The saturated-core fault current limiter (SFCL) is widely used to limit the fault current. However, in the conventional SFCL structure, alternating current (AC) and direct current (DC) coils are wound on different loosely coupled cores. Owing to the leakage inductance, the traditional structure demonstrates relatively large demand for DC excitation power and excessive impedance during saturation. In this study, a new structure for winding closely coupled DC and AC coils on the same core in three phases is proposed to reduce the influence of leakage reactance on the SFCL performance. The leakage magnetic flux generated by both structures is analyzed by performing finite element analysis simulations and utilizing a magnetic field division method. The impedance of the limiter is measured at different DC currents and air gaps to optimize its dynamic performance. A fabricated prototype of the proposed limiter exhibits smaller steady-state losses and high current-limiting capability.

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The saturated-core fault current limiter (SCFCL) has been studied by several scholars in the past decades. However, these studies have mainly focused on the AC coils of the SCFCL, the DC excitation has seldom been mentioned. In this paper, the DC coil of SCFCL is studied as well as the influence of the novel structure of tightly-coupled SCFCL (TSCFCL) on the voltage of DC coil. A novel DC energyreleased circuit is proposed, which overcomes the shortcoming of traditional single topology whose energyreleased speed is limited by withstanding voltage of IGBT. In order to select a suitable structure of air gap for fault current limiter, the effects of different structures on the saturation of the core are studied. A novel simulation method is presented in this paper which can overcome the drawback of traditional finite element analysis cannot simulate the switching characteristics of IGBT under high frequency. Finally, a prototype is manufactured to verify the theory of this paper. INDEX TERMS Saturated-core fault current limiter, DC energy-released circuit, air-gap, finite element analysis, magnetic field division.

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