The operation reliability of high-voltage switchgear depends on the arc ablation resistance, welding resistance and thermal conductivity of the contacts. tungsten copper (WCu/CuW) alloy used in medium and high voltage circuit breakers has become the core arc contact material of vacuum interrupter, GIS equipment and transformer tap changer. This paper provides a landing tungsten copper contact selection scheme for power equipment research and development, procurement, operation and maintenance personnel.

What is a Tungsten Copper Contact?

Tungsten copper contact, also known as WCu contact and CuW contact, is a dual-phase composite pseudo-alloy electrical contact component made by powder metallurgy process. Unlike conventional single alloys, tungsten and copper do not fuse with each other, do not generate intermetallic compounds, and are closely combined with an independent two-phase structure, perfectly fusing the core advantages of the two metals.

In the industry, copper and tungsten contact grades are named after the proportion of metal weight. The mainstream specifications cover a full range of products with 50%-90% tungsten content. Common models include W70Cu30, W80Cu20, CuW70, CuW80, etc. Some high-end models will add trace nickel elements to optimize metal wettability and sintering density, further improving the overall performance.

Tungsten copper alloy contacts are mainly used as arc contacts (ablation contacts), do not bear the long-term current-carrying function, specifically to deal with the arc impact of the opening and closing moment, widely adapted to all kinds of medium and high voltage power switching equipment. Tungsten copper contacts for high voltage switchgear application equipment includes SF6 gas insulated circuit breaker, vacuum circuit breaker, vacuum interrupter, oil-immersed circuit breaker, load switch, isolating switch, grounding switch, and also the core accessories of transformer on-load tap changer (OLTC), high-voltage contactor and high-voltage discharge electrode.

Performance Advantages of Tungsten Copper Contacts

During the opening and closing process of the high-voltage switch, an instantaneous ultra-high temperature arc will be generated, and the arc temperature can reach up to 20000K, accompanied by severe thermal shock, mechanical vibration and electromagnetic stress. Pure copper, pure tungsten single material can not adapt to the operating conditions, and tungsten copper composite materials can achieve complementary performance.

Tungsten phase provides basic wear resistance and ablation resistance. Its 3422 ℃ ultra-high melting point, high hardness and high density characteristics make the contact have extremely strong arc erosion resistance, wear resistance and welding resistance. At the same time, the thermal expansion coefficient is extremely low and it is not easy to deform and crack under high temperature conditions.

The copper phase is responsible for ensuring the electrical and thermal conductivity, with excellent electrical conductivity, thermal conductivity and plasticity, which can quickly export the heat generated by the contact work, reduce the contact resistance, and avoid local overheating failure of the equipment. At the same time, the copper material has strong plasticity, which is convenient for precision machining of various contact structures.

Tungsten copper contacts have a unique "transpiration cooling" mechanism. When the arc temperature exceeds 3000 ℃, the copper component inside the contact will liquefy and vaporize, absorb a large amount of arc heat through phase change, quickly cool down and insulate heat, protect the tungsten skeleton structure from burning to the greatest extent, and greatly extend the service life of the contact.

The tungsten copper contact is made of non-magnetic material, the amount of discharge in vacuum environment is extremely low, the density is stable at 12-17g/cm³, and the conductivity covers 27-60% IACS, which can be perfectly adapted to various high-voltage switch operating environments such as vacuum, SF6 gas, insulating oil, air, etc.

How Are Tungsten Copper Contacts Produced?

The core source of most selection errors is to focus only on the ratio of tungsten and copper, ignoring the production process and micro-quality control. For tungsten copper contacts of the same grade, process differences can lead to several times the difference in service life, and high-pressure equipment must prefer infiltration process products.

1. Powder pretreatment：using 99.9% high purity ultrafine tungsten powder, precise control of particle size distribution, adding trace nickel additives to optimize the wettability.
2. Then the tungsten skeleton blank with uniform pores and stable structure is pressed.
3. High-temperature pre-sintering, which is shaped in a vacuum/hydrogen atmosphere to ensure uniform connectivity of the skeleton pores.
4. Copper liquid infiltration, relying on capillary action at high temperature to make pure copper liquid completely fill the tungsten skeleton pores.
5. Finishing and heat treatment, remove excess copper, annealing to eliminate stress, and finally made into the finished product.

Ratio of Tungsten Copper Contact for High Voltage Switch

At present, the mainstream implementation standards of copper and tungsten contacts in the industry are ASTM B702 "Copper and Tungsten Electrical Contact Materials" and GB/T 8320, which unify the grade division, performance parameters and applicable working conditions, and are the core basis for high-voltage equipment selection and procurement acceptance. The core difference of the grade is the ratio of tungsten to copper, which directly determines the ablation resistance and conductivity of the contact.

