Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network

Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.

Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Protection of Zero-Sequence Power Variation in Mountain Wind Farm Collector Lines Based on Multi-Mode Grounding

The arc-suppression coil(ASC)in parallel low resistance(LR)multi-mode grounding is adopted in the mountain wind farm to cope with the phenomenon that is misoperation or refusal of zero-sequence protection in LR grounding wind farm.If the fault disappears before LR is put into the system,it is judged as an instantaneous fault;while the fault does not disappear after LR is put into the system,it is judged as a permanent fault;the single-phase grounding fault(SLG)protection criterion based on zerosequence power variation is proposed to identify the instantaneous-permanent fault.Firstly,the distribution characteristic of zero-sequence voltage(ZSV)and zero-sequence current(ZSC)are analyzed after SLGfault occurs in multi-mode grounding.Then,according to the characteristics that zero-sequence power variation of non-fault collector line is small,while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance,the protection criterion based on zero-sequence power variation is constructed.The theoretical analysis and simulation results show that the protection criterion can distinguish the property of fault only by using the single terminal information,which has high reliability.

Zero-Sequence Current Suppression Strategy for Open-End Winding Permanent Magnet Synchronous Motor Based on Model Predictive Control

Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the common-mode voltage and the back electromotive force(EMF)harmonic generated by the inverters produce the zero-sequence current in the zero-sequence circuit,and the zero-sequence current has great influence on the operation efficiency and stability of the motor control system.A zero-sequence current suppression strategy is presented based on model predictive current control for OW-PMSM.Through the mathematical model of OW-PMSM to establish the predictive model and the zero-sequence circuit model,the common-mode voltage under different voltage vector combinations is fully considered during vector selection and action time calculation.Then zero-sequence loop constraints are established,so as to suppress the zero-sequence current.In the end,the control strategy proposed in this paper is verified by simulation experiments.

Electromagnetic Zero-Sequence Harmonics Blocker： Modeling and Experimental Analysis

This paper reveals new contributions to the analysis and development of devices for harmonic distortion mitigation. Considering the sequential distribution of harmonic currents, zero-sequence components could be diminished using electromagnetic devices, particularly the eZSB （electromagnetic zero-sequence blocking）. One important characteristic of this device, which has received particular attention on this research, is its robustness and low cost of construction. Theoretical and experimental results related to the behavior of the electromagnetic blocking devices are presented. The results illustrate the consistence of the theoretical aspects related with the model in the frequency domain, as well as the performance of the blocking devices, reducing zero-sequence harmonic currents, mainly by the conjunct action of the eZSF （electromagnetic zero-sequence harmonic filter）, working as a impedance coupler. In this context, aiming the evaluation of the reliability of the results obtained through mathematical modeling, experimental tests have been carried out using a low-power prototype, highlighting particular aspects related to its function as a zero-sequence harmonic blocker.

融合电磁和地声特征的地震预测集成学习方法

地震是极具破坏性与不确定性的自然现象,在人们毫无察觉的情况下地震发生在人口稠密区时,将严重危害人们生命财产安全。人们不断努力了解地震的物理特征和物理危害与环境之间的相互作用,以便在地震发生前发出适当的警报。可靠的地震预测应包含对地震信号的分析,但是这些信号在地震发生前不明显;因此使用数据驱动机器学习的方法来分析这些信号与地震的联系并预测地震。通过建立观测台网连续监测与地震发生相关的各种物理量或化学量,据此获取的地震前兆信息是地震预测的研究基础。地震发生前,地球物理场发生显著变化,伴随电磁和地声等多种前兆信号,其中电磁和地声信号具有临震特性,是开展地震临震观测预测研究的重要数据来源;因此对地下的电磁扰动和地声信号进行实时监测,获取长期观测数据用于数据驱动机器学习方法预测地震。该文基于AETA数据的临震模型预报,针对多分量地震监测预测系统(Acoustic and Electromagnetic Testing All in one system,AETA)在川滇地区记录的电磁和地声数据,提取时域和频域特征,采用基于随机森林算法、轻量级梯度提升决策树和极度随机树的集成学习方法共同预测该区域的发震情况,选取发震概率最大的子区域中心位置作为震中预测结果,进一步训练LightGBM回归模型以预测此子区域的震级,按周对地震三要素进行预测。实验结果表明,该方法在川滇地区地震风险预测上,准确率可达0.64,震级预测的平均误差为0.38,最小误差为0.00,具有良好的预测效果。

