BEHAVIOURAL MODELLING OF HIGH TEMPERATURE SUPERCONDUCTING WIRES AND COILS FOR POWER ENGINEERING APPLICATIONS

Many aspects of the behaviour of high temperature superconducting (HTS) wires are well understood for dc applications. However, models of HTS suitable for use in circuit analysis by power engineers designing HTS applications are not readily available. This paper describes the initial development of suitable models for HTS wire. The V-I characteristics for wires carrying dc transport current can be empirically determined using a power law V=kIn. Experimentally measured V-I characteristics are fitted using the above power law. This enables the simulation of the behaviour of Bi-2223/Ag wire using the well-known circuit simulator PSpice. Other factors affecting the dc critical current density of the wire, such as bending diameter and some aspects of perpendicular and parallel applied magnetic fields have also been considered in the model. The performance of the model with dc current is compared with experimental results from a non-inductive pancake coil prepared using Bi-2223/Ag 27-core multifilament tape, as well as two short HTS tapes with different critical current ratings. This paper discusses the modelling techniques and the behaviour of HTS wires and coils carrying dc currents. Models of wire and of coil behaviour were developed based on V-I characteristics of Bi-2223/Ag wires. The wires were prepared using powder-in-tube processes. The degeneration of critical current due to the bending diameter has also been analysed and incorporated in the model based on the results of measurements of Bi- 2223/Ag 27-core multifilament samples. The dc behaviour of an eight-metre length of tape wound in a non-inductive pancake coil has also been predicted using the model. Four samples from both ends of the wires were used in this work.