| Title |
Trend Analysis of Insulation Condition in Steam Turbine Generator Stator Windings |
| Authors |
구자영(Ja-Young Koo) ; 곽준호(Jun-Ho Kwak) ; 윤호열(Ho-Yeol Yoon) ; 김희동(Hee-Dong Kim) |
| DOI |
https://doi.org/10.5370/KIEE.2026.75.8.1958 |
| Keywords |
dissipation factor; PD; degradation; groundwall insulation; generator; stator windings; micro-delaminations; diagnostic tests |
| Abstract |
Analyzing the temporal trends of AC current, dissipation factor (tanδ), and partial discharge (PD) magnitude enables the evaluation of insulation degradation and the proactive prediction of potential defects in long-term operational generator stator windings. Stator windings in newly manufactured generators often exhibit numerous internal micro-delaminations within the groundwall insulation, which initially leads to elevated baseline measurements for AC current, tanδ, and PD magnitude. However, once the generator enters commercial service, high operational currents induce thermal expansion that gradually minimizes these micro-delaminations over successive operating years. Specifically, the PD magnitude decreases to its minimum after 2～3 years of operation and subsequently increases as insulation aging initiates. Conversely, the AC current increase rate (△I) and dissipation factor increase rate (Δtanδ) require more than a decade of operation to decrease, after which they progressively rise as structural degradation commences within the groundwall insulation. In this study, off-line insulation diagnostic tests were performed to evaluate the degradation state of a steam turbine (S/T) generator (374 MVA, 20 kV) stator winding operated for over 23 years. Based on the diagnostic test results, a detailed trend analysis was conducted using data collected over six measurement intervals during planned maintenance outages over a 15-year period from 2011 to 2026, focusing on AC current, tanδ, and PD magnitude. |