Research on the Aging Behavior and Air-Tightness Failure of Nitrile Rubber for Transformers under the Combined Action of Thermal-Mechanical Stress and Oil Erosion
Lin Yuandi1, Wang Tonglei1, Liang Jiabi1, Li Xuan1, Gao Sihang2
1. Electric Power Research Institute of State Grid Jiangsu Electric Power Co. Ltd Nanjing 211103 China; 2. School of Automation Chongqing University of Posts and Telecommunications Chongqing 400065 China
Abstract：Nitrile butadiene rubber (NBR) is extensively employed for transformer sealing owing to its superior oil resistance and mechanical properties. However, the aging kinetics and the fundamental mechanism leading to air-tightness failure in NBR under the synergistic influence of thermal, mechanical stress, and oil immersion conditions remain inadequately understood. This knowledge gap significantly constrains the accuracy of sealing state assessment and the reliability of long-term service life predictions. Particularly in practical transformer operations, sealing rings are subjected to complex multi-stress coupling effects, yet current research predominantly focuses on single-factor aging, failing to adequately reflect actual service conditions. Consequently, accelerated aging tests were performed under four distinct conditions: thermal-air, thermal-stress-air, thermal-oil, and thermal-stress-oil combination, at 100℃, 110℃, and 120℃. This experimental design enables the isolation and analysis of individual factor effects while capturing their synergistic interactions. The evolution of key mechanical properties, including hardness, tensile strength, elongation at break, and compression set, was monitored throughout the aging process. The measurement intervals were arranged to capture the complete degradation trajectory, with higher frequency sampling during initial rapid degradation phases. A nitrogen pressure-holding test was employed for samples undergoing thermal-stress-oil aging to determine the end-point of functional air-tightness failure. This functional failure criterion represents a more engineering-relevant assessment compared to conventional mechanical property thresholds. To elucidate the underlying physicochemical mechanisms, the aged sealing rings were subjected to Fourier transform infrared (FTIR) spectroscopy and cross-sectional scanning electron microscopy (SEM) analysis. The results demonstrate that the mechanical properties of NBR undergo significant degradation over aging time. The combined application of mechanical stress and oil erosion exacerbates the deterioration, accelerating the decrease in hardness and tensile strength while increasing the compression set rate and elongation at break. The air-tightness functionality failed after 124, 85, and 56 days of continuous thermal-stress-oil aging at 100℃, 110℃, and 120℃, respectively. Air-tightness failure consistently occurred when compression set reached about 65%, establishing a critical threshold for functional failure. Microscopic analysis reveals that the breakage, cross-linking, and oxidation of molecular chains within the rubber matrix lead to severe microstructural damage, manifesting as microcracks, voids, and particle aggregation. This microstructural deterioration causes the collaborative degradation of macroscopic mechanical properties and the ultimate loss of sealing function. In general, NBR exhibited a milder aging reaction, a later appearance of the mechanical property inflection point, and superior overall air-tightness durability. Finally, using the air-tightness failure data as the functional end-point, a service life prediction model for NBR was established based on the Arrhenius equation. The model shows correlation with experimental data. The model forecasts a service life ranging from approximately 9.59 years at 30℃ to 1.07 years at 80℃ for typical transformer operating conditions. This study provides critical experimental data and theoretical support for the accurate assessment of the sealing state and the prediction of the remaining service life of NBR seals in power transformers, thereby contributing to enhanced operational reliability.
林元棣, 王同磊, 梁家碧, 李轩, 高思航. 热-机械应力-油侵蚀综合作用下变压器用丁腈橡胶老化行为与气密性失效研究[J]. 电工技术学报, 2026, 41(17): 5996-6007.
Lin Yuandi, Wang Tonglei, Liang Jiabi, Li Xuan, Gao Sihang. Research on the Aging Behavior and Air-Tightness Failure of Nitrile Rubber for Transformers under the Combined Action of Thermal-Mechanical Stress and Oil Erosion. Transactions of China Electrotechnical Society, 2026, 41(17): 5996-6007.
