Transient stability of NbTi Rutherford cables for energy storage magnet applications

Abstract

Stability and quench behavior against transient perturbation expected during operation of a fast cycling energy storage magnet is an important issue for its design and safe operation. Understanding of thermal stability in terms of minimum quench energy (MQE) of a superconducting cable under specific operating scenario is of primary importance for its magnet application. Process of current redistribution from quench strand to adjacent strands depends on inductive coupling and has influence on quench development in the cable. The electrodynamic and thermal behavior of a ten-strand Rutherford-type cable for SMES program in the centre is studied numerically in the framework of discrete network modeling. Influence of several parameters such as uncertainties of inter-strand transverse and adjacent resistance, cooling conditions with liquid helium, etc. on MQE and quench behavior of Rutherford cable is discussed in this paper. IntroductionThe local disturbances is an important issue for the operation and quench protection of superconducting magnetic energy storage (SMES) magnet in spite of improvement in the manufacturing technique of multi-strand cable. The stability of a superconducting magnet against local disturbances is determined primarily by minimum quench energy (MQE)-the largest instantaneous energy deposited on the superconducting coil without the occurrence of the quench. Stability of the magnet increases with increase in MQE and therefore, MQE may be treated as the index of transient stability [1] of superconducting magnet. Stability of the superconducting Rutherford cable is described in general by a curve representing MQE as a function of transport current to critical current ratio. Stability of the cable primarily depends on [2] adjacent and cross-over resistance, electrical and thermal contact resistance, transport current distribution, mutual inductances among strands, magnetic field, average cooling area of the strand, cooling condition, etc. The critical current of the cable is less than the sum of critical currents of individual strands because of inter-strand coupling. A ten-strand non-keystoned Rutherford cable using NbTi is chosen for the SMES program at VECC [3][4]. The calculation of MQE is a complex task and requires nonlinear multi-physics analysis. The network program CUDI [5] based on electromagnetic and thermal behavior of Rutherford cable is used to simulate the stability of the cable under various operational scenarios. The primary uncertainties of the cable performance might be due to the uncertainties of cross-over and adjacent