On the Effects of Repetitive High-frequency Voltage Impulses on Modern High-voltage Insulation Systems

The present work investigated the behavior of stator bars subjected to high-frequency pulses, such as those expected to be found in converter-fed large generators. The study checked the robustness of the current state-of-the-art mica-based insulation technology in coping with the demands imposed on such converter-fed machinery. To explore the subject comprehensively, and free from test artifacts, real-size Roebel bars were fabricated and installed into slot models that replicate their positioning within a real stator or rotor slot. To generate the required high-frequency excitation for testing, a versatile pulse generator was employed, allowing for adjustable amplitudes, rise times, and repetition rates. The test methodology was based upon the guidelines outlined in the international standard IEC 60034-18-42 and periodic evaluations, involving a variety of diagnostic tests, were conducted along the time to monitor the potential effects of aging. The results demonstrated the suitability of the state-of-the-art insulation technology against the impact of high-frequency pulse phenomena typically encountered in converter-fed generators.