基于高频阻抗曲线匹配的混合直流输电线路纵联保护

混合直流输电具有电压等级高、输送容量大的优点,解决了传统直流受端的换相失败问题.然而,传统直流输电纵联保护依赖送受端拓扑对称下滤波器产生的故障特征,且受分布电容影响大,混合直流输电系统中受端不存在滤波器,因此传统直流输电纵联保护不能直接应用于混合直流输电系统.文中针对这一问题,提出了不依赖于滤波器产生故障特征、不受分布电容影响的纵联保护.通过分析行波的折反射,得到保护在线路正反方向故障时高频测量阻抗的差异,利用波形匹配算法识别故障方向并构造保护判据.该方法利用短窗提取行波高频阻抗特征,并利用分布式电容高频特征构成差异,解决了线路分布电容影响,同时提升了保护动作速度.以实际工程为例,搭建了两端混合直流输电系统模型进行仿真,仿真结果证明该方法能快速、灵敏、可靠地实现区内外故障判别,且具有较好的耐受过渡电阻能力.

Pilot Protection for Hybrid DC Transmission Line Based on High-frequency Impedance Curve Matching

Hybrid DC transmission has the advantages of high voltage level and large transmission capacity, which solves the commutation failure problem at the receiving-end of the traditional DC system. However, the traditional DC transmission pilot protection relies on the fault characteristics generated by the filter under the topological symmetry of the sending and receiving end, and is greatly affected by the distributed capacitance. There is no filter at the receiving end in the hybrid DC transmission system, so the traditional DC transmission pilot protection can not be directly applied to the hybrid DC transmission system. In order to solve this problem, a pilot protection is proposed, which does not depend on the filter to generate fault characteristics and is not affected by the distributed capacitance. By analyzing the refraction and reflection of traveling waves, the difference between high-frequency measured impedances of protection with positive and negative line faults is obtained. The fault direction is identified by the waveform matching algorithm and the protection criterion is constructed. In this method, the short window is used to extract the high-frequency impedance characteristics of traveling waves, and the high-frequency characteristics of distributed capacitors are used to form differences, so as to solve the influence of distributed capacitors and improve the operation speed of the protection. Taking an actual project as an example, a two-terminal hybrid DC system model is built for simulation. The simulation results show that the method can quickly, sensitively and reliably identify the faults inside and outside the region, and has a good ability to withstand the transition resistance.