Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

Macro Impact of the Law on Prevention and Control of Atmospheric Pollution on Power Industry Development

The newly revised and enlarged main contents of the Law of Prevention and Control of Atmospheric Pollution are described, The macro impacts of the law on the power industry development are analyzed mainly in respects to power demand and readjustment of power structure and layout. clean production and pollution control level, scientific management of environmental protection, in accordance with law as well as changes of construction and operation costs. And finally, several questions worthy to be noted in course of implementation of the new law are enumerated.

Serial Failure Diagnosis of a Transmission Line Protection Relaying System by Petri Nets

With the development of large-scale complicated modern power systems, the requirement for the associated protection scheme tends to be more stringent and its combination more complex. However, it is very difficult to figure out the factors of failure of such systems. This paper proposes a Petri net model of a transmission line protection relaying system, including three types of relays as well as an automatic reclosing device, and shows how to diagnose serial failure of the system by analyzing invariant sets of the model. Furthermore, it gives four basic types of failure sequences and its execution is much more intuitive and effective than the traditional method.

Adaptability of the Recloser-Fuse Protection Scheme in the Presence of Distributed Generation

This paper addresses the behaviour of an IEEE(Institute of Electrical and Electronics Engineers)test network when distributed injections are added to the distribution network.The penetration of different dispersed generation technologies,modifies the distribution system characteristics,with impact on a number of parameters,depending on their size and location on the network.For this purpose,this paper comprises three case studies:in the first case an exhaustive analysis is carried out of the occurrence of faults throughout the network,along with the introduction of distributed generators;in the second case the network behavior is assessed against the use of three of the most commonly used types of generators based on rotating machines;in the third case study an evaluation is made of the network performance when the three types of DG(distributed generation)units are distributed in multiple buses.In all cases the protection system is analyzed with the aim of ensuring coordination among the protection devices.All simulations are performed using the Power Factory software package from DigSILENT.From the simulation results,conclusions are drawn that provide insights into the behaviour of protection systems,highlighting the limitations of the original protections and coordination with different distributed generators technologies.

Assessment of the impact of a 10-MW grid-tied solar system on the Libyan grid in terms of the power-protection system stability

The energy market in Libya is expected to face substantial changes in the next few years:electrical energy consumption will increase by 50% within the next 4 years.Therefore,there is a plan to gradually increase renewable energy sources in the power network by 2030 to 30%.Solar photovoltaic(PV)plants will play a significant role in the energy transition and the mix of energy sources in Libya.This article is a study conducted to investigate the challenges of power-flow management and power protection from integrating PV power plants into the Libyan power grid.In particular,a simulation model is built for the Kufra PV power plant(10 MW)with eight buses to assess the power network performance in terms of power quality such as voltage profile,power losses and harmonics.Furthermore,the impact of the PV plant on the short-circuit level and the power-protection system is presented under different operating conditions.The fault ride-through(FRT)is operated using standard ambient temperature and a wide range of irradiation intensity,and is verified by using the Libyan grid code.The results show that the integration of the PV plant into the grid has a significant impact on the short-circuit level and the FRT over the different fault levels and locations on the network.The initial period of the three-phase fault shows that the PV plant will be disconnected from the grid due to a decrease in the root mean square value voltages where the reactive and active power of the grid reach 938 MVAR and 261 MW,respectively.These results show that increasing the fault level will lead to an increase in injecting the active power.This work is considered the first extensive investigation into the challenges of modern power-flow management and power protection for the power network system in Libya.

On the Development of China's Thermal Power in the 21st Century while Saving the Energy and Protecting the Environment

In light of China s Ninth Five-year Plan (1996-2000) for Electric Power Industry & the Long Term Targets by the Year 2010, the paper considers the strategy for developing China’s thermal power in the 21st century shall be the efficiency and cleaning technology of coal use. Especially important is the structure of power sources and configuration of technology process, and secondly the implementation of energy saving and environmental protection ideology in the various stages of thermal power construction and design work.

A micro-power LDO with piecewise voltage foldback current limit protection

To achieve a constant current limit,low power consumption and high driving capability,a micro-power LDO with a piecewise voltage-foldback current-limit circuit is presented.The current-limit threshold is dynamically adjusted to achieve a maximum driving capability and lower quiescent current of only 300 nA.To increase the loop stability of the proposed LDO,a high impedance transconductance buffer under a micro quiescent current is designed for splitting the pole that exists at the gate of the pass transistor to the dominant pole,and a zero is designed for the purpose of the second pole phase compensation.The proposed LDO is fabricated in a BiCMOS process. The measurement results show that the short-circuit current of the LDO is 190 mA,the constant limit current under a high drop-out voltage is 440 mA,and the maximum load current under a low drop-out voltage is up to 800 mA. In addition,the quiescent current of the LDO is only 7μA,the load regulation is about 0.56%on full scale,the line regulation is about 0.012%/V,the PSRR at 120 Hz is 58 dB and the drop-out voltage is only 70 mV when the load current is 250 mA.

