Long-term power composite grease filling process for ultra-high voltage strain clamp suitable for extreme working conditions in northwest

Abstract

The application discloses a long-acting power composite grease filling process of an extra-high voltage strain clamp adapted to the extreme working condition of the northwest, and aims at the defects of cavity ice accumulation, grease loss and hardware heating failure under the local strong wind and sand, large temperature difference, low temperature freeze-thaw and strong ultraviolet environment. According to the filling risk points, the cavity is divided into zones and the differentiated pressure and speed gradient grease injection is adopted to discharge the air in the cavity. After the grease injection, the pressure is stabilized, the grease is supplemented and the grease body shrinkage is compensated, and finally the port is sealed to block the water vapor, sand and dust. The special power composite grease is matched, the alkyl naphthalene and poly-alpha-olefin PAO8 are compounded as base oil, lithium soap and fatty polyurea are compounded as thickening, the hydrophobic fumed silicon dioxide, nano boron nitride and compounded anti-oxidation corrosion inhibitor are matched, and the grease has the characteristics of low temperature flexibility of-45 DEG C, high temperature anti-oil separation and insulation corrosion prevention. The application cooperates the material with the complete process to eliminate the filled cavity, the contact resistance change is small after freeze-thaw, the standardization construction is realized, the application is adapted to the plus or minus 800kV extra-high voltage direct current line, and the long-term stable operation of the new energy external transmission channel is ensured.

Description

Technical Field

[0001] This invention belongs to the technical fields of hardware protection, power lubrication and sealing materials and line operation and maintenance technology for ultra-high voltage transmission lines. Specifically, it relates to an optimized process for filling weather-resistant power composite grease into grease-filled tension clamps for ±800kV ultra-high voltage large cross-section conductors. Background Technology

[0002] Gansu Province is a core national clean energy base and a major land-based energy corridor for the West-to-East Power Transmission Project. It undertakes the important strategic tasks of large-scale new energy aggregation and inter-provincial and inter-regional DC power transmission. The safe and stable operation of ultra-high-voltage direct current (UHVDC) transmission lines is directly related to national energy security, new energy consumption, and the steady development of the regional economy. Gansu has a unique geographical environment, facing extreme conditions such as strong winds, sandstorms, extreme diurnal temperature variations, continuous low temperatures and freezing in winter, and severe seasonal changes in humidity. UHV lines widely use grease-filled tension clamps to achieve sealed protection of conductor joints. Relying on internal electrical grease filling to isolate moisture, prevent oxidation, prevent discharge, and prevent hardware corrosion, this is a key technology to ensure the safety of UHV conductor joints. According to statistics on UHV line faults from 2021 to 2023, multiple main transmission lines within the province, including the ±800kV Tianzhong Line, Qishao Line, and Qingyu Line, experienced consecutive faults such as abnormal overheating of tension clamps, joint failures, and hardware erosion. Through fault tracing, disassembly analysis, and experimental verification, the core causes of the accident were highly consistent: the traditional commercial power composite grease had insufficient weather resistance and the filling process was crude, resulting in incomplete filling of the tension clamp cavity and the existence of air gaps. During operation, the grease separated and lost oil, dried and shrank, and external water vapor and dust continuously invaded the cavity. In the low-temperature season, water accumulated, froze and expanded, eventually causing stress cracking of the clamp, a surge in contact resistance, partial discharge erosion, and line outage.

[0003] Existing technologies suffer from the following common industry shortcomings, making them unsuitable for the extreme operating conditions of the Gansu UHV power transmission line: 1. Traditional electrical greases have a narrow weather resistance range and poor stability. They are prone to oil separation, drying shrinkage, separation and loss under large temperature difference environments. They are also prone to hardening and failure at low temperatures. They cannot maintain a sealed and full state for a long time and are seriously inadequate in adapting to the freeze-thaw and sandstorm conditions in Northwest China.

[0004] 2. The existing filling process lacks a standardized technical route and generally adopts an experience-based one-time grease injection method. Due to the complex structure, numerous dead corners, and uneven gaps of large cross-section tension clamps, hidden defects such as local grease deficiency, residual cavities, and uneven filling are very likely to occur, which pose a major hidden danger for subsequent water ingress and freezing failure.

[0005] 3. The industry lacks a specific optimized filling process for UHV tension clamps to "prevent leakage, prevent shrinkage, prevent cavitation, and resist frost heave". There are no quality control links such as voltage stabilization and shape preservation, secondary grease filling, and grease locking and sealing. As a result, the construction consistency is poor and the long-term operational reliability is low.

