基于暂态综合油流信息的电力变压器数字式重瓦斯保护研究

Because of difficulties in theoretical modeling, principle defects, empirical thresholds and the mechanical structure, malfunctions and refusal-operations of traditional heavy gas relays occur frequently in recent years; this situation has a serious impact on power supply reliability and operating stability. This project studies the generating mechanism and change characteristics of heavy gas transient oil flow surges. Firstly, the arc-in-oil energy model, the gas bubble pulsation and fluid-structure coupling models, the external short-circuit electromagnetism-mechanical-fluid multi-physics coupling model, the thermo-hydro coupling model and the computational fluid dynamics model driven by the oil-pump will be built. Next, the numerical computation methods for the above coupling models will be proposed based the finite-element/finite-volume method to reveal the physical process of the electrical energy converted into oil flow kinetic under different running conditions. Thirdly, the transformer internal arc-in-oil and external short-circuit faults field tests will be performed. With the test data, the theoretical models and the numerical methods will be amended and verified. At last, based on the essence differences of the oil flow characteristics, such as flow velocity, frequency and waveform, among the internal faults, normal running and non-normal running conditions, a novel digital heavy gas protection principle based on transient comprehensive oil flow information and its threshold setting method will be proposed. By using the ultrasonic flowmeter, the implementation technique for the digital heavy gas relay will be studied. Based on the meaningful findings in this project, the old-fashioned heavy gas relay will be transformed to a new stage with quantitative analysis, high reliability and digitization.

传统变压器重瓦斯保护存在理论建模困难、原理缺陷、凭经验取门槛值及机械结构动作性能不足等问题，近年来保护拒动、误动事故时有发生，严重威胁电力系统供电可靠性和运行稳定性。课题以重瓦斯暂态油流涌动机理及特征为研究对象，理论建立油中电弧能量模型、瓦斯气泡脉动与流体-结构耦合模型，外部短路电磁-力-流多场耦合模型、热-流耦合及油泵驱动的流体力学模型，提出基于有限元/有限体积法的多场耦合数值计算方法，研究不同运行条件下电能向油流动能转化的物理过程。开展变压器油中电弧、外部短路现场试验，修正、验证理论模型与计算方法。根据变压器故障、正常、非正常运行状态在油流涌动机理及其幅值、频率、波形等特征上存在的差异，提出基于暂态综合油流信息的重瓦斯保护新原理及门槛值整定方法。利用超声波流量测量装置开展数字式重瓦斯继电器实现技术研究，将从前凭经验和感觉构成的重瓦斯保护提高到定量分析、高可靠性判定、数字化实现的新阶段。

针对变压器传统机械式重瓦斯保护存在的可靠性不足的问题，项目依据油箱内油流涌动的物理机理建立了内外部故障条件下的多场耦合模型，研究了变压器在不同运行条件下重瓦斯油流特征的差异，提出了基于暂态综合油流信息的重瓦斯保护新原理。主要研究工作及成果包括： .1）建立了变压器油中电弧模型、油中电弧瓦斯气泡动力学模型及考虑绝缘油惯性、黏度、重力以及油箱结构的流-固动力学耦合模型，仿真计算了瓦斯气泡产生、脉动作用下的变压器内部流场变化及重瓦斯油流涌动特征，得到故障能量、油流流速以及油箱应力大小之间存在正相关性的结论。.2）建立了外部故障过程中涉及的电磁、力及流场数学模型，综合各物理场之间的耦合关系建立多物理场-路耦合模型，在平衡计算复杂度与结果精度的前提下提出适用于该多物理场耦合模型的计算方法，揭示外部短路及空载合闸过程中绕组的机械形变以及油箱内部油流涌动机理及变化规律。.3）搭建变压器内、外部故障测试试验平台，提出变压器油中电弧故障及外部短路试验方案，通过试验结果修正理论计算模型，验证数值仿真的正确性。.4）根据变压器在不同运行条件下的重瓦斯流速在幅值、频率、波形及持续时间上的差异，结合变压器容量、电压等级、油箱尺寸以及连接管内径等因素，构建依据变压器试验、仿真的油流涌动数据的重瓦斯门槛值整定方法，提出基于暂态综合油流信息的重瓦斯保护新原理。.5）综合考虑经济性、安装条件及保护动作性能等多方面因素，以不改变变压器原有管路结构、不影响管内油流特征为前提，利用外捆式高速超声波流量计实现重瓦斯暂态油流信息的数字化实时测量，设计开发数字式保护装置硬件电路与软件程序，提出基于暂态综合油流信息的重瓦斯保护构成方案，研制数字式重瓦斯继电器实验室样机。