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Study on Over-Voltage of 220 kV Transformer＇s Neutrals and Protection Strategy

Journal of Energy and power Engineering 2011年第11期5卷 1102-1108页

作者： H.P. Yu S.M. Chen P.C. Yang H. Yin G.L. Wu State Key Lab of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Beoing 100084 China Chongqing Electric Power Research Institute Chongqing 401123 China

In order to limit short-circuit current and satisfy the need of relay setting, only part of the 220 kV power transformer is grounded, so on the neutrals of ungrounded transformers will appear the over-voltage. Currently the value of over-voltage on transformer neutral point and the corresponding protection strategy is based on theoretical formula. This article uses the PSCAD/EMTDC software to calculate the over-voltage on the neutral point of 4 ungrounded power transformers in Chongqing 220 kV power grid. The result shows that the power frequency transient over-voltage on the neutrals may reach 178 kV. If the single-phase grounding fault occurs in ungrounded power system, the power frequency over-voltage on the neutrals will be more serious and rise to 138.6 kV. Non-full phase operation may cause serious ferro-resonance over-voltage on the neutrals of no-load transformer, which may last for seconds and may rise to 723.7 kV, causing serious threat to the transformer neutrals and line-side equipment. The article also studies the gap parameter which should be taken on the neutrals of 220 kV transformers at the end.

关键词： Neutral point power transformer arrester gap power frequency over-voltage lightning over-voltage.

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Discussion on tower shunt coefficient of UHV DC transmission line under lightning stroke

Discussion on tower shunt coefficient of UHV DC transmission...

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International Conference on Lightning Protection (ICLP)

作者： S Chen J Hu B Zhang Y Yin M Hua State Key Lab of Control and Simulation of Power Systems and Generation Equipment Tsinghua University Beijing China China Electric Power Research Institute Beijing China Tibet Electric Power Research Institute Lhasa China

ISBN: (纸本)9781479935451

The development of UHV transmission technology brings longer transmission distance, higher towers and more complicated terrain along the transmission lines, which make the shunt performance of transmission line under lightning stroke more diversiform compared to conventional ones. This paper discusses the effects of factors, such as lightning current waveform, footing resistance, transmission line span etc., on the shunt coefficient of UHV DC transmission lines, which is of great significance for setting out lightning-proof measures as well as the location of lightning stroke point. It is referred that lightning current waveform especially its front time as well as tower footing resistance plays a significant role in determine of the tower shunt coefficient under lightning stroke. As the results indicates, the shunt coefficient of ground wire gets larger as the footing resistance increases while it decreases first and then increases as the front time of the lightning current waveform increases. The shunt coefficient of tower is just the opposite.

关键词： EMTDC Educational institutions Poles and towers Wires Wide area networks Lightning

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Fault current suppression for MMC-MTDC with the resistive type superconducting fault current limiter

Fault current suppression for MMC-MTDC with the resistive ty...

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2021 Annual Meeting of CSEE Study Committee of HVDC and power Electronics (HVDC 2021)

作者： G. Liu P. Guo Z. Yuan Y. Zhao Shenzhen Power Supply Corporation Shenzhen China State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing China

With effective properties, a resistive-type superconducting fault current limit (R-SFCL) has become an effective device to restrain DC-side bipolar short fault currents in multilevel modular converter multiterminal DC systems (MMC-MTDCs). However, due to the resistance-energy accumulation-dependent characteristics of the R-SFCL device, the fault durations and different fault current values will produce various output resistances at each fault stage, and the related coordinated protection and control strategy needs to be adjusted accordingly. Therefore, in the first part of this paper, we analysed the DC side short circuit current mechanism and the fault current restraint characteristics of R-SFCLs. Subsequently, to verify the above analysis, the R-SFCL-based four-terminal MMC-MTDC with DC bipolar short fault modelling and simulation are presented in the next section. Finally, based on the above analysis and research, the advanced DC bipolar fault control and protection strategies of the R-SFCL-based MMC-MTDC system are discussed to promote further study of coordinated and protection control and the application of R-SFCLs in subsequent engineering applications.

关键词： fault current limiters short-circuit currents HVDC power transmission HVDC power convertors superconducting fault current limiters

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A Gate Driver with a Negative Turn Off Bias Voltage for GaN HEMTs

A Gate Driver with a Negative Turn Off Bias Voltage for GaN ...

