Physlca C 209 (1993) 277-280 North-Holland Experimental investigation of current-limiting device model based on high-T c superconductors V. Sokolovsky, V. Meerovich a, G. Grader and G. Shterb aElectrical Engineering Department, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva, 84105, ISRAEL* bChemical Engineering Department, Technion, Haifa, 32000, ISRAEL* The model of an inductive current-limiting device consists of a copper coil and a high-T c superconducting ring which are placed on a ferrite core and are coupled magnetically. The rings were prepared by extrusion of the Y B a C u O submicron precursor powder and organic binder, followed by sintering in oxygen atmosphere. The principle of the device's operation is based on a rapid rise of the device's inductance at the transition of the ring from the superconducting to the normal state.The results demonstrate that the device can reduce both the transient and the steady-state fault current significantly. The influence of thermal processes in the ring on the mode of device operation in the circuitis discussed. 1. INTRODUCTION Development of electricpower systems is accompanied by a constant increase in fault currents; these impose enhanced electrodynamic and thermal stability requirements to be met by electrotechnical device components. This in turn leads to a significant increase in size, weight and cost of electricalpower equipment. One method for fault current reduction is the application of high-speed current limiting devices (CLDs) having nonlinear characteristics: low impedance in normal operating conditions and high impedance in fault conditions. A promising option of such devices is the superconducting (SC) CLD [1-3], which is based on swift impedance change due to transition of a superconductor from SC state to its normal state. These transitions can be initiated by superfluous current, magnetic field or temperature, exceeding the respective critical values.~ A variety of SC CLDs and ways of using them have been known for decades. Some experimental CLDs based on low- temperature superconductors operating in liquid helium at temperature 4 K have been already tested throughout the world [1-3]. The advent in 1987 of high-temperature superconductors (HTSC) having critical temperatures higher than 90 K and allowing the use of reliable and inexpensive liquid-nitrogen cooling systems roused interestin C L D based on SC elements [2,3]. 2. DEVICE CONCEPT The device we have investigated is an inductive one; it consists of a primary normal metal coil and a secondary short-circuited H T S C coil which are placed on a ferromagnetic core (Fig. I). The primary coil is connected in series to the circuit to be protected. Under normal conditions of the circuit, the SC coilis in the S C state and its resistance equals zero. The magnetic flux produced by the primary coil is compensated by the flux of induced current in the short-circuitedsecondary coil. The device's impedance is low and is determined only by a leakage flux of the coils. Under short-circuitedconditions the current in the H T S C coil rises quickly up to the *This work was supported by research grants from Ministry of Science & Technology of Israel 0921-4534/93/$06 00 © 1993 - Elsevmr Scmnce Pubhshers B V All rights reserved