Novel butt-lapped PET-mica tape turn insulation for high voltage motors

Turn insulation for high voltage motor coils is normally a glass cloth-backed mica paper tape that is applied to the magnet wire according to specified fabrication methods [1]-[4]. In contrast to the main insulation, turn insulation is much thinner and more easily damaged during production because there are many processing steps. Hence, there is more attention paid to the protection of the turn insulation. Conventionally, turn insulation is protected with a double glass yarn that is applied to the wires [5]. For example, turn insulation for 6-kV motors is lapped with a double layer of glass yarn plus polyimide film, and for 10-kV motors, a double layer of glass yarn plus PET-mica tape is used. However, these conventional turn insulations have several drawbacks; namely, the turn insulation is easily damaged during coil production, and impregnation of vacuum-pressure impregnation (VPI) resin is poor [6]-[9]. Hence, it is desirable to eliminate the glass yarn insulation layer and use PET-mica tape directly as the turn insulation, which also has the additional advantages of good mechanical properties, good impulse strength and corona resistance, better voltage endurance, and lower cost.