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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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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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Vector control for a twelve-phase synchronous motor

Vector control for a twelve-phase synchronous motor

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International Conference on Electrical Machines and systems (ICEMS)

作者： Dejia Zhou Zhengming Zhao Shanming Wang Jianyun Chai State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering and Applied Electronic Technology Tsinghua University Beijing 100084 China State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Tsinghua University Beijing China

A twelve-phase synchronous motor with four Y-connected 3-phase symmetrical windings displaced in turn by 15deg is modeled by using flux linkages as state variables, and an optimized method for the vector control is proposed with the simulation results. The observing model for magnetizing flux linkage at the direct-axis is derived whereby a vector control scheme of a twelve-phase synchronous motor, and related simulation is constructed in this paper. Using switch blocks to model the functions of twelve-phase voltage-fed inverter is convenient for simulating the driving system. The results of the simulations show that the torque and magnetizing flux linkage can be controlled separately, and the dynamic characteristics of the motor are satisfied with the operating requirements.

关键词： Machine vector control Synchronous motors Couplings Magnetic separation Magnetic flux Switches Optimization methods Voltage Inverters Torque control

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Short-term Reliability Online Evaluation Basing On Transient state Probability

Short-term Reliability Online Evaluation Basing On Transient...

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IEEE General Meeting power& Energy Society

作者： Lin Cheng Haitao Liu Xin Zou Yuanzhang Sun Electrical Engineering Department at Tsinghua University Electrical Engineering School State Key Lab of Power System Control and Simulation Tsinghua University

The reliability of the power system in a future short term is studied according to the current state. Basing on this, we can alarm and prevent the outage to assure the safety and reliability of the power system. Traditional reliability is an expected value of long-term reliability level under the fixed operating mode, which cannot reflect the real time reliability level under the current operational state. This essay presents the novel conception and algorithm of online evaluating the short-term reliability in order to study the operational reliability level. The influence of the variable system states on the reliability level is reflected according to the real time operational information provided by the SCADA/EMS/WAMS. Markov process is adopted to solve the transient state probability of the components, so that forecasting the system state basing on the transient probability is possible. The probability of the system state and the reliability indices of the system changes as the time varying. The analysis and the assessment of IEEE RTS-79 system indicates that there are great differences between the short-term and long-term reliability indices, and only the transient probability evaluation can assess the short-term probability properly. In this paper the relationship between the enumerating number of the system states and the forecasting time is also studied. The result indicates that only a few system states are needed to get relative high degree of evaluation accuracy, which can be applied online. IEEE RTS-79 case study is calculated to verify this conclusion.

关键词： power system reliability power system transients power system security Markov processes Real time systems Steady-state Reliability theory Safety Medical services Time varying systems

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Sensitivity analysis for AC/DC hybrid power systems

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Dianli Xitong Zidonghua/Automation of Electric power systems 2007年第12期31卷 45-49页

作者： Liu, Chongru Zhang, Boming Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China State Key Lab. of Power Systems Department of Electrical Engineering Tsinghua University Beijing 100084 China

The interactions between AC and DC systems in the steady-state condition of power systems are investigated. Through a sensitivity analysis, the influence of DC control parameters on the operation of AC/DC systems and that of AC control parameters on other AC parameters with the DC system existing are discussed. The sensitivity matrices and the influence factors between AC and DC systems are analyzed from various points of view. The sensitivity analysis made in this paper is expected to be of practical significance in such problems as load flow control, parameter regulation, voltage estimation, etc.

关键词： Electric power transmission networks

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power Losses for IGCTs and Diodes in MV Three-level Inverters

Power Losses for IGCTs and Diodes in MV Three-level Inverter...

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International Conference on power Electronics and Drive systems (PEDS)

作者： Yuan Liqiang Zhao Zhengming Yang Zhi Department of Electrical Engineering State Key Lab of Control and Simulation of Power System Tsinghua University Beijing China Department of Frequency-converter and Control System GuoDian NanJing Automation Company Limited Nanjing China

The power-loss models for different switching states of IGCTs and diodes in MV (medium voltage) three-level NPC (neutral point clamped) inverters are presented in this paper. The models, simulation implementation and the revisional experiments on IGCT test platform are described in details. The relation between the power losses and the other elements of the inverter is analyzed and discussed.

关键词： Diodes Switches Pulse width modulation inverters power system modeling Medium voltage Variable speed drives Circuits Cooling Pulse width modulation Snubbers

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