配电网单相接地故障柔性消弧与保护协调控制方法研究

Due to the inherent unbalanced line parameters existing in the aerial cable distribution system, the fault phase is difficult to be recognized when high resistance grounding such as single-phase disconnection happens. Meanwhile, the resonant grounding method attenuates zero-sequence current while suppressing the faulty current in single-phase-to-ground fault, which makes it difficult to recognize the faulty feeder and thus the protection devices are unable to clear the faulty feeder. This threatens the safety of both the power system and its neighboring human being. In order to solve the unsettled issue of coordination between arc-suppression and feeder protection, this project plans to work on the following aspects. Firstly, the trajectory of zero-sequence and three phase-to-ground voltages with different faulty resistance under the unbalanced distribution network condition will be studied, aiming to obtain the distribution of magnitude and phase of the single-phase-to-ground voltages. Secondly, a faulty phase recognition method is planned to be proposed by integrating the trajectories of three zero-sequence voltages when single-phase-to-ground fault happens in each phases. Thirdly, a variable impedance control method for flexible grounding device is planned to be proposed, aiming to realize precisely recognition of faulty phase and permanent fault. By studying the above aspects, it is probable to optimize the theory of single-phase-to-ground analysis, fill the gap of reliable arc-suppression and faulty feeder recognition. The technology of dealing with faults in distribution network and the reliability of applying electricity are both to be improved.

架空线路为主的配电网存在固有的线路参数不平衡问题，在发生单相断线等高阻接地故障时，故障相难于判断。同时，谐振接地系统单相接地故障时零序电流特征量微弱，使保护装置难以准确判断故障馈线，导致永久性接地故障无法可靠切除，威胁电网和人身安全。为解决配电网长期存在的单相接地故障消弧与馈线保护协调配合难题，项目计划：1）研究线路参数不对称条件下，单相接地故障时零序电压和三相对地电压随过渡电阻的变化规律，得到单相接地故障电压幅值相位变化区间分布；2）研究不同相接地故障时零序电压变化轨迹，提出基于零序电压幅相特征的单相接地故障相辨识方法；3）研究柔性接地装置变阻抗控制方法，以实现单相接地故障馈线的准确判断和永久性接地故障的可靠识别，从而为保护装置的可靠动作提供准确依据。项目将完善配电网单相接地故障分析理论，弥补单相接地故障可靠消弧和故障馈线准确判断的技术空白，将有望提高配电网故障处理水平，提升供电可靠性。

配电网单相接地故障的快速处置是配电网安全可靠运行的重要保障，柔性消弧技术已成为当前配电网接地故障研究的热点。项目提出了一种柔性混合消弧控制新方法，将大功率无源电压消弧与小功率有源消弧装置相结合，利用大功率变压器补偿主要故障电流，搭配小功率有源装置补偿残余电流，实现瞬时性故障快速熄弧和永久性故障可靠切除故障馈线的目的。研究对称电网和非对称电网的故障相识别问题，根据三相电压的幅值和相角关系，准确地识别出单相接地故障，提出一套基于三相电压幅相变化规律的改进式故障选相判据。所提故障选相和消弧方法不需测量三相对地参数，可全方位地实现对配电网接地故障精确及安全保护。针对传统的有源电压型消弧设备在进行消弧机理分析时未考虑实际存在的线路阻抗，特别是低阻条件下长距离馈线发生单相接地故障时，故障点到母线之间的线路压降会使得配电网呈显著的弱电源特性。采用电压消弧方式会使得故障点电压出现较大的补偿误差，提出了一种差分算法实时地计算配电网线路阻抗，进一步得到考虑实时线路阻抗条件下消弧所需的注入电流值，实现了对中性点电压更加精确地钳制。本项目旨在建立和完善配电网单相接地故障分析理论，弥补单相接地故障可靠消弧和故障相准确辨识的技术空白，从柔性接地装置与配电网的交互影响机理、不同相接地故障时三相对地电压变化轨迹和柔性接地装置变阻抗控制方法三个方面揭示柔性接地装置实现单相接地故障可靠消弧和过电压抑制的原理和方法。项目研究成果可有效实施配电网“瞬时故障安全消弧，永久故障快速隔离”，并在工程上实现高达16千欧高阻接地故障的快速处置，极大地提高了配电网运行的安全可靠性。