Closed-Form Determination of the Impedance Locus Plot of Fault Current Limiters: A Rigor-ous Approach with Graphical Representation

Shayan Behzadi Rafi, Francisco De Leon

Research output: Contribution to journalArticle


In this paper a mathematically rigorous method is presented for the calculation of the limiting impedance of FCLs based on a desirable change of short circuit currents. The method can be easily incorporated into standard short circuit current calculations of power systems. The changes of the short circuit currents for each FCL installed are calculated without having to build a new impedance matrix. In addition, the method gives a clear graphical representation of the impact of the FCL on the power system as a locus in the complex plane. The resultant plots provide valuable insight and information to utilities, system planners, and FCL manufacturers. FCL manufacturers can use these plots to identify the FCL impedance value and angle subject to the manufacturing and system constraints. The plots also allow utilities and system planners to compute the changes of fault current distribution caused by the FCL quickly and accurately. High-limiting FCLs may cause large increase in short circuit currents of other branches and therefore a compromise may have to be made between fault current limitation and the maximum additional currents that are acceptable in other branches. Examples on a three-bus system and an eleven-bus system are presented for illustration and validation.

Original languageEnglish (US)
JournalIEEE Transactions on Power Delivery
StateAccepted/In press - May 19 2018



  • Fault current limiters
  • impedance
  • power sys-tems
  • root locus
  • short circuit calculation
  • superposition

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering

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