Lapped Insulation for a Superconducting Power Transmission Line

摘要

The development of a suitable polymeric tape for use as insulation on ac superconducting cables is a challenging engineering problem for the designer of plastic films. No commercially available tape simultaneously fulfills all of the electrical, mechanical and thermal requirements without modification. Porous, paper-like tapes produced electrically weak cables. Uniaxially oriented polyolefin tapes were found to have tensile properties superior to the nonoriented types, but these materials often fibrillated during cooldown to operating temperature. Further studies showed that commercially produced, 32 mu m-thick, biaxially oriented polypropylene tapes had acceptable tensile properties at both 4.2 and 293 K. The desired tape thickness of 66 mu m and 100 mu m were obtained by laminating two or three layers together with a 2.0 mu m-thick polyurethane adhesive. The loss tangent and permittivity of this laminate meets design considerations. Biaxial orientation was also found to reduce thermal contraction and increase the 4.2 exp 0 K elongation of the polypropylene films. Work has been started to develop a very high modulus, single layer polyethylene tape for use with higher voltage superconducting cables. (ERA citation 04:026282)