[0006] 4. Existing products and processes are mostly adapted to the mild working conditions in inland areas, and have not been designed with material modification and process adaptation for the extreme environment of the Gansu Clean Energy Base. Therefore, they cannot meet the long-term safe, stable and uninterrupted operation requirements of the UHV main line.

[0007] Against the backdrop of the implementation of the national dual-carbon strategy and the large-scale grid connection and transmission of new energy, in order to ensure the safety of inter-provincial energy channels, stabilize the local economy of Gansu, and build a solid national energy security barrier, it is urgent to develop new power composite grease replacement products with high weather resistance, anti-loss, freeze-thaw resistance, and long-term sealing. It is also necessary to develop a new filling process system for large-section tension clamps with precise filling and long-term grease retention, so as to completely solve the problem of frequent failure of UHV tension clamps from both the material and process perspectives. Summary of the Invention

[0008] The purpose of this invention is to develop a long-lasting power composite grease filling process for ultra-high voltage tension clamps that features a wide temperature range, high adhesion, anti-loss, and water-repellent properties, in response to the extreme working conditions of strong winds, sandstorms, large temperature differences, and low-temperature freeze-thaw cycles in Northwest China. This process aims to solve problems such as grease shrinkage, loss, hardening, and sealing failure.

[0009] The technical solution of this invention: A long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China. 1) Identify filling risk points: Disassemble the tension clamps filled in the conventional way to obtain filling dead corners, conductor gaps, and weak sealing areas; 2) Zoned grease injection: Based on the obtained risk points, the tension clamp cavity is divided into zones, and corresponding grease injection pressure and grease injection rate are set for each zone. Power composite grease is injected at the set pressure and rate, filling dead corners at low speed and purging air at high pressure to eliminate internal air gaps and cavity defects. 3) Pressure stabilization and shape retention: After the grease injection is completed, pressure is stabilized and the shape is retained to prevent the grease from rebounding and shrinking; 4) Constant temperature secondary fat replenishment: After the body has stabilized, a small amount of fat is replenished to compensate for the amount of fat body contraction; 5) Port grease sealing: Seal and reinforce the grease injection port and end gaps of the tension wire clamp.

[0010] This is an antifreeze and dust-resistant composite grease with the following composition by weight percentage: alkyl naphthalene 43%, polyalphaolefin PAO8 synthetic oil 32%, lithium dodecyl stearate soap 8%, aliphatic diisocyanate polyurea 4%, polymethacrylate 0.6%, isobutylene butadiene rubber micro powder 2.5%, hydrophobic fumed silica 2.6%, ultrafine talc powder 4%, nano boron nitride 2.5%, di-tert-butyl-p-cresol 0.25%, triphenyl phosphite 0.3%, and benzotriazole 0.25%.

[0011] Preferably, the ultrafine talc powder is 1250 mesh and coated with stearic acid.

[0012] Preferably, the zonal grease injection divides the tension clamp cavity into three areas: a dead zone area for conductor strand gaps, a main cavity filling area, and a weak end seal area. The dead zone area for conductor strand gaps is filled with low-pressure, low-speed immersion grease at a pressure of 0.15–0.25 MPa and a rate of 5–10 g / min. The main cavity filling area is filled with medium-pressure, uniform filling at a pressure of 0.3–0.4 MPa and a rate of 15–25 g / min. The weak end seal area is vented with short-duration pulse venting at a pressure of 0.2–0.3 MPa and a rate of 20–28 g / min to quickly remove excess air and completely eliminate air gaps.

[0013] Preferably, the pressure stabilization and shaping process is as follows: after grease injection, maintain pressure for 2-3 minutes, release pressure, maintain slight pressure at 0.1 MPa, and let stand for 8-15 minutes. This suppresses the rebound and shrinkage of composite grease and the regeneration of pores under the large temperature difference conditions in Northwest China, ensuring that the grease fills densely and uniformly.

[0014] Preferably, the ambient temperature for the constant-temperature secondary grease replenishment is controlled at 15-25℃. In low-temperature environments, the tension clamp is preheated to 15-25℃, and the amount of grease replenished in a single instance is 1.5%-3% of the total grease injection volume. This is specifically designed to compensate for the volume loss caused by the micro-contraction of the grease body and the slight oil seepage due to the extreme temperature difference between day and night in Northwest China.

