Affected by the different fault characteristics of electrochemical energy storage power stations under charging and discharging operating states, the phase comparison distance protection using positive sequence voltage as polarisation voltage may operate incorrectly if phase-to-phase faults occur in the forward direction of the energy storage side protection and the reverse direction of the system side protection. Therefore, an improved distance protection scheme for phase-to-phase faults that can adapt to both charging and discharging states is studied. Firstly, the fault characteristics of the energy storage station under different charging or discharging states are analysed, and the influence mechanism of fault characteristics on phase comparison distance protection operation performance is discussed. On this basis, an improved distance protection scheme for phase-to-phase fault based on polarisation voltage phase reconstruction was proposed. Finally, verification was conducted on the PSCAD/EMTDC simulation platform. The simulation results show that the proposed scheme can effectively reduce the impact of fault characteristics of energy storage power stations. The sensitivity and reliability of phase comparison distance protection during phase-to-phase fault are effectively improved under different charging and discharging states and fault resistance conditions.

When the energy storage power station encounters a fault on the transmission line during charging, active component of its short-circuit current still maintains an inverse relationship with the positive-sequence voltage at its grid connection point, influenced by the converter control strategy. This leads to a large phase difference between the short-circuit currents on both sides of the transmission line, posing a risk of no-trip failure in conventional current differential protection. To address the above issues, this paper proposes a differential protection scheme for transmission line connected to energy storage power stations based on positive-sequence reactive current, which can effectively avoid the influence of energy storage charging and discharging state on the differential current protection. The feasibility of the positive-sequence reactive current differential protection for transmission line connected to energy storage power station is analyzed through theoretical derivation. To address the issue of protection sensitivity being affected by line capacitive current when the fault voltage drop is relatively low, capacitive current compensation is added to the positive-sequence reactive current differential protection criterion. Finally, performance testing was conducted through PSCAD simulation. Results show that the proposed method can eliminate the impact of energy storage charge and discharge differences on the current differential protection performance and has good performance under different fault conditions.

In some wind-photovoltaic-storage power station, energy storage are gathered on 35kV AC lines. The control strategy of energy storage converter will affect the fault current external characteristics of the energy storage system, and then affect the action of line protection equipment and fault removal. To solve the above problems, based on the current mainstream energy storage converter control strategy and national standards, the response of the control strategy during the relay protection operation time are analyzed. Then the fault current external characteristics of the energy storage system are obtained. The effect on the collecting line current protection is analyzed. The accuracy of the external current characteristics of the energy storage system obtained in this paper is verified by simulation. Combined with simulation, The accuracy of the analytical results are further proved by simulation, and the improvement measures of the current protection tuning scheme are proposed.

In recent years, the rapid expansion of large-scale photovoltaic (PV) power stations has necessitated intricate two-stage aggregation systems within stations, where thousands of PV generation units are consolidated via cables and overhead lines before reaching the booster station. Complexity in wiring poses challenges, as malfunctioning coordination of aggregation line protection post-fault can lead to misoperations, tripping non-faulty branches, expanding power outages, and hampering grid-connected efficiency. To enhance reliability and speed of protection, A regional differential backup protection tailored for aggregation lines in large PV stations is proposed in this paper. The traditional differential protection is set as the primary safeguard protection and minimal regional differential protection is set as backup protection. Our strategy, under limited communication constraints, reliably identifies the smallest backup protection zone and, in cases of primary protection refusal, swiftly isolates faults with minimal action scope and duration. MATLAB simulation validates its adaptability to complex PV station wiring, ensuring reliable fault isolation. The synergy between backup and primary protections ensures speed, selectivity, and reliability in protection operation.

In current engineering practice, short circuit current of the energy storage is affected by the pre-fault charging and discharging state, and its active component is consistent with the pre-fault state. Therefore, when energy storage encounters an access line fault in the charging state, the phase difference between the short circuit current of it and that of the system on the other side of the line may be greater than 90 degrees, which brings the risk of current differential protection refusal. In this paper, a modified ratio braking current differential criterion is proposed, which can effectively reduce the phase difference between the fault phase currents on the two sides of access line, avoid current differential protection refusal and improve the protection sensitivity. By simulation, this modified criterion is verified.

