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Chen L.,Sichuan Electric Power Corporation
Advanced Materials Research | Year: 2014

To reduce the interference on communication equipments caused by transient electromagnetic field of switching operation, the shields of cables are connected to grounding grid on both sides in the substations grounding designs. However, when the substation is stroke by lightning or shorted, the huge potential difference called diverting potential difference between the cable core and the shield is generated, which can easily destroy insulation of cables, even producing electrical tree or dielectric breakdown in insulation material. Moreover, the large current flowing through the shield of cables will cause personnel accidents and equipment damages. In this paper, the electric model of cables is established using grounding grid simulation software-CEDGS. The way diverting potential difference changes influenced by grounding grids, soil and other parameters is analyzed. Measures to reduce diverting potential difference are proposed for providing a theoretical basis of construction in practice. © (2014) Trans Tech Publications, Switzerland.

Lu J.-P.,Chongqing University of Technology | Xu B.,Sichuan Electric Power Corporation
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

The transient zero sequence current waveforms show a great discrepancy on both sides of the fault point, and have different energy distribution at different frequencies, when single-phase earth fault occurs in distribution network. Wavelet packet energy relative entropy is defined to distinguish the differences combined with the information entropy and wavelet packet decomposition, realizing fault section location. The energy spectrum distribution characteristics of the transient zero sequence currents from FTU or other measurement device in feeder automation system are obtained based on the wavelet packets decomposition. Then the relative entropy of the zero sequence currents on both ends of every section is calculated. Comparing the results, the entropy of the fault section is the maximum. The influence of non-synchronous sampling is avoided by selecting the maximum energy data segment of transient zero sequence current to calculate relative entropy. This method is immune to transition resistance, fault position, and fault angle, and its effectiveness is proved through the simulation.

Chen D.,Sichuan Electric Power Corporation
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

By theoretical analysis, the calculation model of DC current distribution of AC power grid is built to explore the mechanism of DC current distribution in AC power grid. The forecast and analysis of Jinping-Sunan ±800 kV UHVDC 4950A earth-return current distribution rule in Sichuan power grid as well as substations' taking risks of DC magnetic biasing is carried out in line with the 2014 program. Computation results show that the area of infection is mainly within the radius of 120 km around DC grounding electrode. In the end, the effect of Jinping-Sunan ±800 kV UHVDC on the UHV substation to be built as well as its mitigation measurement is particularly discussed. Evaluation results show that these problems will not be serious.

Shu Z.,Southwest Jiaotong University | He X.,Emerson Electric | Wang Z.,Emerson Electric | Qiu D.,Sichuan Electric Power Corporation | Jing Y.,Southwest Jiaotong University
IEEE Transactions on Power Electronics | Year: 2013

An auxiliary capacitor-based balancing approach is adopted in this paper to equalize the dc-link capacitor voltages of a diode-clamped multilevel converter (DCMC). Four balancing circuits, including the generalized, one-level-capacitor, one-capacitor, and simplified one-capacitor-based configurations are discussed for a five-level DCMC system. These configurations are different in connection of the auxiliary circuits and numbers of the capacitors and switches, but they work on the same principle called ping-pong operation by utilizing the auxiliary capacitor as an equalizer between the capacitors of different voltages. The unbalance phenomenon, ping-pong principle, circuit configurations, and their switching schemes are analyzed, respectively. The superiorities of the proposed approach include balancing operation regardless of load power factor and modulation index, control simplicity, and independence from main circuits when compared to the traditional approaches. Simulations and experimental results verified the performances using the proposed balancing circuits and control strategies. © 1986-2012 IEEE.

Ye L.,China Agricultural University | Sun H.B.,Sichuan Electric Power Corporation | Song X.R.,China Electric Power Research Institute | Li L.C.,China Agricultural University
Renewable Energy | Year: 2012

Microgrids are LV or MV electric networks which utilize various distributed generators (DG) to serve local loads. In this paper, dynamic models of the main distributed generators including photovoltaic (PV) cell, wind turbine, hydro turbine as well as the equivalent power electronic interfaces, battery unit of PV and excitation system of hydro turbine have been made in ElectroMagnetic Transient Program/Alternative Transient Program (EMTP/ATP) software package. Control strategies based on active power/frequency and reactive power/voltage droops for the power control of the inverters have been also developed. Case studies have been carried out in a distribution network to investigate the dynamic behavior of the micro-sources in both steady state and fault scenarios. Simulation results verify the feasibility of the proposed models. © 2011 Elsevier Ltd.

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