Simulation of Corrosion-Induced Cracking of Reinforced Concrete Based on Fracture Phase Field Method

Accurate simulation of the cracking process caused by rust expansion of reinforced concrete(RC)structures plays an intuitive role in revealing the corrosion-induced failure mechanism.Considering the quasi-brittle fracture of concrete,the fracture phase field driven by the compressive-shear term is constructed and added to the traditional brittle fracture phase field model.The rationality of the proposed model is verified by a mixed fracture example under a shear displacement load.Then,the extended fracture phase model is applied to simulate the corrosion-induced cracking process of RC.The cracking patterns caused by non-uniform corrosion expansion are discussed for RC specimens with homogeneous macroscopically or heterogeneous with different polygonal aggregate distributions at the mesoscopic scale.Then,the effects of the protective layer on the crack propagation trajectory and cracking resistance are investigated,illustrating that the cracking angle and cracking resistance increase with the increase of the protective layer thickness,consistent with the experimental observation.Finally,the corrosion-induced cracking process of concrete specimens with large and small spacing rebars is simulated,and the interaction of multiple corrosion cracking is easily influenced by the reinforcement spacing,which increases with the decrease of the steel bar interval.These conclusions play an important role in the design of engineering anti-corrosion measures.The fracture phase field model can provide strong support for the life assessment of RC structures.

Dual-function protective layer for highly reversible Zn anode

The thermodynamic instability of zinc anodes in aqueous electrolytes leads to issues such as corrosion,hydrogen evolution reactions(HER), and dendrite growth, severely hindering the practical application of zinc-based aqueous energy storage devices. To address these challenges, this work proposes a dualfunction zinc anode protective layer, composed of Zn-Al-In layered double oxides(ILDO) by rationally designing Zn-Al layered double hydroxides(Zn-Al LDHs) for the first time. Differing from previous works on the LDHs coatings, firstly, the ILDO layer accelerates zinc-ion desolvation and also captures and anchors SO_(4)^(2-). Secondly, the in-situ formation of the Zn-In alloy phase effectively lowers the nucleation energy barrier, thereby regulating zinc nucleation. Consequently, the zinc anode with the ILDO protective layer demonstrates long-term stability exceeding 1900 h and low voltage hysteresis of 7.5 m V at 0.5 m A cm^(-2) and 0.5 m A h cm^(-2). Additionally, it significantly enhances the rate capability and cycling performance of Zn@ILDO//MnO_(2) full batteries and Zn@ILDO//activated carbon zinc-ion hybrid capacitors.This simple and effective dual-function protective layer strategy offers a promising approach for achieving high-performance zinc-ion batteries.

Laser Protection with VO_2 Film

This paper presents the principle,properties,advantage and disadvantage,associated problems and trend of laser protection with VO 2 film for infrared detectors in the range of 3～5μm and 8～12μm regions and suggests VO 2 film is a potential protection material for infrared detectors.

Study on the instantaneous protection reliability of low voltage circuit breakers

This paper outlines the significance of enhancing the instantaneous protection reliability of low voltage circuit breakers and describes their main failure modes. The instantaneous failure mechanism of low voltage circuit breakers was analyzed so that measures to improve instantaneous protection reliability can be determined. Furthermore, the theory of the instantaneous characteristics calibration device for low voltage circuit breakers and the method of eliminating the non-periodic component of test current are given in detail. Finally, the test results are presented.

Effect of Phase Change Materials on the Thermal Protective Performance of the Multi-layered Fabrics Examined by TPP Tester under Flash Fire

Cotton fabrics treated with phase change materials( PCMs)were used in multi-layered fabrics of the fire fighter protective clothing to study its effect on thermal protection. The thermal protective performance( TPP) of the multi-layered fabrics was measured by a TPP tester under flash fire. Results showed that the utilization of the PCM fabrics improved the thermal protective performance of the multi-layered fabrics. The fabric with a PCM add on of 41. 9% increased the thermal protection by 50. 6% and reduced the time to reach a second degree burn by 8. 4 s compared with the reference fabrics( without PCMs). The employment of the PCM fabrics also reduced the blackened areas on the inner layers. The PCM fabrics with higher PCM melting temperature could bring higher thermal protective performance.

