Lightning overvoltage protection is of great importance to the safety of devices in UHV GIS. In practice, insulation failure of UHV transformer due to lightning strike is often reported. The widely used UHV metal-oxid...
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Wireless power transfer (WPT) has been a research focus in recent decades. Based on magnetically-coupled resonant WPT (MCR-WPT), this paper made a comparison of two basic structures in MCR-WPT: the two-coil structure ...
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Wireless power transfer (WPT) has been a research focus in recent decades. Based on magnetically-coupled resonant WPT (MCR-WPT), this paper made a comparison of two basic structures in MCR-WPT: the two-coil structure and the four-coil structure. Their equivalent circuits were built. To illuminate the difference between these two structures, the input impedance, the transfer efficiency, and the load matching were studied and tested by experimental results. The conclusion is drawn that without reducing the transfer efficiency, the addition of the source coil and the load coil in the four-coil structure makes it easier to match the source and the load than the two-coil structure.
Due to the power electronic devices in doubly fed induction generators (DFIG), it is very time consuming to simulate the electromagnetic transients of DFIG using its detailed model. Thus it is necessary to have approp...
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ISBN:
(纸本)9781849197588
Due to the power electronic devices in doubly fed induction generators (DFIG), it is very time consuming to simulate the electromagnetic transients of DFIG using its detailed model. Thus it is necessary to have appropriately simplified model of DFIG that maintains desirable accuracy. In this paper, the piecewise averaged model of PWM converters is introduced and applied to the modelling of DFIG. The proposed model divides the simulation time interval into switching periods and recalculates the averaged state equations of PWM converters in each switching cycle. In addition, a predictorcorrector based EMTP algorithm is designed to iteratively solve the model. Instead of treating switching events at the time points when they happen, the new algorithm solves all the switching instants in a switching cycle at the same time, which avoids frequency modification of the system conductance matrix and speeds up EMT simulations of DFIG. simulation results of a single-machine infinity bus system with a DFIG show that the proposed model and algorithm can achieve satisfactory accuracy and efficiency.
The dynamic characteristics of space charge in nanocomposite of low-density polyethylene (LDPE) mixed with inorganic nano- fillers. Different from previous qualitatively theoretical works, we investigated the influenc...
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The dynamic characteristics of space charge in nanocomposite of low-density polyethylene (LDPE) mixed with inorganic nano- fillers. Different from previous qualitatively theoretical works, we investigated the influence of trap depth, trap volume charge density and injection barrier height on the space charge and the electric field distribution in the nanocomposite under a DC external electric field (100 MV/m) systematically and quantificationally, through numerical simulations based on a bipolar charge transport model. The simulation re- sults showed that, the increase of trap depth would severely distort the balanced electric field distribution with the highest and the lowest electric field of 119 MV/m and 47 MV/m, respectively. It is concluded that the introduction of nanofillers creates more deep traps, which would block space charges by capturing most of them in the vicinity of electrode and hence reduce the local electric field largely. Further theoretical analysis of the simulation indicates that both the high permittivity and the low local electric field of the nanocomposite contri- buted to the increase of injection barrier height, and almost no charge could overcome an injection barrier higher than 1.25 eV. At last, a mechanism of space charge suppression in the LDPE nanocomposite was presented.
With the rapid development of renewable energies, especially wind power, how to manage unexpected generation variations economically and reliably in dispatch has become crucial for modern powersystems. To address thi...
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With the rapid development of renewable energies, especially wind power, how to manage unexpected generation variations economically and reliably in dispatch has become crucial for modern powersystems. To address this issue, this paper presents an affine disturbance feedback robust dispatch (ADF-RD) methodology for powersystems with large scale wind power integration in the framework of adjustable robust optimization (ARO). This methodology divides the dispatching process into pre-dispatch and re-dispatch. Pre-dispatch decision immunizes against all possible realizations of uncertainties in a set, while re-dispatch which can be regarded as a feedback will be adaptively adjusted using an affine function with respect to the realized uncertainty in real time. The ADF-RD methodology is applied to an hourly ahead dispatch (HAD) problem. The effectiveness and efficiency of the proposed ADF-RD methodology are demonstrated by numerical experiments carried on a five-bus system.
Reactive power optimization with discrete control variables can be formulated as a mixed-integer nonlinear programming problem, which is a typical NP-hard problem in mathematics. This paper proposed a Gaussian penalty...
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Purpose - A fast algorithm is proposed to calculate the lightning electromagnetic field over a perfectly conducting earth surface. Design/methodology/approach - The channel base current is approximated by a number of ...
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power flow exhibits uncertainty when power injections randomly fluctuate. The variables of power flow problem are correlated through the constraints set forth by power flow equations. Affine arithmetic can effectively...
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Lightning is the major cause of interruptions in power transmission lines. Ultra-high voltage (UHV) AC transmission line has been put into operation in China. Due to the large tower height up to 90 m and the high oper...
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In this work, we are interested in space charge dynamics characteristics in the low-density polyethylene(LDPE) nanocomposite mixed with some mass fraction of inorganic nanofillers. Different with all previous qualitat...
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In this work, we are interested in space charge dynamics characteristics in the low-density polyethylene(LDPE) nanocomposite mixed with some mass fraction of inorganic nanofillers. Different with all previous qualitatively theoretical works, numerical simulation based on the bipolar charge transport model was performed to systematically investigate the influence of trap depth, trap concentration, and injection barrier height on the space charge and electric field distributions under DC external electric field of 100 k V/mm. Our simulation results showed that increasing the trap depth would severely distort the electric field distribution at the balanced status with the highest and lowest electric field of 119 k V/mm and 47 k V/mm, respectively. Due to the introduction of nanofillers, more deep traps were created and blocked the space charge movement, capturing most of space charge in the vicinity of the electrode and largely declining the local electric field further. In addition, our theoretical analysis also showed both the high permittivity and low local electric field contributed to the increase of injection barrier height. Once the injection barrier height surpassed 1.25 e V, there was almost no charge that could overcome the injection barrier. At last, a mechanism of space charge suppression in the LDPE nanocomposite was presented.
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