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The graphene modified electrical contact developed by the joint research institute is expected to greatly reduce the failure rate of large capacity circuit breakers

With the steady progress of UHV AC / DC transmission project construction, the research results of UHV power transmission and transformation technology are increasingly abundant, which provides strong scientific and technological support for the construction of an international leading energy Internet enterprise with Chinese characteristics. With the rapid development of power grid, the problem of short-circuit current has gradually become a prominent factor restricting the growth of power grid load and the development of power grid.

The breaking capacity of high-voltage high-power circuit breaker directly determines the safety and reliability of long-term service of power transmission lines. Since 2016, relying on a number of science and technology projects of State Grid Co., Ltd., global energy Internet Research Institute Co., Ltd. and PingGao Group Co., Ltd. have successfully developed new high-performance graphene modified electrical contact products after five years of scientific research. This is of great significance to solve the problem of short circuit exceeding the standard and ensure the safe and stable operation of AC / DC UHV hybrid power grid

Research on upgrading of circuit breaker materials aiming at key requirements

According to relevant statistics, during the peak period of power consumption in summer of 2020, the maximum short-circuit current of some substations in the operation areas of State Grid and China Southern Power Grid will reach or even exceed 63 Ka. According to the statistics of the State Grid Corporation of China, in recent years, among the failures of 330kV and above UHV substation equipment in the company's business area, according to the type of equipment, the fault trips caused by gas insulated metal enclosed switchgear (GIS) and hybrid distribution equipment (HGIS) account for about 27.5%, circuit breakers account for 16.5%, transformers and current transformers account for 13.8%, Secondary equipment and bus accounted for 8.3%, reactor accounted for 4.6%, arrester accounted for 3.7%, disconnector and lightning rod accounted for 1.8%. It can be seen that GIS, circuit breaker, transformer and current transformer are the main equipment causing fault trip, accounting for 71.6% of the total trip.

The analysis of fault causes shows that the quality problems of contact, bushing and other parts and poor installation process are the main factors leading to the fault of circuit breaker. During the operation of SF6 circuit breaker for many times, the inrush current erosion several times higher than the rated current and the mechanical wear between the moving and static arc contacts will cause the contact deformation and produce metal vapor, which will damage the insulation performance of the arc extinguishing chamber.

During the fourteenth Five Year Plan period, Qinghai Province plans to expand the capacity of two 500kV substations to increase the short-circuit current load from the existing 63kA to 80kA. If the circuit breaker material is upgraded, the capacity of substation can be expanded directly, and the huge cost of substation expansion can be saved. The breaking times of high voltage and large capacity circuit breaker are mainly controlled by the life of electrical contacts in the circuit breaker. At present, the development of electric contacts for high voltage circuit breakers in China is mainly based on the technical route of copper tungsten alloy materials. Domestic copper tungsten alloy electrical contact products can not meet the requirements of ultra-high and ultra-high voltage engineering applications in terms of arc ablation resistance and friction and wear resistance. Once they are used beyond the service life range, they are prone to be re penetrated, which directly threatens the insulation performance of power equipment and causes great hidden danger to the safe operation of power grid. The copper tungsten alloy electrical contact products in service have low flexibility and elongation, and are easy to failure and fracture in the process of action, and lack of ablation resistance. During the arc ablation process, copper is easy to accumulate and grow up, which leads to contact cracking failure. Therefore, it is of great significance to effectively improve the key performance indicators of electrical contact materials, such as wear resistance, conductivity, anti welding, anti arc erosion, to reduce the failure rate of circuit breaker and maintain the safe and stable operation of power grid.

Chen Xin, director of the Institute of materials, Academia Sinica, said: "at present, when the short-circuit current of the power grid exceeds the breaking capacity of the circuit breaker, the short-circuit current exceeds the standard, which seriously affects the operation reliability of the power grid, and puts forward higher requirements for the breaking capacity of the circuit breaker and the ablation resistance of the contact. After the contacts in service are cut off at full capacity for many times, the arcing is seriously damaged, so it is necessary to carry out comprehensive maintenance, which is far from meeting the maintenance free requirements of the actual life cycle of SF6 circuit breakers. " He said that the erosion of the contact mainly comes from two aspects: one is the ablation of the pre breakdown arc before closing, and the other is the mechanical wear after the arc contact material becomes soft after ablation. It is necessary to put forward a new technical route to effectively improve the key performance indexes of electrical contact materials“ Technology needs to be continuously optimized and innovated. We should firmly grasp the initiative in our own hands. " Chen Xin said.

