Overvoltage suppression system for suspended phase of power transmission line direct-current ice melting device

Abstract

The invention relates to the technical field of high-voltage engineering and power transmission line ice melting, and discloses a power transmission line direct current ice melting device suspended phase overvoltage suppression system, which comprises a suppression framework, and is characterized in that the suppression framework is set to change a circulation path or an electrical parameter of an unbalanced current in at least one mode; therefore, overvoltage generated at the head end of the suspended phase due to the fact that the unbalanced current flows into the suspended phase is suppressed. The method directly refers to a problem source and unbalanced current. By intervening the circulation path or electrical parameters, the excitation condition generated by overvoltage is eliminated from the source, and the technical span from passive protection to active suppression is realized.

Description

Technical Field

[0001] This invention relates to the field of high voltage engineering and transmission line de-icing technology, specifically to a floating phase overvoltage suppression system for a DC de-icing device for transmission lines. Background Technology

[0002] Icing on transmission lines poses a significant threat to the safe operation of the power grid. Thermal de-icing, especially DC de-icing, has become the mainstream de-icing method due to its low power requirement and high efficiency. Among them, the 12-pulse DC de-icing device is widely used due to its mature technology.

[0003] However, in practice, when using the "one-way" de-icing wiring method, overvoltage occurred multiple times at the beginning of the suspended phase line during the current increase process, forcing the de-icing operation to be suspended. Analysis and simulation revealed that the root cause of this overvoltage problem lies in the phenomenon of unbalanced current. Its mechanism is as follows:

[0004] Causes of unbalanced current: Ideally, the positive and negative outputs of a 12-pulse DC de-icing device should be perfectly symmetrical. However, in practice, due to factors such as thyristor triggering characteristics and three-phase power supply imbalance, there is a slight deviation in the positive and negative output voltages. This deviation generates a common-mode potential difference between the DC side neutral point and ground. This potential difference drives a current called unbalanced current (denoted as ). The current flows from the DC neutral point into the ground.

[0005] The path of the unbalanced current: the unbalanced current It doesn't simply disappear; it needs to form a complete electrical loop. The flow path is as follows: from the DC side grounding point of the DC de-icing device → into any two-phase transmission line connected to the positive and negative terminals of the de-icing device → at the end of the transmission line (three-phase short-circuit point) → merging into the suspended phase line → finally returning to the ground through the ground capacitance of the suspended phase line → converging back to the DC side grounding point. This path constitutes a complete unbalanced current loop.

[0006] This unbalanced current flows through the floating phase and generates a voltage response through its distributed parameters (mainly capacitance to ground), ultimately coupling at the beginning of the floating phase to form a high-amplitude overvoltage. Existing technologies lack effective and systematic suppression schemes for this specific problem. Summary of the Invention

[0007] To address the problem of overvoltage at the beginning of the suspended phase caused by unbalanced current in the existing "one-way" DC de-icing method, this invention provides a system for suppressing overvoltage in the suspended phase of a DC de-icing device for transmission lines.

[0008] This invention is achieved through the following technical solution:

[0009] A system for suppressing overvoltage in a suspended phase of a DC de-icing device for a transmission line is provided. The system includes a suppression architecture, which is configured to suppress overvoltage generated at the beginning of the suspended phase due to the unbalanced current flowing into the suspended phase by changing the flow path or electrical parameters of the unbalanced current in at least one way.

[0010] As an optimization, the suppression framework includes a parameter adjustment unit for increasing the impedance of the unbalanced current loop.

[0011] As an optimization, the parameter adjustment unit is a neutral point grounding resistor connected between the neutral point of the DC ice melting device and the ground.

[0012] As an optimization, the resistance value of the neutral point grounding resistor is configured to simultaneously satisfy the following two conditions:

[0013] (a) The protection gap of the suspended phase line does not experience breakdown discharge;

[0014] (b) The rise in neutral point displacement voltage of the DC de-icing device shall not exceed 30%.

[0015] As an optimization, the parameter adjustment unit is a smoothing reactor connected in series in the output circuit of the DC ice melting device, and the inductance value of the smoothing reactor is set to reduce the unbalanced current.

