Design of a large current-type fault current limiter with YBCO films

Superconducting fault current limiters (FCLs) with YBCO films are under development in a national project in Japan. In this project, Mitsubishi Electric Corporation is in charge of the development of a large current-type FCL with a target capacity of 1 kA/200 V. To develop the FCL, numerical simulations on the combined thermal and electrical behavior of the device have been carried out considering inhomogeneity. The thermal stress of the FCL has also been studied by FEM using the calculated temperature profile. Here, the assumed size of a YBCO film on a sapphire substrate with a metal shunt layer is 30 mm in width and 100 mm in length. The critical current (I-c) of the film is assumed as 210 A +20% or -20%. The main results are as follows: (1) 16 films are arranged as a series of two stacks each consisting of eight films in parallel. (2) A polygonal arrangement is adopted for the YBCO films to obtain uniform current distribution. (3) The maximum temperature is 150 K and the thermal sink on the film effectively reduces temperature increase. (4) The thermal stress caused by the temperature gradient is <10 MPa. Therefore, mechanical breakdown is not a serious problem with this device. (C) 2002 Elsevier Science B.V. All rights reserved.