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

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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Influence of frequency on electrical tree initiation in polyethylene

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Gaodianya Jishu/High Voltage Engineering 2007年第4期33卷 138-142页

作者： Zhou, Yuan-Xiang Wang, Yi-Nan Xing, Xiao-Liang 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 Dept. of Electrical Engineering Tsinghua University Beijing 100084 China

Treeing degradation in dielectric polymers often leads to insulation failures in electrical equipment. In order to make out the breakdown failures, the tree initiation characteristics of ice-water quenched HDPE under AC voltage in frequencies ranging from 50 Hz to 90 kHz are, studied. It is found that the tree initiation voltages (TIV) change a little when the frequency is from 50 Hz to 1 kHz. When the frequency is higher than 1 kHz, the TIV increases with the increase of frequency before reaching a maximum TIV. While the TIV decreases at first then increases at frequency >10 kHz. There are 7 categories of tree shapes, including branch-like, trunk-like, bosk-like, direct breakdown, bosk-trunk, bosk-breakdown and branch-trunk, appeared in the experiment. The categories of tree shapes manifold with the frequency increasing. The TIV of different categories are different apparently. The breakdown shape shows the highest TIV while the branch-like one shows the lowest TIV. The damage degrees to insulation material are different for different categories. It is also found that as the frequency increases, the dispersion of TIV increases remarkably. Though the polymer shows higher average TIV values as the frequency is larger than 1 kHz, the larger dispersion in higher frequency region indicates that the application of polymer insulators in medium or high frequency area would bring a higher breakdown risk as one can find from the frequent insulation failures in high frequency machines. The influence of frequency on electron accelerating process and fatigue effect aggravation in material under high frequency are considered as main causes of the experiment results.

关键词：聚乙烯电树老化电树起始电树形态频率

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Robust neural network and its application to course-keeping for ships

Robust neural network and its application to course-keeping ...

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6th World Congress on Intelligent control and Automation, WCICA 2006

作者： Xianku, Zhang Xiaofei, Lu Chen, Guo Lab. of Simulation and Control of Navigation Systems Dalian Maritime University Dalian 116026

ISBN: (纸本)1424403324

A feed-forward network with seven layers was designed and trained to acquire an open loop controller of course-keeping for ships. The NNC controller with five inputs and one output could follow the tacks of typical course curve with good precision, then a closed loop control system was constructed using closed loop gain shaping algorithm. The robustness of the system is improved because the control strategy connects the adaptability and nonlinear mapping of neural network with robustness of closed loop gain shaping algorithm. This method has the advantages of simple design procedure and obvious physical sense. © 2006 IEEE.

关键词： Naval vessels

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Risk-based study on under voltage load shedding schemes

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2006年第19期26卷 18-22页

作者： Dai, Jian-Feng Zhu, Ling-Zhi Zhou, Shuang-Xi Lu, Zong-Xiang State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Beijing 100084 China

A risk based method is proposed to design under voltage load shedding (UVLS) scheme. Different with traditional methods, the proposed one employs a series of risk indices, which are obtained based on a full-scale contingencies analysis, to determine the operating parameters of load shedding. According to this method, the load bus, in which the UVLS can exert itself with the highest efficiency to prevent voltage collapse, is selected as the first candidate to execute load shedding. And the amount of loads to be shed is identified though a relationship between risk values and shedding amount. The selection of shedding time conforms to the principle that the compound risk brought by failed shedding and unexpected shedding must be the minimum. Experiments conducted for IEEE 39-bus system reveal that the proposed method redound to identify the location, amount and time of load shedding more accurately and reasonably due to taking into account a great deal of uncertain factors.

关键词： Electric load shedding

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Study on probability of voltage instability based on the stochastic characteristic of load margin index

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2006年第13期26卷 26-30页

作者： Dai, Jian-Feng Wang, Hai-Chao Zhou, Shuang-Xi Lu, Zong-Xiang Zhu, Ling-Zhi State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Beijing 100084 China

In order to make up the deficiency of traditional analytical method used in the research of voltage stability problem, we need to know the probability information concerned with voltage instability. Therefore, this paper proposes a method to calculate the probability of voltage instability based on the stochastic characteristic of load margin index. This method firstly determines the stochastic characteristic of load margin index through an analysis about the randomicity of parameters which tie up with the tracing of critical point in continue power flow computation, and then figures out the probability of voltage instability by using moment and cumulate method. Owing to take into account more uncertain factors' influence on the voltage stability, the result acquired by this method is much more accurate and reasonable. A numerical simulation based on IEEE 39-bus system reveals that the proposed method works properly.

关键词： Electric power systems

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Improved simultaneous extrapolation in sharp impulse signals in time and frequency domains

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2006年第18期26卷 133-137页

作者： Zou, Jun Guo, Jian He, Jin-Liang Zhang, Bo Teng, Wen-Rui State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Tsinghua University Beijing 100084 China Dept. of Electrical Engineering Henan University of Technology Zhengzhou 450042 China

The characteristic of the transient response of the grounding system takes on a fast rising and slow damping with the lightning excitation. An improved simultaneous time and frequency domain extrapolation method is presented based on Hermite function expansion, which takes the above mentioned characteristic of the transient signal into account, using early time response and low-frequency data, the complete electromagnetic response is generated. By using mutually complementary data, simultaneous extrapolation in time and frequency domains are carried out by using the Hermite polynomials as the basis function. However, the extrapolation method is not suitable to deal with the transient response with the fast pulse excitation. The improvement for the extrapolation method is to pre- and post-process the transient response data with the fast pulse excitation. As a pre-processed procedure, in order to reduce the condition number of the matrix used for determined the coefficient of basis function, the scale transformation is used in time and frequency domain respectively, and the data in time domain is smoothed and padded with zero. An adaptive algorithm to determine the order of Hermite function is also proposed. As a post-processed step, the transient data are smoothed by using GPOF to obtain a convergent result. The numerical example and the field measurement are presented to illustrate the application of this methodology. The method proposed enhances the ability of the simultaneous time and frequency extrapolation techniques.

