Coated Conductor Based FCL With Controllable Time Response

Performance of fault current limiter demonstrators based on either a single coated conductor (CC) tape or CC assemblies tested in current limitation modus is reported. A primary goal of this work was to achieve a quick reaction of the fault current limiter (FCL) device, and to study possibilities to provide a reliable and controllable time performance of limiting devices. An improved homogeneity of coated conductors was achieved employing a new alternating beam assisted deposition technique. This technique was used for processing of biaxially textured buffer layers with enhanced quality. Typically, the tapes yielded a critical current of 200-300 A per cm width at 77 K and self field. In demonstrators based on single CC tape, a 10 mus transient time of quench was observed. A stack of coated conductors jointed in parallel was employed as an active FCL element. Two alternative cases are studied when (i) CC tapes exhibit an equal and homogeneously distributed critical current and (ii) the critical currents and contact resistances are different in different tapes. As a result, it was experimentally shown that the quench duration can be varied from 10 mus (in case (i)) to 2 ms (in case (ii)). Such artificially smoothed quenches with pre-determined time dependence should play an important role in AC and DC networks where current surges have to be reliably suppressed. We found that the quenching behavior of the entire electrical circuits is consistent with a finite element model that takes into account a non-linear type of resistivity of CC tape. Short recovery time of 0.5 ms was achieved in CC based fault current limiters.