Endurance Test on Nomex 410 to Assess Partial Discharge Activity under High dv/dt Square Voltage

Abstract

Under high dv/dt square voltage, medium-frequency transformers (MFTs) may experience non-uniform turn-to-turn voltage distribution, potentially causing local electrical overstress. Such stresses can initiate partial discharge (PD) activity within the winding insulation and may reduce its lifetime. Under high dv/dt square voltage conditions, conventional IEC 60270 PD measurements become difficult to apply reliably. In addition, sensors used for unconventional PD detection are affected by the switching noise, making the distinction between significant and nonsignificant PD activity challenging. Based on endurance tests and PD measurements under 20 kHz high dv/dt square voltage, this study provides a comparative analysis between time-to-breakdown, PD magnitude and PD repetition rate measured using a UHF sensor. Tests are carried out on Nomex 410 samples commonly used in MFT insulation systems. The results indicate that PD activity leads to a significant reduction in insulation lifetime, even at low PD repetition rates.

Mamadou Djan BALDE, Martin GUILLET, Eric VAGNON, Julien HUILLERY – SuperGrid Institute

Presented at International Conference on Dielectrics (ICD) 2026