IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 24, NO. 3, MARCH 2009 613 Nonsuperconducting Fault Current Limiter With Controlling the Magnitudes of Fault Currents Mehrdad Tarafdar Hagh, Member, IEEE, and Mehdi Abapour, Student Member, IEEE Abstract—In this paper, a diode-bridge-type nonsuperconductor fault current limiter (NSFCL) is proposed. The structure has the capability of controlling the dc reactor current that yields to control the magnitude of fault current. In order to control the magnitude of dc reactor current, a discharging resistor is used in the proposed structure. By controlling the magnitude of dc reactor current, it is possible to reduce the current rating and inductance of dc reactor. In addition, a series connection of dc voltage source with dc reactor is used to compensate the power loss of both nonsuperconducting dc reactor and diodes of fault current limiters (FCLs). By means of proposed NSFCL, it is possible to eliminate all disconnecting switches in the distribution network. The simulation and experi- mental results are presented to clarify the theory and possibility of implementation of the proposed NSFCL. Index Terms—Fault current limiters (FCLs), fault currents, su- perconducting coils. I. INTRODUCTION T HE GROWTH of electric power systems and their inter- connections may result in fault currents levels that are more than the maximum short-circuit ratings of the switchgears in some points of the grid. The most common ways to limit high-level fault currents and their disadvantage are listed as follows: 1) Upgrading and replacement of components: This solution is a relatively expensive solution if transformers and cables or overhead lines are also involved. 2) Sequential switching: This method has some safety risks to people and equipment if it fails to prevent the circuit breaker opening before the fault current has been reduced sufficiently. 3) Using a power electronic converter interface for distributed generators (DGs): Unfortunately, this method suffers from higher power rating, weight, and cost if it be used as a fault current limiter (FCL). 4) Active fault level management: This solution is at an early stage of development and will be very expensive at least in near future. Manuscript received May 21, 2008; revised July 23, 2008. First published March 10, 2009; current version published April 8, 2009. This work was supported by the University of Tabriz under the Research Project entitled Non- superconducting fault current limiter with controlling the magnitudes of fault currents. Recommended for publication by Associate Editor J. Enslin. M. T. Hagh is with the Faculty of Electrical and Computer Engi- neering, University of Tabriz, Tabriz, Iran (e-mail: tarafdar@tabrizu.ac.ir; tarafdarhagh@yahoo.com). M. Abapour was with the University of Tabriz, Tabriz, Iran. He is now with the University of Tarbiat Modares, Tehran, Iran (e-mail: mehdi.abapour@ gmail.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2008.2004496 5) Network splitting and reconfiguration: This method suf- fers from reducing the power quality of network due to the increased source impedance and system losses. 6) Increasing impedance (e.g., by current limiting reactor (CLR) or high-impedance transformers): This solution needs additional effort to maintain the voltage profile, and increases the network losses [4]. A novel idea to limit the fault currents and prevent upgrading of the switchgears is usage of FCLs. The implementation of FCLs in electric power systems is not restricted to suppress the amplitudes of the short circuits; they are also utilized to variety of performances such as the power system transient stability enhancement, power quality improvement, reliability improvement, increasing transfer capacity of system equipment, and inrush current limitation in transformers [1]–[8]. An ideal FCL should have the following characteristics [9]: 1) zero resistance/impedance at normal operation; 2) no power loss in normal operation and fault cases; 3) large impedance in fault conditions; 4) quick appearance of impedance when fault occurs; 5) fast recovery after fault removal; 6) reliable current limitation at defined fault current; 7) good reliability; 8) low cost. Different configurations such as Is-limiters, solid state fault current limiters (SSFCLs) and superconducting fault current limiters (SFCLs) were proposed in previous papers. The SFCL structure offers a good way to control the fault current levels in distribution networks due to natural low losses in superconductors during the normal operation [10], [11], [13]. Unfortunately, because of high technology and cost of supercon- ductors, these devices are not commercially available. There- fore, replacing the superconducting coil with nonsuperconduct- ing coil in FCL makes it simpler and much cheaper [9]. It should be noted that the main drawback of nonsuperconductor fault current limiter (NSFCL) is power losses that is negligible in comparison with the total power, provided by the distribution feeder [9], [12]. This paper proposes a controllable simple structure and cost- effective NSFCL to restrain the magnitude of fault current to a certain predesired value. In addition, the proposed structure is capable enough to reduce the inductance and current ratings in NSFCL and power grid, respectively, in comparison with what proposed in [9]. The circuit operation in normal and fault conditions are simulated and experienced. The experimental results are in good agreement with simulation of circuit op- eration both of which are carried out in distribution voltage levels. 0885-8993/$25.00 © 2009 IEEE