-circuit the three phases of the line; S23: starting the low-frequency ice melting device to melt ice; S24: Observation of ice melting completed; S25: End ice melting, restore the ice-covered line connection, and restore the line switch.

9. The method for low-frequency ice melting of distribution network transmission lines according to claim 7, characterized in that: Including monitoring the temperature of the end knife switch contact point.

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