The development of smart grids is inseparable from the support of new types of power equipment. Superconducting power technology is the most innovative and application-leading frontier technology in power technology, and will certainly provide strong support for the future development of smart grids. This paper introduces the concept of smart grid and its advanced technologies. It describes in detail the technical performance characteristics of superconducting power devices, such as superconducting cables, superconducting current limiters, and superconducting energy storage, The application direction was analyzed.

Zhang Dong, Liu Dongsheng, Cheng Congming/ Baoding Tianwei Baochang Electric Co., Ltd. has continuously developed and applied new technologies in the electric power field. However, for a long time, the power transmission and distribution systems gradually formed in many countries in the world have not appeared. Great progress. In the past 20 years, tremendous changes have taken place in the computer, information and communications technology fields. The modern economic model dominated by informationization and digitization is leading the development trend of the world's economy and technology. This aspect proposes the supply and use of electricity. Increasingly high information requirements, on the other hand, provide powerful technical support for the transformation of traditional power systems to information, digital, and automated management. In addition, saving energy, protecting the environment, and improving safety have become the subject of energy use for all of humanity. This also stipulates the basic standards for future power equipment construction and power supply management. It can be seen that the future development of the power system will highlight two characteristics: the development of new technologies and new power equipment; the second is to establish an information management system and achieve efficient and intelligent management.

In order to cater to and lead the new trend of development in the power sector, the US Department of Energy first proposed the concept of “smart grid”, which is based on an integrated, high-speed two-way communication network, advanced sensing and measurement technologies, and advanced technologies. The equipment technology, advanced control methods and application of advanced decision support system technology to achieve the grid's goals of reliability, safety, economy, efficiency, environmental friendliness, and safety of use. Its main features include self-healing, interaction, and security. The power quality required by users in the 21st century allows for access to various forms of power generation, the start-up of electricity markets and the optimization and efficient operation of power grid assets.

"Smart grids will have the potential to reshape the world's economic and energy landscape, and its concept has attracted widespread attention from countries around the world once it is proposed. The US Obama administration has made building smart grids a national development strategy for the United States. China has also implemented smart grids. Planned research and proposed that a strong smart grid should be fully established by 2020. Regardless of the differences between countries in the definition and focus of smart grids, their core objectives will be “reliable, safe, economical, efficient, and environmentally friendly”. Use safety tips. The construction of smart grids requires the extensive application of various types of advanced equipment technologies to greatly improve the performance of transmission and distribution systems, in particular to increase power density, power supply reliability, power quality, and power production efficiency. These advanced technologies not only include the application of existing advanced technologies, but also include the application of various new and high technologies that may be developed in the future. Application development of the latest scientific research results in superconductivity, energy storage, power electronics, and fault diagnosis will become the focus of development.

Because of the zero resistance and complete antimagnetic properties of superconducting materials, power equipment made of superconducting materials is characterized by high efficiency, low consumption, safety and environmental protection. Its unique performance advantages may make superconducting power equipment a future. With the upgrading of products, the promotion and application of superconducting technology will also promote the renewal of the concept of power system construction, which will lead to a leap-forward development of power grid technology. At present, superconducting power equipment mainly includes superconducting current limiters, superconducting cables, and superconducting energy storage devices, which are described below.

1 The role of superconducting power equipment in the smart grid 1.1 Superconducting current limiter 1.1.1 Technical background The ideal current limiter should be characterized by steady state low resistance, fault resistance and fast recovery, ie when the power grid is transmitting power normally. Low impedance, which can reduce the running loss of equipment and ensure the user voltage stability. When a short-circuit fault occurs in the power grid, the current limiter quickly transitions to a high-impedance state, effectively limiting the magnitude of the short-circuit current. After the short-circuit fault is eliminated, the current limiter quickly returns to a low-impedance state. Although conventional air-core reactors and high-impedance transformers also have the effect of limiting the short-circuit current, they have not yet reached such ideal performance requirements. The application of superconducting materials and technology provides the material basis for the creation of an ideal flow restrictor.

From the nature of current-limiting devices, superconducting current limiters can be classified into resistive and inductive types. Resistive SFCL uses the change of resistance to realize the through current and current limit, while the inductive SFCL uses the change of the induced electromotive force to realize the through current and the current limit. Inductor type can be divided into induction type, shield type, bridge type and saturated core type according to different working principles. Saturated core type SFCL consists of basic parts such as core, AC winding, DC winding, and DC excitation circuit. The principle is similar to that of a saturable iron core reactor, which uses the nonlinearity of the magnetic permeability of the magnetic material for current limiting control. Saturated iron core SFCL principle is clear, the structure is simple, reliable performance, conducive to the production of large-capacity current limiting device, but at the same time facing the core volume and high cost issues.