我国乳业社会性规制现状及改革——阜阳奶粉事件的回顾与反思

从源头上说,食品安全问题真正引起人们关注是始于"阜阳奶粉事件"。尽管其过去多年,但从中反映出来的问题确是具有普遍意义的。在回顾与反思"阜阳奶粉事件"基础上,本文揭示了这一事件产生的根本原因就在于地方保护主义。针对于此,提出了解决这一问题的对策。

司法权中央化改革的误区及修正

推动地方法院人财物的省级统管和设立跨行政区划法院等改革部署彰显出司法权中央化的改革趋向。这种中央化改革的理路背后存在两大误区,即司法权是中央事权、地方化导致司法地方保护。中央化改革将产生冲击基本宪政秩序、损害法治生态多样性、加剧司法系统内部行政化等预料外后果。修正司法中央化改革的路径在于激活地方人大监督职能、改造专门法院系统、保障审级双向独立、落实法官履职保护等。

司法地方化的治理路径研究及创新——以文献分析为视角

破除司法地方化存有两条治理思路:一是针对产生司法地方化的直接原因变革现存制度障碍;二是通过司法系统的其他改革间接实现司法地方化的治理。当前学术界的关注点几乎聚焦于变革现存制度障碍上,然而该思路下的治理路径须以完善司法官以外的司法工作者人事制度、立法固定司法工作者薪酬制度、构建人民检察机关异地检察制度以及推进司法工作者处理案件终身责任制度等方式强化。忽视第二条治理思路无疑减少了防治司法地方化的路径,而由此可通过创新程序设计,如推进司法公开制度改革等,从侧面攻克司法地方化难题。

Characteristic Analysis of UHVAC/DC Hybrid Power Grids and Construction of Power System Protection

Strong DC coupling with weak AC and large-scale renewable energy integration are the two significant characteristics of ultra-high-voltage AC/DC(UHVAC/DC)hybrid power grids in China.Strong coupling between AC and DC grids and the different integration performance of renewable energy sources have profoundly changed the stability characteristics of the power system.The traditional stability control system is inadequate for the stability control of UHVAC/DC power grids.This paper analyzes the requirements for constructing an integrated defense system in a UHVAC/DC hybrid power grid(i.e.power system protection).The definition,connotation,and designing principles of power system protection are put forward.The relationship between the power system protection and the traditional three-defense lines is investigated.The design principles,general hardware structure and main functions of a power system protection are presented.Key problems and technologies are specified in the construction of the power system protection.

Improving the performance of power system protection using wide area monitoring systems

Wide area monitoring(WAM) offers many opportunities to improve the performance of power system protection. This paper presents some of these opportunities and the motivation for their development. This methods include monitoring the suitability of relay characteristics,supervisory control of backup protection, more adaptive and intelligent system protection and the creation of novel system integrity protection scheme. The speed of response required for primary protection means that the role WAM in enhancing protection is limited to backup and system protection. The opportunities offered by WAM for enhancing protection are attractive because of the emerging challenges faced by the modern power system protection. The increasingly variable operating conditions of power systems are making it ever more difficult to select relay characteristics that will be a suitable compromise for all loading conditions and contingencies. The maloperation of relays has contributed to the inception and evolution of 70 % of blackouts,thus the supervision of the backup protection may prove a valuable tool for preventing or limiting the scale of blackouts. The increasing interconnection and complexity of modern power systems has made them more vulnerable to wide area disturbances and this has contributed to several recent blackouts. The proper management of these wide area disturbances is beyond the scope of most of the existing protection and new, adaptive system integrity protection schemes are needed to protect power system security.

Developments of power system protection and control

Synchronized wide area communication has become a mature technology,which makes the real-time interaction between the substations and the wide area protection and control system possible.However,the present protection and control system to handle this real-time data has been recognized to be deficient.This paper begins by reviewing the development history of power system protection,with special attention paid to the recent development in the field of wide-area and integrated protections,in order to look into the future development of protection and control systems.Then the concept of integrated wide area protection and control is introduced,where it can be shown that a hierarchical protection and control system provides the protection and control for wide area or regional power substations/plants and their associated power networks.The system is mainly divided into three levels:the local,the substation/plant,and the wide area/regional.The integrated functions at each level are described in details with an aim to develop an optimal coordination mechanism between each level.The key element in the proposed system is the wide area real-time protection and control information platform,which not only enables the merger of three lines of defence for power system protection and control,but also provides a perfect tool for the application of cloud computing in substations and power networks.

