Applied Mechanics and Materials Vol. 441

Abstract: The paper mainly studies the filters used in grid-connected photovoltaic systems. The parameters of the current ripple are deduced by analyzing the generating mechanism of the ripples in grid-connected PV inverters, and then the filter is designed according to the system needs. A T-type filter is identified and its superiority and correctness are verified by simulation.

Abstract: In allusion to the problem that abandon hydropower computing ignores the grid absorption capacity, the calculation model of the abandon hydropower considering grid absorption capacity is proposed. In generating daily plan for reference, according the quantity that in excess of the plan calculates the abandon hydropower. In the order of each plant coal consumption rate to reduce the thermal power output from high to low. Hydropower to replace this part of thermal power electricity. When the economic benefit and environmental benefit is largest, we calculate the abandon hydropower that can absorbed by the system. Calculate the increasing benefit of the abandon hydropower by the with and without comparison method when a engineering have been operating.

Abstract: The electric power short circuit breakdown may cause low voltage blocking of frequency-converter giving rise to power unit shutdown accident,three typical coal-fired power units are selected to emulate calculations on low voltage ride ability with considering threephase short-circuit earthing fault, threephase short-circuit earthing fault by impedance, single-phase short-circuit earthing fault ,indicating that the short-circuit fault of the lines integrating into power system would result in the voltage of house-service busbar dropping off to 25%-85%,especially threephase short-circuit earthing fault in small operation mode attacks on power unit auxiliary at the most, therefore auxiliary demands complete and dependable low voltage ride through ability. and puts forward to some reform suggestes.

Abstract: According to the geological conditions of upstream cofferdam and foundation of the hydropower station, analysis for the seepage of the upstream cofferdam used SEEP/W module of Geo-studio software. Analysis for the stability used SLOPE/W module with Swedish circle method and Bishop method. Safety factor of the upstream and downstream in different conditions was obtained. The results show that the design of the upstream cofferdam was reasonable, and it will provide theoretical basis for Seepage control design of cofferdam.

Abstract: In this study, the mechanical structural model of helical gear tri-branching transmission system has been established to analyze the power-split characteristics. For the purpose of calculating power-split value, a simplified algorithm is developed through formulating the deformation compatibility condition and the torque equilibrium condition. Under the elastic support, the static equilibrium equations should be built to calculate the power-split under different conditions based on the projection of installation error and elastic deformation on the line of action as described. A numerical example was provided to illustrate the developed theory. The research results herein would be done to improve the applicability of tri-branching transmission.

Abstract: The steam generator is operated under the pressure of 15.5MPa and the temperature 327°C. Under this working condition the junction of the heat transfer tube and tube-sheet is accident-prone areas of the steam generator. By using ANSYS to carry out a thermal structure coupling analysis on the junction, it is found that a large tensile stress along axial and tangential directions occurs on outer surface of the heat transfer tube and is located at the region of 2.0 mm to 6.0 mm high over the tube-sheet. The stress attributes to the rapidly change of temperature on the tube outer surface and leads to the stress corrosions.

Abstract: In this paper a line fault probability calculation method by the combined effects of icing and wind is developed. Considering the force effect of icing and wind on the transmission lines, an icing-wind load is presented. It can be used to calculated the real-time or predict line fault probability using the characteristic exponential model reflecting metal resisting capacity. The example using historical meteorological data and simulating grid is given and the results show that, icing-wind load presented in this paper makes the calculate result of failure probability more serious. The line fault probability is helpful for the further grid security control.

Abstract: Wind power is uncertain. When the proportion of wind power capacity is large, the impact of the randomness of the output power on the grid frequency is more significant. Aiming at system stability influence after integrating a high capacity of wind turbines, this paper introduces the dynamic simulation model for electric power system with wind power, and makes an equivalent transformation processing for the wind turbine and generator. By using improved Euler method, this paper analyzes the impact of system frequency through time-domain simulation when disturbance occurs at wind farm side. Simulation results show that when wind speed changes, the established model and algorithm can effectively simulate the dynamic response of the frequency, and also these results can provide a reference for the frequency stability when wind turbines integrate into power system.

Abstract: Reliable and continued performance of power transformer is the key to profitable generation and transmission of electric power. Failure of a large power transformer not only results in the loss of expensive equipment, but it can cause significant guarantied damage as well. Replacement of that transformer can take up to a year if the failure is not disastrous and can result in tremendous revenue losses and fines. A power transformer in operation is subjected to various stresses like thermal stress and electrical stress, resulting in liberation of gases from the hydrocarbon mineral oil. Dissolved gas analysis is a technique used to assess incipient faults of the transformer by analyzing specific dissolved gas concentrations arising from the deterioration of the transformer. DGA is used not only as a diagnostic tool but also to track apparatus failure. In this research work the dissolved gas values measured for a 230kV / 110kV power transformer which are obtained from electricity board are used as references to the developed neural network. The neural network is trained and the transformer faults are predicted. The trained neural network shows the good performance for the prediction of fault in a 230kV/110kV power transformer.

Abstract: High voltage substation is the junction station of electrical power system. In order to conduct lightning over-voltage simulation and analysation of couple of substations rapidly and intuitively, a serialization supposed simulation program of substation is developed based on the research of EMTP kernel and data format. Model of impulse grounding resistance and improved leader progression is included in the program, which enhance the accuracy as much as possible and satisfying the demand for emulation of different type and voltage level. Through the simulation of some 500kV high voltage substation, the influence to lightning over-voltage of different system operating plan and lightning strike spots is analyzed, which verifies the validity and convenience of the program.