发电机失磁保护阻抗元件定值整定的再讨论——对2007年版《IEEE Guide for AC Generator Protection》的斟酌

发电机失磁保护阻抗元件定值整定中,始终存在防误动和加速动作的矛盾。根据理论分析和运行实践,认为解决矛盾应从阻抗平面的R轴方向扩大阻抗动作区,即将理论上的汽轮发电机静稳边界功角90°,减小为实用的静稳边界功角55°～65°,与此同时,增设无功反向元件。从-X轴方向扩大动作区,以求加速失磁保护动作的做法,缺乏理论依据且欠有实效。

发电机失磁保护定值整定的讨论--对2007年版《IEEE Guide for AC Generator Protection》的斟酌

对2007年版《IEEE Guide for AC Generator Protection》中失磁保护定值整定的几个问题提出不同意见。明确指出:发电机失磁故障必有滑差(s),其平均异步阻抗Xd(js)Xd(s=0),失磁保护中的阻抗元件下端定值为-Xd,已有足够余度,不应该是-(1.1～1.25)Xd;在P-Q坐标与R-X坐标的转换公式中,U值应由"失磁保护动作滞后于低励限制线(UEL)"原则来确定,不应主观选择0.95UN。

Designing a Protection Scheme in Micro-Grid Systems with DG Using Central Protection Unite and Multiple Setting Group Protection Relays

Distributed generators now is widely used in electrical power networks, in some cases it works seasonally, and some types works at special weather conditions like photo voltaic systems and wind energy, and due to this continuous changes in generation condition, the fault current level in network will be affected, this changes in fault current level will affect in the coordination between protection relays and to keep the coordination at right way, an adaptive protection system is required that can adaptive its setting according to generation changes, the fault current level in each case is evaluated using ETAP software, and the required relay setting in each case is also evaluated using Grey Wolf Optimizer (GWO) algorithm, and to select suitable setting which required in each condition, to select the active setting group of protection relay according to generation capacity, central protection unite can be used, and to improve protection stability and minimizing relays tripping time, a proposed method for selecting suitable backup relay is used, which leads to decrease relays tripping time and increase system stability, output settings for relays in all cases achieved our constrains.

A Self-Powered Nanogenerator for the Electrical Protection of Integrated Circuits from Trace Amounts of Liquid

With the increase in the use of electronic devices in many different environments,a need has arisen for an easily implemented method for the rapid,sensitive detection of liquids in the vicinity of electronic components.In this work,a high-performance power generator that combines carbon nanoparticles and TiO2 nanowires has been fabricated by sequential electrophoretic deposition(EPD).The opencircuit voltage and short-circuit current of a single generator are found to exceed 0.7 V and 100μA when 6μL of water was applied.The generator is also found to have a stable and reproducible response to other liquids.An output voltage of 0.3 V was obtained after 244,876,931,and 184μs,on exposure of the generator to 6μL of water,ethanol,acetone,and methanol,respectively.The fast response time and high sensitivity to liquids show that the device has great potential for the detection of small quantities of liquid.In addition,the simple easily implemented sequential EPD method ensures the high mechanical strength of the device.This compact,reliable device provides a new method for the sensitive,rapid detection of extraneous liquids before they can impact the performance of electronic circuits,particularly those on printed circuit board.

Effects of Wind Turbines Equipped with Doubly-fed Induction Generators on Distance Protection

Nowadays wind energy is the fastest growing renewable energy resource in the world.The problems of integrating wind farms are caused by changes of wind speed during a day.Moreover,the behaviors of wind turbines equipped with doubly-fed induction generators differ fundamentally from synchronous generators.Therefore,more considerations are needed to analyze the performances of the distance protection relays.The protection of a wind farm with distance relay is inspected.By changing the conditions of the wind farm,the characteristics of the distance relay are studied.

Research on Technology of Electromagnetic Protection for the Generator Control System

Generator control system decides whether the generator can work as usual or not, as well as its stability of performance. Both types of generators control system composed of the transistor and DSP are sensitive to outward electromagnetic interference, directly related to the generator performance. In this text, we first analyze the electromagnetic interference threat generator control system of transistor type may face, then design a electromagnetic protection plan for the intake, the panel and the sense organ. This work is of great significance in improving its electromagnetic protection ability and stability of performance.

Numerical Protection System Design for Large Hydraulic-Generator In Three Gorges Hydropower Station

Domestic generators will be used in ThreeGorges Hydropower Station in the future, this paper introduces the corresponding protection system design for them, including the special requirements and the configuration of the protection system. To increase compactness and reduce relay cost, the protection equipment will adopt the dual-system structure with a manager system and several subsystems considering the protection funcition redundancy. Some special function principles and methods, the communications, the protection modules and the managing system are also discussed in detail.

