Frequency response characteristics of a 100 MJ SMES coil - measurements and model refinement

Operating the coil of a superconducting magnetic energy storage (SMES) system through a switching type electronic power supply may excite resonances within the coil, thus potentially leading to internal over voltages. The latter may cause degradation of the dielectric insulation over time or, in severe cases, even damaging of the insulation. This paper complements theoretical investigations of these frequency selective voltage amplifications previously published by the authors by comparing them with measurements taken on the assembled 100 MJ/100 MW low-T_C SMES coil stack at room temperature. It has been found that surrounding metal structures such as the temporary mounting plane cause additional damping of resonances. Incorporating the latter into the theoretical model still results in internal voltage amplifications of up to two per units which have been verified by measurements. It is concluded that even with additional damping effects the potential problem of over voltages within large SMES coils persists and that it can be avoided by a careful design of the power electronic interface utilizing a comprehensive computer model of the system.