[0016] As an optimization, the suppression framework includes a path reconfiguration unit, which is configured to change the flow path of the unbalanced current by changing the ice-melting wiring method.

[0017] As an optimization, the path reconstruction unit is set to adjust the one-way de-icing mode to a one-way two-way de-icing mode; wherein, the one-way one-way mode is that the three phases at the end of the line are short-circuited, and only any two phase conductors at the beginning are connected to the positive and negative output terminals of the DC de-icing device; the one-way two-way mode is that the three phases at the end of the line are short-circuited, and at the beginning, any two phase conductors are connected in parallel and then connected to the positive and negative output terminals of the DC de-icing device together with the third phase.

[0018] As an optimization, the unbalanced current is characterized by being caused by the deviation of the positive and negative output voltages of the DC de-icing device, and is generated by the potential difference between the DC side neutral point and the ground.

[0019] As an optimization, the condition for the overvoltage generated at the beginning of the suspended phase is: when the de-icing circuit meets the circuit parameter resonance condition under the one-way de-icing connection method, the voltage response generated by the unbalanced current at the beginning of the third phase suspended line.

[0020] The present invention also discloses a transmission line, wherein the transmission line is equipped with a suspended phase overvoltage suppression system for a DC de-icing device as described above.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] Existing technologies often focus on post-event protection (such as relying on gap breakdown), while this invention directly addresses the root cause of the problem: unbalanced current. By intervening in its flow path or electrical parameters, the excitation conditions for overvoltage are eliminated at the source, achieving a technological leap from passive protection to active suppression.

[0023] The three measures of this invention constitute a complete solution library, providing ample flexibility.

[0024] Path reconfiguration: By changing to a "one-way, two-way" wiring, a low-impedance metallic circuit is provided for unbalanced current, fundamentally eliminating the capacitive coupling problem of the floating phase. This solution requires no additional hardware investment and is suitable for rapid emergency response and non-modification upgrades of existing equipment.

[0025] Parameter Adjustment: This approach offers in-depth, engineering-customized solutions. Neutral Point Grounding Resistor: This solution is economical, efficient, and technologically mature. It directly limits unbalanced current through series resistance and is the preferred device-level modification solution proposed in this invention. Its clear resistance design criteria (balancing insulation safety and equipment compatibility) provide a clear and quantifiable basis for engineering design and acceptance, making it highly operable. Increasing the Smoothing Reactor: This solution addresses the noise source by improving DC power quality to weaken the excitation that generates unbalanced current, a fundamental solution. It is particularly suitable for the optimized design of new ice-melting devices or the technical upgrade of existing devices, improving the purity and stability of operation at the system level.

[0026] The solutions provided by this invention cover the entire spectrum of options, from zero-cost (operation strategy adjustment) to low-cost (adding resistors) and even systemic investment (replacing reactors), allowing users to flexibly configure according to their budget and needs. In particular, the neutral point grounding resistor solution addresses a major safety threat at extremely low cost, offering exceptional cost-effectiveness. The comprehensive application of these measures can significantly improve the success rate and safety of DC ice melting operations, ensuring the stable operation of the power grid under extreme ice disasters, resulting in substantial socio-economic benefits. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 This is a schematic diagram showing the location of the overvoltage suppression measures for the suspended phase line of the 12-pulse DC de-icing device.

[0029] Figure 2 This is a schematic diagram of a faulty circuit for a 12-pulse DC de-icing device. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0031] Example 1: A system for suppressing overvoltage in the suspended phase of a DC de-icing device for power transmission lines.

[0032] The core of the suppression system disclosed in this invention lies in a highly adaptive and configurable suppression architecture. This architecture is designed to systematically disrupt the necessary conditions for the occurrence of unbalanced current at the front end. Specifically, the architecture is configured to precisely intervene in the electrical parameters of the unbalanced current's flow path or loop through one or more combinations of the following methods. The ultimate goal is to suppress the superimposed transient and steady-state overvoltage generated at the front end of the unbalanced current's inductance after it is injected into a floating phase, resulting in capacitive or inductive coupling through the distributed parameters of that phase's line (mainly capacitance to ground and inductance).

