Enhancement of Power System Capacity with Existing Switchgear using Superconducting Fault Current Limiter Apurbo Biswas, Md. Elias Khan and Md. Rafiqul Islam Department of Electrical and Electronic Engineering Khulna University of Engineering & Technology Khulna, Bangladesh rafiq043@yahoo.com Abstract—Superconducting fault current limiter is an attractive electronic device to solve the problem of very high fault current in the power system. In this paper, the performance of enhanced system capacity with existing switchgear by superconducting fault current limiter is studied. At first, a resistive type SFCL is modeled in Simulink. A three phase system with a nominal capacity is designed and then it is replaced by higher capacity keeping switchgear unchanged. Finally, the SFCL is introduced in the higher capacity system. Fault current in this system is limited by SFCL to the level of the presented switchgear. Thus, it is revealed that the outstanding current limiting performance of SFCL can be used to limit the fault to the level of the existing switchgear if the system capacity is improved. Keywords-superconducting fault current limiter; system capacity; fault current; switchgear; simulink/simpowersystem. I. INTRODUCTION The power generation capacity of electric system is being increased because of the growing demand. As a result, fault current level rises which can go beyond the maximum designed ratings of the presented switchgear. The requirement of replacing existing switchgears with higher ratings is a major concern in this situation. But to design switchgear with higher ratings for every different capacity system is not economically feasible [1]. It may result in decreasing the stability and reliability of the system. This huge short circuit current of higher capacity system is limited by fault current limiters which can be an alternative solution rather than replacing existing switchgear. High fault current can be limited to a level of highest designed short circuit current rating of presented switchgear. It creates a cost-effective way to improve the power system capacity keeping switchgear unchanged. Thus, the fault current limiter can be an excellent technique to protect power system equipments. Many types of fault current limiter have been developed in the past few years [2-3]. Superconducting fault current limiter (SFCL) is the most inventive fault current limiting device [4]. It offers many advantages which include having no impact on the system in typical conditions, limiting fault current quickly and response automatically in an abnormal condition. In power system, studies of SFCL are anticipated not only to limit fault current but also to develop stability of the system [5-6]. Many studies have been carried out for the practical application of SFCL in electric power system in the past few years [7-9]. It includes current limiting characteristics of SFCL, optimal resistive value of SFCL to improve transient stability, optimal place to install the SFCL etc. But most of the important practical application concern of SFCL in power system to enhance system capacity with existing switchgear has not been studied. In this paper, a resistive SFCL model is developed with the help of Simulink. The model is used in a single phase system to prove the current limiting behavior of the SFCL. Then a three phase system is designed with a nominal capacity and the fault current characteristics are investigated. Finally, the SFCL is implemented in a higher capacity three phase system and the overall performance is studied. II. BASICS OF SFCL Superconducting fault current limiter is a promising technique to limit fault current in power system. Normally non-linear characteristic of superconductor is used in SFCL to limit fault current. In a normal operating condition SFCL has no influence on the system due to the virtually zero resistance below its critical current in superconductors. But when system goes to abnormal condition due to the occurrence of a fault, current exceeds the critical value of superconductors resulting in the SFCL to go resistive state. This capability of SFCL to go off a finite resistive value state from zero resistance can be used to limit fault current. Different types of SFCLs have been developed until now [10-13]. Many models for SFCL have been designed as resistor-type, reactor-type, and transformer-type etc. In this paper a resistive-type SFCL is modeled using simulink. Quench and recovery characteristics are designed on the basis of [14]. 978-1-4799-0400-6/13/$31.00 ©2013 IEEE