Coordination between Fault-Ride-Through Capability and Over-current Protection of DFIG Generators for Wind Farms

Fault Ride-Through （FRT） capabilities set up according to the grid codes may affect the performance of related protective elements during fault periods. Therefore, in this paper the coordination between the FRT capability and over-current protection of DFIG Wind Generators in MV networks is investigated. Simulation test cases using MATLAB-Simulink are implemented on a 365-MW wind farm in AL-Zaafarana, Egypt. The simulation results show the influence of the FRT capability on the protective relaying coordination in wind farms, showing that the FRT may work in situations where is were expected not to work, and then disabling the over-current protection, which should have worked in this situation.

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.

A NEW APPROACH TO TRANSMISSION SYSTEM PROTECTION WITH FRULT GENERATED NOISE

The use of non-power frequency components for protection measurements in an area that has received relatively little attention. Although work on the use of switched stack tuners has been reported for fault detection, the sensitivity of switched arrangements is limited by scnsitivity of directional detectors for switching purposes. This paper presents an alternative non-switching scheme which is relatively simple.A simplified typical 400kV system with the line trap, stack tuner, coupling capacitor and bus capacitance to earth is considered. Fault studies by using the EMTP have been carried out, frequency-dependent pararnctcrs are used for the line representation. Arcing faults have also bccn investigated and the results show a great promise of the scheme.

A Comprehensive Review of Protection Schemes for Distributed Generation

Due to the increasing demand of energy and the need for nonconventional energy sources, distributed generation (DG) has come into play. The trend of unidirectional power flow has been gradually shifting. With new technology comes new challenges, the introduction of DG into the conventional power system brings various challenges;one of the major challenges is system protection under DG sources. These sources pose a significant challenge due to bidirectional flows from DGs as well as lower fault current contribution from inverter interfaced DGs. This paper reviews existing protection schemes that have been suggested for active distribution networks. Most of these protection strategies apply only to smaller distribution systems implying that they may need to be extended to larger systems with a much higher penetration of distributed generation. In the end, a potential protection scheme has also been recommended as a future work.

Protection of Distributed Generation: Challenges and Solutions

Distributed generation (DG) is the future of energy. This technology allows the bidirectional flow of power within an electrical network. Researchers are faced with many challenges to the accurate implementation of protection schemes for DG-connected distribution network. The schemes designed must satisfy the performance requirements of selectivity, reliability, and sensitivity. Most researchers opine that conventional protection schemes based on over current detection are insufficient to completely and accurately protect a DG-connected distributed power system. There are many challenges?that?need to be tackled before embarking upon the journey to successfully implement these schemes. This paper summarizes the major challenges which one can encounter while designing protection schemes for DG-connected distribution networks. Some possible solutions from the literature are also mentioned. Moreover, a suggested solution for protecting future active distribution networks is provided. It is expected that this paper will act as a benchmark for future researchers in this field to tackle the challenges related to the protection of active distribution networks.

A Generalized Location Privacy Protection Scheme in Location Based Services

When the user getting location based services by the traditional technology,his location information of region is always be exposed.However,in modern mobile networks,even the current geographical region is a part of privacy information.To solve this problem,a new generalized k-anonymity location privacy protection scheme in location based services(LPPS-GKA)with the third trust servicer is proposed.And it can guarantee the users get good location-based services(LBS)without leaking the information of the geo-location region,which has protected the perfect privacy.Analysis shows that LPPS-GKA is more secure in protecting location privacy,including region information,and is more efficient than other similar schemes in computational and communicational aspects.It is suitable for dynamic environment for different user’s various privacy protection requests.

Testing of Lightning Protective System of a Residential Structure： Comparison of Data Obtained in Rocket-triggered Lightning and Current Surge Generator Experiments

We present a comparison of data obtained during testing of lightning protective system of a residential structure in rocket-triggered lightning experiment at the International Center for Lightning Research and Testing(ICLRT)at Camp Blanding,Florida,and current surge generator experiment at Rzeszow University of Technology in Poland.Three different configurations of LPS were tested in Poland with the dc grounding resistances of the entire system 4.09 Ω(LPS 1a),1.65 Ω(LPS 1b),and 2.88 Ω(LPS 2).For LPS 1a with three ground rods the value of the peak current entering the electrical circuit neutral was about 56% of the injected current peak,and for LPS 1b with two additional ground rods and two 5 m long buried horizontal conductors it was about 16%.For LPS 2 with five ground rods interconnected by a buried loop conductor this ratio was 21%.The current waveshapes in the ground rods differed from the injected current waveshapes and the current waveshapes in other parts of the test system,especially,for poorer-grounding LPS 1a.The surge-generator results are consistent with those of triggered-lightning experiments at Camp Blanding,Florida(DeCarlo et al.,2008 [2]).