ASTM B702 Standard Parameters and Scenarios

ASTM B702 divides tungsten copper contacts into 5 large standard grades A, B, C, D and E.

• W50Cu50: copper content 48%-52%, conductivity 56-64% IACS, excellent conductivity and good plasticity, suitable for oil-immersed switches with mild arc intensity and conventional power distribution switches, and suitable for medium operating frequency conditions.
• W60Cu40:The comprehensive performance is balanced, the ablation resistance is better than Class A, and the conductive performance is stable. It is mostly used for medium voltage switches and conventional load switches under medium load arc conditions. It is a common model for middle-end power distribution equipment.
• W70Cu30: High-voltage switch general explosive brand, conductivity 44-52% IACS, moderate hardness, both anti-welding, arc resistance and thermal conductivity, widely used in high-voltage circuit breakers, conventional vacuum switches, suitable for the vast majority of civil and industrial high-voltage power distribution equipment.
• W75Cu25:The tungsten content is increased to 75%, and the arc erosion resistance is greatly enhanced. It can cope with high-intensity arc impact for a long time and is suitable for heavy-duty switching and frequent operation of high-voltage switchgear.
• W80Cu20:Ultra-high tungsten ratio model, top welding resistance, ablation resistance, conductivity 38-45% IACS, specially adapted to extreme working conditions, including high-power short-circuit breaking, SF6 high-voltage circuit breaker, high-end vacuum interrupter and other core equipment. Industry measured data show that W80Cu20 is the gold ratio model with the lowest arc ablation rate.

Industry Customization Tungsten Copper Contact Ratio

In addition to the standard grade, the equipment manufacturer will customize the subdivision grade according to the special working conditions to cover the requirements of the full-scene high-voltage switch. W55Cu45 and W65Cu35 are mostly used for arc contacts of oil circuit breakers and gas-blown circuit breakers; they are W78Cu22 to adapt to heavy-duty arc and resistance welding electrode scenarios.

The W85Cu15 and W90Cu10 are ultra-high ablation resistance models, with tungsten content exceeding 85%, and full fusion welding resistance. They are suitable for ultra-high voltage vacuum switches, spark gap electrodes and extreme short-circuit breaking equipment. They are mainly used for power hubs and heavy industry high-voltage power distribution systems.

Tungsten Copper Contact vs Other High Pressure Contact Material

High-voltage switch contact materials include tungsten copper , silver tungsten, copper chromium, pure copper alloy, pure tungsten 5 major mainstream categories, the performance of different materials, cost, adaptation scenarios significantly different. Accurate distinction between material boundaries is the key to avoiding selection errors.

Tungsten copper (WCu) vs silver tungsten (AgW)

The two arc resistance, anti-welding performance is similar, the core difference is the cost and adaptation environment. Silver tungsten contacts have better conductivity and strong oxidation resistance, and are suitable for air-insulated medium and low-voltage switches, but the cost of silver is extremely high and is not suitable for large-scale high-voltage equipment applications.

Tungsten copper (WCu) vs copper chromium (CuCr)

Copper-chromium alloy is the main contact material of vacuum circuit breaker, which has the advantages of high conductivity, stable contact resistance, low interception value and fast insulation recovery speed, and is suitable for long-term current carrying and conventional breaking conditions. However, copper-chromium contacts are less resistant to extreme arc ablation than copper-tungsten. Under ultra-high voltage, ultra-large short-circuit current and frequent heavy-duty breaking conditions, the anti-ablation and anti-welding performance of tungsten copper contacts is more prominent, so high-end vacuum equipment often adopts the combination design of "copper-chromium main contact + tungsten copper arc contact", taking into account the current carrying and arc resistance.

Tungsten copper (WCu) vs Pure Copper/Copper Alloy

Pure copper and copper-chromium-zirconium alloy has excellent electrical conductivity and thermal conductivity, and is the preferred material for the main current-carrying contact of the equipment. However, pure copper has low melting point, poor arc resistance, rapid ablation and welding adhesion under high-intensity arc, and cannot be used alone as a high-voltage arc contact.

Tungsten copper (WCu) vs Pure Tungsten

Pure tungsten arc resistance, high temperature performance, but poor conductivity, material brittleness, processing difficulty, easy to crack, can not be directly used as electrical contacts. tungsten copper  composite material through the copper phase to make up for the pure tungsten conductive, plastic short board, while retaining most of the arc resistance performance, is the pure tungsten material in the field of power contact practical improvement program.