[0033] The advantage of this invention lies in the fact that it provides not a single solution, but a multi-dimensional, phased-implementable technical system. In engineering practice, the following strategies can be flexibly selected based on the urgency of the situation, budget constraints, equipment status, and technical reserves.

[0034] I. Implementation of the Parameter Adjustment Unit: Refined Design Centered on Impedance Management

[0035] The technical approach of this unit is to change the electrical characteristics of the unbalanced current loop by introducing or adjusting the series impedance. Its core lies in regulation and management.

[0036] 1. Installing a neutral point grounding resistor: an economical and efficient modular solution.

[0037] This scheme involves connecting a grounding resistor R, designed with multi-objective optimization, in series between the neutral point of the DC de-icing device and the ground, along the inevitable path of the unbalanced current.

[0038] Deep working principle and dynamic process analysis:

[0039] Steady-state current limiting effect: According to Ohm's law, the series connection of resistor R will directly limit the unbalanced current. A voltage drop is generated on the path. This voltage drop is related to the drive. The original neutral point potential difference is in the opposite direction, thus forming negative feedback, which effectively limits the steady-state amplitude of I0.

[0040] Transient suppression effect: For rapid transient processes caused by system operation (such as switching on / off switches) or lightning strikes, the resistor R can form an RC damping circuit with the line's capacitance to ground C. This circuit can effectively absorb high-frequency oscillation energy, smooth the voltage waveform, and significantly suppress the peak value and steepness of transient overvoltages. This is a superior characteristic that cannot be achieved by a single capacitor or inductor path.

[0041] Potential clamping effect: The potential of the resistor's mounting point, i.e., the neutral point, relative to the ground is clamped to a more controllable level by the resistor to a certain extent, avoiding free suspension and violent fluctuations of the potential, and improving the stability of the entire DC side potential.

[0042] Systems engineering and quantitative design process for resistance calculation:

[0043] Determining the resistance value R is a typical multi-constraint optimization problem, which requires rigorous simulation calculation and verification.

[0044] Step 1: Determine the lower safety limit ( )

[0045] Method: A high-precision model was established using electromagnetic transient simulation software (such as PSCAD / EMTP or ATP-EMTP). The model should include: a rectifier valve model of the 12-pulse de-icing device, a smoothing reactor, a frequency-varying parameter model of the transmission line (such as the JMarti model), the voltage-breakdown characteristics of the protective gap, and the short-circuit point at the end of the line.

[0046] Operating conditions: Traverse the line length, simulate the worst operating conditions, and find the maximum overvoltage at the beginning of the suspended phase line.

[0047] Criterion: Perform a parameter scan, starting with R=0 and gradually increasing the resistance value. Defined as follows: at this resistance value, simulation results show that the peak overvoltage at the beginning of the floating phase is exactly lower than the 50% breakdown probability voltage (U) of its protective gap. 50 (%) and leave at least a 10% safety margin. If the resistance is less than this value, there is still a risk of breakdown due to overvoltage.

[0048] Step 2: Determine the upper limit of device compatibility ( )

[0049] Method: Based on the design drawings and insulation coordination specifications of the ice melting device.

[0050] Consideration: After a resistor is connected to the neutral point, the neutral point potential (displacement voltage) will rise under rated unbalanced current. This voltage is directly superimposed on the neutral point insulation of the valve-side winding of the converter transformer.

[0051] Criterion: Consult the equipment technical specifications to obtain the maximum allowable operating voltage for neutral point equipment (such as bushings and windings). Defined as follows: at this resistance value, the calculated displacement voltage rise ΔU does not exceed 30% of the equipment's allowable value. This 30% margin is reserved to cope with transient shocks and measurement errors.

[0052] Step 3: Final Value Selection and Resistor Selection

[0053] Value range: The final engineering application value R must satisfy... .

[0054] Power capacity calculation: Rated power of the resistor It must be greater than its heat dissipation during long-term operation. The maximum steady-state unbalanced current needs to be estimated. ,but Where K is the safety factor. At the same time, the ability to withstand larger transient current surges in a short period of time (e.g., 10s) needs to be considered.