1.1.2 Performance Characteristics The superconducting current limiter has excellent current limiting characteristics and is an ideal current limiting device for high-voltage power grids in the power system. High-voltage superconducting current limiters of high voltage class have become extremely developed with their unique advantages. Prospects and market competitiveness of new power equipment. Compared with traditional current-limiting reactors, superconducting current limiters can also be called smart power devices, which meet the requirements of smart grids. Their functional characteristics can be summarized as: low impedance in steady-state operation, reduced equipment pressure, and transmission of power to the grid The impact is small.

High impedance occurs when a short circuit occurs, which greatly limits the short-circuit current and protects the safety of the equipment in the system.

Real-time monitoring system short-circuit short-circuit current generation, rapid response and triggering current limiting action, the entire current-limiting response process can be completed in a few milliseconds, and continue to ensure the current limit state; after the current limit can be quickly restored to meet the requirements of grid reclosing.

1.1.3 Application Prospect The superconducting current limiter can avoid the damage caused by excessive fault short-circuit current to the power equipment, ensure the reliability of the power grid protection system, and improve the safety of the power grid.

The pressure drop of the superconducting current limiter is small, which can improve the quality of power supply and reduce the loss. In addition, reducing the short-circuit current of the system will inevitably lead to the reduction of the requirements of the short-circuit resistance of the electrical equipment in the grid system, especially the breaking capacity requirements of the circuit breaker, so that when the new grid is designed or the old grid is modified, the grid can be greatly reduced through the use of the current limiter. Construction costs.

The impedance of the saturated iron core superconducting current limiter is nonlinear, which can be properly adjusted according to the needs of the power grid system. The optimal combination with a capacitor can also play a role in regulating the reactive power and so on.

The main application scope of superconducting current limiter: Using superconducting current limiter on the key nodes and lines of the power grid can solve the problem of excessive short-circuit current brought by the increase of interconnection capacity of the power grid and enhance the safety of high-voltage and ultra-high voltage power grid interconnection. Sex.

Equipped with a superconducting current limiter for large transformers can improve its ability to withstand short-circuit current and reduce the risk of accidents.

The installation of a superconducting current limiter between a large generator set and the power grid is equivalent to building a "firewall" to cut off the mutual effects of short-circuit accidents.

The superconducting current limiter combined with the advanced relay protection system can form a more reliable protection system, further enhancing the ability of the power grid to prevent short-circuit faults, and making the strong smart grid more realistic.

1.2 Superconducting Cables 1.2.1 Technical Background The basic structure of superconducting cables is very different from conventional cables. Normal temperature insulated superconducting cables, from the inside to the outside, are usually inner support tubes (or common conductors), superconductors, vacuum thermostatic insulation layers, electrical insulation layers, cable shields and sheaths, and other auxiliary components. When the electrical insulation layer is within the vacuum thermostatic insulation layer, ie at a low temperature, it is called a cold insulation superconducting cable.

The operating conditions of superconducting cables are very different from those of conventional cables. That is, conductors require a low-temperature operating environment. Therefore, the terminals of the superconducting cables are very different from those of conventional cables, and a low-temperature refrigeration system is also required. The refrigeration system is usually composed of refrigeration units, liquid nitrogen pumps, insulated pipes, water cooling devices, and liquid nitrogen storage tanks. The cable terminal is a port that connects the superconducting cable and other external electrical equipment. It is also the connection port of the cable cooling medium and the cooling device. In addition to the role of the electrical cable connected to the terminal as a conventional cable, it is also necessary to ensure the temperature transition. The structure of the terminal is matched with the structure of the cable, so the terminal of the room temperature insulated superconducting cable and the cold insulated superconducting cable also have a great difference in structure.

1.2.2 Performance Characteristics The resistance of the superconducting cable is nearly zero, and the loss is extremely low. This feature means that it can be installed in an important place in the power grid and the current on the overloaded line can be diverted to form a new network structure. The transmission capacity of superconducting cables also increases as the temperature of the conductors decreases. Therefore, when there are other line failures, the temperature distribution of the superconducting cable can be further moderated by adjusting the temperature of the superconducting cable conductors, which is more conducive to system stability. Superconducting cables undoubtedly meet the requirements of economical, efficient and safe smart grids. Its performance characteristics are as follows: low loss. The normal operating resistance of the superconducting cable is very small, and the conductor loss of the AC superconducting cable is less than 1/10 of that of the conventional cable (the DC superconducting cable is lower), plus the energy loss of the cooling, the total operating loss is only large as the conventional capacity. . The current transmission capacity of a superconducting cable of the same section is generally 35 times that of a conventional cable.

It can better regulate the power flow distribution of transmission power.

