New chemistry for impregnation of HV machines: influence of compatibility between resin and mica tapes

European regulation changes have pushed electric machine manufacturers to request new materials suitable for impregnation of High Voltage motors and generators that are also compliant with European health restrictions. Until now, the most widely used materials for coils insulation are a blend of epoxy resin and anhydride that impregnates mica tapes, containing an epoxy binder with a Zinc naphthenate catalyst, which has the advantage of stability in storage tanks and good thermal and electrical properties. The development of a new impregnating resin, made with a hybrid epoxy-polyester chemistry, highlighted the need to find a way to improve compatibility with mica tapes. This new resin / tape combination has been visually evaluated, as first step, and then tested on bars, observing how dissipation factor versus voltage change after thermal ageing at high temperatures. Test bars made with new resin/tape combination withstood thermal ageing for a longer time than reference materials, confirming that compatibility between impregnating resin and mica tapes is a crucial factor influencing thermal resistance of a coil main wall insulation system.