[0055] Materials and Structure: Low temperature coefficient resistive materials such as stainless steel and nickel-chromium alloys are preferred to ensure stable resistance. Structurally, a grid or spiral winding design can be adopted, and a forced air cooling or natural cooling heat dissipation system can be provided.

[0056] 2. Increasing the inductance of the smoothing reactor: A traceability solution to improve system-level power quality.

[0057] This solution focuses on improving the output characteristics of the DC side, purifying the excitation that generates unbalanced current at the source, and is a strategy aimed at improving the overall performance of the system.

[0058] Deep working principle and frequency domain analysis:

[0059] Harmonic suppression: The 12-pulse DC output is not ideal DC; it contains characteristic harmonic voltage ripples of the 12kth order (e.g., 12th, 24th). These harmonic voltages contribute to the instantaneous voltage deviation between the positive and negative terminals. The main source. The inductive reactance of the smoothing reactor. The value of L is proportional to the frequency f. Increasing the inductance value L means presenting a higher impedance to harmonic voltages, thereby greatly suppressing the amplitude of harmonic currents (i.e., the AC component of unbalanced currents).

[0060] Current continuity and stability: A larger inductance value helps maintain the continuity of DC current under light load or large firing angle, avoiding severe voltage oscillations caused by current discontinuity, thereby further stabilizing the neutral point potential.

[0061] Fault current limiting: When a fault such as a short circuit occurs on the DC side, the increased smoothing reactor can effectively reduce the rise rate (di / dt) and peak value of the fault current, buying valuable time for the protection system to operate and improving the robustness of the entire de-icing system.

[0062] Optimization and trade-offs in inductance value setting:

[0063] Implementing this solution typically means replacing existing reactors or reserving greater margin in new designs.

[0064] Modeling and Scan Analysis: In PSCAD / EMTP, in addition to building the circuit model, it is also necessary to accurately simulate the switching process of the thyristors. The inductance value L of the smoothing reactor is scanned, ranging from a reference value (e.g., 25mH) to 250mH.

[0065] Optimization goal:

[0066] Main objective: To observe the unbalanced current under different L values. The attenuation of (especially its AC component) is a key objective. The effective value is suppressed to the point that the overvoltage of the floating phase is below the safe threshold.

[0067] Secondary objective: Observe the ripple factor of the DC current, with the goal of reducing the ripple factor to below 5%.

[0068] Factors to be weighed:

[0069] Economic efficiency: The larger the inductance value, the larger, heavier, and more expensive the reactor becomes.

[0070] System response: Excessive inductance will reduce the speed of DC current regulation and prolong the time to reach the set ice-melting current.

[0071] Transient overvoltage: The reactor itself is an energy storage element, and it may generate operational overvoltage when the circuit is quickly tripped. It is necessary to match it with a corresponding energy absorption device (such as a surge arrester).

[0072] Decision Example: Simulation results show that when the L value increases from 25mH to 50mH, the I0 attenuation effect is significant; however, when it increases from 50mH to 250mH, the improvement is no longer significant. Therefore, 50mH is likely the most cost-effective value and was ultimately selected.

[0073] II. Implementation of Path Restructuring Units: A Zero-Cost Solution Centered on Topology Innovation

[0074] This unit represents another ingenious approach to solving the problem: instead of confronting it head-on, the problem is resolved or transformed through a clever restructuring of the system topology.

[0075] Deep working principle and field circuit analysis:

[0076] From capacitive to resistive loop: In a one-way trip configuration, the floating phase is mainly connected to the ground through the distributed capacitance C, forming a high-impedance capacitive loop. The unbalanced current I0 is forced through this high-impedance path, thus generating a high voltage at the beginning. ).

[0077] Providing a metallic low-impedance path: In a one-way, two-back configuration, the previously floating phase is directly connected to the positive or negative terminal via a switch at the beginning, providing a metallic parallel path with extremely low resistance. According to the principle of current shunting, the vast majority of the unbalanced current will choose this low-impedance path, while only a very small amount of current still flows through the capacitor. Therefore, the overvoltage caused by capacitive coupling is fundamentally eliminated.

