10kV配电系统计量方式探讨

对10kV配电系统的计量方式进行探讨,针对三相三线和三相四线计量,分别阐述两种计量方式的接线及特点,并对其优缺点进行分析,提出10kV配电系统的推荐计量方式,可作为计量系统设计、施工、维护、管理的参考。

35 kV电磁式电压互感器铁磁谐振分析与自动消谐

铁磁谐振是非有效接地电力系统中较常见的现象,严重危及系统安全可靠运行。通过变电站实例,阐述变电站铁磁谐振原因,并研究措施防止谐振发生或降低其幅值。

基于高精度故障录波器的中性点不接地系统的高阻接地分析

针对配电网小电流单相接地短路故障,基于高精度暂态故障录波器合成的零序电压开展中性点不接地系统的高阻接地分析,即采集配电网下不同线路、不同位置的高精度故障录波器信号来判断故障线路与位置。真实试验表明,通过零序电压、零序电流研判故障可以有效缩短线路故障恢复时间,实现小电流接地系统接地故障准确定位。

A novel SVPWM strategy considering neutral-point potential balancing for three-level NPC inverter

This paper proposes a novel SVPWM （space vector pulse width modulation） strategy for the three-level neutral-point-clamped voltage source inverter, based on the particular disposition of all the redundant voltage vectors. The new modulation approach shows superior performance for harmonic voltage and balancing control of neutral-point potential compared to the popular eight-stage centered SVPWM. It realizes suppression of inverter neutral-point potential variation by accurately modifying redundant factor of small vectors pairs, only requiring information of DC-link capacitor voltages and three-phase load currents. This is convenient to apply and is compatible of digital computer realization. Feasibility of the proposed control approach is verified by simulation and experimental results.

A Modified Neutral-point Voltage Control Strategy for Three-level Inverters Based on Decomposition of Space Vector Diagram

Capacitor voltage imbalance is a significant problem for three-level inverters.Due to the mid-point modulation of these inverter topologies,the neutral point potential moves up or down depending on the neutral point current direction creating imbalanced voltages among the two capacitors.This imbalanced capacitor voltage causes imbalanced voltage stress among the semiconductor devices and causes increase output voltage and current harmonics.This paper introduces a modified voltage balancing strategy using two-level space vector modulation.By decomposing the three-level space vector diagram into two-level space vector diagram and redistributing the dwell times of the two-level zero space vectors,the modified voltage balancing method ensures minimal NP voltage ripple.Compared to the commonly used NP voltage control method(using 3L SVM[9]),the proposed modified NP voltage control method offers a slightly higher neutral-point voltage ripple and output voltage harmonics but,it has much lower switching loss,code size and execution time.

A neutral-point potential balance control strategy for three-level inverter based on VSVPWM

The topology of diode neutral-point-clamped(NPC)three-level inverter is prone to neutral-point potential offset.When the sum of three-phase current is zero,the virtual space vector pulse width modulation(VSVPWM)scheme does not cause the neutral-point voltage offset,but it lacks the ability to balance the deviation.For this reason,a neutral-point potential control strategy combining virtual space vector modulation and loop width control is proposed.The neutral-point potential is balanced by introducing the distribution factor for the regions with redundant vectors.For other regions,the potential is controlled by selecting a suitable switching sequence.Meanwhile,the effect on the virtual vector modulation is reduced within the loop width by setting an appropriate loop width,thereby improving the balance effect.The simulation results show that the proposed method has a strong ability to control the offset and has excellent potential balance performance under the conditions of balanced load,unbalanced load and asymmetric capacitance parameters.

Comprehensive predictive control of neutral-point voltage balancing for back-to-back three-level NPC converters

A comprehensive predictive strategy was proposed for the neutral-point balancing control of back-to-back three-level converters. The phase currents at both sides and the DC-link capacitor voltages were measured for the prediction of the neutral-point current. A quality function was found to balance the neutral-point, and a metabolic on-times distribution factor was used as a predicator to minimize the quality function at each switching state. Simulation results show that the proposed method produces smaller ripples in tested signals compared with the established one, namely, 9.15% less in a total harmonic distortion(THD) of line-to-line voltage, 1.08% less in the THD of phase current, and 0.9 V less in the ripple of the neutral-point voltage. The obtained experimental results show that the main harmonics of the line-to-line voltage and the phase current in the proposed method are improved by 10 d B and 6 d B, respectively, and the ripple of neutral-point voltage is halved compared to the established one.

