Impact of inverter drives employing fast-switching devices on form-wound AC machine stator coil stress grading

Good performance of conductive armor tape and of the semiconductive, stress-grading tape in stress-grading sytems is imperative in the context of fast rise-time and repetitive serges in motors fitted with inverter drives. However, when the motor is fed by inverter-based drives employing fast switching, a significant impact on the electric, stress-grading system occurs. In a simulation, the groundwall insulation is considered a perfect insulating material. The simulation indicate that during the fast rise-time, a high electric stress can develop right at the slot exit of the stator if the conductivity of the conductive armor tape (CAT) is not high enough. During the rise-time, the semiconductive, stress-grading tape (SSGT) is not performing its intended function. After the rise-time of the pulses, the stress shifts to the SSGT and the grading of the electric stress becomes effective. The stress-grading at the end of the conductive paint section then is achieved by two coordinated layers. The second conductivity layer acts as a high-pass filter, grading the high-frequency components. The sectionalized-grading system not only grades the electric stress but also distributes the heat that is generated. With the aid of infrared cameras, experimental verification of the theoretical model is demonstrated to detect the heat that is generated as a result of the electric stress.