[0015] Preferably, the specific surface area of ​​the hydrophobic fumed silica in the electrical composite grease is 120–160 m². 2 / g. Hydrophobic fumed silica is modified with hexamethyldisilazane, which can stably suppress oil separation and maintain thixotropic sealing under long-term wind and sand vibration conditions.

[0016] Preferably, the boron nitride nanoparticles have a particle size of 30–80 nm. They possess high insulation and high thermal conductivity, reducing the temperature rise during ultra-high voltage current flow. Simultaneously, combined with stearic acid-coated talc powder, they form a composite insulating and wear-resistant system, enhancing the long-term corrosion resistance and anti-discharge performance of the clamps.

[0017] The beneficial effects of this invention are: 1. Completely eliminate typical line accidents: effectively solve the problems of incomplete grease filling of tension clamps, water accumulation in cavities, low-temperature icing, and overheating failure of fittings, significantly reduce the fault tripping rate of UHV lines, and ensure the continuous and stable operation of new energy transmission channels.

[0018] 2. Significantly improved adaptability to extreme environments: The new composite grease is stable over a wide temperature range, resistant to wind and sand, freeze-thaw cycles, and has high adhesion. It does not shrink, leak, or form cavities during long-term operation, making it suitable for the harsh operating environment of the Gansu Clean Energy Base.

[0019] 3. Standardized process and mass production capability: A complete set of material preparation and standardized construction process system can be formed, which can be replicated and promoted in UHVDC transmission lines across the country, reducing operation and maintenance costs and minimizing power outage losses.

[0020] 4. Supporting the national energy strategy and dual-carbon goals: Enhancing the capacity for renewable energy consumption and transmission in Northwest China, consolidating the security of the national land-based energy corridor, and contributing to the stable development of the regional economy and the implementation of the dual-carbon strategy. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the failure principle of cavity defects and water ingress icing in traditional filling processes. Figure 2 This is a flow chart of the filling process of the present invention. Detailed Implementation

[0022] A long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China: 1) Identify filling risk points: Disassemble the tension clamp filled in the conventional way, slice it for observation (with a magnifying glass) to obtain filling dead corners, conductor gaps and weak sealing areas; 2) Zoned grease injection: First, pre-treat the tension clamp cavity. The inner cavity of the tension clamp is purged with high-pressure, dry, oil-free air (0.2MPa) and repeatedly wiped with anhydrous ethanol-coated cotton cloth. It is then dried with 50℃ hot air, and the conductor is polished with a wire brush and wiped with anhydrous ethanol to remove oxidation dust, followed by drying at 40℃. Based on the identified risk points, the tension clamp cavity is divided into zones. A corresponding grease injection pressure and rate are set for each zone. Electrical composite grease is injected according to the set pressure and rate, filling dead corners at low speed and purging air at high pressure to eliminate internal air gaps and cavity defects. 3) Pressure stabilization and shape retention: After the grease injection is completed, pressure is stabilized and the shape is retained to prevent the grease from rebounding and shrinking; 4) Constant temperature secondary fat replenishment: After the body has stabilized, a small amount of fat is replenished to compensate for the amount of fat body contraction; 5) Port grease sealing: The grease injection port and end gaps of the tension clamp are sealed and reinforced. The grease injection port is filled and compacted with high-temperature weather-resistant silicone rubber sealant; a prefabricated EPDM sealing bushing is installed at the conductor outlet of the tension clamp; the outer layer is covered with a weather-resistant and waterproof heat-shrinkable sleeve, and both ends of the sleeve are sealed with sealant. This prevents northwest wind sand, condensation, and icing moisture from entering the clamp cavity.

[0023] The composition ratio of the electrical composite grease was optimized to enhance its antifreeze and dust resistance. The mass percentage of each component is shown in Table 1.

[0024] Table 1. Composition of Electric Complex Lipids .

[0025] Alkyl naphthalene and polyalphaolefin (PAO8) are blended to create a wide-temperature blended oil that balances low-temperature fluidity with high-temperature viscosity stability, addressing the limitations of single-oil blends at high and low temperatures. Lithium dodecyl stearate soap and aliphatic diisocyanate polyurea form a composite thickener, raising the dropping point to above 180°C and inhibiting oil separation at 120°C; it also reduces low-temperature rigidity, preventing freezing and cracking. Polymethacrylate and isobutylene butadiene rubber micropowders act as antifreeze modifiers, weakening low-temperature colloidal agglomeration of the oil, preventing hardening at -40°C, ensuring the paste is flexible and spreadable, and preventing cracking after repeated freeze-thaw cycles. This enhances the paste's elasticity, allowing for synchronized expansion and contraction with metals, and preventing shrinkage and cracking during long-term thermal cycling. Boron nitride and talc are combined to synergistically reduce rigidity.