临震微波动现象回溯性研究——以青海地区为例

为进一步检验临震微波动异常跟踪指标,基于兰州临震微波动实时监控与跟踪系统的数据资料,对青海地区2020~2022年5.0级及以上地震震中距150 km以内台站的波形资料进行分析。结果表明,震中距150 km以内的台站几乎都能记录到临震微波动事件;达到临震微波动异常指标的台站不是震中距最小的测震台站,这可能与区域构造应力、发震断层走向及地震破裂过程等有关;主震震级越大,震前出现临震微波动异常指标的可能性越大。

强震临震微波动现象跟踪实践

为验证和检验强震临震微波动现象及其主要特征,利用甘肃、青海、四川、云南、西藏等区域台网200余个宽频带数字地震台站的实时波形资料和实时跟踪监控技术系统,对2019—2022年间青藏高原发生的44次5级以上地震进行全程实时跟踪及动态监控,进一步检验临震微波动现象的重现性和客观性,验证了临震微波动现象的频谱、时间、空间等特征。

2019年老挝M_(S)6.0地震临震射出长波辐射变化研究

计算2019年11月21日老挝M_(S)6.0地震前后(2019年10月16日—12月15日)震中位置(19.50°N,101.35°E)的潮汐变化。发震时刻引潮力处于高相位点附近,显示引潮力的诱震作用属于典型正断层走滑作用类型。以此引潮力变化周期的各低相位点时间(10月28日、11月13日、11月27日)分别为背景,计算研究区(13°N~23°N,99°E~109°E)范围内,NOAA射出长波辐射数据产品(OLR)各引潮力周期时段长波辐射异常分布及变化。结果显示,无震时的引潮力变化的A、C周期,震中附近无OLR变化;发震的引潮力变化B周期,该地区震前OLR仅震中发生了显著而连续异常变化过程:在空间上OLR异常分布在老挝北部NE-SW走向的奠边府断裂带上,且与震中位置高度吻合,经历了起始增强—异常增强—峰值—减弱—发震—平静的演化过程,与岩石应力加载破裂演化即初始微动破裂—扩张破裂—应力闭锁—地震暴发—平静各阶段力学过程相同;表明天体引潮力对达到临界状态的活跃断层有触发作用,OLR异常则是地震构造应力应变活动过程的辐射表征。

Simplified Cluster Voltage Balancing Control Based on Zero-sequence Voltage Injection for Star-connected Cascaded H-bridge STATCOM

The cluster DC voltage balancing control adopting zero-sequence voltage injection is appropriate for the starconnected cascaded H-bridge STATCOM because no zerosequence currents are generated in the three-phase three-wire system.However,as the zero-sequence voltage is expressed in trigonometric form,traditional control methods involve many complicated operations,such as the square-root,trigonometric operations,and inverse tangent operations.To simplify cluster voltage balancing control,this paper converts the zero-sequence voltage to the dq frame in a DC representation by introducing a virtually orthogonal variable,and the DC components of the zero-sequence voltage in the dq frame are regulated linearly by proportional integral regulators,rather than being calculated from uneven active powers in traditional controls.This removes all complicated operations.Finally,this paper presents simulation and experimental results for a 400 V±7.5 kvar star-connected STATCOM,in balanced and unbalanced scenarios,thereby verifying the effectiveness of the proposed control.