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International Conference on power Electronics and Motion control (IPEMC)

作者： Hang Zhou Matthew Priestley John Fletcher Kai Sun School of Electrical Engineering and Telecommunications University of New South Wales Sydney Australia State Key Lab of Control and Simulation of Power Systems and Generation Equipment Tsinghua University Beijing China

ISBN: (数字)9781728153018

ISBN: (纸本)9781728153025

The GaN HEMT offers fast switching and low on-state resistance which makes it ideal for applications such as high efficiency and high power density power supplies. Unfortunately, the low threshold voltage makes GaN HEMT extremely vulnerable to false turn-on, which compromises the performance and potentially causes shoot-through. In the half-bridge circuit topology, the resonant circuit formed by the parasitic inductance and capacitance can trigger false turn-on with a fast commutation. A practical method to avoid this phenomenon is to apply a negative bias voltage during the commutation by either using a separate power supply or using a capacitor charge pump to produce the negative turn-off bias. The first method necessitates many extra components and the second method cannot provide a fixed negative voltage. This paper rectifies these issues by proposing a negative turn-off bias generator with a new charge pump based approach which offers a stable negative turn-off voltage under different switching frequencies and duty cycles. The proposed circuit has been practically implemented during experimental testing. These results demonstrate that false turn-on events are eliminated without compromising the high-frequency and highspeed characteristics of the GaN HEMT.

关键词： Resistance Charge pumps Switching frequency Capacitors HEMTs Threshold voltage Gallium nitride

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EQUIVALENT CAPACITY OF THE LOWER VOLTAGE RIDE THROUGH FOR WIND FARM FROM OVERCURRENT PROTECTION IN power COLLECTION LINES

EQUIVALENT CAPACITY OF THE LOWER VOLTAGE RIDE THROUGH FOR WI...

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IET International Conference on Developments in power system Protection

作者： Bin Wang Xinzhou Dong Zhiqian Bo State Key Lab of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Alstom Grid

ISBN: (纸本)9781622761050

Magnitude and duration of voltage sags are the most important two factors to the Lower Voltage Ride Through (LVRT) capacity of the wind generator. Since most voltage sags are caused by the system faults, and sag durations are controlled by the tripping time of overcurrent relay in power collection lines based on the sags' magnitude. The specification of the LVRT capacity of wind generator is introduced into the operation characteristics of the relay in power collection lines. The evaluation model of equivalent LVRT capacity to overcurrent protection is proposed in paper, and the equivalent LVRT capacities from zone I and zone II relay are quantified. Improvement measures are also proposed.

关键词： Wind Farm Lower Voltage Ride Through Overcurrent Protection power collection lines

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Comparison of Two Basic Structures in Magnetically-Coupled Resonant Wireless power Transfer

Comparison of Two Basic Structures in Magnetically-Coupled R...

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第十五届中国科协年会

作者： ZHANG Yiming ZHAO Zhengming CHEN Kainan State Key Lab of Control and Simulation of Power Systems and Generation Equipments Department of Electrical EngineeringTsinghua UniversityBeijing 100084China

Wireless power transfer (WPT) has been a research focus in recent *** on magnetically-coupled resonant wireless power transfer (MCR-WPT),this paper made a comparison of 2 basic structures in MCR-WPT,namely the 2-coil structure and the 4-coil *** equivalent electric circuits were *** illuminate the difference between these 2 structures,the input impedance,the transfer efficiency,and the load matching were studied and verified by experimental *** conclusion can be drawn that without reducing the transfer efficiency,the additions of the source coil and the load coil in the 4-coil structure make it easier for the system to perfectly match the source and the load.

关键词： wireless power transfer magnetic resonance comparison structure

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Risk Assessment with Generic Energy Storage under Exogenous and Endogenous Uncertainty

arXiv

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arXiv 2022年

作者： Qi, Ning Cheng, Lin Wan, Yuxiang Zhuang, Yingrui Liu, Zeyu State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing100084 China Tianjin University China

Current risk assessment ignores the stochastic nature of energy storage availability itself and thus lead to potential risk during operation. This paper proposes the redefinition of generic energy storage (GES) that is allowed to offer probabilistic reserve. A data-driven unified model with exogenous and endogenous uncertainty (EXU & EDU) description is presented for four typical types of GES. Moreover, risk indices are proposed to assess the impact of overlooking (EXU & EDU) of GES. Comparative results between EXU & EDU are illustrated in distribution system with day-ahead chance-constrained optimization (CCO) and more severe risks are observed for the latter, which indicate that system operator (SO) should adopt novel strategies for EDU uncertainty. © 2022, CC BY.

关键词： Energy storage

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ANALYSIS OF FATIGUE LIFE LOSS OF DRIVETRAIN OF DOUBLY-FED WIND TURBINES UNDER SHORT-CIRCUIT FAULT OF power GRID

ANALYSIS OF FATIGUE LIFE LOSS OF DRIVETRAIN OF DOUBLY-FED WI...