[1] 刘泳斌, 高景晖, 钟力生, 等. ±320kV直流电缆交联聚乙烯/三元乙丙橡胶附件击穿特性[J]. 电力工程技术, 2023, 42(3): 72-80. Liu Yongbing, Gao Jinghui, Zhong Lisheng, et al.Breakdown property of ±320 kV HVDC cable system XLPE/EPDM accessories[J]. Electric Power Engi-neering Technology, 2023, 42(3): 72-80. [2] 周浩, 李原, 周凯, 等. 温度及溶胀影响下的硅油-硅橡胶复合绝缘水分平衡特性[J]. 电工技术学报, 2025 ,40(13) : 4058-4070. Zhou Hao, Li Yuan, Zhou Kai, et al.Moisture equilibrium characteristics of silicone oil-silicone rubber composite insulation system under temperature and swelling[J]. Transactions of China Electro-technical Society, 2025, 40(13): 4058-4070. [3] 丁一铭, 焦宇阳, 翟涵君, 等. 基于动态受阻硫脲键的自修复硅橡胶的绝缘性能[J]. 电工技术学报, 2024, 39(增刊1): 150-158. Ding Yiming, Jiao Yuyang, Zhai Hanjun, et al.Insulation properties of self-healing silicone based on dynamic hindered thiourea bond[J]. Transactions of China Electrotechnical Society, 2024, 39(S1): 150-158. [4] 陈贝贝,李晓涵,刘金凤,等. 电热联合故障下天然气合成油分解特性[J]. 电力工程技术, 2025, 44(5): 168-175. Chen Beibei, Li Xiaohan, Liu Jinfeng, et al.The decomposition characteristics of gas to liquid insulating oil under electric-thermal fault conditions[J]. Electric Power Engineering Technology, 2025, 44(5):168-175. [5] 周俊杰, 吴治诚, 王少琦, 等. 梯度声学超材料增强的油纸绝缘局部放电声学检测方法[J]. 电力工程技术, 2026, 45(3): 2-10. Zhou Junjie, Wu Zhichen, Wang Shaoqi, et al.Acoustic detection method of partial discharge in oil-paper insulation enhanced by gradient acoustic metamaterial[J]. Electric Power Engineering Technology, 2026, 45(3): 2-10. [6] 纪多, 李春阳, 杨旭, 等. 表面接枝电压稳定剂改善三元乙丙橡胶界面绝缘性能[J]. 电工技术学报, 2025, 40(15): 4941-4953. Ji Duo, Li Chunyang, Yang Xu, et al.Enhanced interface insulation performance of EPDM by surface grafting of voltage stabilizer[J]. Transactions of China Electrotechnical Society, 2025, 40(15): 4941-4953. [7] 王振龙, 季昌国, 韩哲文, 等. 不同加速老化条件对500 kV变压器用丁腈橡胶老化行为的影响[J]. 绝缘材料, 2025 ,58(06) : 105-114. Wang Zhenlong, Ji Changguo, Han Zhewen, et al.Effect of different accelerated ageing conditions on ageing behavior of nitrile rubber for 500 kV transformer[J]. Insulating Materials, 2025 ,58(06) : 105-114. [8] 兰佳琪, 田双双, 李晓涵,等. C6F12O/N2混合气体与密封材料丁腈橡胶的相容性研究[J]. 电工技术学报, 2022, 37(5): 1285-1293. Lan Jiaqi, Tian Shuangshuang, Li Xiaohan, et al.Compatibility between C6F12O-N2 gas mixture and sealing material nitrile butadiene rubber[J]. Transactions of China Electrotechnical Society, 2022, 37(5): 1285-1293. [9] 高维, 杜钢, 范伟男, 等. 变压器密封用丁腈橡胶湿热老化特性及机理[J]. 高电压技术, 2023, 49(2): 608-617. Gao Wei, Du Gang, Fan Weinan, et al.Aging characteristics and mechanism of nitrile butadiene rubber for transformer sealing in humid environment[J]. High Voltage Engineering, 2023, 49(2): 608-617. [10] 李志刚, 王慧明, 王芳芳, 等. 湿热作用对聚氨酯材料力学性能影响的研究[J]. 