Developing a power monitoring and protection system for the junction boxes of an experimental seafloor observatory network

A power monitoring and protection system based on an embedded processor was designed for the junction boxes(JBs) of an experimental seafloor observatory network in China. The system exhibits high reliability, fast response, and high real-time performance. A two-step power management method which uses metal-oxide-semiconductor field-effect transistors(MOSFETs) and a mechanical contactor in series was adopted to generate a reliable power switch, to limit surge currents and to facilitate automatic protection. Grounding fault diagnosis and environmental monitoring were conducted by designing a grounding fault detection circuit and by using selected sensors, respectively. The data collected from the JBs must be time-stamped for analysis and for correlation with other events and data. A highly precise system time, which is necessary for synchronizing the times within and across nodes, was generated through the IEEE 1588(precision clock synchronization protocol for networked measurement and control systems) time synchronization method. In this method, time packets were exchanged between the grandmaster clock at the shore station and the slave clock module of the system. All the sections were verified individually in the laboratory prior to a sea trial. Finally, a subsystem for power monitoring and protection was integrated into the complete node system, installed in a frame, and deployed in the South China Sea. Results of the laboratory and sea trial experiments demonstrated that the developed system was effective, stable, reliable, and suitable for continuous deep-sea operation.

A Technical Review of Hydro-Project Development in China

This paper summarizes the development of hydro-projects in China,blended with an international perspective.It expounds major technical progress toward ensuring the safe construction of high dams and river harnessing,and covers the theorization of uneven non-equilibrium sediment transport,inter-basin water diversion,giant hydro-generator units,pumped storage power stations,underground caverns,ecological protection,and so on.

为什么关税保护比汇率低估更为常见?

汇率低估与关税保护具有相似的经济效果,而且本币汇率低估可以使本国企业在国际市场上更具竞争优势,但是多数国家都选择了汇率高估政策。这是因为关税保护政策作为更精准的保护主义工具,可以选择性地实施,不会增大企业成本,更为权势利益集团偏好;而汇率低估政策作为普惠性的保护主义工具,较为迟钝而且有可能增加企业成本,因此无法得到更多的使用。

Human reliability analysis in maintenance team of power transmission system protection

The requirement for reliable electrical energy supply increases continuously because of its vital role in our lives.However,events due to various factors in the power grid can cause energy supply to be interrupted.One of these factors is human error and thus human reliability analysis is a serious element in the industry.The first step is to identify the roots of human error,on which there has been limited research in this area.In this paper,the potential and actual causes of human error in maintenance teams of power transmission system protection are identified and predicted within a framework of human factors analysis and classification system method.Then,human error factors are ranked to help improve human reliability.The proposed method is implemented in the Fars Electricity Maintenance Company.

Fault Location Method for STATCOM Connected Transmission Lines Using CCM

Determining the fault location using conventional impedance based distance relay in the presence of FACTS controllers is a challenging task in a transmission line. A new distance protection method is developed to locate the fault in a transmission line compensated with STATCOM with simple calculations. The proposed protection method considers the STATCOM injected/absorbed current to correct the fault loop apparent impedance and accordingly calculates the actual distance to the fault location. The comprehensive equations needed for apparent impedance calculation are also outlined and the performance is evaluated and tested with a typical 400 KV transmission system for different fault types and locations using MATLAB/SIMULINK software. The evaluation results indicate that the new protection method effectively estimates the exact fault location by mitigating the impact of STATCOM on distance relay performance with error less than 0.3%.

A Niche-Based Evolutionary Tabu Search Algorithm for Optimal Coordination of Protection Relays in Power Networks

In this paper, refusal of operation and the degree of constraint violation are considered as one part of the objective function for optimizing the protection relay setting coordination of over current relays in power systems; a new expression of objective function in this optimization problem is proposed. To combine the advantages of both Tabu search （TS） and evolutionary algorithms （EAs）, a new niche-based evolutionary Tabu search algorithm （named NETS） is presented to solve this optimization problem. Moreover, in two cases of power networks, comparisons between NETS and two published algorithms are given. Experimental results show the expression of the objective function for protection relay setting is feasible and reasonable, and the proposed algorithm NETS exhibits a good performance.