Parameter Plane Synthesis and Performance Investigation of a Three-Phase Neutral-Point Clamped Bidirectional Rectifier

In this paper, parameter plane synthesis of a three-phase neutral-point clamped bidirectional rectifier has been performed. The converter involves one outer-loop PI voltage controller and two inner-loop PI current controllers for the closed-loop control. D-partition technique has been employed for the precise design of the voltage controller. The performance of the converter has been evaluated using MATLAB/Simulink software. An experimental prototype of converter has been developed and the experimental investigation of converter in closed-loop has been carried out. DSP DS 1104 of dSPACE has been used for real-time implementation of the designed controller. The performance of the converter has been found satisfactory using the designed controller parameters.

中压不接地配电网三相潮流新方法

在大量分布式电源接入中低压配电网的新形势下,三相潮流计算是分析其影响的基本手段。针对现有中压不接地配电网三相潮流研究主要采用人为设置参考中性点/零序电压的方式,导致无法仿真分析中性点/零序电压偏移、不接地网络零序潮流和相-地电压不平衡等情况,提出一种中压不接地配电网三相潮流新算法。首先,提出不接地配电网三相潮流在节点变量和导纳矩阵方面的特殊性。然后,设计基于功率平衡方程和牛拉法,采用导纳矩阵可逆化处理和矩阵替换技术实现约束零序电流为零的不接地配电网三相潮流算法。最后,基于6节点系统和修改的IEEE123算例仿真不接地配网的潮流,结合PSCAD验证所提方法在不同场景下的准确性以及在大电网中的适用性和收敛性,并在地市电网中进行实际应用。算例分析表明,所提算法计算结果准确,具有良好的工程实用性。

非接地负刚度动力吸振器动力学设计及优化

接地负刚度动力吸振器有着良好的振动控制效果,但是在实际工程应用中,负刚度元件往往无法与地面直接相连。提出一种非接地负刚度动力吸振器,根据所建理论模型,得到系统的频响函数,利用最大值最小化理论获得非接地负刚度动力吸振器的最优设计参数,并与其他典型的动力吸振器模型进行对比。计算结果表明,由于引入负刚度元件,非接地负刚度动力吸振器的振动控制效果显著优于传统线性动力吸振器,为负刚度动力吸振器的工程应用提供了一定理论参考。

中性点非有效接地配电网弧光接地的物理模拟研究

弧光接地是中性点不接地配电网中最常见的故障,对电网设备的绝缘性能有严重威胁,从而影响电网运行的稳定性,亟需进行弧光接地故障研究。研究提出弧光接地的物理模拟方法,设计实现弧光模拟装置,通过精确控制放电间隙及放电极移动速度,实现稳定模拟的电弧接地、间歇性电弧接地、弧光渐变等各种弧光接地现象。记录试验波形,并进行分析波形,发现弧光放电的规律。结果表明,物理模拟方法能够可控模拟弧光现象,记录下的波形数据可为处理弧光接地故障提供参考。

基于过电压衰减比的柔性接地控制参数设计方法

为实现柔性接地装置对中性点电压的准确控制,提出过电压衰减比的概念,并以配电网不接地系统为例提出了控制系统设计方法。首先,分析了不接地系统的中性点过电压产生机理,建立了柔性接地装置接入配电网的等效模型。其次,给出了双闭环控制系统的框图并推导出双闭环控制下的零序输出电压表达式,在此基础上提出了过电压衰减比的概念。文中以双比例控制器为例,提出了基于过电压衰减比指标的控制系统参数设计方法,通过内、外环参数解耦设计,实现了衰减比和系统稳定性的独立控制。最后,搭建了10k V配电网不接地系统仿真模型和低压实验回路,验证了所提设计方法有效性。

