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Jiao Z.,Xian Jiaotong University | Ma T.,Shaanxi Electrical Power Design Institute | Qu Y.,Xian Jiaotong University | Zhang M.,Xian Jiaotong University | Suonan J.,Xian Jiaotong University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2014

To improve the performance of power transformer protections, a novel excitation inductance-based transformer protection scheme was studied. By analyzing the characteristics of excitation inductance in T-type equivalent circuit under the condition of normal operation, iron-core saturation and internal fault, the magnitude and the fluctuation of excitation inductance were used to distinguish internal faults from external faults and iron-core saturation conditions. Under normal operation or external fault conditions, the magnitude of excitation inductance is large. When an internal fault occurs, the magnitude of calculated excitation inductance is small because the fault current is included in the differential current. The fluctuation of excitation inductance can be detected if iron-core saturation occurs. The proposed excitation inductance-based protection scheme can detect faults of power transformers sensitively and rapidly with considering iron-core saturation in constructing the criteria. The proposed power transformer protection scheme was verified by many dynamic tests in our laboratory. The test results show that the proposed protection scheme can reliably detect and isolate the fault. © 2014 Chin. Soc. for Elec. Eng.

Liu Y.J.,Xian University of Technology | Shi H.Y.,IBM | Chang H.B.,Shaanxi Electrical Power Design Institute | Yang J.L.,Xian University of Technology
Environment, Energy and Applied Technology - Proceedings of the 2014 3rd International Conference on Frontier of Energy and Environment Engineering, ICFEEE 2014 | Year: 2015

Effective image segmentation is a challenging task in computer vision and object recognition. Watershed segmentation algorithm is simple and accurate, but over segmentation is a major drawback of this method. An improved watershed image segmentation algorithm is proposed to solve the problem of over-segmentation by classical watershed algorithm by preprocessing step to limit the number of regions. Then detecting edges of image and computing watershed transformation is done. The experiment results show that this method is effective on solving the problem of over-segmentation. © 2015 Taylor & Francis Group, London.

Wang Y.-L.,Xian Jiaotong University | Wei B.,Xian Power Supply Bureau | Hao X.-W.,Xian Jiaotong University | Liu H.-Y.,Shaanxi Electrical Power Design Institute | Zhang G.-J.,Xian Jiaotong University
Gaoya Dianqi/High Voltage Apparatus | Year: 2010

To get rid of the latent danger induced by the current neutral point grounding way of transforms in Xi'an power grid, an optimal grounding method of 330 kV auto-transformers and 110 kV transforms through a low reactance is proposed. The simulation results reveal that after grounding through low reactance with appropriate value, the single-phase grounding short-circuit current on the 110 kV bus-bar of 330 kV auto-transform decreases clearly, and the over-voltage on neutral point of other 110 kV transforms is significantly reduced to a lower level, which guarantee safe insulation of neutral point and enhance reliability of the power grid.

Cheng Y.,China Electric Power Research Institute | Ding S.,China Electric Power Research Institute | Lu X.,China Electric Power Research Institute | Tan R.,Shaanxi Electrical Power Design Institute
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2012

To analyze refreezing of frozen ground and its influence on foundation stability in the Qinghai-Tibet DC Transmission Line Engineering, temperature monitoring for a freezing-thawing process is carried out for the assembling prototype foundations and frozen soil in Wudaoliang area on the Tibetan Plateau. Combining with atmospheric temperature data in the area, the ground temperature changing characteristics with time and distributing along the depth of undisturbed and backfill coarse-grained frozen soil are analyzed. Monitoring results show that:(1) Ground temperature is periodic fluctuation and its amplitude decreases with increase of depth. There is a freeze-thaw state alternating layer in the upper undisturbed and backfill soil. (2) In the monitoring period, the frozen soil below foundation slab is in frozen state and the foundations are stable. (3) The maximum thawing depths of undisturbed and backfill frozen soil are 3.0 and 3.2 m respectively. Through the establishment of ground temperature estimation formula, and based on the results of ground temperature change amplitude and mean value, etc., it is obtained that the permafrost table is 3.1 m, which is consistent with the results of engineering survey and monitoring. (4) Using heat transfer theories, ground heat transfer model of high porosity frozen soil backfilled in winter is established. The heat transfer ability and air natural convection velocity effects on refreezing of ground are analyzed. The results indicate that:(1) Backfill disturbance of frozen soil aggravates temperature fluctuation amplitude and increases the thawing depth, but the effect degree and range are limited. (2) Construction of transmission lines in frozen soil and assembly foundations in winter and keeping proper porosity of the backfill frozen soil in freeze-thaw active layer are beneficial not only to accelerate the ground refreezing, but also to increase compaction degree because of soil natural consolidation and thawing settlement. So, the frozen state in the warmer seasons could keep while heat diffusion to deeper ground weakens.

Song G.,Xian Jiaotong University | Rao J.,Xian Jiaotong University | Rao J.,Shaanxi Electrical Power Design Institute | Gao S.,Xian Jiaotong University | And 2 more authors.
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2013

Based on the distributed parameter model of the HVDC transmission line, the compensating voltage at the end of the protection zone is calculated according to the electrical quantities measured at local convert station. A new monopole protection principle can then be constructed with the calculating voltage and the measuring voltage. When a metallic ground fault or low-impedance ground fault occurs in the line, as the compensating voltage at the end of the line has opposite polarity with measuring voltage at the local convert station, the protection criterion can act instantaneously. When a high-impedance ground fault occurs in the line, compensating voltage at the end of the line is lower than the preset threshold which is set according to the transition resistance. And the protection criterion can act in concert with interrelated protection principles. The coordination rule of this protection principle should cooperate with other interrelated protection principles. It is complete, and it can be put into operation during the whole process of fault. Simulation results have testified the feasibility of the principle. © 2013 State Grid Electric Power Research Institute Press.

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