[0078] Improved electromagnetic environment: This method also changes the electromagnetic field distribution around the line, reduces the asymmetry caused by single-phase suspension, and helps to reduce the induced voltage and interference of adjacent lines.

[0079] Specific operations, definitions, and security logic:

[0080] Precise definition:

[0081] One-way trip method: The three phases at the end of the line are short-circuited, and at the beginning, only any two phase conductors (such as phase A and phase B) are connected to the positive and negative output terminals of the DC de-icing device respectively. The third phase (phase C) is completely suspended at the beginning and electrically isolated from the device.

[0082] One-way-two-back configuration: The three phases at the end of the line are short-circuited, and at the beginning, any two phase conductors are connected in parallel (e.g., phase A and phase B in parallel), and then connected together with the third phase (phase C) to the positive and negative output terminals of the DC de-icing device. Its core feature is that no phase is in a state of complete electrical isolation at the beginning.

[0083] Switch operation logic and interlocking: Figure 1 For example, to achieve the mode where phases A and B are connected in parallel to the positive terminal and phase C is connected to the negative terminal, it is necessary to close the de-icing switches Q11, Q13, and Q15, while ensuring that Q12, Q14, and Q16 are in a reliably open position. In engineering practice, strict electrical or program interlocks must be set in the control system to prevent any misoperation that could lead to a short circuit in the DC power supply. For example, it is strictly forbidden to close Q11 and Q14, Q12 and Q15, or Q13 and Q16 simultaneously.

[0084] Complete de-icing sequence planning: Taking the complete de-icing of three-phase lines A, B, and C as an example, a rigorous three-step operation method needs to be formulated:

[0085] First ice melting (Mode 1): Close the switch to connect phases A and B in parallel to the positive terminal of the ice melting device, and connect phase C to the negative terminal of the ice melting device. At this time, the ice melting current mainly flows through phases A and B, while phase C, as one of the current return channels, has its potential clamped.

[0086] Second de-icing (Mode 2): After Mode 1 is completed, disconnect the relevant disconnect switches, then close them to connect phase A and phase C in parallel to the positive terminal, and phase B to the negative terminal. This mode ensures that phase B is fully heated.

[0087] Third de-icing (Mode 3): After Mode 2 is completed, operate the disconnect switch to connect phase B and phase C in parallel to the positive terminal, and phase A to the negative terminal. At this point, all three phase conductors have received equivalent current heating, and the de-icing task is completed.

[0088] In-depth analysis of specific application cases

[0089] Case Background: A 500kV double-circuit transmission line on the same tower in a mountainous area, at a high altitude with distinct microclimate characteristics, suffers from severe icing in winter. The maintenance unit used a 12-pulse DC de-icing device with a rated current of 5000A for emergency repairs. When using a 4000A de-icing current to de-ic the A and B phases of the #1 line in a one-way, one-way manner, the overvoltage monitoring system installed at the head end of phase C (suspended phase) repeatedly recorded transient overvoltages with peak values ​​exceeding 200kV, accompanied by a clear sound of protection gap breakdown discharge. The de-icing operation was forced to be urgently stopped.

[0090] The entire process of applying the solution of this invention:

[0091] In-depth diagnosis and root cause verification:

[0092] The technical team retrieved the fault recording data and found that the overvoltage waveform and the current surge occurred simultaneously.

[0093] Subsequently, a detailed model of the line was built using PSCAD, including tower dimensions, conductor type, and electrical parameters after icing. The simulation successfully reproduced the field phenomenon: when the positive and negative voltages deviated by 2%, an unbalanced current of approximately 989A was generated in the model, and an overvoltage as high as 262.3kV was calculated at the floating C-phase terminus. This result conclusively confirms that "unbalanced current-capacitive coupling" is the sole cause of the overvoltage, eliminating other interfering factors.

[0094] Multi-option comparison and emergency decision-making:

[0095] The on-site command center is under pressure and urgently needs to restore power. This invention provides three solutions: A. Install a grounding resistor (requires a 2-week construction period); B. Increase the size of the smoothing reactor (requires returning it to the factory, resulting in a longer cycle); C. Use a one-way, two-round path reconstruction.

