Huang L.,Nanjing Southeast University |
Hu M.,Nanjing Southeast University |
Liu J.,Hohai University |
Yu H.,Nanjing Southeast University |
And 2 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2017
Research on linear generators for direct-drive wave energy conversion has mostly focused on inner-secondary sole permanent magnet (PM) linear generators, among which vernier hybrid machine and flux-switching generators are considered as the best selection. In this study, an outer-secondary tubular superconducting hybrid excitation linear generator is presented to increase the power density and reduce the voltage regulation. Double-buoys direct-drive WEC is introduced. The operation under hybrid excitation is analyzed. With consideration to cogging force, the linear generator is optimized. The generator performance is evaluated using the finite element method. Based on the on-load performance, a hybrid excitation method is proposed and is compared with only the PM working. According to the working point of the proposed generator, losses of the superconducting hybrid excitation windings are calculated. A PM flux-switching generator is employed to verify the analysis results. The results show that the proposed generator has the advantages of larger air-gap effective area, higher power density, and more steady output power and voltage. © 2002-2011 IEEE.
Guan Z.-C.,Tsinghua University |
Liu M.,Tsinghua University |
Wang L.-M.,Tsinghua University |
Zhang F.-Z.,China Southern Power Grid Co. |
Zhao F.,Hefei Power Supply Corporation
Gaodianya Jishu/High Voltage Engineering | Year: 2010
To research the semi-conducting glaze and porcelain insulator string (S-P insulator string) in connection with the defect of the semi-conducting insulators, such as aging and energy loss, the finite element method was used to analyze the potential of S-P insulator string, and the pollution flashover were experimentally compared with other types of insulators. Experimental results show that the pollution flashover voltage when semi-conducting glaze insulator lies in the high-voltage side is significantly higher than that in the low-voltage side; For the flashover voltage of unit insulated length and unit creepage distance, S-P combined insulator string is lower than semi-conducting insulator string, but higher than porcelain and composite insulator. For the pollution on the semi-conducting insulator surface, ESDD and NSDD on porcelain insulator raise, the leakage current raises, potential distribution is more uniform, the heat raises, and surface discharge is curbed, therefore, the flashover voltage is increased.
Sun Q.S.,Hefei Power Supply Company |
Lei Q.S.,State Grid Electric Power Research Institute of China |
Ke R.,State Grid Electric Power Research Institute of China |
Li M.Y.,State Grid Electric Power Research Institute of China
Applied Mechanics and Materials | Year: 2013
This paper presented the loss of the power grid and elaborated the distribution features of the power grid in Anhui, pointed out that measures should be taken to improve the structure of Anhui power grid for energy-saving according to its own specific characteristics. Suggestions includes the construction of UHV power grid, the breaking out of looped network, the construction of multi-circuit transmission lines on the same tower, scientific adjusting the grid operation voltage, improving the power factors, and adjusting the load. Based on the rules and characteristics of grid power loss, measures should be adopted on special ways to get the largest energy-efficient operations and achieve the aim of less investment to increase economic efficiency. © (2013) Trans Tech Publications, Switzerland.
Jia J.,Wuhan University |
Jia J.,Taiyuan Power Supply Company |
Gong Q.,Wuhan University |
Li X.,Wuhan University |
And 2 more authors.
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2013
When a transient single-phase fault occurs on shunt reactor compensated transmission lines, there exist components of power frequency and low frequency during voltage recovery stages. This forms the pat frequency phenomenon. Currently, the adaptive reclose criterions based on this have poor performance against disturbances, and cannot be used to identify circuit arc extinguishing time. A new signal processing method-the atomic sparse decomposition method is used to analyze nonlinear fault signals as well as to extract the low frequency components of recovery voltage when the transient single-phase fault occurs. The fault properties can also be identified. Atomic sparse decomposition is more accurate in determining the circuit arc extinguishing time because of its powerful time domain and frequency domain analysis capabilities. The algorithm also has coincidence time setting capability which provides the basis for circuit breaker overlap time setting. The simulation results show that the method proposed can effectively improve the adaptive reclose performance. ©2013 State Grid Electric Power Research Institute Press.
Li J.,Xi'an Jiaotong University |
Ji S.,Xi'an Jiaotong University |
Zhu L.,Xi'an Jiaotong University |
Wu P.,Jiangsu Electric Power Research Institute |
Cao T.,Hefei Power Supply Company
IEEE Transactions on Power Delivery | Year: 2016
Audible noise of can-type filter capacitors in high- voltage direct current converter stations originates from the vibration of capacitor cases, so it is meaningful to investigate the vibration characteristics. However, no experiment under practical excitations or thorough theoretical analysis was presented for the vibration characteristics. This study theoretically and experimentally investigated the vibration characteristics of can-type filter capacitors with stacked elements parallel to bottom. The vibration amplitude was found to be proportional to voltage squared. If the frequency spectrum of excitation voltage included several harmonics (more than three), vibration amplitude on some specific frequencies was related with the phases of these voltage components. Each capacitor surface had a concavo-convex vibration shape and the vibration of the bottom surface and the side surfaces were in opposite phases. The vibration amplitude of the bottom surface was the largest. Moreover, frequency characteristics of capacitor vibration were studied. The frequency response of the bottom surface was bigger than that of narrow and broad side surfaces for lower frequencies, while was smaller for higher frequencies. It was inferred that bottom surface vibration was mainly caused by elastic forces from direct contact and side surfaces vibration mainly came from damping forces from dielectric liquids. © 1986-2012 IEEE.