7 Key Factors of Choosing Tungsten Copper Contact for High-voltage Switch

The selection of tungsten copper  contacts is by no means a simple comparison of grades, but needs to be combined with the equipment operating environment, electrical parameters, mechanical properties, processing technology and other multi-dimensional comprehensive determination. If the parameters are not matched properly, the contact ablation is too fast, welding adhesion, contact resistance soaring, equipment trip and other faults are easy to occur.

Tungsten copper ratio

The high-voltage switch shall be strictly based on the arc intensity, voltage level and breaking current to select the tungsten-copper ratio. The higher the copper content, the better the electrical conductivity, thermal conductivity and plasticity of the contact, and the lower the contact resistance, which is suitable for conventional urrent-carrying and mild arc conditions. The higher the tungsten content, the stronger the contact hardness, high temperature strength, arc ablation resistance, and welding resistance. It can withstand large short-circuit current and high-frequency sub-opening and closing operations, but the conductivity will decrease accordingly.

Equipment Operation Environment and Media

The arc characteristics of different insulation media are very different, which directly determines the purity and microstructure of the material required for the contact, which is the key reference item for selection.

Vacuum switchgear has the highest requirements for contact quality. It must use low air content and vacuum fine-grained tungsten copper materials, strictly control the content of oxygen and nitrogen impurities, avoid air pollution in the vacuum chamber, and ensure stable insulation performance.

SF6 gas insulated high-voltage equipment arc energy concentration, temperature is extremely high, preferred 70%-85% medium and high tungsten grades, relying on strong ablation resistance to resist continuous high temperature arc impact.

Oil-immersed switchgear is under mild working conditions, and medium copper ratio grades can be selected, taking into account conductivity and economy. Air insulated switches should be carefully selected to avoid copper oxidation causing contact resistance to increase year by year.

Electrical and Arc Condition Parameters

The three core parameters of equipment rated voltage, continuous working current and short-circuit breaking current shall be specified before selection. The greater the short-circuit current, the stronger the arc energy and the higher the required contact tungsten content.

At the same time, the operation frequency and design service life of the equipment should be considered. High-voltage switches with high-frequency sub-opening and long-life design need to upgrade high-tungsten ablation-resistant grades to reduce contact loss and reduce operation and maintenance replacement costs. Vacuum equipment also needs to focus on intercepting indicators and match customized contacts with low intercepting characteristics.

Mechanical and thermal stability performance requirements

There are severe mechanical impact and high frequency vibration during the opening and closing process of the high voltage switch, and the contact shall have sufficient hardness and compressive strength to avoid deformation, cracking and falling off. The high tungsten ratio contact has stronger mechanical stability and is suitable for heavy-duty impact conditions.

Thermal stability is also critical, and the low thermal expansion coefficient of tungsten copper contacts ensures dimensional stability under frequent hot and cold cycling conditions. With a transpiration cooling mechanism, it can quickly dissipate the arc heat and prevent local overheating and contact softening failures.

Microstructure and Production Quality Control Index

The same grade of tungsten copper contacts, different manufacturers of product performance gap is very large, the core difference lies in the micro process. Even if the nominal W80Cu20, the porosity is too high, the copper phase is unevenly distributed, and the grains are coarse, it will cause the contact to burn out and fail in advance.

High-quality contacts must meet the standards of high density (relative density ≥ 98%), low porosity, continuous and uniform copper network, and controllable grain size. Vacuum-specific tentacles require the use of vacuum fine crystal process, strict control of impurities and gas content, from the microscopic level to ensure long-term operation stability.

Adaptability of contact structure and assembly

Common structures of high-voltage switch contacts include tulip flap type, rod type, disc type, and groove type. Different structures have different arc control and heat dissipation effects, and need to match the corresponding tungsten copper material process.

At present, the mainstream of the industry adopts bimetal composite structure, with pure copper/copper chromium zirconium as the substrate, the surface cladding tungsten copper contact layer. The structure takes into account the high conductivity of the substrate and the arc resistance of the surface layer, and at the same time adapts to the brazing assembly process, the cost performance is much higher than the overall tungsten copper alloy contact.

Industry standards, testing and cost balancing

The contacts of high-voltage complete equipment must conform to the authoritative standards of ASTM B702 and GB/T 8320. When purchasing, the manufacturer shall provide batch inspection reports, including the measured data such as density, hardness, conductivity and metallographic structure, and only the nominal parameters shall be rejected.

The cost level needs to be considered: the purchase price of high tungsten brand is higher, but it is resistant to loss and has a longer life, which can greatly reduce the cost of equipment downtime and maintenance replacement, and the comprehensive ratio under high pressure and heavy work is higher.

How to Choose a Reliable Tungsten Copper Contact Manufacturer?