风廓线雷达资料在典型天气过程预报预警中的应用

本文基于上海市宝山站2020年11月建成的探测高度16 km的对流层风廓线雷达(TWP16型)资料,结合多普勒雷达产品、宝山自动站观测和MICAPS高低空环流实况数据,对比分析了影响宝山地区的寒潮大风、强对流大风和台风大风过程中TWP16型风廓线资料的演变特征。结果表明:TWP16型风廓线资料对宝山地区上空垂直方向上高时空分辨率的风场变化有一定的刻画能力,能较好地反映出三类大风天气过程中高低空急流、垂直切变、冷暖平流的结构及变化,对影响本地的大风天气监测预警有一定的指示作用。

2023年12月2日芒市M_(S)5.0地震前地震活动异常

总结2023年12月2日云南芒市M_(S)5.0地震发生前地震活动异常,发现震前存在中期、短期和临震异常。其中:(1)中期阶段:滇西地区M≥5.0地震存在东西迁移规律,且M_(L)≥4.0地震活动具有由滇西北向小滇西迁移的特点;(2)中短期阶段:小滇西地区中小地震活动显著增强,3、4级地震围成孕震空区并伴随出现M_(L)≥3.0地震条带;(3)短期阶段:出现逼近地震和前兆震群,临震前10天发生前震。分析认为,“逼近地震”和前兆震群的发生,是地震孕育过程从中期转入短临阶段的拐点。

Preliminary inquiry into the causes of anomaly increase of air temperature by an impending earthquake

In this paper, the causes of the occurrence of the temperature increase by an impending earthquake of low altitude atmosphere and on the ground surface have been preliminarily expounded through several simulative controlexperiments. Air polarized by the anomalous atmospheric static electric field is regarded as the primary factor tocreate air temperature increase to a large degree and over a large area in the sunlight. In addition, another causeis considered as the temperature increase effect of “polluted” air.

Regional Prediction of Impending Debris Flow Based on Doppler Weather Radar

Debris flow prediction is one of the important means to reduce the loss caused by debris flow. This paper built a regional prediction model of impending debris flow based on regional environmental background （including topography, geology, land use, and etc.）, rainfall and debris flow data. A system of regional prediction of impending debris flow was set up on ArcGIS 9.0 platform according to the model. The system used forecast precipitation data of Doppler weather radar and observational precipitation data as its input data. It could provide a prediction about the possibility of debris flow one to three hours before it happened, and was put into use in Liangshan Meteorological Observatory in Sichuan province in the monsoon of 2006.

A Preliminary Study on the Phenomenon of Microseismic Fluctuations before Impending Strong Earthquake

Based on repeated comparison studies of broadband digital seismic records before the Wenchuan MS8. 0,Yushu MS7. 1 and Qingchuan MS5. 4 earthquakes,the possible microseismic fluctuations before impending earthquakes were preliminarily identified. In order to verify and test this phenomenon,a real-time tracking technical system was established by using continuous waveform records of more than 200 wide-band digital seismic stations in regional networks such as Gansu,Qinghai,Sichuan,Yunnan and Tibet.Through real-time tracking and dynamic monitoring of 24 earthquakes with M≥5. 0 occurring in the Qinghai-Tibetan block during the period of 2012-2014 and the observations of stations in some non-seismic areas,the reproducibility and objectivity of the impending earthquake phenomenon were verified. The main characteristics of the microseismic fluctuation phenomena immediately preceding the strong earthquakes are as follows:(1)the spectrum range is wider,the dominant frequency is 11-16 Hz,and the spectrum shape is more regular;(2)it appears 6-24 days before the earthquake,averaging about 15 days;(3)it is possible to be recorded by the stations within the epicenter distance of 50 km,and the stations with the epicenter distance of more than 50 km generally cannot record it;(4)this phenomenon is directional,i. e. the direction in which the activity degree,N-value,varies significantly may be related to the location of the seismic source,the seismogenic fault and the distribution of aftershocks of the strong earthquake. The preliminary study shows that the impending-earthquakes microseismic phenomena may be related to the pre-activity,micro-vibration and micro-rupture in the source region in the imminent stage,or the microactivity and micro-rupture associated with the active tectonics.

