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Effects of morphology on movement of space charge packet in polyethylene

Gaodianya Jishu/High Voltage Engineering 2008年第11期34卷 2385-2389页

作者： Zhou, Yuan-Xiang Wang, Yun-Shan Wang, Ning-Hua Sun, Qing-Hua Nie, Qiong Liang, Xi-Dong Guan, Zhi-Cheng State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Dept of Electrical Engineering Tsinghua University Beijing 100084 China China Electric Power Research Institute Beijing 100085 China

Polyethylene is a major kind of internal insulating material. This paper measured the space charge phenomenon in low-density polyethylene (LDPE) by the pulsed electro-acoustic (PEA) method and observed the space charge packet. This research got the LDPE films of different morphology by different annealing rate and discussed the effect of morphology and electrical field stress changing on space charge packet's moving velocity. The research shows that morphology of LDPE affects the velocity of space charge packet remarkably;bigger crystallinity results in lower velocity of space charge packet. The intensity of electrical field has little affection to the velocity. The average mobility of different crystallinity under different electric field was calculated. The relationship between crystallinity and mobility was found. The results further demonstrate there are inherent relationships among higher crystallinity, more space charge accumulation, lower mobility and deeper trap depth. Lower mobility and deeper trap depth have a monotone relationship.

关键词：空间电荷空间电荷包聚乙烯微观形态迁移率 PEA

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Optimal design of SVC-based subsynchronous damping control using genetic and simulated annealing algorithm

Optimal design of SVC-based subsynchronous damping control u...

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International Conference on Information and Automation (ICIA)

作者： Tingzhi Yang Xiaorong Xie Shiyu Liu Donghui Zhang State Key Laboratory of security control & simulation of power systems and large-scale generation equipments Department of Electrical Engineering Tsinghua University Beijing China

In this paper, an optimal approach based on genetic and simulated annealing algorithm (GASA) is prosposed to design more effective and robust subsynchronous damping control (SSDC) of Static Var Compensator (SVC) for multimodal SSR damping improvement. A practical multi-machine series compensated power system suffering multimodal SSR has been studied to demonstrate the effectiveness of the approach. The developed SSDC comprises independent modal control path, each with separate feedback gains and phase-shifts, to damp different torsional mode. The problem of simultaneously tuning all the control parameters for robust stabilization of multiple torsional modes over various system conditions is formulated into a standardized constrained optimization problem. With the proposed GASA, the problem is efficiently solved and the SVC SSDC is optimized. Both eigenvalue analyses and electromagnetic simulations have been conducted on the test system to validate the approach and the designed SVC-based SSDC.

关键词： Static VAr compensators Damping Generators Gallium power system dynamics Optimization power systems

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Study of Non-Conventional Instrument Transformer and IEC61850 impact on current differential protection

Study of Non-Conventional Instrument Transformer and IEC6185...

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IEEE/PES Transmission and Distribution Conference and Exposition: Latin America

作者： K. L. S. Shenxing X. Dong Z. Bo State Key Lab of Control and Simulation of Power System and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China Tsinghua University Beijing Beijing CN State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing China AREVA T&D Automation슠and Information Systems Stafford UK

Non conventional instrument transformer (NCIT) and IEC 61850 are crucial technologies in digital substations. But they bring some new uncertainties to protection IEDs, especially the time synchronization issue in current differential protection. The paper analyzes the time delay of transferring sampled values from NCIT to current differential relay in NCIT and IEC61850 based digital substation, then finds out the delay-non-deterministic problem, at last presents a novel current differential protection scheme by using phase-locked loops (PLL ) technology.

关键词： Substations Delay effects Ethernet networks Phase locked loops IEC Synchronization Data communication

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Current differential protection based on Non-Conventional Instrument Transformer and IEC61850

Current differential protection based on Non-Conventional In...

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International Universities power Engineering Conference (UPEC)

作者： Kun Liu Xinzhou Dong Zhiqian Bo State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing China AREVA T&D Automation슠and Information Systems Staffordshire UK

Non Conventional Instrument Transformer (NCIT) and IEC 61850 are crucial technologies in digital substations. But they bring some new uncertainties to protection IEDs, especially the time synchronization issue in current differential protection. The paper analyzes the time delay of transferring sampled values from NCIT to current differential relay in NCIT and IEC61850 based digital substation, then finds out the delay-non-deterministic problem, at last presents a novel current differential protection scheme by using Phase-Locked Loops (PLL ) technology.

关键词： Substations Delay effects Synchronization IEC Phase locked loops Data communication Ethernet networks

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Novel active damping control scheme for a three-phase active rectifier with LCL-filter

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Diangong Jishu Xuebao/Transactions of China Electrotechnical Society 2008年第9期23卷 86-91页

作者： Huang, Yuqi Jiang, Xinjian Qiu, Arui State Key Lab. of Security Control and Simulation of Power Systems and Large Generation Equipments Tsinghua University Beijing 100084 China

A novel active damping control scheme is developed to eliminate stability problems arisen in the current control of a three-phase voltage source active rectifier (VSR) with LCL-filter. A converter side inductance voltage feedback loop is introduced in the traditional voltage oriented control to stabilize VSR. A simplified discrete model including the current control loop and LCL-filter is established with one sample delay, considering time delays induced by S/H (sampling and holding), processing and modulation. The amplification coefficient of the converter side inductance voltage feedback loop is tuned up to change the unstable poles of LCL-filter. Parameter estimate methods are used to remove unnecessary sensors. simulation and experiment of VSR with LCL-filter demonstrate the proposed active damping control scheme and the stability analyses.

