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Li W.,North China Electrical Power University | Luo Y.,North China Electrical Power University | Qiu Y.,Smart Grid Research Institute | Cui X.,North China Electrical Power University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

The switching delay of high-voltage solid-state transfer switch (HV SSTS) is about half power cycle presently. The residual voltage at the time of transfer process is important because approximately 10 ms transfer time from main power to backup is objective existence. The profile, value, frequency and decay time constant of residual voltage have to be concluded in order to suppress inrush currents and to improve the success rate of switching. The residual voltage is related to the load character and SSTS valve design. Therefore, based on the mathematic model of the SSTS switching transformer with capacitor loads, induction motor loads and no load, the characteristic of residual voltages was deduced via an analytical analysis method in accordance with two switch approaches. First, the load current is transferred successfully from the vacuum breaker to the thyristor valve and is cut off at the crossing zero point. Secondly, the load current is transferred from the vacuum breaker to the thyristor valve unsuccessfully and is turned off by the vacuum breaker with chopping currents. The validity can be verified by MATLAB simulations and engineering tests. The paper provides a theoretical foundation for control parameter design of SSTS transferring different loads. © 2013 Chin. Soc. for Elec. Eng. Source


Li W.,North China Electrical Power University | Xiao X.,North China Electrical Power University | Luo Y.,North China Electrical Power University | Qiu Y.,Smart Grid Research Institute | Cui X.,North China Electrical Power University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

In a medium-voltage solid-state hybrid switch (MV SSHS) which is made of the vacuum breaker and the thyristor valve in parallel connection, the transient process of switching off capacitor load is that the capacitor load current transfers from the vacuum breaker to the thyristor valve, then it can be cut off at the crossing zero point. Transient parse of the capacitor current and the voltage of thyristor valve was deduced based on the mathematics model which consist of dynamic snubber circuits of the thyristor valve, the piecewise linear voltage-current characteristic curve of arc, the series-wound reactor and capacitor. Accordingly the following result can be drawn: the optimal trigger time of the thyristor valve and the theoretical foundation for thyristor valve design are established in order to transfer the current from vacuum breaker to the thyristor valve. It can overcome reignition and overvoltage by the current of capacitor switched off at the time of the crossing zero point. Transient capability of the middle-voltage solid-state hybrid switch is similar to TSC (thyristor switch capacitor), but SSFC has advantages of compact, low cost and high reliability. The validity can be verified by Matlab simulation and engineering tests. © 2013 Chinese Society for Electrical Engineering. Source


Liu Y.,Beihang University | Chen D.,Xian Jiaotong University | Yuan H.,Beihang University | Ji L.,Smart Grid Research Institute | And 2 more authors.
International Journal of Applied Electromagnetics and Mechanics | Year: 2015

Aimed to provide a more close-to-reality and rapid calculation method for optimization design of low voltage circuit breaker with complex mechanism, an interruption model is constructed, which can describe the coupling of air blast process with arc model, complex mechanical movement, magnetic field, and electric circuit. The model is based on the non-stationary gas conservation equations, and considers the influence of the chamber structure on the gas dynamics. To realize the interaction between the arc movement and the gas flow simply, on the one hand, the moving electric arc is deemed an energy input source of the chamber gas. On the other hand, the movement equation of the arc considering action of the gas flow is built. With this model, the general principle of the chamber gas flow, arc voltage and current during the interruption process of an actual breaker are calculated and compared with the experiment results. As an application, the influence of the chamber vent size on the arc movement is studied with the model as well. © 2015 - IOS Press and the authors. All rights reserved. Source


Wang H.,Smart Grid Research Institute | Cao J.,Smart Grid Research Institute | He Z.,Smart Grid Research Institute | Yang J.,Smart Grid Research Institute | And 2 more authors.
IEEE Transactions on Power Delivery | Year: 2016

Due to the rapid development of the voltage-source converter (VSC), the demands for HVDC cables have increased significantly. Although more than ten VSC-HVDC projects are under construction and many more are in operations globally, the testing criteria for HVDC XLPE cables are mainly referenced to test guideline TB 496 recommended by CIGRE. Due to the large stray capacitance of the VSC-HVDC cables, the switching impulse overvoltage stress of the cables is the main electrical parameter concerned, a unified overvoltage factor of 2.1 p.u. being generally accepted. However, the switching impulse overvoltage stress of a VSC-HVDC cable system depends on not only the VSC topology but also the cable parameters and the volt-ampere characteristics of the dc cable surge arresters used. This paper studies the switching impulse overvoltage stresses for the dc cable system of a symmetrical monopole VSC-HVDC transmission system using the modular multilevel converter technology. The studies were performed according to the key technical parameters for a typical 1000-MW/320-kV VSC-HVDC transmission scheme, the XLPE dc cable links being assumed. The results show that a switching impulse overvoltage level of 2.3 p.u. should be applied during the type test of the overvoltage capability of the HVDC cables. © 2015 IEEE. Source


Zhao G.,North China Electrical Power University | Li W.,North China Electrical Power University | Chen W.,State Grid Corporation of China | Cai B.,Smart Grid Research Institute | Qiao E.,Smart Grid Research Institute
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2015

The paper focuses on the cascaded STATCOM (Static Synchronous Compensator) with energy gained from a transformer on the AC side. To study the DC voltage distribution of the converter and analyze the reason for its imbalance, an equivalent circuit that contains an energy-gaining unit is built for the converter during pre-charging. Based on it, a method for balancing DC voltages is proposed where the parameter differences in the energy-gaining unit are taken into account, which is also verified by LV physical experiment. ©, 2015, Chinese Machine Press. All right reserved. Source

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