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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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Analysis of the toroidal HVDC grounding systems in horizontal multilayer soils

Analysis of the toroidal HVDC grounding systems in horizonta...

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作者： Zou, J. Lui, Y.Q. Yuan, J.S. He, J.L. Cao, L. Lee, J. Chang, S. State Key Lab of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China Electrical Environment and Transmission Group Korea Electrotechnology Research Institute Changwon 641600 Korea Republic of

A Fredholm integral equation of the first kind has been developed for analyzing the performance of the toroidal high-voltage direct current (HVDC) grounding system buried in the horizontal multilayer soil. The method of moment is used to solve the equations. The formulation of potential in the earth due to a circular current is proposed in closed form by means of conception of the complex resistivity and depth, which leads to the saving of the computational time greatly. The numerical results show the good agreements with those in other papers and the measured data. © 2006 IEEE.

关键词： Electric grounding

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Development of a frequency dependent network equivalent based RTDS-TSA hybrid transient simulation platform with heterogeneous architecture

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Dianli Xitong Zidonghua/Automation of Electric power systems 2014年第16期38卷 88-93页

作者： Hu, Yizhong Wu, Wenchuan Zhang, Boming Department of Electrical Engineering Tsinghua University Beijing100084 China State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments Tsinghua University Beijing100084 China

For the simulation of large-scale AC/DC hybrid systems, both the precision of the DC parts and the efficiency of the whole system should be considered. Thus a real-time hybrid transient simulation platform is proposed by combining the real-time digital simulator (RTDS) and a transient stability analysis (TSA) program. A latest GTFPGA card is used to realize the high speed digital communication between RTDS and the computer deploying TSA program. Moreover, the frequency dependent network equivalent (FDNE) is implemented in this simulation platform to improve the accuracy of simulation results. By simulating a modified New England 39-bus test system incorporating high-voltage direct current (HVDC) components, the validity of the proposed simulation platform is verified.

关键词： Transient analysis

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A PI-based control scheme for primary cascaded H-bridge rectifier in transformerless traction converters

A PI-based control scheme for primary cascaded H-bridge rect...

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作者： Xinghua, Tao Yongdong, Li Min, Sun State Key Lab of Control and Simulation of Power System and Generation Equipments Dept. of Electrical Engineering Tsinghua University China Dept. of Electrical Engineering Naval Engineering University China

ISBN: (纸本)9788986510119

Cascaded H-Bridge rectifier (CHBR) is a more attractive solution in traction application for its transformerless structure. Because of the currents of different cells are exactly the same one, it is a challenge job to regulate the voltages of cells with only one current controller. In this paper, a PI-based control scheme is presented to deal with the voltages balance issue in CHBR. To satisfy the demand of rectifier such as unity power factor and regulated output DC voltages, the proposed control scheme consists of two parts. One is for shaping the grid current waveform and regulating the sum of DC-link voltages of all the cells;the other one is for balancing DC-link voltages. The latter is more concerned in this paper and is discussed in detail especially. simulations and experiments are carried on. The results verified the feasibility and effectiveness of the proposed scheme.

关键词： Electric rectifiers

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Optimization of tool-path generation for material extrusion-based additive manufacturing technology

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Additive Manufacturing 2014年 1卷 32-47页

作者： Jin, Yu-an He, Yong Fu, Jian-zhong Gan, Wen-feng Lin, Zhi-wei The State Key Lab of Fluid Power Transmission and Control Systems Department of Mechanical Engineering Zhejiang University Hangzhou310027 China Zhejiang Province's Key Laboratory of 3D Printing Process and Equipment Department of Mechanical Engineering Zhejiang University Hangzhou310027 China