关键词： Inductance

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Maximum flow algorithm based on adjustment of net flow on nodes and its application

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2008年第SUPPL.期28卷 31-34页

作者： He, Guang-Yu Sun, Ying-Yun Chen, Chao State Key Lab of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Haidian District Beijing 100084 China

For calculating the maximum capacity transported from source node to sink node in a network, a maximum flow algorithm was proposed. Based on the concept of net flow on nodes (NFN) and layered increment network (LIN), the plus flow process (PFP) and minus flow process (MFP) on LIN were defined. By performing PFP and MFP on NLP over and over, the maximum flow problem was solved when the sink node can't get a mark again. Compare to the existing max flow algorithm, the proposed method needs no complex data structure in processing, which makes the algorithm implemented easily. Based on the algorithm, a thermal economic dispatch software package which includes fixed electricity plant was developed and had been put into practice and had a good performance. Furthermore, the algorithm runs in O(n2m) (n, m is the number of nodes and arcs of the network) was proved.

关键词： Scheduling

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Eigenvalue analysis of multi-mode sub-synchronous resonance for multimachine plant-to-grid transmission systems with fixed series compensation

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2008年第SUPPL.期28卷 13-18页

作者： Zhang, Shu-Qing Xie, Xiao-Rong Yang, Ting-Zhi Liu, Shi-Yu State Key Lab of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Haidian District Beijing 100084 China

For some domestic large thermal power plants delivering electric energy over long distances, the sub-synchronous resonance (SSR), which is induced by the fixed series compensation (FSC), attracts much attention. Eigenvalue analysis is one of the primary methods to assess the risk and explore the countermeasure. However, for handling multi-machine and multi-mode SSR problems, no practical toolkit based on eigenvalue analysis is on hand for the moment. In this paper, a systematic modeling approach and analysis flows for the purpose of eigenvalue analysis of multimachine plant-to-grid transmission systems with FSC were proposed. The equating technique of machines and networks was presented, and the effect of the q-axis damping windings on the SSR was also explored. The applicability of the proposed method was verified with an actual multimachine system. Furthermore, its advantage over existing SMIB based eigenvalue analysis was clarified by a comparative study between the original multi-machine system and the simplified single-machine system.

关键词： Eigenvalues and eigenfunctions

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Impedance fault location algorithm for UHV long transmission lines with single-line-to-ground faults

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Dianli Xitong Zidonghua/Automation of Electric power systems 2008年第14期32卷 25-29页

作者： Wang, Bin Dong, Xinzhou Bo, Zhiqian Klimek, Andrew State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China AREVA T and D Automation Co. Stafford ST17 4LX United Kingdom

Ultra-high-voltage (UHV) transmission lines (over 750 kV) normally have larger shunt capacitance and longer transmission radius, which impose limitations of direct application of traditional impedance algorithm. A novel impedance fault location algorithm is proposed for UHV transmission lines with single-line-to-ground faults due to higher voltage level than 750 kV. It is based on the precondition that the negative sequence current phase at meter location can precisely describe the phase information of negative current in fault path or fault voltage. The algorithm is immune to the influence of shunt capacitance with distributed parameters modeling for transmission line, and is not disturbed by fault resistance with fault location calculation at zero-crossing point of voltage at fault point. Theoretical analysis and simulation prove that the proposed method can guarantee good fault location accuracy, and fulfill the requirements in the field.

关键词： Electric lines

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H∞ analysis method for the small signal stability of power system

H∞ analysis method for the small signal stability of power ...

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26th Chinese control Conference, CCC 2007

作者： Mei, Shengwei Che, Wenyan State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)7900719229

This work is concerned with the small signal stability problem in multi-machine systems. By means of H∞ theory, firstly the math model with disturbances is constructed;and secondly, the excitation control law for each generator is designed based on solving Riccati Equation. Finally, simulations performed on 4-machine system shows that the proposed H ∞ method has more advantages over LQR method in both damping ratio and H∞ norm of the corresponding closed-loop system and so can enhance the small signal stability of power system greatly.

关键词： Electric power systems

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Breakdown phenomena caused by electrical tree degradation in high density polyethylene under high frequency voltage

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Gaodianya Jishu/High Voltage Engineering 2007年第12期33卷 14-18页

作者： Zhou, Yuan-Xiang Xing, Xiao-Liang Nie, Qiong Wang, Yun-Shan Wang, Ning-Hua Liang, Xi-Dong Guan, Zhi-Cheng State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China

The shape change of electrical tree propagating in ice-water quenched high-density polyethylene (HDPE) film under AC voltage of different frequency ranging from 50 Hz to 90 kHz as well as the breakdown phenomena caused by the treeing degradation under high frequency condition were studied. The electrical treeing aging experiment is carried out at room temperature. The shape change of electrical tree and the arcing process during the experiment is observed via a digital micro-observing system. It is found that the arcing process can be obviously observed under a high frequency voltage compared with that under low frequency voltage. It is also found that under different frequency voltages the electrical tree initiation shape is different. Most of the electrical trees are branch-shape tree under lower frequency voltage. When the frequency is higher than 5 kHz, trunk-shape tree and bosk-like tree appears. Once the frequency is higher than 50 kHz, breakdown tree can be found out. It is shown that the tree shape conversion is influenced by the frequency. The electrical tree usually has a simple shape and rarely changes under low frequency voltage in one hour or more. However, under a high frequency voltage, the electrical tree shape changes more frequently and has a large probability to breakdown. The influence of frequency on material polarization process, fatigue and thermo effect is considered as the main causes of the experiment results. The more serious destruction caused by high frequency electrical treeing degradation can well explain the reason of insulation premature inactivation in mid-frequency or high-frequency electrical equipment.

关键词：聚乙烯树老化电树形态转换击穿频率

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