科学技术与工程, 2013,13(8): 2178-2181. Li Zhigang, Wang Huiming, Wang Fangfang, et al.Effects of hydrothermal on the mechanical properties of polyurethane materials[J]. Science Technology and Engineering, 2013,13(8): 2178-2181. [11] Alcock B, Jorgensen J K.The mechanical properties of a model hydrogenated nitrile butadiene rubber (HNBR) following simulated sweet oil exposure at elevated temperature and pressure[J]. Polymer Testing, 2015, 46: 50-58. [12] Zhao J, Yang R, Iervolino R, et al.Changes of chemical structures and mechanical property levels during thermo-oxidative aging of NBR[J]. Rubber Chemistry & Technology, 2013, 86(4):591-603. [13] 阙刚, 彭旭东, 沈明学, 等. 丁腈橡胶热空气老化力学性能分析及贮存寿命预测[J]. 润滑与密封, 2018, 43(2): 18-25. Que Gang, Peng Xudong, Shen Mingxue, et al.Mechanical properties analysis and storage life prediction of hot air aging of NBR[J]. Lubrication engineering, 2018, 43(2): 18-25. [14] Wang SQ, Wang, CG, He AH. Accelerated aging behavior and degradation mechanism of nitrile rubber in thermal air and hydraulic oil environments[J]. Polymer Engineering and Science, 2023, 63(7): 2218-2232. [15] 钱艺华, 聂明浩, 赵耀洪, 等. 热油压缩下丁腈橡胶老化性能研究[J]. 应用化工, 2016, 45(11): 2043-2046. Qian Yihua, Nie Minghao, Zhao Yaohong, et al.Ageing study on nitrile rubber under hot oil compression[J]. Applied Chemical Industry, 2016, 45(11): 2043-2046. [16] Liu X, Zhao JH, Yang R, et al.Effect of lubricating oil on thermal aging of nitrile rubber[J]. Polymer Degradation and Stability, 2018, 151: 136-143. [17] 罗恒煜, 李斐婕, 李俊宇, 等. 氟橡胶和丁腈橡胶的耐热氧老化性能与寿命预测研究[J]. 橡胶工业, 2026, 73(7): 503-508. Luo Hengyu, Li Feijie, Li Junyu, et al.Thermal-oxidative aging behavior and life prediction of FKM and NBR[J]. China Rubber Industry, 2026, 73(7): 503-508. [18] 韩哲文, 季昌国, 林林, 等. 丁腈橡胶热空气和热油老化力学性能研究及服役寿命预测[J]. 绝缘材料, 2024, 57(12): 66-73. Han Zhewen, Ji Changguo, Lin Lin.Mechanical properties research and service life prediction of nitrile rubber in thermal air ageing and oil ageing[J]. Insulating Materials, 2024, 57(12): 66-73. [19] 李秀杰, 孙书, 刘丽霞, 等. 基于湿热老化试验的航天器用丁腈橡胶贮存寿命预测[J]. 航天器环境工程, 2022, 39(5): 539-544. Li Xiujie, Sun Shu, Liu Lixia, et al.Prediction of storage life of nitrile butadiene rubber for spacecraft based on hygrothermal aging test[J]. Spacecraft Environment Engineering, 2022, 39(5): 539-544. [20] GB 2536—2025 电工流体变压器和开关用的未使用过的矿物绝缘油[S]GB 2536—2025 电工流体变压器和开关用的未使用过的矿物绝缘油[S]. 北京: 中国标准出版社, 2025. [21] GB/T 531.1—2008 硫化橡胶或热塑性橡胶压入硬度试验方法第 1 部分:邵氏硬度计法(邵尔硬度)[S]. [22] GB/T7759.1—2015 硫化橡胶或热塑性橡胶压缩永久变形的测定第 1 部分:在常温及高温条件下[S]. [23] GB/T 528—2009 硫化橡胶或热塑性橡胶拉伸应力应变性能的测定[S] [24] 门业堃,任志刚,郭卫,等. 高压电缆缓冲层烧蚀气体红外光谱分析方法[J]. 电力工程技术, 2026, 45(2): 93-100. Men Yekun, Ren Zhigang, Guo Wei, et al.Infrared spectroscopic analysis of ablative gases in the buffer layer of high-voltage cables[J]. Electric Power Engineering Technology, 2026, 45(2): 93-100. [25] Tobolsky A V, Callinan T D.Properties and structure of polymers[J]. Physics Today, 1961, 14(10): 72. [26] Flory P J, Rehner J Jr.Statistical mechanics of cross- linked polymer networks II. swelling[J]. Journal of Chemical Physics, 1943, 11(11): 512-520. [27] Wright C D.Environmental stress cracking of plastics[J]. Lightning Source, 1996.
2026, Vol. 41 