关键词： Signal processing

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Adaptive Galerkin approach of the indirect boundary element method for calculating 3D linear magnetostatic field

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2006年第1期26卷 96-100页

作者： Zou, Jun He, Jin-Liang Yu, Hai-Yu Teng, Wen-Rui State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Tsinghua University Beijing 100084 China Dept. of Electrical Engineering Henan University of Technology Zhengzhou 450042 China

The indirect boundary element method has some special advantages for the 3D linear magnetostatic field calculation by using the equivalent magnetic surface charge. In order to improve the accuracy of solutions and decrease the computational costs, an adaptive Galerkin approach to solve the magnetostatic integral equation is presented by using the h-type refinement technology. The basic idea of the proposed approach can be summarized as follows. The error of magnetic flux density is globally minimized in the Galerkin sense in the implementation, so the continuity error of magnetic flux density of each element can be served as a criterion to guide the adaptive refinement. The singularity of geometric corners and edges can be overcome due to the scheme of the discretization of the integral equation with Galerkin's approach. In addition, a local resolution technology is proposed, which leads to the minimal refined unknown. The numerical examples show the proposed method is efficient and accurate by comparison to the analytical solutions and the measured results.

关键词： Magnetic fields

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New method on design of robust controller for unstable process

New method on design of robust controller for unstable proce...

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International Conference on Machine Learning and Cybernetics, ICMLC 2005

作者： Zhang, Xian-Ku Lab. of Simulation and Control of Navigation Systems Dalian Maritime University Dalianl 16026 China

ISBN: (纸本)078039092X

In the formulation of H∞ weighted mixed sensitivity problem, any unstable poles of the plant inside the specified control bandwidth will be shifted approximately to its jω-axis mirror image once the feedback loop is closed with an H∞ controller. The symmetric values of zero-poles in the open right-half plane of the unstable process about the imaginary axis are defined as their mirror-images. An unstable process is transformed into a minimum-phase system through mirror-injection in the paper, then solving the robust controller using closed-loop gain shaping algorithm. When the plant is a pure unstable process whose all poles lie in the open right half plane it is loop-shaped through adding left half plane poles and zeros so that the system is converted into a regular unstable system, then the loop-shaped unstable process is transformed into a minimum-phase system through mirror-injection, the robust controller is acquired using closed-loop gain shaping algorithm. Because its largest singular value curves are similar before or after the unstable process is mirror-injected, and the closed-loop gain shaping algorithm constructs directly the robust controller using parameters having engineering sense according to the shape of the singular value curves of the robust performance index, the designed controller has equally robustness to the unstable process. The method has the advantages of simple design procedure and obvious physical meaning. © 2005 IEEE.

关键词： Robustness (control systems)

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Transfigured Loop Shaping controller and its Application to Underwater Vehicle

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International Journal of Automation and computing 2005年第1期2卷 48-51页

作者： Xian-Ku Zhang Yi-Cheng Jin Lab. of Simulation and Control of Navigation Systems Dalian Maritime University Dalian PRC

A kind of transfigured loop shaping controller is presented in this paper. A transfigured loop shaping system puts a controller K in a feedback loop, while putting the dc gain of the controller K on the reference signal line. It is shown through frequency domain analysis and simulation that a transfigured controller can improve the dynamic behavior of a system. The transfigured loop shaping controller method is simple and effective and corresponds to the mixed sensitivity method of robust control theory, which improves the behavior of a system by iterative tuning of weighting functions. Satisfactory control results are obtained when it is applied to the design of an underwater vehicle. Keywords Loop shaping controller - underwater vehicle - transfiguration Zhang Xianku graduated from Beijing Institute of Clothing Technology, China, in 1990. He received the M. S. degree from Dalian Maritime University (DMU), China, in 1993 and the Ph.D. degree from DMU, in 1998. He is currently a professor at the lab.ratory of simulation and control of navigation systems, Dalian Maritime University. His research interests include ship motion control and robust control. Jin Yicheng graduated from Zhejiang University, China, in 1967. He is currently a professor at the lab.ratory of simulation and control of navigation systems, Dalian Maritime University. His research interests include simulating system of ship steering and visual control.

关键词： Loop shaping controller underwater vehicle transfiguration

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Reinforcement learning control for ship steering using recursive least-squares algorithm

Reinforcement learning control for ship steering using recur...

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作者： Shen, Zhi-Peng Guo, Chen Yuan, Shi-Chun Lab. of Simulation and Control of Navigation Systems Dalian Maritime Univ. Dalian 116026 China State Key Laboratory of Intelligent Technology and System Tsinghua University Beijing 100084 China

ISBN: (纸本)008045108X

Recursive least-squares temporal difference algorithm (RLS-TD) is deduced, which can use data more efficiently with fast convergence and less computational burden. Reinforcement learning based on recursive least-squares methods is applied to ship steering control, as provides an efficient way for the improvement of ship steering control performance. It removes the defect that the conventional intelligent algorithm learning must be provided with some sample data. The parameters of controller are on-line learned and adjusted. simulation results show that the ship course can be properly controlled in case of the disturbances of wave, wind, current. It is demonstrated that the proposed algorithm is a promising alternative to conventional autopilots. Copyright © 2005 IFAC.

关键词： Learning algorithms

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