分布式电源接入对变压器中性点工频过电压特性的影响及对策

为避免一刀切的“间隙安装策略”带来的成本高问题,有必要针对分布式电源从配电网接入情形给出间隙安装策略的建议。通过建立配电网发生单相接地故障时的复合序网络,分析不接地变压器中性点工频过电压的产生机理;在PSCAD/EMTDC中搭建计及低压侧分布式电源接入的110 kV电网模型,对比分析不同类型和容量分布式电源接入下变压器中性点的电压值或电压波形的变化规律。结果表明:接入PQ控制型逆变型分布式电源且其容量显著大于低压侧负荷容量时对变压器中性点绝缘安全的威胁程度最高;根据不同变压器中性点绝缘水平、接入分布式电源的类型和容量应选择不同的间隙安装方案。

配电网三相电压不平衡的成因分析和实践

针对配电网正常运行状态下长期存在的一起变电站母线三相电压不平衡问题,通过实际运行数据和三相潮流仿真过程,深入分析了长期存在的母线三相电压不平衡的原因。研究表明,不接地配电网挂接不平衡的电容型电压互感器,其存在的电容值容易造成系统的正常运行状态下的三相不平衡。将该分析流程用于工程实际的电压不平衡的成因分析过程中,通过三相潮流和现场数据能够最大限度地减少分析工作量,提高效率,为后续的不平衡问题治理提供方向。

室外路灯辅助等电位联结必要性的探讨

从供电低压侧发生接地故障、10 kV电源端中性点不接地、小电阻接地以及10 kV负荷侧发生接地故障等方面,结合TN/TT系统分析上述接地故障时对路灯安全危害,论证路灯设置辅助等电位联结的必要性。

道路照明接地系统研究

当前道路照明接地系统以TN系统为主,TT系统鲜有被采用。笔者试图通过低压、中压系统发生接地故障时产生的故障电压与应力电压,对人员与电气装置的影响与危害,将二者作出定性与定量分析比对,供同行判断与选择。

铁芯不接地对介质损耗和电容量的测量分析

阐述变压器绕组介质损耗与电容量测量时,受到铁芯不接地因素的影响,出现测量误差,探讨铁芯接地与铁芯不接时对介质损耗和电容量的测量原理,结合某测量项目,分析测量方案与测量结果。

电容电流过大造成的过电压讨论

通过一起现场实际发生的变电站事故案例,对电容电流过大可能对故障相造成的危害进行讨论。案例中变电站10 kV母线是不接地系统,由于单相接地电容电流过大导致弧光过电压,对接地相产生了比不接地相更严重的绝缘损坏,最终击穿整段母线的接地相,造成更严重的负荷损失。根据这一现象提示,现场发生接地相绝缘损坏很有可能是电容电流过大造成。

原型结构与非常形结构的建筑离地性阐释——从勒·柯布西耶到雷姆·库哈斯

将“离地性”研究作为切入点,通过引入离地建筑形式结合抗衡重力的结构语言——原型结构和非常形结构,分析结构所使用的材料和构造、结构逻辑的创新和架空悬挂的营造等方法,研究结构如何呼应建筑荷载及结构支撑和协调作品的设计意图,为现代建筑在离地新语境下拓展新的结构逻辑以契合设计意图提供了新的思考方式。

基于消弧消谐柜自身故障引发的接地事故分析及改进措施

某变电站35 kV不接地系统采用单母分段接线,每段母线配置一面消弧消谐柜,因设计阶段消弧消谐柜电源侧仅配备隔离开关。因未配置断路器,当其自身发生故障时,无法及时有效切除故障点,仅能通过母线全停方式解决问题,造成电力用户被迫停产,产生较大经济损失。尤其单相接地故障,因消弧消谐柜属于全封闭式柜体,接地点查找难度大,大大增加了事故处理时间及难度;又因母线停送电操作复杂,进一步增加了系统接地时间,给系统安全稳定运行造成隐患。针对此问题,提出了消弧消谐自身单相接地故障的查找方法、预防及改进措施。