A Preliminary Study on the Use of NCEP Temperature Images and Additive Tectonic Stress from Astro-Tidal-Triggering to Forecast Short-Impending Earthquakes

Taking the three earthquakes which occurred in Tibet, China during the period of July 12 to August 25, 2004 as an example,the paper analyses the M_S≥6.0 earthquakes that occurred in China and M_S≥7.0 earthquakes that occurred overseas since May of 2003 by combining the image data from the National Center for Environmental Prediction of America(NCEP)with the additive tectonic stress from astro-tidal-triggering (ATSA) and makes the following conclusions: The abnormal temperature image data of NCEP can better reflect the spatial-temporal evolution process of tectonic earthquake activity; The ATSA has an evident triggering effect on the activity of a fault when the terra stress is in critical status; using the NCEP images and the ATSA to forecast short-impending earthquake is a new concept; The three earthquakes occurred during the same phase of the respective ATSA cycle, i.e. that occurred at the time when the ATSA reached the relatively steady end of a peak, rather than at the time when the variation rate was maximal. In addition, the author discovered that the occurrence time of other earthquake cases during 2003～2004 in Tibet was also in the same phase of the above-mentioned cycles, and therefore, further study of this feature is needed with more earthquake cases in other areas over longer periods of time.

2021年茫崖M_(S)5.8地震前地震条带短临异常分析

1研究背景。大量震例研究表明,在中强地震孕育过程中,一定区域中小地震活动会出现由凌乱、分散的分布转为集中成带的现象(刘蒲雄等,1969),即地震条带。地震条带的震兆性在我国的地震预报实践备受重视,广泛运用于日常震情跟踪与中强地震危险性分析。

基于动态重力信息的地震前兆与强震短临预报

地震预报是当今世界尚未破解的重大科技难题,短临地震预报是地震预报的难点,有效的前兆信息则是短临预报的关键。笔者围绕短临地震预报难题,研制了高精度动态固体潮汐重力仪和大气潮汐重力仪,成功捕获到2010~2023年间的玉树7.1级地震、土耳其7.8级地震等震前几十个小时的动态重力场变化信息。这些信息再现了强震孕育-发生的过程,初步揭示短临阶段“基本稳定→闭锁蓄能→震前平静→能量释放”的强震物理机制,可作为短临地震预报的前兆信息。为实现对短临地震“时−空−强”的准确预报,提出通过动态重力场变化组网观测和分布式前兆信息数据库建设,进一步揭示不同类型地震的动态重力信号响应规律,建立强震发生概率、时间、震中位置及震级预报模型的可行性路径,渴望破解强震短临预报的世界难题。

“治将病”理论在眼病中的应用

“治将病”是冯俊主任医师基于对当代临床中医病症辨治思维模式和西医诊疗模式的深入研究提出的理念,本文主要探讨“治将病”理论的溯源以及在眼科辨治体系中的实践,并以高血压性视网膜病变为例进行深入阐述。“将病”是处于眼科“未病”“已病”之间的状态,并根据不同表现将其分为有临床指征但可暂无明显症状的“显病”和有一定眼部症状而眼科常规检查并不能发现与症状对应体征的“藏病”。“显病”可以通过定期眼部检查、眼保健工作的重心下移等途径解决,而“藏病”可以通过增强“治将病”理论对实践的指导以及多学科合作融合等方式解决。“治将病”理论是时代变化、医学研究进步的结果,是当代医家在特殊的历史时间段和特殊环境中经过大量实践的经验再积累,适用于眼病的中西医结合预防及治疗,能够为防盲治盲发挥重要的作用。

2022年四川3次强震的断层位移协调比短临形变异常

1研究背景2022年四川连续发生了3次6级以上强震。分别是6月1日雅安芦山M_(S)6.1、6月10日阿坝州马尔康M_(S)6.0及9月5日甘孜州泸定M_(S)6.8。其中泸定地震造成当地人员较大伤亡和严重的建筑物破坏(徐泰然,2022;罗若帆,2022)。