Applied Mechanics and Materials Vols. 672-674

Abstract: Ice accretion on transmission line conductor exists widely in nature, which can bring a lot of hazards. It is important and necessary to obtain characteristics of ice on different conductors for analyzing ice hazards or developing ice protection technology. A numerical method based on CFD technology for predicting ice accretion on transmission line conductor was presented in the present paper. Ice accretion on a conductor with a diameter of 26 mm was then predicted with the numerical method and an icing wind tunnel experiment. The results showed that it was acceptable to use clear cylinder as actual conductor for icing study, and the numerical results were credible. The effects of droplet diameter, liquid water content, air speed and time on icing were then investigated with the numerical method. The law that ice thickness, limit and volume varied with different icing conditions was obtained, which built a good foundation for further research.

Abstract: This paper proposes a convenient and safe method for removing extra matters on overhead lines by distantly irradiating the extra matters with high-energy laser beam. Theoretical study and field experiments on the feasibility of this method were carried out according to the thermal properties of the main components of overhead lines and common extra matters on them. Results show that infrared laser is a better choice to be used to remove the extra matters than ultraviolet and visible laser lights. Experimental results also indicate that there is a large feasible scope of laser power density in which common extra matters can be efficiently removed while the conductors and grounding lines get no harm. Moreover, preliminary design of the laser removing system is given in this paper for practical application.

Abstract: For the structure of active distribution network can flexibly adjust, an optimal distributed generator allocation model considering reconfiguration is proposed. This model is implemented in the GAMS software and solved using SBB solver based on branch and bound method, due to it is a 0-1 nonlinear mixed integer programming. IEEE 33 standard example is used to simulate for this model. Results show that reconfiguration can increase the capacity of absorbing DG, providing thoughts and guidance for confirming the capacity of DG, and for planning and operation of active distribution network.

Abstract: The calculation formula for divergence of DC grounding current was put forward. The divergence of DC grounding current at different directions in the earth was studied. The main factors include the pattern of electrode, distance between sending end area and receiving end area, earth structure, etc. Some important conclusions were discovered. When observation point is close to DC grounding electrode, the pattern electrode has a big effect on the divergence of DC grounding current. When observation point is far from DC grounding electrode, soil structure has an effect on the divergence of DC grounding current. When the distance between DC grounding electrodes in the sending end area and receiving end area is short, the interaction of two electrodes should be considered.

Abstract: DFACTS devices can synthetically manage power quality problems. As one of the most DFACTS devices, the coordinated control of multi-distribution static var compensator should be considered. Controllers are separately designed aiming at different functions, that means the controllers are isolated even contradictory. In allusion to the problem that the separately designed DFACTS controllers exist interactions, the paper turns the coordination of the DFACTS controller into multi-objective optimization problem, takes the single-load infinite-bus distribution system with two DSVC as the research object, using the Non-dominated Sorting Genetic Algorithm with elitism approach (NSGA-II) for DFACTS controller parameters optimization, and the simulation results show the effectiveness of the algorithm.

Abstract: This paper proposes the optimization method on reactive power compensation of distribution network. The objective is that total loss difference between before being compensated and after should get maximum. The method adopts back/forward sweep method for calculating power flow to obtain total active network loss. Then global neighborhood searching strategy and aspiration criterion for fixed parallel capacitor are established by tabu search algorithm. The optimal installation location and compensation capacity of fixed parallel capacitor are determined. Optimizing simulation on a 34 nodes distribution system is realized, and optimal planning scheme is obtained. Results show that the proposed method is feasible and effective in optimal planning on reactive power compensation of distribution network.

Abstract: The interference on the geo-electrical resistivity observation from DC power lines is a key issue puzzling seismic monitoring. According to the working principle of geoelectrical resistivity observation instrument,the reason of interference on geoelectrical resistivity observation is analyzed.The calculation formulas of potential in soil, which is represented as horizontal two-layer electrical model, are derived by equivalent complex image method which responding to the ground electrodes of DC power line with various models: one vertical ground electrode, horizontal double-ring ground electrode and four vertical ground electrodes.In this way, the values of interference on geoelectrical resistivity observation from DC power lines under various situations are calculated and researched.The results show that the value of interference could be reduced 50% for horizontal double-ring ground electrode, and four vertical ground electrodes could be reduced 75%.

Abstract: The UHF method is one of the most important partial discharge (PD) detection means for GIS, while sensor technique is the key factor of the UHF method. In comparison with external sensors, built-in sensors can achieve higher sensitivity. In this paper, two parameters were quoted to evaluate the performance of the sensor, which are He and S₁₁. He refers to the PD detection sensitivity of sensor; S₁₁ refers to the impedance matching property of the sensor. The paper firstly designed a simulation model of sensor performance evaluation, and then studied the performance differences of four typically used or researched built-in UHF sensors (i.e., disc-type, dipole-type, spiral-type and logarithmic-type) by simulation tools of CST. The conclusions of the paper can provide a reference for performance evaluation and type selection of UHF built-in sensor. Keywords: Gas Insulated Switchgear (GIS), Partial Discharge (PD), UHF, Sensor, Sensitivity

Abstract: In order to grasp the state of full life cycle of the power transformer, A new method for power transformer life analysis based on risk assessment is proposed in this paper. Firstly power transformer risk assessment is conducted and fault tree is established accordingly to make the complex transformer faults system subdivide into various kinds of basic types directly; Secondly, the Fuzzy Analytical Hierarchy Process (FAHP) is designed to analyze the fault tree, so the complex system of transformer can be quantitatively described and the reliability of transformer can be obtained; Finally, transformer aging model is established to research the change rules of the transformer runnung state and determine the duration that the transformer stays in each stages of life. In addition, the application result shows the feasibility and effectiveness of the method above.

Abstract: Based on the large number of experimental data analysis and processing, a new inter-turn short circuit transformer diagnostic methods is proposed. In this paper, take the grounding current of transformer core as the signal source. Using wavelet multi-resolution technology the signal wavelet multiscale decomposition, we can get high frequency components of the signal. Achieve short-circuit fault diagnosis between transformer winding turns by comparing the number of the high-frequency component contained in different signals in the decomposition of the same scale.