特高压直流输电中直流偏磁对变压器发热及振动影响分析与在线监测方法研究

When Ultra high Voltage Direct Current(UHVDC) transmission is running in monopole mode, neutral point grounding transformer on the inverter AC side may generate DC bias. Since core saturation, magnetic flux leakage, overheating and abnormal vibration caused by the DC bias would harm transformer safe running and due to lack of deep research of transformer heating and vibration during DC bias both in the domestic and abroad, study of influence of DC bias towards on transformer heating and vibration，and monitoring on line during UHVDC transmission is very necessary. This project research includes layered soil model of DC grounding pole in different soil construction and calculation of ground potential and magnetic bias current, calculation of transient eddy curernt and flux density distribution in transformer when DC bias happens, calculation of transformer inner temperature field with different bias current, model of vibration amplitude and its relationship with bias, influence pattern of DC bias towards to transformer inner temperature field and vibration in different soil construction, online detection and location of transformer internal overheating point and vibration source. Research results of this project are important to ensure safe operation and design of UHVDC transmission system.

特高压直流输电单极运行时会对逆变交流侧中性点接地变压器造成直流偏磁。直流偏磁引起的铁心饱和、过热及异常振动危害变压器的安全运行与寿命，目前对变压器直流偏磁状态下的发热及振动以及在线监测方法还没有深入的研究，因此开展特高压直流输电中直流偏磁对变压器发热及振动的影响分析和在线监测方法的研究是十分必要的。本项目拟研究直流输电线接地极不同土壤结构的分层模型和接地极电位及偏磁电流计算；研究直流偏磁时变压器内的瞬态涡流计算和磁通密度分布；研究基于磁通密度分布的不同偏磁电流下变压器内部温度场计算方法；研究不同偏磁电流下变压器铁心和绕组受到的电磁力；研究能够表征偏磁电流与变压器振动关系的数学模型；研究不同土壤结构对偏磁电流以及变压器的温度场与电磁振动影响规律；研究局部过热点和振动源的在线监测及定位方法。项目的研究成果可以用于特高压直流输电系统的设计与运行，具有重要的工程价值与理论意义。

本项目组经过一年的研究工作，完成了以下几方面的研究：1. 直流输电线接地极不同土壤结构的分层模型和接地极电位及偏磁电流计算；2. 直流偏磁时变压器内的磁通密度分布、铁芯和绕组的损耗分析，不同土壤结构对变压器的温度场影响分析；3.变压器铁心和绕组受到的电磁力和形变的的建模与仿真分析；4. 变压器偏磁振动分析和实验；5. 变压器振动的在线监测系统。. 取得的成果有：1. 建立了直流接地极附近的土壤结构（特别是冻土结构）分层模型并获得了土壤结构对地电位的影响情况；2.得出变压器偏磁电流与振动强度之间的关系，建立了分析模型并通过实验验证了正确性与可行性；3. 研制出了变压器振动在线监测系统并已在云南电网中实际应用；4. 发表相关论文3篇：① A NOVEL AC ELECTRIC ARC FURNACE MODEL AND SIMULATION FOR POWER QUALITY STUDY，Journal of Theoretical and Applied Information Technology,Vol.49,No.3,2013.pp.887-892.②Development and Application of On-line Monitoring Device of Transformer Vibration，TELKOMNIKA, Vol. 11, No. 8, 2013, pp.4721~4728. ③ Research on Frozen Soil Structure Influence over Transformer DC Magnetic Biasing in UHVDC Transmission, Accepted by Research Journal of Applied Sciences, Engineering and Technology,2013.9. 及已投稿论文3篇（电工技术学报、IEEE ICIT2014、IEEE ICIEA2014）；5.培养博士和硕士各一人。项目的研究成果可以用于特高压直流输电系统的设计与运行，具有重要的工程实用价值与理论意义。