[0026] Industrialized preparation process Step 1: Base oil premixing Add all the alkyl naphthalene oil and polyalphaolefin PAO8 oil to the reactor, start stirring (60 r / min), and stir for 15 min to mix completely; add di-tert-butyl-p-cresol, triphenyl phosphite, and benzotriazole, and stir until all solid additives are dissolved and transparent.

[0027] Step 2: Saponification to prepare lithium-based thickening phase The system was heated to 85°C, dodecyl stearic acid was added, and the mixture was stirred and melted. Lithium hydroxide aqueous solution (concentration 12%) was slowly added dropwise, and the saponification reaction was carried out at a constant temperature for 90 minutes. After completion, the system was heated to 145°C and vacuum dehydrated to remove all free water, ensuring that there were no water bubbles and no emulsification.

[0028] Step 3: Polyurea thickening synthesis (temperature-controlled polymerization) The temperature was stabilized at 150℃. Organic amines were pre-dissolved in the system, and aliphatic diisocyanates were added in batches. The mixture was stirred at a constant speed for 60 minutes. The aliphatic diisocyanates reacted with the amino groups in the system to form polyurea, which formed a lithium soap-polyurea composite thickened network. After the reaction was completed, the mixture was kept at a constant temperature for 30 minutes to allow the colloid to mature evenly.

[0029] Step 4: Compound dispersion of fillers and functional additives Cool to 90℃, then add hydrophobic fumed silica, ultrafine talc powder, nano boron nitride, polymethyl methacrylate, and isobutylene butadiene rubber micro powder in sequence; increase the stirring speed to 120 r / min and disperse at high speed for 45 min, so that the powder is completely wetted and dispersed, with no particle agglomeration and no white spots.

[0030] Step 5: Homogenization and degassing post-treatment The material is transferred to a three-roll mill for two rounds of grinding to control the fineness to ≤5μm, resulting in a smooth paste without particles. After grinding, the mixture is transferred to a vacuum mixing vessel and degassed at 120℃ and -0.096MPa for 30 minutes to eliminate bubbles and prevent freeze-thaw bubble cracking. After naturally cooling to room temperature, the product is filtered and packaged to obtain the finished electrical compound grease.

[0031] Electric compound grease specifications: dropping point ≥ 210℃; Cone penetration (25℃): 260~290 (NLGI2, moderately soft and hard, neither too soft nor too hard); Cone penetration (-40℃): ≥240, no hardening; 120℃ oven for 24 hours: no oil separation, no dripping, weight loss <1.2%; Hydrophobic: No water absorption after 24 hours of immersion in water; 50 freeze-thaw cycles (-40℃↔80℃): No cracking, no shrinkage; T2 Copper corrosion test grade 1a: no corrosion; Aluminum corrosion test grade 1a: no white spots or pitting. Evaporation loss at 120℃ ≤0.8%.

[0032] The zonal grease injection method divides the tension clamp cavity into three areas: a dead zone for conductor strand gaps, a main cavity filling area, and a weak end seal area. The dead zone for conductor strand gaps is filled with low-pressure, low-speed grease, at a pressure of 0.15–0.25 MPa and a rate of 5–10 g / min. The main cavity filling area is filled with medium-pressure, uniform grease, at a pressure of 0.3–0.4 MPa and a rate of 15–25 g / min. The weak end seal area is filled with short-duration pulse venting and filling, at a pressure of 0.2–0.3 MPa and a rate of 20–28 g / min, using intermittent pulse grease injection (2 seconds of injection followed by a 1-second pause) to expel air from the cavity and completely eliminate air gaps. The peak pulse pressure does not exceed 0.3 MPa, and an overflow pressure relief valve is provided to prevent instantaneous high-pressure impacts on the conductor gaps.

[0033] The pressure stabilization and shaping process is as follows: after grease injection, maintain pressure for 2-3 minutes, release pressure, maintain slight pressure at 0.1 MPa, and let stand for 8-15 minutes. The cross-sectional area is ≤720 mm². 2 Hold pressure for 2 minutes, release pressure, maintain slight pressure at 0.1 MPa, and let stand for 8–10 minutes; cross-sectional area 800–1250 mm². 2 Hold pressure for 3 minutes, release pressure, and hold pressure at 0.1 MPa for 12-15 minutes.