[0096] Following a risk assessment, Option C was chosen as the preferred contingency measure. Its core advantages are: zero cost, zero construction period, controllable risk, and immediate results.

[0097] Solution implementation and data-driven effectiveness verification:

[0098] The maintenance personnel strictly followed Mode 1 of the three-step operation method formulated in this invention, changed the switch status, and switched the system to one-way two-way operation.

[0099] While maintaining the exact same 4000A de-icing current as before, comparative monitoring was conducted using the same set of high-precision probes and waveform recorders. The results were encouraging: the peak voltage to ground at the C-phase head end dropped sharply from over 262.3kV to a stable 27.25kV, with a smooth waveform and no oscillations. This voltage is lower than the protection gap of its de-icing busbar. (Approximately 37.7kV), insulation safety is absolutely guaranteed. The de-icing process continued smoothly until its end.

[0100] Long-term cure and enhanced efficacy:

[0101] To fundamentally solve the problem and prepare for more frequent and flexible de-icing operations in the future (including using a round-trip method to save time), the power company implemented a permanent upgrade by adding a neutral point grounding resistor during the subsequent maintenance period.

[0102] Based on simulation calculations and A high-power grounding resistor cabinet with a resistance of 40Ω, a rated power of 700kW, a protective enclosure, and temperature-controlled air cooling was selected and installed.

[0103] After the modification was completed, comprehensive testing was conducted. Under the "one-way" operation, the measured neutral point displacement voltage rise was 25.9% (meeting the <30% requirement), while the overvoltage of the floating phase was stably suppressed below 32kV. The two core measures proposed in this invention passed emergency verification and long-term fundamental verification in this case, together forming a double insurance for the future anti-icing and de-icing of this line.

[0104] Example 2: An ice-resistant reinforced transmission line equipped with an overvoltage suppression system

[0105] Embodiment 2 of this invention discloses a transmission line system specifically designed for heavy icing areas. This system not only physically enhances its anti-icing capabilities but also deeply integrates the suspended phase overvoltage suppression system of the DC de-icing device for transmission lines disclosed in Embodiment 1 into its electrical design and operation strategy, forming a comprehensive ice disaster prevention and control system that combines active defense and active elimination.

[0106] 1. Overall integrated design of the line system

[0107] During the design phase of this transmission line, DC de-icing and its potential safety hazards (such as overvoltage of suspended phases) have been taken as core considerations for forward-looking integrated design.

[0108] Preset integration of the de-icing device: In the supporting substation of the line, a fixed installation location and interface have been pre-planned for the 12-pulse DC de-icing device, including a dedicated valve hall, cable trenches, and a dedicated grounding electrode that is reliably connected to the in-station grounding grid. The design of this grounding electrode takes into account the discharge requirements of unbalanced current during de-icing, and its grounding resistance is required to be controlled at an extremely low level (such as <0.1 Ω).

[0109] Adaptive design of the line itself:

[0110] Conductor selection: On the premise of meeting the current-carrying capacity, conductors with a higher allowable continuous operating temperature are preferably selected to provide a margin for withstanding large currents during de-icing.

[0111] Insulation coordination: Based on the overvoltage suppression level calculated by simulation of the present invention, the number of insulator strings of the line, the air gap distance of the tower, and the specific breakdown voltage value of the protection gap at the head end of the suspended phase are rechecked and determined. Ensure that after applying the suppression system of the present invention, the insulation configuration of the line is both safe and economical.

[0112] Monitoring and sensing: High-precision overvoltage monitoring sensors, leakage current monitoring devices, and micro meteorological stations (monitoring temperature, humidity, wind speed, ice thickness) are pre-installed at the head-end tower, end-end tower, and possible key points of the line. These sensors are networked with the de-icing device control system to provide real-time data support for the selection of suppression measures and the evaluation of their effects.

[0113] 2. Deep integration configuration of the suppression system and the line

[0114] The key point of this embodiment is that the suppression system in Embodiment 1 is not an after-the-fact addition, but a standard configuration or an optional module of the line.