Some Technical Solutions for Environmental Protection System during Accidents at Nuclear Power Plants

The paper reports some technical solutions, which suggested or used for increasing of environmental protection during accidents at NPPs. For NNPs with two protective shells and pressure release system such as WWER-1000 a comprehensive, passive-mode environmental protection system of decontamination of the radioactive steam-air mixture from the containment and the intercontainment area was suggested. This system includes the “wet” stage (scrubbers, etc.), the “dry” stage (sorption module), and also an ejector, which in a passive mode is capable of solving the multi-purpose task of decontamination of the air-steam mixture. For WWER-440/230 NPPs three protection levels: 1) a jet-vortex condenser;2) the spray system;3) a sorption module were suggested and installed. For modern designs of new generation NPPs, which do not provide for pressure release systems, a new passive filtering system together with the passive heat-removal system, which can be used during severe accidents in case all power supply units become unavailable, was proposed and after modernization was installed at the KudanKulam NPP (India).

A Protection Method of VSC-HVDC Cables Based on Generalized S-Transform

Generalized S-transform is a time-frequency analysis method which has higher resolution than S-transform. It can precisely extract the time-amplitude characteristics of different frequency components in the signal. In this paper, a novel protection method for VSC-HVDC (Voltage source converter based high voltage DC) based on Generalized S-transform is proposed. Firstly, extracting frequency component of fault current by Generalized S-transform and using mutation point of high frequency to determine the fault time. Secondly, using the zero-frequency component of fault current to eliminate disturbances. Finally, the polarity of sudden change currents in the two terminals is employed to discriminate the internal and external faults. Simulations in PSCAD/EMTDC and MATLAB show that the proposed method can distinguish faults accurately and effectively.

The Research on Grounding Protection for 110kV Resistance Grounding Distribution System

Using the neutral grounding method by the resistance in 110?kV system, it can limit the voltage sag and short circuit current when one-phase grounding fault occurred, but it will change the sequence of the network structure and parameters. This paper analyzes the size and distribution of zero sequence voltage and current when one-phase grounding fault occurred in the 110 kV resistance grounding system, and puts forward the grounding protection configuration setting principle of this system combining the power supplying characteristics of 110?kV distribution network. In a reforming substation as an example, the grounding protection of 110 kV lines and transformer have been set and calculated.

Advancement in Wide Area Monitoring Protection and Control Using PMU’s Model in MATLAB/SIMULINK

A big step forward to improve power system monitoring and performance, continued load growth without a corresponding increase in transmission resources has resulted in reduced operational margins for many power systems worldwide and has led to operation of power systems closer to their stability limits and to power exchange in new patterns. These issues, as well as the on-going worldwide trend towards deregulation of the entire industry on the one hand and the increased need for accurate and better network monitoring on the other hand, force power utilities exposed to this pressure to demand new solutions for wide area monitoring, protection and control. Wide-area monitoring, protection, and control require communicating the specific-node information to a remote station but all information should be time synchronized so that to neutralize the time difference between information. It gives a complete simultaneous snap shot of the power system. The conventional system is not able to satisfy the time-synchronized requirement of power system. Phasor Measurement Unit (PMU) is enabler of time-synchronized measurement, it communicate the synchronized local information to remote station.

Special Problems in Pilot Protections of Transmission Lines Connecting Wind Farms

As the penetration of wind power into power grids increases,higher demands are made on the stability and protection of power systems.Unlike traditional synchronous generators,wind turbines are different on the short-circuit and impedance characteristics,thus some problems exist in pilot protections of transmission lines connecting wind farms.When a single-phase fault occurs on a transmission line,the phase selector based on current-difference sudden-change may mistake the single-phase fault for a phase-to-phase fault.This paper studies the impedance characteristics of an asynchronous wind generator,and analyzes the behavior of a fault phase selector under different conditions.Then,the paper explains that inequality between positive and negative branch coefficients is the cause for the mal-operation of the fault phase selector.Finally,some simulations are done in MATLAB to validate analysis results.

