A Characterization Method for Main Insulation Degradation of Generator Stator Bars Based on Polarization Current and De-Trapping Current
Wang Siyu1, Zhou Kai1, Zhu Guangya1, Yang Shuai2, Zhang Yue2
1. College of Electrical Engineering Sichuan University Chengdu 610065 China; 2. Dongfang Electric Machinery Co. Ltd Dongfang Electric Group Deyang 618000 China
Abstract：The main insulation of large generator stator bars is inevitably subjected to thermal stress during operation. The internal epoxy resin will undergo physical phenomena such as post-curing and degradation. Degradation will directly reduce the dielectric performance of the entire main insulation system, thereby affecting the safe and stable operation of the entire generator set. The existing research mainly focused on the dielectric response method. The evaluations of the insulation performance of stator bars are mainly from a macro perspective They cannot delve into the micro field. A trap charge density and trap depth detection method was adopted to evaluate the post-curing and degradation status of the insulation. The method was based on polarization current and de-trapping current. This method can characterize the degradation state and mechanism of generator main insulation under thermal stress. The samples of epoxy-mica flakes were prepared. The extraction method of the de-trapping current was analyzed. The related theory of characterizing the trap charge density and trap depth with the de-trapping current was defined. The samples were injected with trapped charge using a needle plate electrode. The influence of the polarization and depolarization current (PDC) method testing field strength, charge injection time, and charge injection voltage on the de-trapping current were discussed. The low polarization field strength could make it difficult for trap charges to de-trap. The higher polarization field strength might introduce space charge limiting current. It may affect the de-trapping current. The increase in injection time leads to an increase in trapping charge. Traps with depth between deep and shallow traps trap more charge. The equivalent trap depth was shifting in a moderate direction. The low injection voltage could make it difficult to inject charges, while the high voltage could cause charges to accumulate in deep traps. The higher voltage might damage the sample. Finally, it was determined that the polarization field strength was 4 kV/mm, the charge injection time was 15 minutes, and the injection voltage was 10 kV. Subsequently, the samples were subjected to thermal aging at 135℃ for 0 d, 5 d, 10 d, 20 d, and 30 d. Then the aged samples were subjected to de-trapping current testing. Through the evolution process of trap charge density and trap depth, the mechanisms of insulation post-curing in the early stage of thermal aging and insulation degradation in the later stage of thermal aging were clarified. Finally, the breakdown field strength test, differential scanning calorimetry (DSC) test, and partial discharge test were carried out. The overall dielectric strength change rule, molecular chain defect evolution mechanism, and air gap defect evolution mechanism during the post-curing and degradation process of insulation were characterized. The evolution of exothermic and endothermic peaks existed in DSC testing. The post-curing and degradation processes of the epoxy resin molecular chains inside the main insulation were clarified. The evolution law of the size of the internal air gap and the degree of air gap accumulation at the interface of the main insulation were clarified through partial discharge testing. The feasibility of characterizing the degree of degradation of epoxy-mica through de-trapping current was proved in this article.
王思宇, 周凯, 朱光亚, 杨帅, 张跃. 一种基于极化电流和脱陷电流的发电机定子线棒主绝缘劣化表征方法[J]. 电工技术学报, 2025, 40(1): 285-299.
Wang Siyu, Zhou Kai, Zhu Guangya, Yang Shuai, Zhang Yue. A Characterization Method for Main Insulation Degradation of Generator Stator Bars Based on Polarization Current and De-Trapping Current. Transactions of China Electrotechnical Society, 2025, 40(1): 285-299.
