Aramid papers with improved dimensional stability

Meta-aramid (Nomex Type 410) papers are used as insulation in a wide variety of applications in motors, generators and transformers. These papers are prone to moisture absorption under high humidity conditions, which causes these papers to expand by about 1.0% (from bone dry to 90% RH; 23C) in the machine direction. This expansion can pose issues with their use in large generators despite their acknowledged toughness in the application. A new version of aramid papers, based on para-aramid fibers has been developed that has less than 1/7th the change in length of meta-aramid papers. The properties of this new product are discussed and compared with those of meta-aramid papers.