Northwest China Grid Company

Xi'an, China

Northwest China Grid Company

Xi'an, China
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Guo C.-X.,Zhejiang University | Zhu C.-Z.,Hangzhou Electric Power | Zhang L.,Northwest China Grid Company | Peng M.-W.,Zhejiang University | Liu Y.,Zhejiang University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2010

A novel support vector machine (SVM), i.e. multiclass multiple-kernel learning support vector machine (MMKL-SVM), for the fault diagnosis of power transformers is proposed in this paper. Unlike traditional SVM that may fail under some circumstances, the fault diagnosis method based on MMKL-SVM has some good theoretical properties, e.g. it only deals with a simple objective function, and the classification results can be obtained by direct calculation on the basis of a simple decision function; it can conduct calculation with an optimal kernel function composed of linear combinations of basic kernels, further boosting the overall performance; the solutions for it can be efficiently gained by iteratively solving two convex optimization functions with a low computation cost and high speed. Diagnosis test results show that the MMKL-SVM method has high classification accuracy, which proves its effectiveness and usefulness. © 2010 Chin. Soc. for Elec. Eng.


You S.,North China Electrical Power University | Liu Y.,North China Electrical Power University | Lu F.,North China Electrical Power University | Wan Q.,State Grid Electric Power Research Institute of China | And 3 more authors.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2012

In order to research the effect of altitude on corona onset voltage of corona cage bundle conductors, a calculation model for corona onset voltage of corona cage stranded conductors was established, and corresponding tests were performed. A charge simulation method was adopted to calculate the space electric field strength of the stranded conductor. According to self-sustained discharge criterion in severe Non-uniform electric field, a calculation model for corona onset voltage of corona cage bundle conductors at different altitudes was established. At the EHV/UHV artificial climate laboratory, corona onset voltages of six-bundle conductors were tested systematically at 19~4000 m altitude range with 500 m interval. Corona onset voltages of corona cage bundle conductors 6×LGJ-400/50, and 6×LGJ-500/45 were obtained. Conductor corona onset voltage curves at different altitudes, bundle spacing, bundle numbers and surface roughening coefficient were obtained, and surface roughening coefficient calculation results at different stranded radius and numbers of outmost alum wires were obtained. Analysis results show that the calculation model can effectively calculate the corona onset voltage of a stranded conductor in a corona cage; with 350~500 mm bundle spacing range, a bundle conductor's corona onset voltage decreases as the bundle spacing increases, and increases as the bundle number increases; the stranded conductor surface roughening coefficient is related to the ratio of a stranded conductor's outermost aluminum wire radius and the stranded conductor's radius. © 2012 Chinese Society for Electrical Engineering.


Suonan J.,Xi'an Jiaotong University | Wang C.,Xi'an Jiaotong University | Kang X.,Xi'an Jiaotong University | Ma C.,Xi'an Jiaotong University | Liu X.,Northwest China Grid Company
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

To eliminate the capacitive current's influence on line protection of long-distance and high-voltage transmission lines, this paper proposed a novel transmission line protection scheme based on model identification method and on the point that matrix pencil algorithm can extract the characteristic frequencies of the transmission line reliably. By studying the fault network topology of distributed parameter lines, the frequency-domain models of external and internal fault states were built. The fault model for external fault states is a distributed capacitive model, while the fault model for internal fault state is an equivalent system impedance model. The two kinds of unbalanced currents were defined as two model errors to identify different fault models. When an external fault occurs, the fault data corresponds with the distributed capacitive model and its unbalanced current is smaller than that of the equivalent system impedance model. When an internal fault occurs, fault data corresponds with the equivalent system impedance model and its unbalanced current is smaller than that of the distributed capacitive model. Therefore, external and internal faults are distinguished. Theoretical analysis and simulation results show that the new principle can remove internal fault quickly and reliably, free from the influence of capacitive current and transition resistances. © 2013 Chin. Soc. for Elec. Eng.


Su P.,Northwest China Grid Company | Zhang K.-S.,Xi'an University of Technology
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

The LVRT control strategy and protection schemes of DFIG are discussed in condition of large external voltage dip. On the basis of analyzing active IGBT Crowbar circuit topology as well as the effect of the Crowbar circuit to the fault during grid voltage dip, the DFIG mathematical model with considering the changed grid voltage is adopted and the control model of LVRT is established. The switching strategy of Crowbar is researched in detail during simulation. The simulation results verify that Crowbar circuit and the control strategy are active and prove that Crowbar control strategy could limit the over current in the rotor and the over voltage of the DC bus as well as the transient oscillation of the electromagnetic torque efficiently. Moreover, a reactive current is injected into the grid to assist the recovery of the grid voltage, which is in favor of achieving the LVRT of DFIG.


Trademark
Northwest China Grid Company | Date: 2015-01-09

THROWS.


Trademark
Northwest China Grid Company | Date: 2015-01-09

DECORATIVE PILLOWS; BED PILLOWS; BED RESTS.


Trademark
Northwest China Grid Company | Date: 2014-11-19

Throws.


Trademark
Northwest China Grid Company | Date: 2014-12-30

DECORATIVE PILLOWS; BED PILLOWS; BED RESTS.


Trademark
Northwest China Grid Company | Date: 2015-01-29

FOOT POCKET THROWS.


Sun H.,China Electric Power Research Institute | Zhang Z.,Northwest China Grid Company | Lin W.,China Electric Power Research Institute | Tang Y.,China Electric Power Research Institute | And 2 more authors.
Dianwang Jishu/Power System Technology | Year: 2012

On February 24, 2011, equipment fault occurred at 35kV side of Qiaoxi substation connected with the first wind farm of Gansu province, and this fault caused a serious wind turbine generators tripping accident, so that 598 wind power generators were tripped off and the lost output of the wind farm was 837.34 MW during the fault period because the wind turbine generators did not possess low voltage ride-through ability and the reactive power compensator of the wind farm did not possess the ability of automatic regulation. Operational condition of Northwest China power grid before the accident is presented in detail and detailed description of occurrence, expansion and restoration of the fault are given, and the reappearance of the fault is carried out by simulation. Experiences and lesson of the fault are summarized. To prevent the recurrence of such a serious wind turbine generators tripping accident and to ensure the secure and stable operation of power grid, following suggestions are proposed: strengthening the maintenance of protective relayings; enhancing low voltage ride-through ability of wind turbine generators; improving the renovation and management of reactive power compensation devices of wind farms; standardizing the operation of wind power generation units under the 1.1 time of rated voltage; directly switching out the 35kV feeder, in which single-phase short-circuit fault occurs.

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