Accident of Large-scale Wind Turbines Disconnecting from Power Grid and Its Protection

There were many accidents of large-scale wind turbines disconnecting from power grid in 2011.As singlephase-to-ground fault cannot be correctly detected,single-phase-to-ground fault evolved to phase-to-phase fault.Phase-to-phase fault was isolated slowly,thus leading to low voltage.And wind turbines without enough low voltage ride-through capacity had to be disconnected from the grid.After some wind turbines being disconnected from the grid,overvoltage caused by reactive power surplus made more wind turbines disconnect from the grid.Based on the accident analysis,this paper presents solutions to above problems,including travelling waves based single-phase-to-ground protection,adaptive low voltage protection,integrated protection and control,and high impedance fault detection.The solutions lay foundations in theory and technology to prevent large-scale wind turbines disconnecting from the operating power grid.

风电场集电线路单相接地故障柔性电压消弧与动态保护新原理

为解决风电场集电系统长期存在的线路单相接地故障处理难题,提出风电场中性点柔性接地方式,理论推导获得柔性接地风电场三序等效电路,与集电线路单相接地故障复合序网模型,建立风电场零序电压柔性调控理论,提出集电线路单相接地故障柔性电压消弧方法,可主动将故障点电压及故障残流迅速抑制到零,实现单相接地故障电弧的可靠消除。进一步提出基于零序电流动态增量的高阻故障辨识与保护方法,通过柔性调控零序补偿电流,逐渐放大故障残流,实现永久性单相接地故障的灵敏感知与保护。利用PSCAD/EMTDC搭建含双馈异步风电机(doubly-fedinduction generator,DFIG)的规模化风电场模型,模拟多种运行与故障条件对所提方法进行验证,仿真结果表明,该方法能够在考虑系统不平衡电压的情况下精准调控集电线路故障点电压,实现瞬时性单相接地故障快速可靠消弧,动态感知并持续抑制永久性单相接地故障残流,实现集电线路高阻接地故障的灵敏保护。该技术有望提升风电场运行灵活性与故障防御能力,有力保障新能源电能外送的持续性、可靠性。

相变储能材料在建筑工程建设中的应用

相变储能材料能与建筑材料复合实现节能效果。合理开发利用相变储能材料是优化居住空间、推动建筑领域绿色发展的有效途径。本文综述了相变储能材料的概念、分类及应用价值,介绍了相变储能材料在建筑中的节能原理,并具体阐释了相变储能材料的应用领域。

对称故障下变流器控制对差动保护影响及优化策略

变流器输出故障特征的强可控性给交流系统继电保护带来了严峻挑战。该文分析并网线路发生对称故障时跟网型变流器的控制响应过程,从故障期间变流器电流控制目标不能自动匹配故障回路功率需求的角度,分析推导变流器网侧电压相位发生跳变并不断旋转的变化特征。受故障回路阻抗约束,变流器输出短路电流相位与网侧电压相位同步变化,造成并网线路差动保护性能严重下降。基于变流器网侧电压相位变化机理,从电流控制目标与锁相环控制两个维度,提出兼顾保护需求和供电需求的变流器控制优化策略。仿真结果表明,并网线路对称故障时所提策略能有效抑制两侧电流相位差,显著提升了差动保护动作性能。

构网控制目标下系统故障特征及保护性能

分析了构网目标下的典型同步控制及故障穿越策略,提出了构网型变流器在故障分析时的等效电路。在此基础上,在相量平面分析了含构网型变流器系统稳态运行及各类故障工况下的电气量特征,指出构网控制目标下的故障特征与传统同步机系统的异同。重点针对当前电网中主流配置的电流差动保护与距离保护开展构网控制目标下的动作性能评估,并通过构建PSCAD仿真模型验证理论研究结果。分析表明,相比于传统跟网型控制,构网变流器控制技术通过模拟同步发电机的基本特性,为系统中的继电保护创造了一个相对良好的运行环境,有利于提高保护整体动作性能。