With the continuous access of large-scale distributed power sources to the grid and the expansion of the distribution network scale, it is difficult to ensure the accuracy of the traditional fault-line selection scheme for distribution networks. Considering that the new distribution network contains a large number of power electronic devices, characteristic signals can be actively injected for fault-line selection. A low-frequency signal active injection method based on the control strategy of energy storage power stations and its parameter selection principle are proposed in this paper. The different fault characteristics presented by the low-frequency injected signals in the faulted and non-faulted lines when a single-phase grounding fault occurs in the distribution network are analyzed, and a selection criterion based on low-frequency signals in zero sequence current was proposed. Finally, the correctness of the theory and the effectiveness of the scheme are verified by PSCAD/EMTDC simulation.

Sudden Variable Distance Protection (SVDP) has been utilized in power systems due to its extensive protection range and strong resistance to transition resistance. An in-depth study examined the fault characteristics of Doubly Fed Induction Generators (DFIG) under short circuit conditions. Special focus was given to the disparity between the positive and negative sequence impedances of DFIG and how this affects the operational performance of power frequency SVDP. In wind power systems, when a fault occurs, the positive and negative sequence impedances at the wind farm side are unequal, with the positive sequence impedance being significantly higher than the negative sequence impedance. This disparity significantly diminishes the effectiveness of the sudden variable relay. A thorough analysis was conducted on the protection operation characteristics under various conditions (including no-load and loaded scenarios), revealing that factors such as increased wind power system impedance, higher system load, and improved reliability coefficient broadly impact the protection range of SVDP. Simulation verification was performed to confirm these findings. The study's conclusions offer a theoretical foundation for enhancing the protection range of SVDP and improving its operational characteristics in wind power grid-connected systems.

The substantial incorporation of renewable energy sources into power grids has profoundly influenced the setting calculations and accurate functioning of relay protection systems. Presently, the primary forms of renewable energy generation encompass photovoltaic (PV) systems, energy storage systems, direct-drive wind turbines, and doubly-fed induction generator (DFIG) wind turbines. Different types of power sources exhibit distinct fault characteristics and equivalent impedances, generally categorized into inverter-based sources and doubly-fed induction sources. Due to differences in control methods, the fault characteristics of various renewable energy generation devices vary. When performing relay protection setting calculations, it is essential to consider the characteristics and control methods of renewable energy generation devices. Given that their fault current characteristics differ from those of traditional generation equipment, different setting methods are required to ensure that protection devices can accurately identify faults and respond promptly. To ensure the reliability and stability of relay protection systems under various operating conditions, it is crucial to thoroughly study the fault characteristics and equivalent impedances of renewable energy generation devices. Through simulation studies and experimental analysis, reasonable relay protection setting calculation methods can be developed, providing a basis for the optimization of protection devices and thereby ensuring the safe operation of power systems.

Aiming at the problem of low accuracy of single terminal fault location in DC distribution network,this paper proposes a single terminal fault location scheme based on transient voltage ratio. By analyzing the characteristics and mathematical expressions of the fault capacitance at both ends of the current-limiting reactor,a fault location scheme based on the transient voltage ratio at both ends of the current-limiting reactor is constructed in the time domain, and the influence of the transition resistance on the ranging accuracy is reduced by an iterative method. The method uses single-ended electrical gas. It has strong resistance to transition resistance,has no strict requirements on communication, and does not need to install synchronization device, thus improving the accuracy of single-ended fault location of DC distribution network lines. The multi-terminal DC distribution network model is built on the PSCAD/EMTDC platform, and the simulation analysis of the proposed location method is carried out. The results show that accurate fault location based on single terminal gas volume can be realized.

随着直流配网的发展与分布式发电的普及,其复杂的结构拓扑与工作模态的多样性,对快速准确的故障定位提出了新的挑战.本文在研究现有直流配网故障测距方法的基础上,提出一种基于限流电抗器电压特性的多端故障测距方法.由保护安装处分别计算到故障点的电压相等得到关于故障点到保护安装处距离的方程,利用限流电抗器的电压特性求解该方程得到故障点位置.该方法较好地消除了过渡电阻和数值微分项的影响,提高了直流配网测距的精度.在PSCAD/EMTDC平台搭建多端直流配网模型,大量仿真结果证明本故障测距方法在一定的过渡电阻下可以准确动作.