Corrosion Prevention of the Generator Stator Hollow Copper Conductor and Water Quality Adjustment of Its Internal Cooling Water

On the basis of expounding the corrosion mechanism of the stator hollow copper conductor in the water-cooling generator, methods of preventing corrosion of the stator hollow copper conductor in the wa-ter-cooling generator through adjusting water quality of its cooling water have been proposed. For internal water cooling systems which are airtight, the corrosion of the hollow copper conductor can be prevented through keeping foreign oxygen and carbon dioxide from entering the system, and the amount of oxygen in the internal water can be lowered by blowing high purity nitrogen. For systems not airtight, the corrosion of the hollow copper conductor can be inhibited through lowering the amount of oxygen to some extent by sealing and increasing pH value by processing part of cooling water with bypass small flow sodium-type mix-bed.

Dynamic shared segment protection algorithm with differentiated reliability in GMPLS networks

To improve the resource utilization ratio and shorten the recovery time of the shared path protection with differentiated reliability （SPP-DiR） algorithm, an algorithm called dynamic shared segment protection with differentiated reliability （DSSP-DiR） is proposed for survivable GMPLS networks. In the proposed algorithm, a primary path is dynamically divided into several segments according to the differentiated reliability requirements of the customers. In the SPP-DiR algorithm, the whole primary path should be protected, while in the DSSP- DiR algorithm, only partial segments on the primary path need to be protected, which can reduce more backup bandwidths than that in the SPP-DiR algorithm. Simulation results show that the DSSP-DiR algorithm achieves higher resource utilization ratio, lower protection failure probability, and shorter recovery time than the SPP-DiR algorithm.

Integrated dynamic shared protection algorithm for GMPLS networks

The path protection approach is widely investigated as a survivability solution for GMPLS networks, which has the advantage of efficient capacity utilization. However, there is a problem of the path protection approach that searching a disjoint backup path for a primary path is often unsuccessful. In order to resolve this problem, an integrated dynamic shared protection （IDSP） algorithm is proposed. The main idea of the proposed algorithm is that the path protection approach is first used to establish a backup path for the primary path; if the establishment is unsuccessful, then the primary path is dynamically divided into segments whose hop count are not fixed but not more than the limitation calculated by the equations introduced. In this proposal, backup bandwidth sharing is allowed to improve the capacity utilization ratio, which makes the link cost function quite different from previous ones. Simulation experiments are presented to demonstrate the efficiency of the proposed method compared with previous methods. Numerical results show that IDSP can not only achieve low protection failure probability but can also gain a better tradeoff between the protection overbuild and the average recovery time.

Impact Analyses of Wind Farm on Performances of Transmission Line Relay Protection

A simulation system for power grid with concentrated large-scale wind farm integration is established based on the electro-magnetic transient model of wind turbine equipped with doubly-fed induction generator (DFIG),which is built by real-time digital simulator (RTDS).Using the hardware communication interface of RTDS,a closed-loop testing experiment is accomplished to study the impacts of large-scale wind farms on the existing relay protection devices for wind farm outgoing transmission line.This paper points out problems existing in current relay protection devices as follows:fault phase selector can select unwanted phase due to the changes of fault features caused by special network connection of wind farms;blocking condition for distance protections needs to be re-examined due to the weak power-feed characteristics of wind farms;and power frequency parameter based relay protection devices cannot accurately operate due to the special transient voltage and current characteristics of wind farms during fault period.Results lay the foundation for improving the performances of the existing relay protection device and developing new principle relay protection.

Short-circuit Current Characteristics of Wind Generators

To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreement has not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation is performed in the same system integrated with different kinds of wind generators,and their results are compared with those reported in IEEE papers.The detection possibility by overcurrent relay(OCR)is discussed based on the simulation results.

ABSTRACTSR-esearch on vibration protection strategy of large rotating machinery at hydropower station

The vibration protection strategy of large rotating machinery in thermal power and petroleum industry hasbeen applied for many years, but it still develops without breakthrough in hydropower unit operation due to thecomplication of its operation and vibration. According to this situation, the vibration protection strategy is proposedbased on the analysis of unit vibration mechanism. The vibration protection strategywith two functions of timelyprotection and fault diagnosis are of great engineering application value.