Save material. Superconducting cables with the same transmission capacity use less metal and insulation than conventional cables, and the superconducting cables have fewer circuits.

Environmental protection. The superconducting cable uses liquid nitrogen as a coolant and releases it into the air without causing environmental pollution. However, conventional oil-filled cables have the problems of flammability, oil leakage and environmental pollution; cold-insulated superconductors with superconducting shielding layers The cable also greatly reduces the electromagnetic radiation because of its large capacity, low loop, and small footprint, which can save land. Superconducting cables are laid underground and can be installed using existing lines (including railway lines, highway lines, pipeline lines, etc.) without affecting the appearance of the city, reducing the cost of upgrading the grid and reducing the impact on the environment.

Installation costs are lower than ordinary cables. The cross-section of the superconducting cable is small, and the installation weight and space are small, which greatly saves the construction and installation costs when laying ordinary cables and busbars. In addition, superconducting cables can deliver large amounts of power at low voltages, thus saving expensive high-voltage equipment and reducing the loss of voltage conversion.

Can limit the fault current. Superconductors have a natural current limiting ability. Once the current caused by the short circuit of the power grid increases to a certain degree, they lose their superconductivity and become resistive as ordinary conductors. With a proper design, the superconducting cable can reach a sufficient value for the time-out resistance to attenuate the short-circuit current.

1.2.3 The application prospect of 26.8 billion kW.h, which is calculated based on the transmission loss rate of 8% in China, means that the loss of transmission lines in China is as high as more than 200 billion kWh per year, equivalent to the annual output of more than 30 million kilowatt-class units. Power generation. Applying superconducting cables is a great way to reduce power grid losses. Since superconducting power transmission does not require high pressure, the transmission loss, electromagnetic pollution and the width of the occupied corridor can be minimized, which truly represents the world's most advanced transmission technology. For China's strong smart grid planning, superconducting cables may realize their value in the following areas in the near future: High density load areas in urban centers, where the use of more conventional cables or overhead lines is limited by space or environmental protection, it can solve the power bottleneck problem, and Bring more environmental benefits.

High-current transmission buses in power plants and substations.

Large cities with rapid development of demand can use superconducting cables to directly replace conventional cables in existing pipelines and increase the power supply capacity.

1.3 Superconducting Energy Storage Superconducting energy storage is the use of superconducting coils to store electromagnetic energy directly and return electromagnetic energy to the grid or other load when needed. The superconducting energy storage device is composed of superconducting coils, a cryogenic vessel, a refrigeration device, a converter device, and a measurement and control system. The superconducting coil is a core component of the superconducting energy storage device. It can be a spiral coil or a toroidal coil. Spiral tube coil structure is simple, but the surrounding stray magnetic field is larger; while the scattered magnetic field around the toroidal coil is smaller, but the structure is more complex.

The working principle of the superconducting energy storage device is to store excess electric energy when the grid operating load is at a low level, and to send the stored electric energy back to the grid when the grid operation is at peak usage. Since the energy storage coil is wound by the superconducting wire and maintained in the superconducting state, the stored energy in the coil can be almost permanently stored without loss until it needs to be released. The superconducting energy storage device can not only be used to regulate the peaks and valleys of the power system, but also can be used to reduce or even eliminate the low-frequency power oscillation of the power grid, thereby improving the voltage and frequency characteristics of the power grid, and can also be used for the adjustment of reactive and power factors to improve power. System stability.

The magnetic field generated by the superconducting energy storage coil is very strong, and the stored energy density is very high. Compared with other energy storage methods, such as battery storage, compressed air energy storage, pumped energy storage and flywheel energy storage, there are many obvious advantages: long-term energy-free storage of energy, its conversion efficiency of up to 95%. By adopting Converters of power electronic devices are connected to the grid and have a fast response (milliseconds).

Since the capacity of its energy storage and power modulation system can be independently selected over a large range, the desired high-power and large-energy systems can be built.

There is no rotating part except the vacuum and refrigeration system, which has a long service life.

It is not limited by location at the time of construction, it is easy to maintain and has little pollution.

2 Conclusions The development of a smart grid cannot be separated from the support of new power equipment made of superconducting materials. As the main product for the application of superconducting characteristics, superconducting current limiter can reduce the short-circuit current level of the power grid, improve the safety of the power grid, improve the quality of power supply, and greatly reduce the cost of power grid construction or reconstruction. The superconducting cable has excellent characteristics such as low loss, large capacity, and environmental protection; superconducting energy storage can adjust the peak-to-valley of power consumption in a near-destructive manner and improve the stability of the power system.

At present, with the introduction and implementation of smart grid planning in various countries, and the rapid progress in the application of superconducting power technology, superconducting power equipment will surely usher in more room for development, and its good market prospects are worth looking forward to. EM

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