This paper introduces a distribution network reclosing scheme considering the low-voltage ride-through characteristics of distributed power supplies. In this paper, the impact of reclosing failure on distributed power supply off-grid is analyzed, and different reclosing strategies are adopted for circuit breakers located at different locations of faults to improve the utilization efficiency of DG and guarantee reliable power supply to loads. The simulation results show that the reclosing logic proposed in this paper can effectively reduce the off-grid rate of DG and shorten the load outage time when permanent faults occur on the line.

Inverter-interfaced distributed generator (IIDG) adopts positive sequence component control strategy. When an asymmetric fault occurs, IIDG only outputs positive sequence current, making the distribution coefficients of positive and negative sequence current on IIDG side seriously unequal, which results the degradation of the performance of phase selectors based on mutation of 2-phase current difference and symmetric component. Based on traditional phase selection principle, the influence of IIDGs access to the distribution network on phase selectors is analyzed. Results show that phase selectors on system side are less affected by the connection of IIDGs. And they can correctly identify the fault phase regardless of fault types. However, phase selectors on IIDG side cannot select fault phase correctly. A line model is built on PSCAD/EMTDC and the fault simulation is then carried out. The simulation results verify the correctness of the theoretical analysis. Finally, the prospection on the possible application of the phase selector criterion for contact lines containing IIDGs is given.

With the widespread application of clean energy in power systems, traditional distribution networks have become multi-source power grids containing large-scale distributed power sources. When a fault occurs in the distribution network, it is necessary to consider the control strategy and corresponding output characteristics of distributed power sources in order to accurately remove the fault point. Inverter-Interface Distributed Generator (IIDG), represented by photovoltaic power generation, is one of the typical clean energy sources. After IIDG is connected to the grid, it will have a significant impact on the operating characteristics of the instantaneous overcurrent protection in the distribution network, especially the quick break protection on the source side of distributed power sources. This article provides a detailed study of the relationship between the capacity of distributed power sources and fault currents, analyzes the impact of inverter type power sources on the action characteristics of source side instantaneous overcurrent protection in distribution networks, and provides a calculation method for the proportion of distributed energy with complete rejection of current protection to system capacity, i.e. the critical permeability. This provides a reference for subsequent research on current protection and new energy admission capacity.

交直流混合配电网是从交流配电网向直流配电网过渡的有效解决方案.为提升交直流混合配电网传输容量与供电可靠性,多端供电结构逐渐被广泛采用.从两端电源供电结构入手,研究当发生单极接地故障时的直流侧故障特征及接地方式.通过对故障回路的分析,研究了发生故障后电流的阶段性特性,推导故障电压与电流的时间表达式,并通过数学简化得到故障过电流峰值与达到峰值时刻的简单计算式.在此基础上,通过实例给出了选择接地电阻阻值的方法.研究分析了当两侧回路参数不对称时的故障电流振荡现象和规律,并提出基于等效拆分法的四阶微分方程回路计算方法进行故障电流计算.仿真结果表明,所提出的计算方法和接地方式适用于两端电源供电的交直流混合配电网的直流侧,有助于交直流混合配电网的安全、稳定、可靠运行.

交直流混合电网的系统结构有利于接入分布式能源及直流负荷,是未来电网研究与发展的方向。目前对于交直流混合电网接地方式及不同接地方式对配网的影响探讨较少,较多研究基于单一接地方式的系统展开。建立了直流配网模型,在研究直流侧接地方式对故障特性影响的基础上,详细研究了直流系统故障后的选极方法。通过分析直流线路限流电抗器两端暂态电气特性,针对不同的接地方式,提出了具有针对性的故障选极方案:在电容中点经小电阻接地方式下,选取基于暂态能量差的选极方案;在电容中点经大电阻接地方式和直流出口并联大电阻中点接地方式下,选取基于暂态能量比的选极方案。基于PSCAD/EMTDC仿真平台,验证了所提出的选极方案具有良好的可靠性和灵敏性,且具有较强的抗过渡电阻能力。

随着新能源的发展与应用,适用于光伏发电的逆变电源越来越多地投入电网中使用.由于分布式逆变电源与传统电源的故障特性和输出特性不同,电网原有的距离保护动作特性将会有所改变.详细分析了分布式逆变电源的故障特性及其对电网距离Ⅱ段保护的影响.结合不同故障类型下传统距离Ⅱ段保护的分支系数,对含分布式逆变电源线路的距离Ⅱ段保护整定的分支系数进行修正.提出适用于含分布式逆变电源的输电线路的距离Ⅱ段保护整定方案,提高了含新能源电网的距离保护动作的准确性和可靠性.最后在PSCAD/EMTDC中搭建了含分布式逆变电源的电网模型进行仿真分析,验证了所提出的自适应距离II段保护整定方案的有效性,提高了距离Ⅱ段保护动作的灵敏性和可靠性.