适用于双馈风电场送出线的纵联方向保护研究

考虑风电场接入电网时,传统方向元件在短路故障发生时易受到风电场内部电力电子器件动态特性的干扰影响,导致频率特性偏移,系统参数不稳定和弱馈性等问题,使继电保护装置不能及时或正确判断故障发生区域。针对上述问题,首先对含有风电场的故障附加网络进行分析,寻找故障发生后纵联保护安装处各测量点电气量之间的关联性,确定其故障逻辑关系。其次通过对常用的相模变换解耦方式进行分析,选择一个合理的方法代入相关性表达式,根据相关系数值完成故障区域判定。最后利用PSCAD/EMTDC搭建双馈风电场并网模型,设置各种不同的故障类型和场景,并利用Matlab进行保护算法验证,检验故障区域判断结果,验证所提保护方法的正确性与合理性,并且仿真结果表明该方法具有较高的可靠性。

基于初始电流行波相位的多端混合直流线路单端保护方案

为了解决LCC-MMC型多端混合直流系统线路保护存在的问题,提出一种基于初始电流行波相位的多端混合直流线路单端保护方案。首先基于多端混合直流输电线路发生不同位置和类型的故障工况,推导直流线路入射电压行波的解析式并计算其高频段相位。其次结合线路边界行波折反射原理和测量波阻抗特性,提出利用初始电压行波相位的区内外识别判据,并根据雷击和短路故障的入射行波低频相位特性构建雷击干扰判据。在PSCAD/EMTDC中搭建昆柳龙多端混合直流系统模型进行验证,证明所提方案仅利用单端量信息即可满足故障判断和选线要求,满足速度性的同时具备一定的抗过渡电阻能力(500Ω)。

通信限制下多DG接入配网的新型电流差动保护

差动保护是解决分布式电源(distributed generation, DG)接入下配电网保护难题的有效手段,然而配网现有通信建设水平很大程度上制约了差动保护的构建。首先,融合电流相位与相量差动保护思想,同时将电流相位信息进行变换,实现通信信息降容。应用递推最小二乘法实现短路电流相位参数的快速估计,提出了短路电流相位修正策略,以应对CT饱和与直流分量对保护的干扰。最后,提出适用于含多DG配网的新型电流差动保护构建原则与保护判据。基于PSACD/EMTDC平台搭建仿真模型,验证了所提出的电流相位参数预测方法的精度与新型差动保护的性能。算例结果表明:所提电流相位参数预测方法速度快、精度高,具有良好的抗CT饱和能力;所提新型差动保护原理具有良好的性能。

大型抽水蓄能发电电动机变压器组保护的研发与应用

针对抽水蓄能机组的特点,本文给出了发电电动机变压器组保护的配置方案;介绍了基于采样数据源分区的全工况保护算法,满足抽水蓄能机组保护算法的需求;提出了抽水蓄能机组工况综合判别方法,引入断路器、电气隔离开关以及监控信息的双位置辅助接点,同时设计了一种状态机机制、电气量辅助判别和开关位置报警功能,保证了抽水蓄能机组工况识别的准确性和可靠性;介绍了一种电气量和开入量综合判别的相序保护方案。研制的发电电动机变压器组保护装置已在300MW抽水蓄能机组投入应用,应用效果良好。

卫星用高能激光防护技术发展现状

高能激光技术不断发展,逐渐成为卫星在轨安全的威胁。介绍了高能连续激光和脉冲激光武器对卫星损伤机制的研究进展。针对卫星太阳电池阵、相机、星敏感器等光学系统以及热控多层、复合材料推进剂储箱等非光学关键结构防护特点,总结分析了线性光学防护薄膜、非线性光学防护薄膜、相变材料、机械快门、高损伤阈值薄膜和防护罩等各种高能激光防护技术的主要原理、发展现状和技术特点。