Electrical properties of commercial sheet insulation materials for cryogenic applications
ABSTRACT Dielectric properties of electrical insulation materials are needed for low temperature power applications. Performance of materials and their compatibility determine the size of the electrical insulation in power equipment. In this work we report the dielectric properties of some commercially available materials in sheet form. The selected materials are polypropylene laminated paper from Sumitomo Electric Inc., porous polyethylene (Tyvektrade) from Dupont and polyamide paper (Nomextrade) from Dupont. The dielectric properties are characterized with an electrical impedance analyzer in the frequency domain. The impedances are recorded in a cryocooler in the temperature range from 50 K to 300 K. The dielectric breakdown characteristics of the materials are measured in a liquid nitrogen bath at atmospheric pressure.
- [show abstract] [hide abstract]
ABSTRACT: Superconducting power cables with so-called "cold dielectric" insulation system normally use tape dielectrics impregnated with pressurized liquid nitrogen (LN2). The AC and lightning impulse (LI) dielectric strength of four commercially available dielectrics have been measured under nitrogen pressures in the range 0.15-0.35 MPa, absolute. A planar test cell is used, and slits were made in the dielectric sheets to simulate butt gaps. Polypropylene laminated paper (PPLPreg) and mica filled polyamide based paper (Nomexreg 418) show AC and LI breakdown field in the range 50-80 kV/mm and 130-160 kV/mm, respectively, whereas Kraft paper and polyethylene paper (Tyvekreg) are found to have a significantly lower dielectric strength. Most of the results are reasonably consistent with previous studies. However, as opposed to other investigations, the dielectric strength for PPLPreg and Nomexreg is not found to increase with increasing nitrogen pressureIEEE Transactions on Dielectrics and Electrical Insulation 01/2007; · 1.36 Impact Factor
Conference Proceeding: Breakdown statistics of polyimide at low temperatures[show abstract] [hide abstract]
ABSTRACT: The dielectric breakdown data of polyimide at liquid nitrogen temperature are investigated. The applicability of the Weibull distribution is discussed. A new distribution function is proposed, and its utility and strength are illustrated distinctly by employing the Monte Carlo method.Electrical Insulation and Dielectric Phenomena, 2006 IEEE Conference on; 11/2006
- [show abstract] [hide abstract]
ABSTRACT: The electrical characteristics and insulation design strength of liquid-nitrogen-impregnated synthetic insulation were considered. The impregnation of liquid nitrogen into insulation paper can be monitored by measuring the electrostatic capacitance of the cable. ∈ tan δ, an index of the dielectric loss, was 0.31% for cellulose paper and 0.18% for semisynthetic paper, polypropylene laminated semisynthetic paper, and biaxially oriented polypropylene laminated paper. It was found that the decline of the thickness dependence of the breakdown strength of the liquid-nitrogen-impregnated insulating cable was steeper than that of the oil-filled cables. It is possible to design the insulation strength of the 66 kV cable to be 10 kV/mmIEEE Transactions on Power Delivery 11/1992; · 1.52 Impact Factor