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(Dept.of Electronics Engineering, Engineering College, Myongji University)
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(Korea Electrical Engineering and Science Research Institute)
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(Korea Electric Power Corporation)
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(명지대 공대 전기공학과)
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(명지대 공대 전기공학과)
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(기초전력공학공동연구소)
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(한국전력공사)
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Current transformer (CT) saturation may cause a variety of protective relays to malfunction. The conventional CT is designed that it can carry up to 20 times the rated current without exceeding 10% ratio error. However, the possibility of CT saturation still remains if the fault current contains substantial amounts of ac and/or dc components. This paper presents a design method of iron-cored CTs for use with protective relays to prevent CT saturation. The proposed design method determines the core cross section of the CT; it employs the transient dimensioning factor to consider relay's operating time (duty cycle) and dc component as well as ac components contained in the fault current, and symmetrical short-circuit current factor to consider as well as ac components contained in the fault current, and symmetrical short-circuit current factor to consider the biggest fault current. The method designs the cross section of CTs in cases of reclosure and no reclosure.