[0034] The ambient temperature for the constant-temperature secondary grease application is controlled between 15 and 25°C. The amount of grease applied in a single application is 1.5% to 3% of the total grease volume (1.5% to 2% at room temperature (15-25°C), and 2.5% to 3% after preheating in winter). In low-temperature environments, the tension clamp is preheated to 15-25°C. Hot air heating is used for localized preheating of the tension clamp, with real-time temperature control via an infrared thermometer, suitable for field construction scenarios.

[0035] After filling and sealing, allow the material to cool to room temperature. Use industrial CT scanning to check the fullness of the cavity filling; there should be no continuous through-cavities inside. Test the initial contact resistance; it should not exceed twice the resistance of a wire of equal length. If the resistance exceeds this limit, the workpiece must be reworked and re-greased.

[0036] The reliability of this invention was verified through contact resistance testing, high and low temperature freeze-thaw cycle testing, and long-term operation tracking comparison. An evaluation system for filling fullness, sealing reliability, and weather resistance stability was established, and standardized operating instructions were developed for large-scale promotion and application.

Claims

1. A long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, characterized by: 1) Identify filling risk points: Disassemble the tension clamps filled in the conventional way to obtain filling dead corners, conductor gaps, and weak sealing areas; 2) Zoned grease injection: Based on the obtained risk points, the tension clamp cavity is divided into zones, and corresponding grease injection pressure and grease injection rate are set for each zone. Power composite grease is injected at the set pressure and rate, filling dead corners at low speed and purging air at high pressure to eliminate internal air gaps and cavity defects. 3) Pressure stabilization and shape retention: After the grease injection is completed, pressure is stabilized and the shape is retained to prevent the grease from rebounding and shrinking; 4) Constant temperature secondary fat replenishment: After the body has stabilized, a small amount of fat is replenished to compensate for the amount of fat body contraction; 5) Port grease sealing: Seal and reinforce the grease injection port and end gaps of the tension wire clamp.

2. The long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 1, is characterized by: This is an antifreeze and dust-resistant composite grease with the following composition by weight percentage: alkyl naphthalene 43%, polyalphaolefin PAO8 synthetic oil 32%, lithium dodecyl stearate soap 8%, aliphatic diisocyanate polyurea 4%, polymethacrylate 0.6%, isobutylene butadiene rubber micro powder 2.5%, hydrophobic fumed silica 2.6%, ultrafine talc powder 4%, nano boron nitride 2.5%, di-tert-butyl-p-cresol 0.25%, triphenyl phosphite 0.3%, and benzotriazole 0.25%.

3. The long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 2, is characterized by: The ultrafine talc powder is 1250 mesh and coated with stearic acid.

4. The long-life power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 1, is characterized in that: The zonal grease injection divides the tension clamp cavity into three areas: the dead zone of the conductor strand gap, the main cavity filling area, and the weak end sealing area, and injects grease in sequence. The dead zone area of ​​the conductor strand gap is filled with low-pressure, low-speed grease injection, with an injection pressure of 0.15-0.25 MPa and an injection rate of 5-10 g / min; the main cavity filling area is filled with medium-pressure, uniform filling, with an injection pressure of 0.3-0.4 MPa and an injection rate of 15-25 g / min; the weak end sealing area is vented with short-time pulse venting, with a pressure of 0.2-0.3 MPa and an injection rate of 20-28 g / min, to quickly remove excess air and completely eliminate filling air gaps.

5. The long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 1, is characterized in that: The pressure stabilization and shaping process is as follows: after grease injection, maintain pressure for 2-3 minutes, release pressure, maintain slight pressure at 0.1 MPa, and let stand for 8-15 minutes.

6. The long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 1, is characterized in that: The ambient temperature for the constant temperature secondary grease replenishment is controlled at 15-25℃. In low temperature environments, the tension clamp is preheated to 15-25℃, and the amount of grease replenishment per session is 1.5%-3% of the total grease injection volume per session.

7. The long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 2, is characterized in that: The specific surface area of ​​the hydrophobic fumed silica in the electrical composite grease is 120-160 m². 2 / g.

8. The long-lasting power composite grease filling process for ultra-high voltage tension clamps adapted to extreme working conditions in Northwest China, as described in claim 2, is characterized in that: The boron nitride nanoparticles have a particle size of 30–80 nm.

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