Ji S.-C.,Xi'an Jiaotong University |
Zhu L.-Y.,Xi'an Jiaotong University |
Shen Q.,Xi'an Jiaotong University |
Cao T.,Hefei Power Supply Company
Gaodianya Jishu/High Voltage Engineering | Year: 2011
Audible noise of AC filter capacitor installation has become one of main sources in HVDC converter station, in order to reduce the capacitor's noise level, it's necessary to do further research on the audible noise of filter capacitor. Based on the academic analysis on the generation mechanism of capacitor's noise, a vibration and noise experimental system was set up in hemi-anechoic room, the vibration acceleration and the sound pressure level produced by filter capacitor were measured respectively, through academic analysis and experiments it was verified that the bottom surface of capacitor was the main source of audible noise. Based on the boundary element theory, the radiation noise model of single capacitor was established. The simulating calculations on the radiation noise of capacitor were carried out by using the vibration data as the boundary condition. Compared with the measurement results, the error of noise data gained by calculation method was within 2 dB, which validated the noise model founded, and then the contribution of each capacitor surface element to the whole noise was analyzed, from which it was concluded that the vibration of bottom surface was the main cause for the generation of capacitor noise. The results gained provides an important reference for the study on audible noise control measures of the single capacitor.
Du Z.,Wuhan University |
Zhang Y.,Jiangxi Electrical Power Corporation |
Ruan J.,Wuhan University |
Ruan X.,Hefei Power Supply Company |
And 2 more authors.
Gaodianya Jishu/High Voltage Engineering | Year: 2012
Heavy iced transmission line is one of the important factors threatening the safety and stability of China's power system. Difficulties of coupling between the tower and conductors and iced load handling make it difficult for the traditional calculation method to establish an accurate model to accurately calculate the unbalanced tension of tower-line system. Consequently, we used the beam element and cable element to establish an finite element method(FEM) simulation model of tower-line system by the ANSYS software, and analyzed the maximum stress, deformation of the towers-line structure by considering the ice thickness, wind direction, and wind speed parameters, and also analyzed the causes for collapsed towers under the condition of real uneven icing and wind. Moreover, the weakness of the transmission line was pointed out and modification proposals were presented based on simulation analysis. The simulation results of the 500 kV heavy iced overhead transmission line show that the proposed method is credible.
Zheng T.,North China Electrical Power University |
Zhu X.,Hefei Power Supply Company |
Xu Z.,Shandong Energy Group Co. |
Liu L.,North China Electrical Power University
Dianwang Jishu/Power System Technology | Year: 2013
The impacts of grid-connected resistance-type of DC bias suppression devices on distance relay of transmission line is analyzed in this paper. Based on the analysis of mal-operation of distance relay caused by the insertion of DC bias suppression devices, a protective scheme which combines zero sequence reactance relay with phase-to-phase impedance relay has been put forward. phase-to-phase impedance relay is used to protect phase-to-phase fault and zero sequence reactance relay is applied for protecting the ground fault. Corresponding setting criteria are also given in this paper. Finally, PSCAD simulation results show that the proposed scheme can provide effective protection for the asymmetrical fault of transmission line with the insertion of resistance-type of DC bias suppression device.
Guo L.-N.,University of Sichuan |
Liu T.-Q.,University of Sichuan |
Cheng D.-W.,Hefei Power Supply Company |
Li X.-Y.,University of Sichuan |
Wu X.,University of Sichuan
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2013
In order to suppress the low frequency oscillation caused by the interaction of AC and DC system, a strategy based on sensitivity theory of single HVDC system is proposed. The key point of this strategy is using Prony algorithm to identify the critical oscillation modes and applying TLS-ESPRIT algorithm to choose the generator with high participation of system's critical oscillation modes. By testing the rotor speed change of the important generator under different DC modulation, the most efficient DC line in damping critical oscillation mode can be found out. Simulation with small mode DC modulation controller for a multi-terminal HVDC system shows its effectiveness.
Jia J.,Hubei Engineering University |
Gong Q.,Hubei Engineering University |
Li X.,Hubei Engineering University |
Zhang Y.,Hubei Engineering University |
And 2 more authors.
Dianwang Jishu/Power System Technology | Year: 2012
The reclosing moment for faulty transmission line greatly influences transient stability of power system. In allusion to the difficulty of online determination of the optimal reclosing moment, a method of online seizing on the reclosing moment, in which the trajectory prediction technology is merged with, is proposed. The core of the proposed method is to determine the dominant mode of oscillatory generation units by use of their trajectory prediction information of units' power angles and the units are divided into groups according to the dominant mode, thus the complex power system transient stability problem is turned into corresponding power angle stability analysis of one machine infinitive bus (OMIB) system, and the average stability margin of the first three swings of OMIB system mapping is chosen as the index to determine optimal reclosing moment. Because the amplitude of power angle in system mapping is inversely proportional to stability margin, so a practicable criterion is given as following: the minimum of the average power angle amplitudes of the first three swings of OMIB system mapping is the very condition satisfying the optimal reclosing moment. Finally, a complete design scheme for the proposed method is given.