[1] 高俊国, 孟睿潇, 胡海涛, 等. 电机定子绝缘老化寿命预测研究进展[J]. 电工技术学报, 2020, 35(14): 3065-3074. Gao Junguo, Meng Ruixiao, Hu Haitao, et al.Research progress on prediction of aging life of motor stator insulation[J]. Transactions of China Electrotechnical Society, 2020, 35(14): 3065-3074. [2] 王新, 杨敏, 金泱, 等. 基于热老化的发电机定子线棒局部放电特性研究[J]. 绝缘材料, 2021, 54(4): 58-63. Wang Xin, Yang Min, Jin Yang, et al.Partial discharge characteristics of typical defects in generator stator after thermal ageing[J]. Insulating Materials, 2021, 54(4): 58-63. [3] 杨敏, 王新, 童小忠, 等. 热老化对发电机定子线棒用环氧—云母绝缘频域介电特性的影响[J]. 高压电器, 2021, 57(1): 94-99. Yang Min, Wang Xin, Tong Xiaozhong, et al.Effect of thermal aging on frequency domain dielectric properties of epoxy-mica insulation for generator stator bars[J]. High Voltage Apparatus, 2021, 57(1): 94-99. [4] 陈庆国, 赵寒, 付强. 电老化对大型电机定子线棒主绝缘频域介电谱特性的影响[J]. 高电压技术, 2022, 48(11): 4255-4263. Chen Qingguo, Zhao Han, Fu Qiang.Effect of electric aging on frequency domain dielectric properties of main insulation of generator stator[J]. High Voltage Engineering, 2022, 48(11): 4255-4263. [5] 宋扬. 电老化对发电机定子主绝缘介电特性影响的研究[D]. 哈尔滨: 哈尔滨理工大学, 2020. Song Yang.The Study on the influence of electric aging on the dielectric characteristics of main insulation ofgenerator stator[D]. Harbin: Harbin University of Science and Technology, 2020. [6] 冯钜. 发电机定子线棒主绝缘机械冲击损伤失效诊断研究[D]. 成都: 西华大学, 2022. Feng Ju.Research on failure diagnosis of mechanical impact damage of generator stator bar main insulation [D]. Chengdu: Xihua University, 2022. [7] 郝艳捧, 谢恒堃. 红外光谱法研究运行23年大电机定子绝缘中环氧的老化机理[J]. 电工技术学报, 2008, 23(3): 19-23. Hao Yanpeng, Xie Hengkun.Degradation behavior of epoxy in stator insulation of large generators in service for 23 years based on infrared spectrometric analysis[J]. Transactions of China Electrotechnical Society, 2008, 23(3): 19-23. [8] 郝艳捧, 谢恒堃. X射线衍射法研究大电机定子绝缘的老化过程[J]. 电工技术学报, 2007, 22(9): 16-21. Hao Yanpeng, Xie Hengkun.Degradation behavior of stator insulation for large generators using X-ray diffraction method[J]. Transactions of China Electrotechnical Society, 2007, 22(9): 16-21. [9] 葛臣忠, 宁苏辉, 付强, 等. 大型发电机定子绕组绝缘性能影响因素[J]. 大电机技术, 2014(3): 35-40. Ge Chenzhong, Ning Suhui, Fu Qiang, et al.Impact factors on large generator stator windings insulation property[J]. Large Electric Machine and Hydraulic Turbine, 2014(3): 35-40. [10] 陈庆国, 单志铎, 付强, 等. 基于FDS的电机线棒环氧云母绝缘电老化特性[J]. 复合材料学报, 2017, 34(9): 1926-1933. Chen Qingguo, Shan Zhiduo, Fu Qiang, et al.Electrical ageing characteristics of epoxy-mica insulation of generator based on FDS[J]. Acta Materiae Compositae Sinica, 2017, 34(9): 1926-1933. [11] 付强, 单志铎, 陈庆国. 大型电机定子线棒主绝缘老化性能的介电响应研究现状[J]. 大电机技术, 2018(1): 10-14. Fu Qiang, Shan Zhiduo, Chen Qingguo.Dielectric response research status on ageing characteristics of larger electric machinery stator bar main insulation[J]. Large Electric Machine and Hydraulic Turbine, 2018(1): 10-14. [12] Farahani M, Borsi H, Gockenbach E.Dielectric response studies on insulating system of high voltage rotating machines[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2006, 13(2): 383-393. [13] 付强, 宋扬, 陈庆国, 等. 基于热刺激电流的大电机VPI主绝缘电老化特性[J]. 高电压技术, 2021, 47(5): 1780-1787. Fu Qiang, Song Yang, Chen Qingguo, et al.Electrical aging characteristics of VPI main insulation of large generator based on thermally stimulated current[J]. High Voltage Engineering, 2021, 47(5): 1780-1787. [14] 曹雨, 吴建东, 刘松, 等. 