柔性直流电网的继电保护与故障定位新原理研究

HVDC Flexible power transmission systems have bright future in island power supply systems, new energy power supply systems, distribution systems of the central cities and other fields. The commercialization of the DC circuit breaker will promote the development of multi-terminal HVDC and HVDC grids. The HVDC Flexible systems are based on Voltage Source Converter, and with huge capacitors in parallel at the terminals of the transmission lines. So,the convertor stations will provide remarkable current when faults occur on the DC transmission lines. And the current of faults is closely related to the scale of the grids and the time of fault duration.In order to isolate faults rapidly, to reduce faults influence on the operation of the remanent DC power grids, and to minimize the current impact on DC equipments and circuit breakers, it is necessary to study the theories and strategies of ultra high-speed and reliable protections, and they will have important influence on security and stability of operation of DC girds. Relay protections operate according to the fault characteristic, which depends on the topology structures and control characteristics of the HVDC Flexible transmission system. Thus, this project proposes to systematically analyse fault characteristic by considering the effects of topology structures and control characteristics of the DC power transmission system. Then the quick-action non-communication protections and fault location principles based on the topological structure of the DC transmission system, back up protections based on the control characteristics of the DC power transmission systems, and the high sensitive pilot protection principles using multi-terminal electrical quantities will be presented in this project. Moreover, the research works will provide perfect theoretical basis and technical support for the secure and reliable operation of HVDC flexible power transmission systems.

柔性直流输电在海岛供电、新能源接入系统和城市配电网等领域具有广阔应用前景，直流断路器的商用化将加速直流电网的形成。柔性直流输电采用电压源换流器方式，故障时电容放电会产生大的短路电流，且短路电流与电网规模和故障持续时间有关。为了快速隔离故障、减少故障分支对健全电网的影响，同时减小故障电流对直流设备和直流断路器造成的冲击，研究超高速与高可靠性相结合的直流电网继电保护新原理，对于保障直流电网的安全可靠运行意义重大。继电保护反应故障特征而动作，而直流系统故障特征又取决于其拓扑结构与控制特性，故本项目拟建立计及拓扑结构和控制特性的直流电网故障特征理论分析体系，系统地提出基于拓扑结构的直流电网单端电气量快速主保护与故障定位新原理、基于控制特性的直流电网后备保护新原理、以及利用多端电气量的高灵敏后备保护新原理。本项目的研究为柔性直流电网的安全可靠运行提供完备的继电保护理论基础。

柔性直流输电技术采用可关断器件脉宽调制技术，克服了传统高压直流输电易发生换相失败等缺点，在可再生能源并网、孤岛供电等领域具有广阔的应用前景。柔性直流输电故障承受能力差，所以研究适用于柔性直流系统的高性能保护十分必要。项目组严格按照任务书规定内容，在建立了基于两电平的柔性直流电网模型的基础上深入分析了柔性直流线路的故障特征并基于各种故障特征构造了多种保护判据，单端量保护主要包括基于高低频电流幅值比的全线速动保护、基于拓扑结构参数识别的距离保护、基于拓扑结构参数识别的行波保护等，双端量保护包括基于分布参数的电流差动保护、基于电流突变极性比较的纵联保护以及基于对端电气量计算值的双端量保护等，并提出了高可靠性的柔性直流输电线路保护方案，最后提出了多种单端量和双端量故障定位方法。项目组在任务书规定的研究内容之外，还提出了针对行波保护的雷击识别方法并初步开展了柔性直流配电网的建模和继电保护研究。