Fault analysis is an essential prerequisite for fault detection, location and isolation. A detailed fault analysis method on the steady state of the pole-to-pole fault for voltage source converter (VSC) based DC systems is presented in this paper. According to fault characteristics under different transition resistances (TRs), the steady-state response is divided into three scenarios: low transition resistance with blocked converter (LTRBC), medium transition resistance with blocked converter (MTRBC) and high transition resistance with unblocked converter (HTRUC). When TR is relatively low, fault currents through insulated gate bipolar transistors (IGBTs) are large and the converter is blocked. After an in-depth study of freewheel diodes' conduction states, the iterative method is utilized to solve the steady state under blocked converter. When TR is relatively high, fault currents through IGBTs are not large enough to block the converter. With the unblocked converter, control strategy and pulse width modulation (PWM) are investigated to obtain steady-state fault currents. Finally, a reasonable simulation model was built in PSCAD/EMTDC software. The simulation results verified the fault analysis accuracy, with much less calculation error than that of the conventional method. Besides, the proposed analysis method was proved applicable to fault scenarios under different TRs.

Voltage source converter-based DC systems face severe overcurrent problem under DC line faults, which causes significant influence on security, reliability and stability of the power system. As the theoretical basis for relay coordination and protection, the transient fault analysis of voltage source converter-based DC systems needs an in-depth study. Based on the conventional fault analysis, an accurate transient fault analysis method for the DC pole-to-ground fault and pole-to-pole fault through freewheeling diode switch state signals is proposed. In the capacitor discharge stage, fault current calculation error is reduced by taking into consideration the current fed from the grid side. In addition, through detailed analysis of the conduction condition and state of the freewheeling diode, clear calculation equations of transient fault currents are obtained. With the prior knowledge of fault response characteristics, definitions of freewheeling diode switch state signals assist in unifying calculation processes of different fault stages and simplifying transient fault calculation. Finally, a typical simulation model of the voltage source converter-based DC system was built in PSCAD/EMTDC software. The simulation results verified the conciseness and correctness of the proposed fault analysis method compared with the conventional fault analysis.

不同电压等级双回线运行方式复杂,线路间存在复杂的耦合,考虑到目前对断线故障还缺少相应的故障分析研究,因此提出一种不同电压等级同杆双回线断线故障分析方法.根据不同电压等级同杆双回线的解耦思路以及系统阻抗修正方法,画出断线故障时六序分量序网图,针对单回线断线的特殊条件提出序网图的简化版.根据Ⅰ、Ⅱ回线正序网有源的特点,列出各序分量方程式.根据断线时的边界条件,在电压约束或者电流约束唯一条件下,画出各复合序网图,进而算出序电流和序电压,但该方法计算复杂,因此提出解方程组法直接计算各序电压和各序电流,进而计算出断口电压和相电流.计算结果与PSCAD仿真结果对比,验证了不同电压等级同杆双回线断线故障分析的正确性.

逆变电源不同的控制策略影响着其输出特性与故障特性,从而影响接入配电网原有的电流保护动作特性.首先分析了在电网电压暂降以及不对称电网电压暂降情况下逆变电源的控制策略,得到逆变电源的输出特性与故障特性,基于逆变电源特殊的输出特性,再结合配电网的三段式电流保护原理,研究了含分布式逆变电源接入的配电网不同故障类型电流保护整定值的计算方法,从而提高分布式电源接入后配电网电流保护动作的可靠性.最后在PSCAD/EMTDC中搭建了含分布式逆变电源的配电网模型,利用不同控制策略,控制逆变电源的输出,并对所提出的电流保护整定计算进行仿真验证,验证了所提整定方法的正确性和有效性.