Applied Mechanics and Materials Vol. 492

Abstract: Biomass is one of the significant fuel sources that can potentially contribute to the worlds energy demands. The most used technology that takes advantage of biomass heating value is still direct combustion which still suffers from significant inefficiencies creating therefore, the need for alternative processes to be analyzed. In this study Aspen Plus simulation package was used to develop a model for the gasification of corncob residues. The effects of equivalence ratio (ER) and steam to biomass ratio (SBR) on syngas composition and gasification temperature were investigated. The results showed that ER values of 0.34-0.35 and SBR values of 0.8 - 1 corresponding to a gasifiers temperature of 854-890°C were the optimum conditions for corncobs gasification.

Abstract: Mold shell with higher thermal conductivity was introduced in the article. Reinforced by the carbon fiber, the new type sol silicate mold shell could be made with much less layers while without reducing its strength. Therefore, the new-type mold shell should have higher thermal conductivity. Then measure its thickness, bend strength, analyze the dendritic crystal of the casting manufactured with the new-type mold shell. It was proved that the thickness had reduced by 25% and the bend strength did not decrease. And it performs better in the detection: the dendrite crystals are refined, the primary and secondary dendrite arm space are decreased, the secondary dendrite arms are restrained.

Abstract: In order to improve the energy transmission of an electromagnetic wave in microwave frequency regime propagating through a slab made of a polymeric material, we integrated conductive metamaterials particles in the polymeric medium and used an optimization method for determining the overall size and geometrical characteristics of the metamaterial element that can meet the desired energy transmission requirements. The numerical results show that to attain high transparency the effective parameters of the homogenized medium can be manipulated as required by optimizing the geometry of the metamaterial, the unit cells size and their distribution. To validate this design approach, we present the results of the experimental tests conducted on a 300 mm x 300 mm x 4 mm board with optimized metamaterials structures.

Abstract: Single-phase ground fault line selection problem has never been satisfactorily resolved in small current neutral grounding system in china. According to such a situation and combining theoretical analysis and simulation research with reports published in literature, existing faulty line selection technologies are generalized, and working principles, application conditions and existing defects of these technologies are analyzed, meanwhile the feasible improvement of these technologies and the up-to-date research achievements, and deficiencies of applications in this field are summarized. Finally, the development trend of faulty line selection technology for small-current neutral grounding system is pointed out.

Abstract: The existing system of partial discharge location in substation utilizes Omni-directional UHF sensors array which can achieve single-source partial discharge source location. But for multi-source UHF partial discharge signals, the system is inaccurate and can’t distinguish types of partial discharge. This paper proposed to the method multi-source partial discharge signals acquisition and separation based on different characteristics of different types of UHF partial discharge signals in the time domain and frequency domain. Through continuously collected and stored UHF partial discharge pulse waveform, the sampling pulse sequence is analyzed in time-frequency domain to extract characteristic parameters. And then using fuzzy cluster, it can distinguish multi-source UHF partial discharge signals and discharge signals generated by the interference to achieve multi-source UHF partial discharge signals location. And it can lay the foundation of identification of the type of partial discharge. Field tests show that the method is feasible.

Abstract: This paper concerns the problem of regulating the frequencies of the evolving electric energy systems. The currently implemented frequency regulation approach is found unable to relieve the impact of the increasingly integrated variable sources such as renewable power plants and price responsive loads. Even several key underlying assumptions of this approach are not likely to hold in this situation. In this paper we propose an enhanced frequency regulation approach by differentiating units participating in frequency regulation both with respect to their location and ability to respond. This approach models the governorturbine-generator dynamics of each individual generator and develops a linearized model of the interconnected power system. Moreover, the singular perturbation technique is employed to reduce the unnecessary complexity of the linear system and simplify the control design. An optimal feedback control law is then designed based on the reduced order model via Linear Quadratic Regulator method. Comparative simulations on a 3bus test power system show the improved control performance obtained by the proposed approach.

Abstract: A differential relay that is very sensitive relay operating even at its limits may be used for protecting a power transformer. However, this characteristic may lead to unnecessary tripping due to transient currents. In order to avoid this unnecessary tripping, estimated harmonics of these currents may be required which need great computation efforts. In this paper, a new frame work is proposed using PC interfaced with a data acquisition card AD622, which acquires real-time signals of the currents, process them numerically in the computer and outputs tripping signal to the circuit breaker. All algorithms of differential protection function and blocking techniques have been implemented using the Simulink/Matlab. To validate the present work, the performance of developed relay is tested by signals generated by Simulink/MATLAB simulator under different conditions. The test results show that this proposed scheme provides good discrimination between the transient currents and the internal fault currents.

Abstract: In reality, load variations in power systems are random in nature. Therefore, the automatic generation control (AGC) performance of the power system needs to be investigated under random load disturbances so as to have a realistic evaluation of the control strategy. This paper reports results for one such investigation. The intelligent control strategy, based on fuzzy gain scheduling of a proportional-integral (PI) controller, is developed and implemented for a multi-area multi-unit thermal power system with reheat nonlinearity. The paper also investigates the effect of superconducting magnetic energy storage (SMES) system on the AGC performance. For the sake of comparison, the behavior of the system for the same load disturbance is also investigated with a conventional PI controller. Simulation studies indicate that the proposed intelligent control strategy is very effective under random load disturbances and provides significant improvement over the conventional PI controller.

Abstract: This paper discusses the research and implementation of the mid-frequency power (MFP). The paper analyzes the present research situation and the existence question of 400Hz mid-frequency power supply. Then the research of full digital control realization process of mid-frequency power supply with high power factor and multiple closed-loop feedback (MCLF) is given. The principle and characteristic of the closed-loop control system are provided. Finally the experimental prototype taking DSP of TMS320F2812 type as control device is developed. The experimental results verify the rationality .

Abstract: The paper briefly introduces the function and characteristics of the ground simulation software CDEGS, and computes the grounding grid model by using the MALZ module. The grounding grid GPR (Ground Potential Rise) and the percentage of reference power bus GPR are analyzed after the exciting current source injected into the grounding grid, and compared and analyzed with CDEGS softwares simulation calculation results, it is easy to diagnose defect and locate defect position in the grounding grid.