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Tham khảo tài liệu 'wind energy management part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 108 Wind Energy Management 5. SFCL in wind farms Fault current limiter is a novel device developed quickly in the recent decade. In principle it is a device with variable resistances which can show small resistance at the rated current and show large effective resistance at over-currents. From the state transition curve shown in Figure 1 superconductor is excellent candidate to fault current limiter. Superconducting fault current limiter SFCL was proposed shortly after the commercial HTS wire is available. However in practical operation it is not so simple to achieve even substation level SFCL as that expected. The key problem in SFCL is finding suitable method to transform microscopic effects to macroscopic ones with high energy efficiency quick response and recovery and safety as well. In wind farms SFCL can be utilized as overcurrent protection for generators and bus buffer against surges from the grid and or adjacent wind plants. In such usage the over-current is 1000 A with voltage around 35 kV. This makes a market for MW level SFCL. Various topologies and structures are proposed for SFCL in the past years. Currently SFCL of the bridge type the resistance type and the magnetic saturation type are tested in grids and promising in industry applications. Figure 21 shows schematic structures of these types. a b c Fig. 21. Schematic structures of SFCL in the resistance type a bridge type b and magnetic saturation type c . Many prototype SFCL use the superconducting state transition to generate an appropriate resistance and achieve its current limiting functions. According to the definition of jc when the fault disappears SFCL can automatically reset and the circuit protected by the SFCL will then return to its low resistance state. As shown in Figure 21a the resistance type SFCL uses directly the normal state resistance to limit the fault current. It is simple and combines the fault detection and reaction together thus quick in response at most cases. The drawbacks