In this study, we propose a tool-path generation approach for material extrusion-based additive manufacturing (AM) that considers the machining efficiency and fabrication precision, which are inherent drawbacks of general AM techniques compared with conventional manufacturing methods. The proposed approach aims to tackle the generation of direction-parallel tool-paths for the interior filling of simple connected areas, which comprises three main steps: (1) determining the inclination of reference lines;(2) generating and grouping tool-path segments into individual sub-paths;and (3) linking sub-paths based on specific requirements. These three modules interact to affect the efficiency and precision of AM significantly. In order to find an optimal inclination, we first analyze the impacts on the fabrication efficiency and manufacturing accuracy with different inclinations. A comparatively accurate building time model is developed subsequently to obtain the optimal tool-path inclination, but without compromising the machining precision, based on the analysis of a geometrical accuracy model. The proposed approach employs different inclinations in distinct layers according to specific manufacturing scenarios and technological requirements. After determining the reference lines, the tool-path segments are selected and grouped based on some characteristics (e.g., the number of intersections between reference lines and boundaries) to make up individual sub-paths, which are then connected to a zigzag-shaped path with short line segment connections. In the module for sub-path linking, some strategies are introduced to decrease the number of useless tool-paths, i.e., uncut paths, which could jeopardize the manufacturing quality by frequently turning the print head on and off. In addition, parametric curves are used to link the final sub-paths to avoid deceleration/acceleration processes in the end/starting parts of the sub-paths. The proposed approach has been used in practice

关键词： 3D printers

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A look-ahead generation dispatch method considering discrete generation regulation constraints with large-scale wind power integration

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Dianli Xitong Zidonghua/Automation of Electric power systems 2014年第10期38卷 36-42页

作者： Li, Zhigang Wu, Wenchuan Zhang, Boming Sun, Hongbin Department of Electrical Engineering Tsinghua University Beijing100084 China State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments Tsinghua University Beijing100084 China

Look-ahead generation dispatch is a critical measurement to accommodate large-scale integration of wind power generation. In real application, the model for conventional generators should involve generation regulation constraints including regulation frequency constraints and discrete output constraints. Look-ahead generation dispatch with regulation constraints is a large-scale nonlinear mixed-integer programming problem, and it could be hardly solved strictly within acceptable time. An efficient three-stage method for solving this problem is developed, together with a forward-backward-pass dynamic programming approach for handling generation regulation constraints. Numerical tests are taken on IEEE 31-bus systems and a large-scale 264-bus power system to verify the high efficiency and practicability of the proposed method.

关键词： Wind power

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Research on surface electric field of parallel gap

Research on surface electric field of parallel gap

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2011 7th Asia-Pacific International Conference on Lightning, APL2011

作者： Yu, Junjie Yu, Zhanqing Zeng, Rong Chen, He Peng, Xiang State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Beijing 100084 China Maintenance and Test Center of EHV Power Transmission Company China Southern Power Grid Co. Ltd. Guangzhou 510663 China

ISBN: (纸本)9781457714665

With parallel gap, by controlling the motion path of the electric arc, effectively avoid burning and damaging the insulator during lightning strike so that the effect to reduce the accident rate of line is obvious. Because of simple structure, convenient installation and good economical efficiency, its importance in measures of lightning protection for transmitting line is continually improved. Electric field characteristics on the surface of parallel gap electrode have obvious influence on corona generation and the gap breakdown position and are the key parameters that must be considered in the design. Based on the finite element method, this paper sets up the analysis model of electric field of parallel gap including the tower, the conductor and the insulator, uses ANSOFT software for simulation, studies the surface electric field characteristics of parallel gap electrode, compares the electric field of four types of parallel gap put forward in the paper and analyzes the law of influence of parallel gap electrode parameters on the electric field characteristics. The results show that, when the short circuit distance is increased, the maximum values of electric field of ball end and snap ring body are obviously increased;the opening angle of snap ring is larger and the maximum value of electric field of ball end is higher;when the pipe diameter is increased, the maximum value of electric field of snap ring body is reduced considerably;the ball end is bigger and the maximum value of electric field of ball end is less;the ring pipe diameter is the structure parameter having the largest influence on the surface electric field;for the ball end at the end of ring electrode, the structure parameter having the largest influence on the electric field is the diameter of ball end. Reducing the distance that the ball end stands out of the ring plane can decrease the maximum value of electric field of ball end. © 2011 IEEE.

