Applied Mechanics and Materials Vol. 700

Abstract: Corn straw was used as the main raw material, rice husk, peanut shell and sawdust were used as auxiliary materials; First using qualitative analysis method determined the samples of moisture, ash content, volatile matter, calorific value and the content of cellulose, hemicellulose lignin. Secondly in sulfuric acid as catalyst, ethylene glycol as liquefied agent, ethanol as auxiliary liquefied conditions, corn straw is liquefied. On this basis, single factor experiment was used to investigate the effects of reaction time, reaction temperature, catalyst dosage and liquefied agent on the liquefaction reaction. The experiment results show that reaction temperature is 250°C, reaction time is 2h, dosage of sulfuric acid is 2.9%, the liquefaction rate is 80%. And infrared spectrum analysis of liquefied products and scraps show that lignin, cellulose and hemicellulose have been broken down into different components, and two liquefaction are joined at the same time, the corn straw happen two different reactions.

Abstract: As environment problem becomes increasingly prominent and energy supply becomes more and more tension, wind power as a kind of clean and renewable energy is more and more popular. The installation of large scale wind farms has been paid much attention. Collector system consolidates the power generated by turbine units to a substation from where the generated power is transmitted to the power system. Where designing a wind farm collector system, the economics and reliability of operation should be taken consideration. This paper introduces the concept and some typical layouts of the wind farm collector system, then take comparison of those layout around the economics and reliability, this may help to choose an appropriate cable layout when building a new wind farm.

Abstract: In the traditional outage model, the failure rate of the wind turbine is often given as a long-term statistics value on average, that is only one value for a wind turbine, this calculation method is not reflect the real reliability level of wind turbines. According to historical failure data, the factors that affect the wind turbine outage are divided into several categories. Based on Markov Process, the calculation methods for wind turbine failure rate under single factor and multi-factor are given respectively. On this basis, the calculation methods for wind turbine failure rate under different levels of single factor and multi-factor are given respectively based on statistical analysis method. Because different factors are taken into account in the failure rate calculation, the failure rate will change according to the actual factors and then it could reflect the real risk level of power systems when uses this failure rate. Simulation calculation is carried out on a real wind farm; the results show the effectiveness of this proposed method.

Abstract: This paper put forward a fault diagnosis project which includes fault knowledge representation, fault diagnosis arithmetic based on comprehensive investigation and engineering practice. After that a fuzzy petri net diagnosis model is come into being and the precise diagnosis of power grid elements can be realized. The simulation results given in this paper illustrate that this fault diagnosis model can make a rapid diagnosis in complex fault situation and give the accurate result to power grid fault diagnosis.

Abstract: The finite element method has been applied to calculate the 50Hz electric fields nearby the transmission lines. The electric field strengths nearby multi-circuit transmission lines on the same tower under different arrangement of phase sequence, nearby the cross-arm are calculated. According to the foreign and domestic security standards of 50Hz electric field, the impacts of overhead transmission lines on environment are evaluated and the adoptable measures to reduce electric field strength are proposed. Meanwhile the distributing pattern of the electric field nearby the cross-arm is analyzed and proposals for further protection measures during maintenance operation are provided.

Abstract: This paper presents the selection methods of typical substations based on grey correlation analysis method, and proposes classification principles of load characteristics. The actual example shows that using this method in process of statistical synthesis method modelling, the typical substations selected could be more representative, and the popularization and application of the modelling results are more accurate and effective.

Abstract: The purpose of this research is to assess the ability to resist disasters of urban power grid, find the vulnerabilities of system and put forward the evaluation results and improvements. Firstly, according to the actual disaster relief demand of urban power grid, the fault tree analysis method is proposed in this paper to analyze the causes of the accident and in accordance with this to establish the evaluation index system of capacity to prevent disasters of urban power grid. Secondly, the analytic hierarchy process (AHP) which is based on exponential scale is used to collate and calculate the indicators in the evaluation process of disaster resistance of urban power grid. The research achievement is helpful to recognize the grid’s vulnerabilities and reduce the risk of accidents caused by disasters in urban power grid’s planning and construction of disaster resistance.

Abstract: According to the problems that there are less distribution transformer state variables and the condition assessment of distribution transformer carry out difficultly, a method of distribution transformer condition assessment based on core state variables is presented. The initial results of distribution transformer condition assessment are obtained by using core state variables. Then through calculating the sensitivity of the non-core state variables to the evaluation results, the initial assessment results are modified to ensure more accurate results.

Abstract: This paper presents a power consumption model with harmonics existing in power system, the influence of harmonic linear load and the influence of nonlinear load energy metering is discussed, then the analysis of the impact of the harmonic of induction watt-hour meter and electronic watt-hour meter measurement features is given. In the next part, the measurement principle of harmonic watt-hour meter is introduced, and a new type of electric energy metering scheme based on harmonic watt-hour meter is given, so that the electric energy metering fairness problem caused by power grid harmonic will be solved effectively.

Abstract: According to the lightning monitoring data recorded by lightning location system of Guangdong power grid in the past 10 years (from 2003 to 2012), we gain the lightning parameters of Shenzhen power grid and fit the lightning current amplitude distribution curve. The research results show that the fitting expression format of the lightning current amplitude distribution gotten from lightning location system adopted by IEEE is better than that adopted by national power industry regulations. And the lightning current in Shenzhen area ranging from 20kA to 40kA shows obvious packing effect. It’s recommended to take anti-accident measures in the weak sections of mountain areas to improve the shielding failure lightning protection performance.