Characteristic Analysis And Optimization Design Of The Flux-coupling Type Superconducting Fault Current Limiter

In the modern power system with a large scale and high reliability requirements,excessive short-circuit current may not only cause the system to lose stability due to the difficulty of removing the fault,but also damage the power installation due to the generated electromagnetic force and temperature rise.In order to solve the problem of excessive short-circuit current in the present power system,Fault current limiter(FCL)has become a new type of power device with high demand and is one of the current research hotspots.Although many types of FCLs have been proposed,including the use of superconducting materials,there are still many technical difficulties under high voltage and high current parameters,and there is still a large gap from commercialized products.The flux-coupling type superconducting fault current limiter(FC-SFCL)generates a current-limiting impedance through the decoupling superconducting parallel inductance based on the circuit breakers' fractional interruption.The principle is simple and the impedance is low during normal operation.It can directly use the existing circuit breaker to open a short circuit that is much higher than its own breaking capacity.However,the magnetic-flux-reversed coupling parallel inductance,its operating loss,and the parameters coordination with the circuit breakers and the power grid are still to be further studied.This paper aims to promote the engineering application of the FC-SFCL,focusing on superconducting parallel inductance,and studies several technical issues related to engineering application.The specific work contents and results are as follows:(1)Researches on the winding structures and the operating characteristics of coupling characteristics,voltage distribution and AC losses of the parallel inductance of the FC-SFCL are processed,and a 400 V/20 A small-capacity prototype experimental platform is built.Some tests on current-limiting effect,and voltage distribution are carried out.The feasibility of superconducting parallel inductance windings is verified,and its operating characteristics along with the analysis methods for the operating characteristics are verified.The simulation and experiment results show that: The FC-SFCL can operate stably and the current-limiting ratio exceeds 50 %.The coupling degree,impedance,and loss of the limiter with different winding structures are different,and the winding structure of the limiter needs to be selected according to different applications.The single-pancake winding and layer winding structures have more advantages,and can be used preferentially for the engineering prototype.(2)In order to improve the technical economics of superconducting parallel inductance of the FC-SFCL engineering prototype,two schemes of core-type parallel inductance and quenched-type parallel inductance are proposed,and the electromagnetic design and performance comparison are completed.For the former,in order to reduce the risk of security caused by local heat accumulation damage to the magnet,an improved superconducting winding for the non-quenching parallel inductance to reduce the AC losses in the currentlimiting state is proposed.For the latter,an electromagnetic design method based on the simplified calculation of the number of parallel tapes is proposed,which simplifies the design process and reduces the design difficulty of the quenched FC-SFCL.The analysis results show that: Compared with the air-core structure,the iron-core structure of the non-quenching FCSFCL has a higher coupling degree and can reduce the cost of tapes,but excessive volume and weight will limit its application in the engineering prototype.Compared with the non-quenching structure,the technical economics of the quenched FC-SFCL is more prominent,and it can be used preferentially for engineering prototypes.(3)In order to further study the technical problems and solutions of the engineering implementation of the FC-SFCL,the design and selection of the parallel inductance of the10 k V/1.5 k A/60 k A FC-SFCL are carried out based on the exploration schemes of the engineering prototype implementation.According to an actual power system,the parameters and design indicators of the limiter are determined,and the tape selection,working temperature zone selection and coil insulation design of the parallel inductance are completed.The electromagnetic optimization design of the pancake-solenoid-type parallel inductance is carried out.Aiming at the problem of uneven current distribution of the multi-coil parallel inductance,a current sharing strategy of the solenoid-type multiple pancake coils in parallel was proposed.This strategy has obvious effects,but limitations exist in the method of eliminating circulating current.In order to further solve the problem of current sharing and circulating current of the FC-SFCL,a ring-shaped parallel inductance scheme with automatic current sharing and no circulating current is proposed,and the electromagnetic optimization design is carried out.By comparing the two design schemes,and combining the operational stability and technical feasibility of the magnet,the ring-shaped design scheme is selected.(4)The multi-section separation calculation method is used to approximately calculate the AC losses of the selected ring-shaped design scheme of the parallel inductance.It solves the problem of the difficulty of the loss calculation of the three-dimensional model.Based on the electromagnetic-thermal coupling calculation model,the operating thermal stability of the parallel inductance is evaluated.Then the supporting structure of the parallel inductance is designed and checked,and the configuration of the low temperature system is completed.The comprehensive electromagnetic-thermal-mechanical design scheme of parallel inductance is given,and the types of matching electrical components are determined.Finally,the overall conceptual design of the 10 k V/1.5 k A/60 kA FC-SFCL engineering prototype is completed.