In the face of the urgent need of the national power transmission and transformation equipment for the upgrading of the electrical contact materials of the core components of the high-voltage circuit breaker, from 2016, the Institute of electrical new materials of the Joint Research Institute, the European Institute, the joint Pinggao group and other units jointly carried out technical research on the new graphene modified copper based electrical contact materials, and carried out international cooperation relying on the European Institute and the University of Manchester, UK. Help to improve the performance of high voltage circuit breaker.

Team work together to solve a number of technical problems

Synergistic improvement of arc ablation resistance and friction and wear resistance is the key to mass production of high performance electrical contacts. The research on high-voltage electrical contact materials in foreign countries started earlier, and the technology is relatively mature, but the core technology is blocked to our country. Relying on a number of scientific and technological projects of the company, the project team, in collaboration with overseas R & D capability, industrial group type test verification and application demonstration of provincial power companies, has established a young scientific and technological team with "80" backbone as the main body.

Key members of the team took root in the R & D front line in the R & D stage of material mechanism and preparation process; In the trial production stage, the company stationed at the manufacturer to solve the technical problems on site, and finally broke through the difficulty of the balance between the material properties, composition, organizational structure and preparation process, and made a breakthrough in the key technology of improving the material performance; In the stage of type test, I stayed in Pinggao group high voltage test station, discussed with Pinggao group technology center and high voltage station R & D team for many times, debugged repeatedly, and finally achieved a qualitative leap in the breaking capacity of high voltage high current circuit breaker electrical life.

With continuous efforts, the research team has successfully obtained the formulation system of high-performance graphene reinforced copper based composite electrical contact materials, broken through the key technologies of graphene electrical contact materials directional design process and activation sintering infiltration integrated molding, and realized the industrial preparation of multi model graphene modified electrical contact materials. For the first time, the team developed graphene modified copper tungsten alloy electrical contact for sulfur hexafluoride circuit breaker facing 252kV and above. The key performance indicators such as conductivity and bending strength are better than those of the active products, greatly improving the electrical life of the active high-voltage circuit breaker, filling the technical gap in the field of graphene modified high-voltage switch electrical contact materials, It improves the company's independent research and development level of high current and large capacity switch electrical contacts, and helps to ensure the safe and reliable operation of power system.

The project results support the independent design and localization application of circuit breaker

From October 29 to 31, 2020, according to the optimal verification scheme formulated by the joint research institute and Pinggao group after many discussions, the new open column type 252kV / 63kA SF6 circuit breaker of Pinggao group based on the electric contact successfully achieved 20 times of one-time full breaking capacity. Zhong Jianying, chief engineer of Pinggao group, said: "according to the opinions of the project acceptance expert group, the overall technology of the project has reached the international advanced level, and the main technical indicators have reached the international leading level. Only by making breakthroughs in core technologies can we better help enterprises control costs and ensure the supply of key materials. In the future, we should continue to strengthen the research on systems engineering and promote the industrial transformation of scientific research achievements. "

This achievement strongly supports the independent design, development and domestic application of 252kV porcelain post circuit breaker with rated short circuit breaking current of 63kA and rated current of 6300A in Pinggao group. 252kV / 63kA pole type circuit breaker has large market demand and wide coverage area. The successful development of this type of circuit breaker plays an important role in further developing the domestic and foreign markets of domestic circuit breakers, which is conducive to improving the R & D strength and technical level of the company in the field of high-end switchgear, and has good social and economic benefits.

The market demand of high-voltage electrical contacts in China is about 300000 sets per year, and the total annual market sales is close to 1.5 billion yuan. New high voltage electrical contact materials have broad market prospects in the future development of power grid. At present, the project achievements have reached cooperation and transformation intention with Pinggao, Xikai, taikai and other high-voltage switch enterprises, laying a foundation for the subsequent demonstration application and large-scale promotion in the field of ultra-high voltage and ultra-high voltage power transmission and transformation. The project team will continue to focus on the frontier of energy and power science and technology, continuously strengthen innovation and practice, and continue to promote the independent research and development and localization application of core materials for high-end electrical equipment.

Post time: Jul-08-2021