Development of Quench Propagation Models for Coated Conductors

Due to their intrinsic thermal properties that lead to very slow heat diffusion, coated conductors are very difficult to protect against thermal instabilities and quench. This is particularly critical as the device increases in size and stored energy. Many experiments showing low quench propagation speeds and surface voltage distributions have identified the problem but, as of today, no models are available to perform high fidelity simulation of the quench process in a single tape, or in a full device. YBCO tapes are very promising conductors that would allow the development of high power density power devices such as generators and motors operating at liquid nitrogen temperature. The Department of Defense through the Air Force Research Laboratory launched a new project aiming at simulating quench propagation in YBCO tapes. The first step of the project deals with the understanding of the current diffusion in the different layers forming the tape. Experimental data on normal propagation zone (NZP) velocities and fault current limiters using this material show that the quench is most likely a 3D phenomenon involving many non trivial physical phenomena. Experimental data will help to understand the physics of the quench and develop a local electromagnetic/thermal model of YBCO tapes. This paper presents the preliminary results of this work including a discussion of the physics of current sharing between layers. We will evaluate different commercial codes and present a simplified 3D homogenized model applicable to a racetrack coil.