Guenter Ries

Resistive current limiters with YBCO films

The aim of this work is to develop a function model of a resistive HTSC fault current limiter. The switching elements of the fault current limiter are bath-cooled in a liquid nitrogen cryostat. The elements consist of YBaCuO films which are deposited on different substrates with critical current densities of up to 3/spl middot/10/sup 6/ A/cm/sup 2/. For the most effective limiting samples so far the peak let-through current was twice tile nominal current and the steady short-circuit current below nominal current. The concept of a 100 kVA function model is introduced.

HTS flux pump for cryogen-free HTS magnets

A reliable method for persistent-current mode operation of HTS magnets is still not available. As an alternative solution to external high-current power supplies we have developed a cryogen-free operating transformer-rectifier type HTS flux pump. Using this device only small ac currents have to be supplied into the cryogenic system. Both thermally triggered HTS thin film switches as well as cryogenic MOSFET switches have been used to operate a conduction-cooled 0.5 T HTS magnet coil. This paper presents results of experimental test and modeling of the flux pump operation.