Experimental study on the relationship between the trigger current of transformer-type superconducting fault current limiter and the fault phase

Superconducting fault current limiters (SCFCLs) are expected to be introduced into power systems, because they can reduce fault current and capacity of circuit breakers. Furthermore, SCFCLs are expected to improve stability of power systems, which was confirmed by some experiments. Therefore, various kinds of SCFCLs have been proposed and studied. To introduce SCFCLs into power systems, there should be some specifications such as the impedance, the trigger current level, the recovery time and so on. Fault analyses point out that the accuracy of the trigger current level is requested. Therefore, a transformer-type SCFCL with adjustable trigger current level was proposed, designed, made, and tested. By some tests, adjustability of the trigger current level at quasisteady operation was confirmed. The trigger current level of SCFCLs in power systems may depend on the phase at fault occurrence. For the above discussion, limiting tests of the SCFCL were carried out at various fault phases. The results of the limiting tests are described in this paper. The relation between the trigger current level of the SCFCL and the fault phase is shown, then some discussions on the instantaneous trigger current level are described.