New Solid-state Limiting Its Application

Along with the electrical power system development, the problem of short-circuit capability increasing becomes day by day serious, which not only directly affects the selection and investment of electrical equipments, also brings the enormous hidden danger to the electrical power system safe and stable operation. Therefore, it has the vital significance to uses practically effective measure to limit the short circuit to a reasonable low level. With years research and development, already has emerged multitudinous special fault current limiting method at present, namely Fault Current Limiter, especially the superconductivity fault current limiter, the solid state fault current limiter and so on already used in some demonstration projects. This enormously impels the fault current limiting technology through the research work to practical advancement.This paper firstly outlines the development of fault current limiting techniques and Fault Current Limiters, mainly introducing the typical topology and operation principle of the superconductivity fault current limiter (SFCL) and solid state fault current limiter (SSFCL). The research progress of novel solid state fault current limiter is narrated in details and its typical topologies, parameter design method, normal operation and fault current limiting control strategies, as well as prototypical experiment results, are summarized. The DC reactor magnetizing transient of the transformer coupling solid state current limiter in double power supplies and the ferromagnetic resonance in the pure capacitance load experiment duo to coil saturation of the coupling transformer both have been discussed in details, also proposed the method and measures to reduce the adverse effect.The normal operation of the transformer coupling solid state fault current limiter is under the system nominal current and the voltage which the coupling transformer withstands is very low .However the voltage and electric current through it are much higher during fault current limiting operating. So, with the work done before, the topology and operation principle of the saturated transformer type SSFCL is analyzed. When normal operation the saturated transformer type SSFCL is equivalent to original transformer coupling solid state fault current limiter, but the coupling transformer coil enters deep saturation when short circuit fault occurs. After the SCR bridge withdraws from the system connection, the saturated coil reactance and the leakage reactance of coupling transformer play the role of limiting stable short-circuit current, equivalent to SSFCL with bypass inductance. Further more the parameter design method of the saturated transformer type SSFCL is proposed, which reduces the coupling transformer and the DC reactor design capacity and does not affects the normal system operating and short-circuit limiting effect. The normal operation,satisfactory short current limiting results are also confirmed by the software simulations.Then analyzed the influence of load impedance characteristic on the solid state fault current limiter operating, which points out that the transformer (saturated or not) coupling SSFCL has some application limitation under the capacitance loading condition. The relations between the application limitations and power factor are analyzed and then the method and measures to avoid the adverse effect proposed.