直流电场下油纸绝缘界面电荷产生机制及影响因素的研究

The space charges at the interface of oil-paper insulations directly influence the distribution of local electric field and are thus key to the design of HVDC converter transformers. Currently, the prevailing design of the converter transformers builds on the resistiance-capacitance model, i.e. RC model. Though certain margins have been predicted in the process of design, discharge of unknown preseasons still frequently takes place during factory test and on-site operation. Besides, existing researches have revealed that the space electric field in oil-paper insulation, when applied with direct current voltage of different polarities, shows great difference in terms of its performance during the transient procedure and at the steady state. Such apparent polarity effects are not yet able to be explained by RC model. One of the possible causes could relate to the generation mechanism and affecting factors of the interface charges of oil-paper insulation in the DC electric field. With the adoption of space charge PEA measurement, oil-paper dielectric property measurement, TSC trap distribution measurement, SEM microscopic observation and space ecletric field real-time optical measurement, the proposed research project aims to study the transfering process of positive and negative charges of oil-paper insulation, the adsorption effect of dielectric media over the charges, as well as the dynamic and static characteristics of the space electric field in order to explore the generation mechanism and physical development process of the interface charges of oil-paper insulation in the DC electric field. Through changing electric field intensity, temperature and dielectric media during the laboratory experiments, it is expected to capture the factors that affect the generation and development of the interface charges. The ultimate goal of the proposed project is to put forward a pysycal model for oil-paper insulation with interface charges in the DC electric field, which could serve as supporting evidence for optimized design of HVDC convert transformers.

油纸绝缘的界面电荷会对电场分布产生影响，是换流变绝缘设计的关键问题。目前的设计均采用电阻率-介电常数模型（RC模型），虽然考虑了裕度，但在实际中仍会出现放电；另外，已有的研究发现，不同极性直流电压下油纸绝缘空间电场的暂态和稳态特征差异显著，极性效应明显。RC模型难以做出解释。这可能是由于油纸绝缘中界面电荷在直流电场作用下的产生过程及影响因素存在特殊性所致。 本项目拟从油纸绝缘正负电荷的迁移过程、介质对电荷的吸附作用以及空间电场的动态与静态特性出发，利用电声脉冲测量、油纸介电特性测量、热刺激电流陷阱分布测量、微观结构扫描电镜观测、空间电场光学实时测量等手段，探索直流电场下油纸绝缘界面电荷产生机制和迁移过程。通过改变场强、温度、介质类型等参量，获得油纸绝缘界面电荷产生和迁移过程的影响因素及作用机理。最后，提出具有普适性的直流电场下界面电荷存在时油纸绝缘的物理模型，为换流变的优化设计提供依据。

换流变压器是制约工程造价与供电可靠性的关键设备之一，其作用无可替代，绝缘结构复杂、多样，承受直流电压、交直流复合电压和极性反转电压等多种电压应力，运行工况更为复杂。目前在换流变压器绝缘设计和校核过程中所采用的RC模型为正负电荷等值迁移模型，在油纸绝缘界面存在电荷的情况下，RC模型无法反应其电场特性的真实情况。本项目从油纸绝缘正负电荷的迁移过程、介质对电荷的吸附能力以及空间电场的动态与静态特性出发，利用空间电荷电声脉冲测量、油纸介电特性测量、热刺激电流陷阱分布测量、微观结构扫描电镜观测、空间电场光学实时测量等手段，探索了直流电场下油纸绝缘界面电荷产生机制和迁移过程，并且通过改变电场强度、温度、介质类型等条件，获得了不同条件下界面电荷和空间电场的动态与静态特性，揭示了油纸绝缘界面电荷产生和迁移过程的影响因素及影响机理。在此基础上，本项目基于离子流模型，提出具有普适性的直流电场下界面电荷存在时油纸绝缘的电场分析物理模型和计算模型，通过实测结果和计算结果的比较，模型计算结果最大偏差为7.1%。项目研究成果可为提升换流变压器设备的自主化设计水平以及换流变压器装备的运行可靠性提供重要的技术支撑。