Advanced Materials Research Vols. 805-806

Abstract: Under the situation of energy crisis, air source heat pumps are paid more attention recently. In order to save energy, the feasibility and performance of air source heat pump are studied by experiment, and variation laws of exhaust temperature, evaporator outlet temperature and outlet presser of compressor were analyzed in this paper. Air source heat pump apparatus were set up and the experiment was during 10°C, 20°C, 30°C and 40°C. The results were as follows: exhaust temperature of compressor increases gradually with the increase of tank temperature, but the temperature difference between exhaust temperature of compressor and tank temperature becomes little; temperature difference in evaporator decreases; Compressor outlet pressure increases obviously.

Abstract: The optimum working conditions of 11 working fluids under different heat source temperatures for an organic Rankine cycle (ORC) were located in our previous work. In the current work, the system irreversibility of each candidate were calculated and compared at their optimal operating conditions. Obvious variation trends of both the cycle efficiency and irreversibility were found for different types of organic fluids. It is suggested, when selecting working fluid for our ORC system, the critical temperature should be as close as possible to the heat source temperature to achieve high cycle efficiency but avoid large irreversibility. The relationships between the structure of the molecules and the critical temperature of the working fluids are investigated qualitatively and potentially meaningful for the rational selection of proper organic fluids for certain ORCs.

Abstract: Coke constitutes the major portion of ironmaking cost and its production causes the severe environmental concerns. So lower energy consumption, lower CO₂ emission and waste recycling are driving the iron and steel industry to develop alternative, or coke-free, ironmaking process. Midrex and HYL Energiron are the leading technologies in shaft furnace direct reduction, and they account for about 76% of worldwide production. They are the most competitive ways to obtain high quality direct reduced iron (DRI) for steelmaking. Therefore, in the present paper, some detailed information about these two processes are given. Much attention has been paid on process scheme, the feedstock, DRI product, heat recovery, reforming gas, hot discharge and transportation, and by-product emission. Its very important for direct reduction development in both natural gas-rich counties and natural gas-poor counties.

Abstract: This article is devoted to the formation of the electrical equipment state estimation for power stations and substations. The article also addresses to the use of fuzzy logic for the knowledge base formation on the basis of expert judgements using membership functions. The article presents the example of calculation of the electrical equipment state estimation.

Abstract: Power quality monitoring products are very popular to monitor and control the power quality in recent years. The uncertainty of voltage unbalance is an important parameter designed in these monitoring products. Some standards specify several sinusoidal waveforms to detect the uncertainty of voltage unbalance. But these waveforms seem not enough and some manufactures do not follow the standards to design the detection process. So this paper proposes a method of detecting the supply voltage unbalance accuracy and gives some detection waveforms for uncertainty of voltage unbalance. The simulation results show good agreement with the IEC standards.

Abstract: The correct and reliable identification of SLG(single-line-to-ground) fault is the foundation of starting the fault line selection and location device in neutral un-effectively earthed system. The traditional method based on the zero sequence voltage is invalid when the fault happens with high impedance, because the zero sequence voltage in bus is small. So a new algorithm based on the variation of voltage including the zero sequence voltage and phase voltages is proposed. The algorithm is not affected by the unbalance of system, and the sensitivity and the reliability of the algorithm are considered simultaneously. The algorithm is proved effectively by the large numbers of simulations using PSCAD/EMTDC program.

Abstract: A nonlinear once-through coal-fired boiler-turbine unit model is introduced and analyzed for the purpose of control system design. Firstly, input-output variable pairing configurations for this 3×3 system are obtained based on static relative gain array and row-Gershgorin band analysis using its linearization model at 100% load. A decentralized PI control system is then deployed and tuned to explore its control system performance as the basis of further study. Results show that the decentralized control structure has good setpoint tracking performance, while the disturbances between loops are still notable due to non-diagonal dominance, thus control strategy of decoupling or disturbance rejection is necessary.

Abstract: Introducing substation to substation communication interface, tunneling communication and gateway communication described in IEC61850-90-1. For current differential protection, by adopting the idea of object-oriented modeling, dividing functions into logical nodes, gives the protection logic node model, shows the function of logic nodes and the realization of function based on the protection principle; Using Unified Modeling Language (UML) technology of collaboration diagram and sequence diagram, describes the protection logic node interaction and communication process from the messaging level and time level, providing reference to the design and development of Intelligent Electronic Devices (IED).

Abstract: Nowadays, there are various devices to detect the power quality of AC grid, where uncertainty of voltage deviation is an important parameter to investigate the power quality. National standards specify several sinusoidal waveforms to detect it, usually implemented into the detecting devices. But these waveforms are not enough and a novel method of detecting measurement uncertainty of voltage deviation is proposed in this paper. A series of detection waveforms are designed using this method. The simulation results verify that the method is available to measure uncertainty of voltage deviation more accurately. Moreover, it can be used to justify whether the basic measurement time interval of voltage deviation meets IEC standard requirements.

Abstract: This paper focuses on the estimation of the stability index of a power system after a severe disturbance. The description of the stability margin has always been a challenging issue but by introducing a ball-on-concave-surface system, the assessment of the power system stability is equivalent to the analysis to the motion state of the ball on concave. According to the continuous measurement of PMU, the parameter of the concave can be determined which is useful to judge the stability margin of the power system. Tests have been conducted on the systems with two generators and results show it can be accurate and reliable.