Single Line to Ground (SLG) faults in non-effectively grounded networks are difficult to detect. Immune to neutral point grounding type, load conditions and system operation conditions, traveling-wave based method is ...
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ISBN:
(纸本)9781467380416
Single Line to Ground (SLG) faults in non-effectively grounded networks are difficult to detect. Immune to neutral point grounding type, load conditions and system operation conditions, traveling-wave based method is an effective fault line identification method. However, due to the strong coupling between the double-circuit lines, the wavefront magnitude of them are the same, and the polarity of them are opposite. Thus, the mal-identification will be resulted under such condition. This paper analyzed the traveling wave characteristics of double-circuit lines, and proposed an improved fault line identification method based on the initial process of zero sequence currents and voltage traveling waves. Tests show that, the proposed method has high effectiveness in fault line identification of double-circuit lines in distribution networks.
Voltage fluctuations occur frequently in wind farms as a result of wind power perturbation, while reactive powercontrol of various devices is always uncoordinated and often has a time lag when the system operates in ...
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Shielding failure of lightning is the key problem for safe operation of transmission lines. Compare to Electro-geometry Method, Leader Progress Method more suitable for lightning protection analysis because the physic...
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Shielding failure of lightning is the key problem for safe operation of transmission lines. Compare to Electro-geometry Method, Leader Progress Method more suitable for lightning protection analysis because the physical model is used instead of empirical formula. The relationship between amplitude of lightning current and other parameters, such as wires position, ground tilt angle, was analyzed.
This paper proposed a novel hybrid power converter topology based on cascaded H-bridge (CHB) and matrix converter (MC) in order to improve the performance of the conventional energy management systems in EV/PHEV appli...
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This paper proposed a novel hybrid power converter topology based on cascaded H-bridge (CHB) and matrix converter (MC) in order to improve the performance of the conventional energy management systems in EV/PHEV application. The power demand by the load is supplied by the generator and batteries, which are connected to the primary winding of the medium frequency transformer (MFT) by the matrix converter and the cascaded H-bridge respectively. The power transfer between the sources and load can be controlled and isolated by using the MFT. The cascaded H-bridge, as the energy control unit, can be used to balance the voltage/SOC of battery packages individually, significantly improve the modularity, stability and safety of EV system.
Regarding the power transmission mode from energy base to load center as the heart of the matter, a joint optimal operating model for both sending- and receiving- end power grids is established. In this model, the car...
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This paper focus on the fault characteristic by experimental research. A test rig is built for the direct driving stall fix-pitch horizontal axis wind turbine. 8 signals are collected by the experiment system, includi...
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This paper focus on the fault characteristic by experimental research. A test rig is built for the direct driving stall fix-pitch horizontal axis wind turbine. 8 signals are collected by the experiment system, including wind speed, rotor rotational speed, shaft torque, the output electric power, vertical and horizontal vibration displacement of main shaft, vibration acceleration of the front bearing pedestal and the back bearing pedestal. 11 common wind turbine faults are researched by experiment. These faults are rotor mass imbalance, pneumatic asymmetry, airfoil changed, yaw fault, shaft horizontal misalignment, shaft vertical misalignment, front bearing pedestal looseness, rear bearing pedestal looseness, front bearing outer ring fault, front bearing inner ring fault, and front bearing roller fault. Several signal analysis methods, which are waveform analysis, orbit analysis, amplitude domain analysis, frequency domain analysis and envelope spectrum analysis, are adopted to extract characteristics from vibration signals. The influence on output power and vibration characteristics of these faults is presented by comparing with normal operation. The findings can be used to guide wind turbine fault diagnosis in engineering applications.
Surge Impedance Relay(SIR) is applied to DC system. Characteristics of SIR in DC line are analysed. A DC SIR algorithm implementing wavelet transform applied to HVDC line protection is proposed. The feasibility of DC ...
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ISBN:
(纸本)9781849198349
Surge Impedance Relay(SIR) is applied to DC system. Characteristics of SIR in DC line are analysed. A DC SIR algorithm implementing wavelet transform applied to HVDC line protection is proposed. The feasibility of DC SIR is verified and the performance of DC SIR is simulated and analysed.
This paper presents a new control strategy for three-level neutral point clamped (NPC) pulse width modulated (PWM) rectifier without power source voltage sensors. The relationship between instantaneous power and volta...
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The signal of travelling wave has the merit of immunity to system oscillation, transition resistance, CT saturation and the neutral point operation modes;it has been widely applied in field of fault detection and prot...
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ISBN:
(纸本)9781849198349
The signal of travelling wave has the merit of immunity to system oscillation, transition resistance, CT saturation and the neutral point operation modes;it has been widely applied in field of fault detection and protection. Especially in isolated neutral grounded wind farm distribution network, the algorithm using multiple-bay travelling wave's information can exclusively achieve the fast fault feeder selection and tripping. However, travelling wave sampling frequency tends to reach 500 to 1000 times of that in algorithms with power frequency signal. The direct of travelling wave sampling data sharing in process bus would produce the communication block, and weaken the security of whole substation automation. To solve this problem, the performance of communication in process bus is theoretically analyzed and simulated in this paper, the communication requirement of travelling waves is quantified, and then a feasible scheme is proposed with data pre-processing and fault characteristic abstraction moving forward into the merging unit. simulations prove its validity. The work in paper can promote the wide application of travelling waves in substation based on IEC61850.
The distribution network detection devices are generally using two kinds of instrument current transformer (ICT), of which one is used to transform the travelling wave and transient signals, while the other is used to...
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ISBN:
(纸本)9781849198349
The distribution network detection devices are generally using two kinds of instrument current transformer (ICT), of which one is used to transform the travelling wave and transient signals, while the other is used to transform the power frequency signals. Such scheme is neither necessary nor economical. This paper analyses the influences of sampling resistance, stray capacitance and magnetizing inductance on the frequency characteristic of ICT. Considering that fault zero sequence transient current has big transient component and small power frequency component, an ICT with wide band frequency accuracy has been chosen. Practical experiments have been done. The technical parameters given by the instrument factory are only within 20-20kHz. The characteristics in higher frequency are seldom reported due to the lack of test means. The experiments in this paper is based on the transient tester instrument and current amplifiers developed by our lab.ratory, which can output wide frequency band current within 20Hz-100kHz up to 50A. Experiment shows that, the predicted results were in good agreement with the measured ones.
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