Analytical and Experimental Studies on the Hybrid Fault Current Limiter Employing Asymmetric Non-Inductive Coil and Fast Switch

This paper deals with design and operating test of a novel hybrid FCL. The FCL system consists of a coil, a fast switch and a resistor for bypassing the fault current. The switch is driven by novel non-inductive coil suggested in this paper but an extra driving coil is required for fast switch in existing hybrid FCL. We used two kinds of HTS wire for the coil. The impedance of the coil was negligible in normal operation. But different quench characteristics of HTS wires caused asymmetric current distribution which induced effective magnetic flux in the coil during faults. The switch was opened by repulsive force from this magnetic flux in fast response to the fault. Then, all current were flew through the normal conductive bypass resistor connected in parallel to both the coil and the switch. Electromagnetic analysis of the coil based on finite element method was performed. Also, a small-scale asymmetric non-inductive coil was designed, fabricated and tested. The proposed hybrid FCL system showed fast and efficient current limiting characteristic.

I. Introduction

Fault CURRENT limiters (FCLs) have been suggested to solve serious problems from excessive fault current in electric power grids. Many active researches about various types of FCL such as resistive, inductive and hybrid types have been performed. In the recent researches, resistive FCLs using YBCO coated conductor (CC) have been developed and tested [1], [2]. To minimize the impedance of the FCLs, non-inductive winding methods using CC wires were suggested and there was rarely a magnetic flux in the coil during both normal and fault condition [3]. Resistive FCLs, however, have to endure a large fault current for 3–5 cycles until the circuit breaker (CB) cuts it off and the fault current causes high temperature rise in the high temperature superconducting (HTS) wire. FCLs are required to have a fast recovery within 0.5 s for the sake of protection coordination in electric power distribution grids in Korea and it is hard to achieve required recovery time with resistive FCLs. To reduce a recovery time and an amount of HTS wire, there have been some researches about new concept with superconductors and fast switches such as vacuum interrupter (VI), and solid state device [4]. Thus, an additional coil was needed to commutate the fast switch.