Large hydro-generators require a 100% protected area for stator ground protection. Because the fundamental voltage criterion has low sensitivity near the neutral point, a high sensitivity third harmonic voltage criter...
Large hydro-generators require a 100% protected area for stator ground protection. Because the fundamental voltage criterion has low sensitivity near the neutral point, a high sensitivity third harmonic voltage criterion is needed to ensure that the generator can accurately respond to stator ground fault. This paper analyzes the third harmonic voltage characteristics of two large hydro-generators, calculates the sensitivity of the existing third harmonic criterion, and points out that the impedance parameters of the grounding transformer should be considered. In view of the lack of sensitivity of the third harmonic criterion for large hydro-generators, this paper proposes a stator ground protection criterion based on the third harmonic voltage variation, which has zero action quantity under the generator non-fault conditions and zero braking quantity after a ground fault occurs, and thus has high sensitivity and can effectively respond to high-resistance ground faults. PSCAD/EMTDC simulation results show that the proposed method has high sensitivity at different fault locations and transition resistances, which can provide theoretical support for the improvement of stator grounding protection in practical engineering.
Lithium‐metal anodes are recognized as the most promising next‐generation anodes for high‐energy‐storage batteries. However, lithium dendrites lead to irreversible capacity decay in lithium‐metal batteries (LMBs)...
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Lithium‐metal anodes are recognized as the most promising next‐generation anodes for high‐energy‐storage batteries. However, lithium dendrites lead to irreversible capacity decay in lithium‐metal batteries (LMBs). Besides, the strict assembly‐environment conditions of LMBs are regarded as a challenge for practical applications. In this study, a workable lithium‐metal anode with an artificial hybrid layer composed of a polymer and an alloy was designed and prepared by a simple chemical‐modification strategy. Treated lithium anodes remained dendrite‐free for over 1000 h in a Li–Li symmetric cell and exhibited outstanding cycle performance in high‐areal‐loading Li–S and Li–LiFePO 4 full cells. Moreover, the treated lithium showed improved moisture stability that benefits from the hydrophobicity of the polymer, thus retaining good electrochemical performance after exposure to humid air.
As a potential alternative gas of SF6, CF3I is focused on. We calculated the electron energy distribution function (EEDF), normalized effective ionization coefficient, and critical reduced electric field of CF3I terna...
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The widespread use of power electronics has led to increasing problems with harmonics in power systems. The ip-iq detection method is a common method to detect harmonics. If there is a symmetry of the three phases of ...
The widespread use of power electronics has led to increasing problems with harmonics in power systems. The ip-iq detection method is a common method to detect harmonics. If there is a symmetry of the three phases of the power system, the ip-iq detection method can have very large errors in detecting the harmonic current. To solve this problem, an new method for detecting harmonic currents is proposed in this paper. The method solves the phase between the positive sequence voltage of each phase and the actual voltage by using the delay method to obtain the positive sequence fundamental signal of the fundamental current error problem. The simulation was then carried out using MATLAB/SIMULINK, and the simulation results confirmed the method still accurately detects harmonic currents in all cases. Therefore, this method is of great research importance for the elimination of harmonics.
Faraday shield (FS), a thin-wall metal structure with slits, is used in inductive coupled plasma (ICP) sources to protect the ceramic tube from plasma erosion and eliminate capacitive coupling. electromagnetic energy ...
Faraday shield (FS), a thin-wall metal structure with slits, is used in inductive coupled plasma (ICP) sources to protect the ceramic tube from plasma erosion and eliminate capacitive coupling. electromagnetic energy is coupled into the driver through the slits, which makes FS an important component of ICP sources. Material and structure, which are critical for FS, should have effects on the distribution of electromagnetic field and temperature. In this contribution, discussions on various materials and structures’ impact on electromagnetic and thermal performance arise. FS made of copper, aluminum, molybdenum and stainless steel, as well as FS of different thickness, slit width, slit numbers and slit shapes, are investigated by numerical simulations referring to the parameters of an actual ICP source. electromagnetic field, RF power loss, temperature and stress of different FS are compared. The results show that Mo has similar electromagnetic performance with Cu but better thermal performance than Cu for FS. As for structure, RF power transfer efficiency decreases slightly as FS thickens. Appropriate slit width and number are required to allow a sufficient RF coupling and acceptable plasma heat flux to ceramic tube. RF efficiency of z-shaped slotted FS and normally slotted FS is almost the same.
The research on wide-area backup protection for high-voltage transmission lines has made certain progress in recent years, but there are few reports published on substation-area backup protection for low-voltage 10kV ...
The research on wide-area backup protection for high-voltage transmission lines has made certain progress in recent years, but there are few reports published on substation-area backup protection for low-voltage 10kV transmission lines. Based on the characteristics of shared information in intelligent substation, a substation-area backup protection scheme to deal with the failure of 10kV line protection device is proposed in this paper. This scheme uses the device self-test information and heartbeat mechanism to monitor the operation status of 10kV line protection devices; to realize the substation-area backup protection for the 10kV transmission lines when any line protection device fails, the protection criterion is constructed by the action results of power directional elements of transformer protections and other 10kV line protections. The proposed scheme can greatly improve the speed of the fault isolation and has low requirements for data demand and synchronization. PSCAD simulation results show that the proposed method is with high correctness and feasibility.
Flexible Multi-states Switch based on power electronics technology can realize the flexible interconnection between feeders, elastically control feeder power flow and solve the serious unbalance of feeder power flow i...
Flexible Multi-states Switch based on power electronics technology can realize the flexible interconnection between feeders, elastically control feeder power flow and solve the serious unbalance of feeder power flow in the distribution network. To solve the problem, this paper proposes that using flux-controlled variable reactor as the topology of flexible multi-states switch in distribution network. Firstly, flux-controlled variable reactor's principle will be introduced; Then, we analyze the principle of feeder power flow's control using variable reactor; After that, the control strategy for the flexible multi-states switch with different access methods is proposed; At last, a MATLAB simulation model and the prototype experiment platform are built. The results verified the power flow control function of flexible multi-states switch and effectiveness of proposed controlled strategy.
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