[0115] Configuration scheme of the parameter adjustment unit:

[0116] Scheme A (standard configuration): For all newly built heavy-ice area lines, the neutral grounding resistance cabinet is listed as a standard accessory of the de-icing system. Its resistance value (such as 40 Ω) has been calculated and determined during the design phase according to the specific parameters of this line (length, voltage level, capacitance to ground), and is purchased and installed together with the main equipment. The resistance cabinet is arranged near the neutral point of the de-icing device and connected by a large cross-section copper bar.

[0117] Option B (High-Performance Configuration): For particularly important lines or lines with frequent de-icing, a smoothing reactor with a larger inductance value (e.g., 50mH) can be specified. This requires reserving larger equipment foundations during the civil engineering phase and considering its impact on the system during electrical design.

[0118] Option C (Flexible Configuration): To cope with ice conditions of varying severity, adjustable grounding resistor cabinets or reactors that can be switched in groups can be configured, and the optimal suppression effect can be dynamically adjusted through the control system.

[0119] Configuration scheme for path reconstruction unit:

[0120] De-icing switch cabinet at the beginning of the line (such as...) Figure 1 The disconnectors (Q11 to Q16) and their operating mechanisms must possess all the functions required for a one-out-two-out wiring mode. The rated current and dynamic / thermal stability current of the disconnectors must meet the stringent requirements for two-phase parallel operation.

[0121] The line operation and maintenance procedures must clearly define the standardized operating procedures for the one-out-two-back connection method and make it one of the default safe operating procedures for de-icing operations, and mandatory training and assessment should be conducted for operation and maintenance personnel.

[0122] 3. Intelligent selection of suppression strategies based on line characteristics

[0123] The advantage of this embodiment is that it does not mechanically apply suppression measures, but intelligently selects the optimal strategy based on the actual condition of the line and the de-icing requirements.

[0124] Decision-making logic process:

[0125] Initial assessment: Upon receiving the de-icing command, the control system first reads data from the micro-weather station and line icing monitoring data to assess the severity and urgency of the icing situation.

[0126] Strategy selection:

[0127] Scenario 1 (Fast Response / Light to Moderate Icing): If rapid de-icing is required and the system is equipped with a reliable disconnector mechanism, the path reconfiguration unit should be activated first, using a one-to-two-back approach. This solution offers the fastest startup and the highest safety.

[0128] Scenario 2 (Ultimate Efficiency / Hardware Requirements): If extremely high de-icing efficiency is required (e.g., completion in the shortest possible time), and it is confirmed that the neutral grounding resistor is in operation and in good condition, a one-way trip method + parameter adjustment unit (grounding resistor) can be used. This solution requires only two operations to complete three-phase de-icing, saving time.

[0129] Scenario 3 (Most Severe Operating Condition / Transient Suppression): If thunderstorms or switching overvoltage risks are forecast, a combination of a one-way trip and a parameter adjustment unit (grounding resistance + large inductance smoothing reactor) can be used to provide the highest level of overvoltage suppression by utilizing the dual effects of RC damping and inductor filtering.

[0130] Execution and Monitoring: Based on the selected strategy, the system automatically or manually executes corresponding disconnector operations and device switching. Throughout the de-icing process, the overvoltage monitoring system operates in real time; if an anomaly is detected, the system can automatically trigger an alarm or switch to a safer suppression mode.

[0131] Specific application case: Planning and drills for a newly built ultra-high voltage transmission line in a heavy icing area.

[0132] A planned ±800kV ultra-high voltage direct current transmission line needs to traverse a hundred-mile-long, icy mountainous region. The concept of Embodiment 2 of this invention was adopted during the design phase.

[0133] During the design phase, based on the line parameters, the design institute calculated through simulation that a 40Ω / 700kW neutral grounding resistor was required to suppress overvoltage in the floating phase, and selected a 50mH smoothing reactor. These specifications were included in the tender documents. Simultaneously, the design drawings for the de-icing switchgear clearly included the electrical connections and mechanical interlocks for all one-to-two-circuit wiring modes.

[0134] Construction phase: All the above-mentioned equipment is constructed, installed and commissioned simultaneously with the main structure as part of the line project.

