- The current limiting or self-limiting transformer (CLT, SLT) is a multifunctional device which combines the functions of a usual power transformer with the functions of a current limiter. Various constructions of the CLT and fault current limiters (FCL) were investigated in order to realize the optimized constructional outline. Small scale devices were investigated with one or more YBCO rings and BSCCO tape(s). The rings were placed on one or two limbs of the devices. The HTS ring was replaced with HTS tape in order to realize a new FCL construction. The main goal is to decrease the leakage field and to increase the mainfield reactance. The magnetizing current is to be reduced. The upscalability i.e. increase of the power rating is investigated as well. The CLT was investigated experimentally for both sudden short circuit and steady state (transformer) operation modes in cases of several selected configurations. The activation currents of the devices were determined in cases of sudden short circuit and transformer operation modes. The results are used to find the optimum constructional outline realization of the current limiting transformer.