单因子老化中定子线棒等温松弛电流的研究[J]. 电工技术学报, 2015, 30(1): 242-248. Cao Yu, Wu Jiandong, Liu Song, et al.Isothermal relaxation current research of stator bar insulation in single factor aging experiments[J]. Transactions of China Electrotechnical Society, 2015, 30(1): 242-248. [15] 中华人民共和国国家市场监督管理总局, 中国国家标准化管理委员会. 旋转电机定额和性能: GB/T 755—2019[S]. 北京: 中国标准出版社, 2019. [16] 国家市场监督管理总局, 国家标准化管理委员会. 旋转电机绝缘结构功能性评定成型绕组试验规程绝缘结构热机械耐久性评定: GB/T 17948.6— 2018[S]. 北京: 中国标准出版社, 2018. [17] Shen Wenwei, Mu Haibao, Zhang Guanjun, et al.Identification of electron and hole trap based on isothermal surface potential decay model[J]. Journal of Applied Physics, 2013, 113(8): 083706. [18] 国家市场监督管理总局, 国家标准化管理委员会. 塑料环氧树脂差示扫描量热法: GB/T 41928— 2022[S]. 北京: 中国标准出版社, 2023. [19] 国家市场监督管理总局, 国家标准化管理委员会. 旋转电机绕组绝缘第1部分:离线局部放电测量: GB/T 20833.1—2021[S]. 北京: 中国标准出版社, 2021. [20] 李明志, 周凯, 黄科荣, 等. 基于极化-去极化电流测试的XLPE中陷阱电荷脱陷特性[J]. 高电压技术, 2020, 46(9): 3194-3201. Li Mingzhi, Zhou Kai, Huang Kerong, et al.Trapped charge de-trapping property of XLPE based on polarization and depolarization current test[J]. High Voltage Engineering, 2020, 46(9): 3194-3201. [21] Zhou Kai, Lin Siyan, Li Yuan, et al.Realizing quantitative evaluation of trap energy distribution in polymers with an electric field stimulated depolarization current method[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2021, 28(2): 550-554. [22] Simmons J G, Tam M C.Theory of isothermal currents and the direct determination of trap parameters in semiconductors and insulators containing arbitrary trap distributions[J]. Physical Review B, 1973, 7(8): 3706-3713. [23] 雷清泉, 刘关宇. 如何理解工程电介质中极化与电导两个基本物理过程及其测量的科学原理与方法[J]. 中国电机工程学报, 2018, 38(23): 6769-6789, 7113. Lei Qingquan, Liu Guanyu.How to understand the two basic physical processes of polarization and conductance in engineering dielectrics and scientific principles and methods of their measurement[J]. Proceedings of the CSEE, 2018, 38(23): 6769-6789, 7113. [24] 周士贻, 门业堃, 刘博, 等. XLPE电缆绝缘片晶周期性结构演变及其对电性能的影响[J]. 中国电机工程学报, 2024, 44(3): 1205-1214. Zhou Shiyi, Men Yekun, Liu Bo, et al.Lamellar periodic structure evolution of XLPE cable insulation and its influence on electrical properties[J]. Proceedings of the CSEE, 2024, 44(3): 1205-1214. [25] 龚华勇, 杨国涛, 严鹤翔. 不同压力和温度下电缆用乙丙橡胶绝缘的极化电流研究[J]. 绝缘材料, 2023, 56(10): 91-97. Gong Huayong, Yang Guotao, Yan Hexiang.Study on polarization current of EPDM insulation for power cable under different pressure and temperature[J]. Insulating Materials, 2023, 56(10): 91-97. [26] 王国栋, 周凯, 李原, 等. 基于失效时间统计特性的交联聚乙烯电寿命模型修正[J]. 电工技术学报, 2023, 38(4): 1042-1050. Wang Guodong, Zhou Kai, Li Yuan, et al.Modification of cross-linked polyethylene electrical life model based on statistical characteristics of failure time[J]. Transactions of China Electrotechnical Society, 2023, 38(4): 1042-1050. [27] 陈祎林, 周凯, 林思衍, 等. 短时高热运行对XLPE电缆绝缘聚集态结构及介电性能的影响[J]. 高电压技术, 2023, 49(2): 588-596. Chen Yilin, Zhou Kai, Lin Siyan, et al.Effect of short-term high-temperature operation on the aggregate structure and dielectric properties of XLPE cables insulation[J]. High Voltage Engineering, 2023, 49(2): 588-596.
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