High-voltage switch contacts belong to the power core precision accessories, supply chain stability and technical expertise directly determine the quality of equipment. In the stage of selection and landing, the standardized cooperation mode of manufacturers is the key to avoid quality hidden dangers.

Core Manufacturer Screening Criteria

Priority is given to the source manufacturers with independent infiltration production lines and deep-cultivated high-voltage switch accessories, and the middlemen are rejected for OEM products. Manufacturers need to have ISO9001 quality system certification, products can be fully standard ASTM B702, GB/T 8320 authoritative standards. At the same time, it is necessary to check the testing capability of the manufacturer, and the density, hardness, conductivity, metallographic structure and gas content testing can be completed independently, and batch exclusive testing reports can be provided. Priority is given to professional manufacturers with high-voltage switch OEM supporting experience, customizable vacuum fine crystal, double metal composite structure.

Technology docking standardization process

When purchasing and docking, the equipment working condition parameters, including voltage level, breaking current, insulation medium, operation frequency, contact structure size and assembly method, shall be provided completely, so that the manufacturer can accurately match the brand and process.

Clear technical index tolerance, impurity control standards, surface accuracy requirements, for vacuum equipment need to be separately agreed low outgassing, fine crystal micro-view requirements, to avoid fuzzy parameters lead to product inconsistent working conditions.

Quality control and acceptance mechanism

The sample test must be completed before formal mass production, and the performance shall be verified by simulating arc impact, temperature rise and mechanical life test. Mass production batches need to be accompanied by the material certificate, test report, so that the whole process can be traced.

Sign a quality agreement, clarify the process change notification mechanism, defective product treatment plan, to prevent manufacturers to adjust the powder, sintering, infiltration parameters caused by performance fluctuations.

FAQ About Tungsten Copper Alloy

Q1: What is the core difference between tungsten copper alloy and tungsten carbide?

Tungsten copper is a tungsten copper dual-phase conductive composite material, the main conductive, arc-resistant, special electrical contact material; tungsten carbide is a hard wear-resistant ceramic material, insulation is not conductive, only used for mechanical wear-resistant accessories, completely not suitable for power contact scene.

Q2: Can tungsten copper contacts process complex special-shaped structures?

You can. Compared with pure tungsten, tungsten copper alloy has excellent plasticity and machinability, and can process complex structures such as grooves, petals, special-shaped surfaces, etc., which is suitable for precision contact design of various high-end high-voltage switches.

Q3: Will the tungsten copper contact rust and corrode?

There is no risk of corrosion, but long-term open air environment operation, the surface copper phase will be slightly oxidized, slightly increased contact resistance. Therefore, the tungsten copper contact is more suitable for closed working conditions such as vacuum, SF6 and insulating oil, and the air working condition requires regular maintenance.

Q4: What are the core factors affecting the quality of tungsten copper contacts?

The core factors include powder purity, tungsten skeleton pore uniformity, melting density, grain size, gas impurity content, processing heat treatment process, in which the melting process and microstructure uniformity is the key.

Q5: How long is the conventional service life of tungsten copper  contacts?

Life depends entirely on the condition and selection of matching degree. Conventional medium-pressure temperature and working conditions can guarantee tens of thousands of operations, high-voltage heavy-duty, frequent short-circuit conditions, high-tungsten high-quality contacts can greatly extend the equipment maintenance-free cycle.

Q6: Can tungsten copper contacts be used for vacuum circuit breakers?

You can. Special low gas, vacuum fine crystal grade tungsten copper contact should be selected, oxygen and nitrogen impurity content should be strictly controlled, and vacuum cavity pollution should be eliminated. It is the preferred material for high-end vacuum arc extinguishing chamber arc contact.

Q7: How to quickly select W70, W75, W80 and W85?

Conventional high-voltage general-purpose scene preferred W70Cu30; frequent operation heavy-duty scene selection W75Cu25; short-circuit breaking, extreme arc scene preferred W80Cu20 (optimal corrosion ratio); ultra-high pressure extreme operating conditions selected W85Cu15.

Q8: Is the tungsten copper contact magnetic?

The standard tungsten copper alloy is a non-magnetic material, which will not produce hysteresis loss and electromagnetic adsorption during operation, and is fully adapted to the electromagnetic operating environment of high-voltage power equipment.

Conclusion

The precise selection of tungsten copper contacts can effectively reduce the probability of equipment ablation, welding and heating failure, greatly extend the service life of high-voltage switchgear, reduce the operation and maintenance costs of the power system, and ensure the safe and stable operation of the distribution network. COMBAT has more than ten years of manufacturing experience in tungsten copper  alloy materials. Contact us to obtain precision tungsten copper contact supply.