Fast Fourier transform (FFT) is commonly used in engineering for harmonic analysis due to relatively low computational complexity. However, FFT make sure that the length of the data must satisfy certain conditions, such as 2/3/4 or other inter powers. Aiming at the fact that the length of the data window is a non-integer power, an improved interpolated zero-padded FFT harmonic measurement algorithm is proposed. The core of the algorithm is to transform the interpolation correction of the zero-padded FFT into the fitting correction of the spectral response based on the zero-padded window function. 5-term maximum side lobe decay speed window is used to correct the data. The proposed algorithm is suitable for any zero-padded window function and avoids to derive a modified formula. Simulation and experimental results verify the effectiveness of the algorithm in harmonic analysis.
Distribution lines are susceptible to induced lightning overvoltage and lightning accidents, the installation of lightning protection facilities on the distribution line can effectively reduce the impact of induced lightning overvoltage on the line, the conventional lightning protection facilities are installed without taking into account the topography of the line is located in the problem, resulting in poor technical economy, there is a certain degree of blindness. This paper establishes the induced lightning overvoltage calculation model in ATPDraw, simulates and analyses the level of induced lightning resistance of the line. And according to the topographic and geomorphological characteristics of Guangxi, distribution network line tower spacing, conductor type and regional minefield level, the distribution line lightning protection level is divided into A, B, C three levels, and different lightning protection schemes are used for them. Wen through the distribution line lightning protection facilities differentiation research, can effectively reduce the impact of induced lightning overvoltage on the line, improve power supply reliability, reduce operating costs, while the relevant conclusions of the study can guide the production practice, reduce the pressure of the first-line workers overhaul.
Malignant accidents caused by single-phase grounding of distribution lines in neutral grounding system via arc suppression coil occur from time to time, and reliable and selective protection technology is an effective response. The sudden change of phase current generated by single-phase grounding can detect single-phase grounding fault sensitively and reliably, but its duration is short, which can not meet the selective requirements. In this paper, the criterion of phase current mutation based on rolling algorithm is improved, and the supplementary criterion and time delay criterion for judging whether the fault still exists based on phase current mutation and then locking the zero-sequence current are proposed. The zero-sequence current variation proposed in the scheme can still correctly judge the fault under unbalanced load. In this paper, the simulation model of PSCAD single-phase grounding protection is developed, and the simulation results show that the proposed method can selectively and reliably protect single-phase grounding fault from the influence of distribution network unsymmetrical load.
In response to the national “dual carbon” development strategy, the current power grid has formed a new energy system architecture with green energy as the main body, and a large number of fans and photovoltaics have been connected to the grid, bringing unprecedented challenges to the traditional power grid relay protection. Especially, the impact of distributed photovoltaic access on the protection of the traditional distribution network is mostly stuck in the theoretical analysis stage. No relevant experimental evidence has been found. In this paper, the project team selected two typical 10kV distribution network scenarios of distributed PV connected to the grid to carry out artificial short circuit test. Through the analysis of test wave recording data, the analysis of low penetration current characteristics in the distributed PV transient process was completed, and the impact of distributed PV access on distribution network protection was quantitatively demonstrated. It is of theoretical significance to explore the adaptive boundary of protection for distributed PV grid connection.
提出一种基于电磁时间反转(EMTR)理论的电网故障定位新方法.首先讨论了EMTR技术在重大故障诊断中的适用性,利用经典的频域传输线方程,推导出解析表达式并推断故障的位置.其次讨论了所提出方法的准确性与记录故障产生的电磁暂态所采用的观测点数量的关系.然后举例说明了所提方法在时域的扩展.以一个小型同轴电缆系统为例,对实际故障进行硬模拟,验证了所提方法的有效性.最后,介绍了所提出的基于EMTR数据的故障定位方法在电磁瞬变电磁仿真案例中的应用.
