Researchs On New Method Of Limiting Fault Current And Bridge Type High Temperature Superconducting Fault Current Limiter

With the gradual expansion of our country power system capacity, the network short circuit capacity and the level of network short circuit current is risen continually. To ensure the safe and stable running of power system and limit short circuit current quickly, the power application of superconducting fault current limiter is regarded highly by many countries and becomes one of advanced subjects of power network technology research in 21 century.In this dissertation, bridge type high temperature superconducting fault current limiter and new limiting fault current method are researched thoroughly. From chapter 1 to chapter 3, the more urgent demand of power network for superconducting fault current limiter is clarified firstly. The status on superconducting fault current limiter at home and abroad and the research signification are analyzed. The basic theory of superconductor is analyzed in detail, including basic physical properties of superconductor, microstructure of traditional superconductor, high temperature superconducting characteristic and high power application of high temperature superconductor. The principle of each type of superconducting fault current limiter is introduced. Their characteristics are analyzed and the full theory scheme of superconducting current limiter is formed. According to superconducting coil whether to be superconducting state during superconducting fault current limiter limiting fault current, fault current limiter includes without-quench type and quench type. Superconducting coil always be in superconducting state for bridge type superconducting current limiter, furthermore the electric current that flows through the superconducting coil is DC during the stable state. There isn't AC loss in superconducting coil. This dissertation takes bridge type high temperature superconducting fault current limiter as object of study.In chapter 4, the basic operating theory of single phase bridge type superconducting fault current limiter is firstly studied. The levels of the short fault current on conditions of installing the superconducting fault current limiter or not are compared by digital simulation software. Then, the effect of limiting fault current of superconducting fault current limiter is verified in this paper. The influence on limiting fault current characteristic of superconducting fault current limiter is analyzed when the parameters of superconducting fault current limiter varying. Aiming at the problem in setting of DC bias power for bridge type superconducting fault current limiter, the new circuit(i.e. double-bridge hybrid bridge type high temperature superconducting fault current limiter) and new method of limiting fault current are presented to overcome the problem in setting the DC bias source . For this new fault current limiter, its principle of limiting fault current is analyzed. Its model is set up and simulated. The influence on characteristic of limiting fault current is analyzed when parameters of superconducting fault current limiter varing. This new scheme provides a theoretical basis for the design of new limiter prototype in Laboratory and engineering application. This fault current limiter which uses a bridge type rectifier power instead of normal DC bias source has excellent performance of limiting fault current. By analyzing and simulating the characteristics of three-phase bridge type superconducting fault current limiter, results of simulation show that the without-quench type superconducting fault current limiter can not only limit the first peak current of the fault current but also limits the growth of fault current. However, it can not limit the steady fault current. Three-phase bridge type superconducting fault current limiter is connected to power network based on transformer coupling which reduces the requirement for insulation performance.In chapter 5, the working principle of single phase half-control bridge type superconducting fault current limiter without DC bias source is analyzed. The load effect cause by without DC bias source is emulated and researched. The effect of cutting fault current automatically of half-control bridge type superconducting fault current limiter is tested and verified. Because of its property restriction, the ability of thyristor on cutting fault current is limited. So a new method is applied to single phase half-control bridge type superconducting fault current limiter that replacing normal DC bias source with a equivalent direct current partial source, which make a new single phase half-control bridge type superconducting fault current limiter be brought forward . The new fault current limiter can also work as fast solid state circuit breaker and can solve the problem brought by DC bias source. The steady state value of fault current can be reduced if a limiting current resistance was put in series with superconducting coil in fault state.In chapter 6, a single-phase double-bridge hybrid bridge type superconducting current limiter experimental prototype is developed by using self-winding high temperature superconducting coil. The experiment of fault current limiter prototype is carried out. The results of experiment show that the new type superconducting fault current limiter has good ability of limiting fault current and can be used in engineering practice. An engineering application scheme of new fault current limiter is designed. The principle of system composing is analyzed and system function of each part is described. An engineering installation scheme of new fault current limiter used 10kV distribution system is proposed. The new superconducting fault current limiter has practical value of engineering application.Aiming at technical problem of setting DC bias source, the thorough theory and application technology are researched. Further the results of creativity research are obtained. The new way of the bridge type superconducting fault current limiter is provided in power system application.