关键词： Finite element method

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Research on generation and execution of coordination strategy for bi-directional and interactive coordinated voltage control between provincial and district levels

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Dianwang Jishu/power System Technology 2013年第12期37卷 3426-3432页

作者： Wang, Bin Guo, Qinglai Sun, Hongbin Li, Haifeng Luo, Jianyu Zhang, Boming Wu, Wenchuan State Key Lab of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Haidian District Beijing 100084 China Jiangsu Electrical Power Dispatching and Control Center Nanjing 210024 Jiangsu Province China

To achieve the goal of bi-directional and interactive coordinated voltage control between provincial and district levels, the study is focused generation and execution of coordination strategy for bi-directional and interactive coordinated voltage control between provincial and district levels. Firstly, the method to generate the bi-directional and interactive coordination strategy between provincial and district levels is proposed, and the gateway coordination state transition diagram is designed to intuitionally express the criterion of the interaction between the AVC systems belonging to the upper and lower level systems respectively;then, the regularization method for expanded coordinated secondary voltage control suitable to provincial power network and the regularization method suitable to district power network are put forward respectively to realize mutual support between power networks in provincial level and district level. Results from simulation examples and on-site operations show that the proposed method is feasible and effective as well.

关键词： Electric power transmission networks

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The Research of Asymmetric Parallel Gaps in EHV Transmission Lines

The Research of Asymmetric Parallel Gaps in EHV Transmission...

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2017 2nd International Conference on Electrical and Electronics: Techniques and Applications（EETA2017）

作者： Jin-bo WU Zhan-qing YU Hong-jun ZHEN Chao SU Rong ZENG Jin-liang HE State Key Lab.of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering Tsinghua University Electric Power Science Institute of Yunnan Power Grid Co. Ltd

As a new kind of lightning protection, parallel gaps have simple structure, easy installation, good economy, and many other advantages. The traditional parallel gap due to the large short distance, can lead to lightning trip-out rate increases. Based on arc movement characteristics this paper presents a design of new type of parallel gaps and the analysis of the surface field strength, and the verification test, design a new kind of parallel gap are obtained.

关键词： Arc movement Parallel gaps Surface electrical field

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Breakdown processes of solid composite insulation system with defects under high frequency

Breakdown processes of solid composite insulation system wit...

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Conference on Electrical Insulation and Dielectric Phenomena, (CEIDP)

作者： Q. Nie Y.X. Zhou X.L. Xing Y.S. Wang State Key Lab of Control and Simulation of Power Systems and Generation Equipments Dept of Electrical Engineering Tsinghua University Beijing China

Behaviors of composite insulation system are strongly affected by the performance of interface between dielectrics, which mostly correlates to the direction of applied electrical field and the frequency of applied voltage. In this paper, experiments were carried out to study the breakdown characteristics of solid composite insulation system, consisted of a polyethylene (PE) film (with a copper needle electrode) and a glass slice. A sine wave power supply with a frequency range from 50 Hz to 100 kHz was established to fit our purposes. Voltage was smoothly raised from 0 kV to 5 kV. The processes of breakdown can be divided into four stages: (1) Electrical tree inception and propagation in polyethylene; (2) Sliding discharge along the interface between polyethylene and glass; (3) Streamer across the glass; (4) Return streamer initiation from the ground electrode and breakdown. A model was established to analyze the mechanism of sliding discharge between solid dielectrics. The influence of frequency on thermo effect is considered as the main causes of the experiment results, which can well explain the reason of insulation premature inactivation in high-frequency electrical equipment.

关键词： Electric breakdown Solids Frequency Dielectrics and electrical insulation Polyethylene Glass Voltage Electrodes Plastic films Copper

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