[0135] Pre-commissioning drill: Before the line was put into operation, a comprehensive ice-melting system simulation drill was conducted during the ice-free season. The drill tested the following in sequence:

[0136] System stability using only a one-way trip method.

[0137] Overvoltage suppression effect under the one-way and one-way grounding resistor connection method.

[0138] Simulate sensor malfunction and practice emergency response plan for manually switching suppression mode.

[0139] Value proposition: Through the deep integration and forward-looking design of Example 2, this UHV line possessed mature, reliable, and flexible overvoltage suppression capabilities for de-icing from the outset. The operation and maintenance team is intimately familiar with its performance, and when a real ice storm occurs, they can calmly and confidently choose the optimal solution to carry out de-icing operations, ensuring the absolute safety and smooth operation of this vital energy artery under extreme weather conditions.

[0140] In summary, Example 2 elevates the innovative technology of Example 1 from a solution to a system-level product. It defines a new, intelligent, and inherently safe ice-resistant hardened transmission line, providing a new standard and paradigm for power grid planning, design, and construction.

[0141] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for suppressing overvoltage in the suspended phase of a DC de-icing device for transmission lines, characterized in that, The suppression system includes a suppression architecture configured to suppress overvoltage generated at the beginning of a floating phase due to the unbalanced current flowing into the floating phase by changing the flow path or electrical parameters of the unbalanced current in at least one manner.

2. The overvoltage suppression system for the suspended phase of a DC de-icing device for transmission lines according to claim 1, characterized in that, The suppression framework includes a parameter adjustment unit, which is used to increase the impedance of the unbalanced current loop.

3. The overvoltage suppression system for the suspended phase of a DC de-icing device for transmission lines according to claim 2, characterized in that, The parameter adjustment unit is a neutral point grounding resistor connected between the neutral point of the DC ice melting device and the ground.

4. The overvoltage suppression system for the suspended phase of a DC de-icing device for transmission lines according to claim 3, characterized in that, The neutral point grounding resistor is configured to simultaneously satisfy the following two conditions: (a) The protection gap of the suspended phase line does not experience breakdown discharge; (b) The rise in neutral point displacement voltage of the DC de-icing device shall not exceed 30%.

5. The overvoltage suppression system for the suspended phase of a DC de-icing device for transmission lines according to claim 2, characterized in that, The parameter adjustment unit is a smoothing reactor connected in series in the output circuit of the DC ice melting device, and the inductance value of the smoothing reactor is set to reduce the unbalanced current.

6. The overvoltage suppression system for the suspended phase of a DC de-icing device for transmission lines according to claim 1, characterized in that, The suppression framework includes a path reconfiguration unit, which is configured to change the flow path of the unbalanced current by altering the de-icing wiring method.

7. The overvoltage suppression system for the suspended phase of a DC de-icing device for transmission lines according to claim 6, characterized in that, The path reconstruction unit is configured to adjust the one-way de-icing mode to a one-way two-way de-icing mode. In the one-way mode, the three phases at the end of the line are short-circuited, and only any two phase conductors at the beginning are connected to the positive and negative output terminals of the DC de-icing device. In the one-way two-way mode, the three phases at the end of the line are short-circuited, and any two phase conductors at the beginning are connected in parallel and then connected to the positive and negative output terminals of the DC de-icing device together with the third phase.

8. A system for suppressing overvoltage of suspended phase in a DC de-icing device for transmission lines according to any one of claims 1-7, characterized in that, The unbalanced current is caused by the deviation of the positive and negative output voltages of the DC de-icing device, and is generated by the potential difference between the DC side neutral point and the ground.

9. A system for suppressing overvoltage of suspended phase in a DC de-icing device for transmission lines according to any one of claims 1-7, characterized in that, The condition for the overvoltage generated at the beginning of the suspended phase is: when the de-icing circuit meets the circuit parameter resonance condition under the one-way de-icing connection method, the voltage response generated by the unbalanced current at the beginning of the third phase suspended line is as follows.

10. A power transmission line, characterized in that, The transmission line is equipped with a suspended phase overvoltage suppression system for a DC de-icing device as described in any one of claims 1 to 9.

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