考虑交直流系统故障相互影响的变压器保护及换流站后备保护原理研究

Undesired tripping of transformer protection in AC/DC hybrid power system during complex electromagnetic transient results in instability and insecurity of power system. The differential relays of power transformers will be influenced by nonlinear characteristics of converters and iron cores of transformers. These influences are exacerbated by the coupling between converters and iron cores of transformers. Furthermore, the harmonic voltages on the buses of converters caused by energizing of power transformers will result in undesired tripping of backup relays in HVDC system. In this proposal, we will study on the coupling mechanisms between converters and iron core of transformers, and we will also propose novel transformer protection schemes and substation area information (SAI) -based backup protection schemes for HVDC system and converter substation. Firstly, by analyzing the dynamic characteristics of iron core and converter during complex electromagnetic transient, the coupling mechanisms of AC/DC hybrid power system in disturbance or fault conditions are studied. The relationship of voltages and harmonic currents between AC system and DC system are analyzed in order to study the influence to traditional protections, including primary protection of power transformer or backup protection of AC and DC system. Secondly, we propose novel protection schemes for transformer and AC/DC hybrid power system based on the technologies of smart grid and smart substation. Based on the electronic current or voltage transformers (ECT/EPT), we propose some novel primary protection schemes for power transformers according to the methods of parameters and circuit model identification. Moreover, we also proposed some novel backup protection schemes for AC and DC system based on the measurements and information shared in the converter substation areas. Finally, the proposed protection schemes will be verified by simulation data, test data and field data. We will create a novel theoretical system for fault analysis and protection of AC/DC hybrid power system in order to ensure security and stability of power system.

交直流输电系统复杂电磁暂态过程影响变压器保护的性能，进而影响电力系统的安全稳定运行。换流器和变压器铁芯都具有非线性特征，两者在故障状态下相互作用，严重影响了带二次谐波制动的变压器差动保护的性能。同时，铁芯的非线性在换流母线上产生的谐波电压也将导致现有直流系统后备保护的不正确动作，影响功率传输及电网安全。基于此，本项目拟从分析故障状态下换流器与变压器铁芯的电磁耦合机理入手，以变压器铁芯动态行为为突破口，以谐波和电压耦合关系为主线，研究交直流混联系统复杂电磁暂态过程的特征以及对变压器主保护和交直流系统后备保护的影响。在智能变电站先进硬件的基础上，进一步深入研究基于实时磁化曲线形状识别和T型等效电路模型识别的变压器保护原理，提出利用站域信息共享的交直流系统一体化自适应后备保护的原理和方案。本项目的研究将建立新的交直流混联系统变压器保护和后备保护理论体系，对于保证电能传输和电网安全具有重要的意义。

针对交直流混联输电系统复杂电磁暂态过程影响变压器保护性能的问题，提出了基于矩阵束原理的工频相量自适应估计算法，该算法能够根据暂态信号的复杂程度自适应调整数据窗的长度，提高了交直流混联系统相量计算的精度；提出了基于励磁电感参数识别的变压器快速保护算法，以及基于等效磁化曲线特征识别的变压器快速保护算法，抓住变压器内部故障的本质特征构建识别判据，这两种算法不受励磁涌流的影响，提高了电力变压器继电保护的性能。分析了交流系统变压器空载合闸导致直流系统50Hz/100Hz保护不正确动作的原因，给出了变压器空载合闸产生负序二次谐波解析表达式，并分析了影响变压器励磁涌流负序二次谐波的因素，提出了励磁涌流产生的谐波传播放大的多主元模态分析方法，给出了励磁涌流引发谐波过电压及直流系统后备保护不正确动作的在线评估方法，解决了交流系统对直流系统后备保护影响的问题。分析了直流系统控制策略导致交流系统过电压保护不正确动作的因素，提出了自适应直流系统功率突变和滤波器组投切策略的自适应交流过电压保护原理，在保证设备安全的情况下，调整过电压保护的定值，避免直流系统控制过程中过电压保护的不正确动作。针对智能变电站电子式电流互感器传变高频信号的误差问题，建立了罗氏线圈的模型，给出了罗氏线圈各变换环节的传递函数表达式，分析了罗氏线圈电流互感器不正确传变的原因，给出了解决方案。通过本项目的研究，提出了新型变压器主保护方案，解决了交直流混联系统变压器保护的不正确动作问题，提出了交直流混联系统自适应后备保护的新方法，解决了后备保护缺乏配合导致不正确动作的问题，达到了预期的目标，对保证电能传输和电网安全具有重要的意义。