Polyamide 66 as a cryogenic dielectric

Improvements in superconductor and cryogenic technologies enable novel power apparatus, e.g., cables, transformers, fault current limiters, generators, it etc., with better device characteristics than their conventional counterparts. In these applications electrical insulation materials play an important role in system weight, footprint (size), and voltage level. The trend in the electrical insulation material selection has been to adapt or to employ conventional insulation materials to these new systems. However, at low temperatures, thermal contraction and loss of mechanical strength in many materials make them unsuitable for superconducting power applications. In this paper, a widely used commercial material was characterized as a potential cryogenic dielectric. The material is used in "oven bags" which is a heat-resistant polyamide (nylon) used in cooking (produced by Reynolds^®, Richmond, VA, USA). It is first characterized by Fourier transform infrared and X-ray diffraction techniques and determined to be composed of polyamide 66 (PA66) polymer. Secondly the complex dielectric permittivity and dielectric breakdown strength of the PA66 films are investigated. The dielectric data are then compared with data reported in the literature. A comparison of dielectric strength with a widely used high-temperature superconductor electrical insulation material, polypropylene-laminated paper (PPLP ™ a product of Sumitomo Electric Industries, Japan), is provided. It is observed that the statistical analysis of the PA66 films yields 1% failure probability at 127 kV mm^{- 1}; this value is approximately 46 kV mm^{- 1} higher than PPLP ™. Comparison of the mechanical properties of PA and PPLP ™ indicates that PA66 has low storage and loss moduli than PPLP ™. It is concluded that PA66 may be a good candidate for cryogenic applications. Finally, a summary of dielectric properties of some of the commercial tape insulation materials and various polymers is also provided.