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International Conference on Renewable power generation

作者： Qiu Shilong Li Hui Gong Lijiao Wang Bin Chai Zhaoseng Wu You Department of Mechanical and Electrical Engineering Shihezi University Shihezi China State Key Laboratory of Power Drivetrain Equipment and System Security Chongqing University Chongqing China State Key Lab of Control and Simulation of Power Systems and Generation Equipments (Department of Electrical Engineering) Tsinghua University Haidian District Beijing China State Key Laboratory of Power Drivetrain Equipment and System Security Chongqing University Chongqing China

ISBN: (数字)9781839531248

ISBN: (纸本)9781839531255

The shafting drivetrain of the doubly fed wind turbine is the part with the highest failure rate. The electromagnetic torque fluctuation caused by the grid fault easily results in the torsional vibration fatigue loss of the shaft. Accordingly, the influences of drivetrain fatigue life loss under different grid faults require investigation. Firstly, the four-mass model of the drivetrain is constructed on the basis of MATlab/Simulink. Secondly, the electromagnetic torque response under short-circuit fault of the grid is obtained via model simulation. Finally, the effects of different types of grid faults on the fatigue life of the drivetrain are analysed through Mlife. Results show that the electromagnetic torque fluctuation load generated by grid fault has no apparent influence on the fatigue life of the drivetrain in the short term, but the cumulative effect of short-term damage will aggravate the fatigue life loss of the drivetrain and increase the failure risk of the component. The electromagnetic torque generated by the three-phase symmetrical short-circuit is the most violent and has the maximum effect on the fatigue life of the drivetrain.

关键词： WIND TURBINE SHORT-CIRCUIT FAULT TORSIONAL VIBRATION FATIGUE LIFE DRIVETRAIN

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Automatic voltage control of wind farms based on model predictive control theory

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Dianli Xitong Zidonghua/Automation of Electric power systems 2015年第7期39卷 59-67页

作者： Xu, Fengda Guo, Qinglai Sun, Hongbin Lan, Haibo Liu, Haitao Liu, Xiaomin Department of Electrical Engineering Tsinghua University Beijing100084 China State Key Laboratory of Control and Simulation of Power System and Generation Equipments Tsinghua University Beijing100084 China State Grid North Hebei Grid Company Limited Beijing100053 China

Voltage fluctuations occur frequently in wind farms as a result of wind power perturbation, while reactive power control of various devices is always uncoordinated and often has a time lag when the system operates in the traditional control mode that only uses the current data for decision-making. In this case, a method for coordinated control of the reactive power of wind turbine generators (WTGs) and static var generators is proposed based on model predictive control (MPC). Unlike the traditional voltage control method, the control method proposed has the realization of optimization of the voltage control curve and the dynamic process of reactive power regulation in the future window of time as its objective. An auto regression moving average (ARMA) model is used to predict the active power of WTGs while the reactive power of WTGs and the SVG is forecasted using a first-order inertia link and a proportional integral (PI) link, respectively. Voltages in the wind farm are solved with the help of a sensitivity matrix. Thus an optimization model is developed for both the minimization of PCC voltage deviation and the maximization of SVG reactive power reservation in a future window of time. The optimizing model is solved using CPLEX tools with the dual simplex algorithm. In order to test the performance of the MPC controller, multiple cases with different wind circumstances are simulated on a DIgSILENT platform. simulation results reveal that by predicting the states of various instruments in wind farms during a period of time in the future, the proposed control method is able to rationally arrange fast/slow reactive power to respond to predictable changes of the system in advance and keep voltage stable. ©2015 state Grid Electric power Research Institute Press

关键词： Reactive power

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simulation of lightning strike in 2-D and 3-D with fractal theory and its application

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2010年第22期30卷 127-134页

作者： Xu, Wei Chen, Shui-Ming He, Jin-Liang State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Haidian District Beijing 100084 China

Lighting causes great damage to power systems due to the stochastic nature of lightning discharges and the vulnerability of lightning leaders to various environments in the process of inception and propagation. In this work, the growth of diffusion limited aggregation (DLA) was adopted for reproducing branches and tortuosity of lightning channels in both 2-D and 3-D simulations. By comparing the fractal dimensions of natural lightning discharges and simulation results on various discharge settings, we discovered that a fractal coefficient η = 2 can deliver a credible model of lightning strikes. We further proved the consistency between simulation results and observations conducted in Japan during 2005 and 2006 winter seasons on lightning strikes to a windmill and its lightning-protection tower. But the credibility of the result needs to be verified by further experimental data, when the model extended from 2-D to 3-D. Moreover, striking probability and the shielding effect in the actual condition were analyzed with the proposed simulation model. © 2010 Chin. Soc. for Elec. Eng.

关键词： Fractal dimension

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