Electrical Insulation Performance Comparisons between Kapton and Teflon Coil Insulation Systems for Pulse Power Applications

Current pulse power alternator windings operate at high current densities and high electromagnetic field levels. Consequently, the winding insulation systems must be designed to withstand high electrical voltage stress and large mechanical loads. Finite element analysis of pulse alternator windings has indicated that good bonding strengths, inter-laminar tensile strength and inter-laminar shear strength, at winding insulation tape interfaces are required to maintain mechanical integrity. These bonding interfaces include the conductor to barrier tape (Teflon or Kapton), barrier tape to barrier tape, barrier tape to glass armor tape, glass armor tape to glass armor tape layers and glass armor tape to composite support structures. Although bonding strength data from adhesive manufacturers is available for bonding metal to metal, bonding strength data for Teflon/Teflon, Kapton/Kapton, Teflon/woven glass and Kapton/woven glass are practically non-existent. Therefore a testing program was developed to determine the mechanical properties of various combinations of barrier tapes and adhesives that were suitable for the high voltage pulse power application. A survey and an evaluation of adhesive properties and performance were conducted to select the prospective adhesives. A total of 11 adhesives were selected and matched with the two prospective barrier tapes: Kapton and Teflon. To further enhance bonding and adhesion, both sides of the tapes were chemically etched. In addition, an evaluation was performed of Teflon tape samples bonded using tapes which came with adhesive on one side with no etching on the opposite side. Multiple samples of all of the candidate barrier tape/adhesive combinations were manufactured and prepared for testing. Testing was performed per specification of ASTM D897 - 01, Standard Test Method for Tensile Properties of Adhesive Bonds. Three rounds of performance testing were conducted to down-select from the initial list of tape-adhesive combinations to the final one tape/adhesive combination that showed the best performance.