Accurate Fault Location Modeling for Parallel Transmission Lines Considering Mutual Effect

:A new accurate algorithms based on mathematical modeling of two parallel transmissions lines system(TPTLS)as influenced by the mutual effect to determine the fault location is discussed in this work.The distance relay measures the impedance to the fault location which is the positive-sequence.The principle of summation the positive-,negative-,and zero-sequence voltages which equal zero is used to determine the fault location on the TPTLS.Also,the impedance of the transmission line to the fault location is determined.These algorithms are applied to single-line-to-ground(SLG)and double-line-to-ground(DLG)faults.To detect the fault location along the transmission line,its impedance as seen by the distance relay is determined to indicate if the fault is within the relay’s reach area.TPTLS under study are fed from one-and both-ends.A schematic diagrams are obtained for the impedance relays to determine the fault location with high accuracy.

Identification Method for Single-line-to-ground Faults with Line Break Based on Phasor Measurement in Distribution Networks

The single-line-to-ground faults with line breaks(SLGFs-LBs)occur more and more frequently in distribution networks and can cause major safety accidents.It is difficult to distinguish the single-line-to-ground faults(SLGFs)in resonant grounding systems and ungrounding systems due to the same electrical characteristics on the source side and uncertain operation conditions of distribution networks.This paper proposes a method for distinguishing SLGFs-LBs and SLGFs.First,the source-side and load-side voltage characteristics of SLGFs and SLGFs-LBs are analyzed,and the phase difference between the voltages of the fault phase and non-fault phase on the load side is selected as the identification criterion.Phasor measurement units(PMUs)are selected as measuring devices.Then,the effects of operation conditions and external devices in distribution networks on the proposed method are discussed,and the phase errors caused by them are calculated to correct the identification method.Finally,the field testing and simulation experiments are conducted to verify the effectiveness and robustness of the proposed method.

Calculation Method for Commutation Failure Fault Level in LCC-HVDC System Under Single-line-to-ground Faults Considering DC Current Variation

Earlier studies have reported some calculation methods for commutation failure fault level(CFFL) in line-commutated-converter based high-voltage direct current(LCCHVDC) system under single-line-to-ground(SLG) faults. The accuracy of earlier methods is limited because they only consider the commutating voltage drop and phase shift, while neglecting the DC current variation. Hence, this paper proposes a CFFL calculation method under SLG faults considering DC current variation, for better planning and designing of LCC-HVDC systems. First, the fault commutating voltage magnitude and phase shift are calculated. Then, the fault DC voltage during different commutation processes is deduced. Based on the commutating voltage magnitude and phase shift, and DC voltage during different commutation processes under SLG faults, the characteristics of CFFL with different fault time are demonstrated and analyzed. Next, the transient time-domain response of the DC current after the fault is obtained based on the DC transmission line model. Discrete commutation processes are constructed based on the commutation voltage-time area rule to solve the extinction angle under different fault levels and fault time. Finally, the CFFL is calculated considering the fault time, commutating voltage drop, phase shift, and DC current variation. The accuracy of the proposed method compared with the traditional method is validated based on the CIGRE benchmark model in PSCAD/EMTDC.

电磁环网线路无故障跳线和单永故障稳定性分析

以川电东送通道的陈家桥—长寿电磁环网为例 ,分析了《电力系统安全稳定导则》中规定的对单回高一级电压线路电磁环网进行无故障跳线和单永故障分析的必要性。研究表明 ,在电磁环网潮流较强的情况下 ,单回高一级电压线路电磁环网的无故障跳线比单永故障严重。主要原因是发生单永故障时 ,尽管短路故障有加速机组功角摆开的作用 ,但三相断线前的单相断线使得线路的功率分批转移到其他线路 ,起到一定的缓冲作用。并且 ,随着线路潮流的加强 ,当功率的分批转移效果逐渐超过短路故障的加速作用时 。

川电东送通道的电压水平对系统稳定性的影响

分析了川电东送通道上陈家桥—长寿电磁环网存在的稳定性问题 ,提出了该通道变电站母线电压的控制策略 ,以及提高川电东送通道系统稳定水平的措施。在川电东送 60 0 MW时 ,建议将洪沟变电站的母线运行电压保持在 5 0 8k V以上 ,长寿、万县变电站的母线运行电压保持在 5 2 2 k V以上 ;也可以通过采取重庆电网多开机、在长寿或万县变电站装设 SVC等措施 。

基于5次谐波突变量的小电流接地系统选线

为了解决小电流接地系统选线难的问题,在对小电流接地系统单相接地故障的特点进行详细分析的基础上,提出通过综合比较各线路的故障相和非故障相的5次谐波电流突变量以及本线路和相邻线路故障相的5次谐波电流突变量两个判据进行故障选线。对故障后5 s和故障前1 s的数据之差进行傅里叶滤波得到5次谐波电流突变量。利用所提方法做了大量的仿真试验,结果表明,该选线方法不受暂态过程、故障点过渡电阻、线路长度等因素的影响,可以正确选线。

三相串联MMC直流换流站在交流故障下的控制策略研究

三相串联MMC将三个单相MMC串联,在承受相同直流电压的情况下,相比传统的三相并联MMC,可以减少三分之一的开关器件,造价更低,但三相串联MMC在不平衡交流电压下的控制保护是一个难题。推导了静止α?β坐标系下的交流侧有功功率平衡方程,通过平衡各单相MMC交流侧的有功功率实现交流故障下的直流侧均压,该策略可以根据故障的严重程度自动调整换流器交流故障下的功率输送。此外,提出了静止α?β坐标系下防止换流器过电流的参考电流整定方法。构建了基于比例谐振控制器的总体控制框图。最后,在PSCAD/EMTDC中搭建了三相串联MMC换流站仿真模型,对交流电网单相和两相接地故障进行了仿真验证。仿真结果表明:三相串联MMC换流站在所提的控制策略下具有良好的故障穿越能力。

低惯量不接地微电网单相接地故障研究

提出了一种新的小惯量不接地微电网SLG(单相接地)故障保护方案。该方案包含微电网接口保护和单元保护。微电网接口保护是基于微电网互联变压器零序电压角和零序电流角的差值来快速选择故障馈线。微电网单元保护是基于负载或分布式能源的每个连接点的三个零序电流方向的比较。所提出的方案对可能发生在电网和微电网中的SLG故障做出响应。建立了PSCAD仿真模型,对不接地的低惯量微电网进行了仿真研究,验证了所提方案的可靠性。