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Selective maintenance is widely used as a reliability-centered maintenance strategy due to the limited maintenance resources. However, existing selective maintenance studies only consider basic reliability, which cannot systematically describe the operating mechanism of a multistate system, thereby resulting in the inability to obtain an optimal maintenance strategy. Moreover, intelligent manufacturing systems are highly representative of typical multistate industrial systems. In this study, a mission reliability-oriented selective maintenance optimization model for intelligent manufacturing systems that considers the uncertain maintenance effect was proposed. First, a new connotation and modeling method for mission reliability based on multistate system theory was presented to comprehensively characterize the operating mechanism of intelligent manufacturing systems. Second, a quantitative model between maintenance resources and quality based on real-time data was established to reflect the uncertain characteristics caused by repairmen and tools. Third, a selective maintenance decision model of a multistate manufacturing system was developed under the constraints of maintenance cost and time. This constraint combination optimization problem was solved using the particle swarm optimization algorithm. Finally, a case study of selective maintenance optimization for a cylinder head manufacturing system was presented to verify the proposed method.

The classic export coefficient model has been questioned due to its fixed coefficient, especially for those large-scale watersheds where great temporal-spatial heterogeneity exists. In this paper, a dynamic export coefficient model (DECM) was proposed for simulating non-point source (NPS) pollution by incorporating the impacts of factors on export coefficients. The relationships between rainfall, slope, soil, land use, other factors and export coefficients were constructed at relatively smaller catchment based on the information of mechanistic-based model, while these dynamic export coefficients were then extended to the large ungauged basins. This new model was tested in the Three Gorges Reservoir Region (TGRR), China. The results indicated the new method improved the accuracy of large-scale NPS prediction as well as reducing the computation burden. The rainfall temporal variability was identified as the major factor influencing the variability of flow and NPS pollution with the coefficient of variation being 0.1678 and 0.2046, respectively. Using the new method, the Long watershed, the Jialing watershed, the Quxi watershed, the Xiangxi watershed and the main stream in the TGRR were identified as those sensitive regions under the changing environment. The DECM could be extended to other large scale to quantify the NPS pollution, especially data-poor watersheds.

Optimizing long-term best management practices (BMPs) is of vital importance for water quality management, especially for nonpoint source (NPS) pollution. However, changes in the efficiency of BMPs over time have not been incorporated and a proper method for determining long-term BMP configuration strategies is still lacking. In this study, the long-term BMP optimization method (LBMP-OM) was developed for recommending the BMP maintenance-replacement strategies and optimizing the BMP configuration. This new method was then tested in the Daning Watershed, Three Gorges Reservoir Region, China. Based on the results, a 1-year maintenance period and a 3-year replacement period was recommended for a filter strip by considering a changing BMP effectiveness rather than a constant effectiveness and by discussing the rationality of experts' suggestions for maintenance and replacement strategies regarding the regulation of NPS pollution. At the watershed scale, the total cost dropped by 57.36% by introducing the LBMP-OM method compare to the original method. This new method extended the long-term management and configuration of BMPs.

The solubility of 9 sparingly soluble pesticide active ingredients (PAIs) was predicted in 133 deep eutectic solvents (DESs) based on 7 hydrogen bond acceptors and 19 hydrogen bond donors, using a COSMO-RS model. 13 DESs with superior solubility of water-insoluble PAIs were screened out and verified with experiments. The actual measurement results agree well with the forecasting results. When compared with the solubility in pure water, some PAIs can even be mutually dissolvable with tetraethylammonium chloride: decanoic acid (1:2), tetrabutylammonium chloride: decanoic acid (1:3), and tetrabutylammonium chloride: phenol (1:5), such as butachlor, acetochlor, and metolachlor. IR and 1H NMR spectra suggested that hydrogen bonding between DESs and PAIs molecules played a crucial role in solvation. Crucially, the study indicated that it’s feasible to replace toxic organic solvents with DESs in emulsifiable concentrates formulations. The effects of different concentrations of tetraethylammonium chloride: decanoic acid (1:2) on the growth of wheat seedlings were also explored. The results showed that it did not affect the germination rate of wheat seeds, but with the increase of concentration, the growth indexes such as the lengths of shoots and roots grew shorter, the fresh weight of aboveground and underground decreased. This study not only provides COSMO-RS as a useful and reliable tool to screen DESs but also highlights that DESs can be an alternative to replace toxic and harmful organic solvents in emulsifiable concentrates (EC) formulations, which provide ideas and a basis for designing new green pesticide formulations.

Capillary water absorption coefficient is one of the important wet parameters that characterize the liquid water absorption capacity of porous building materials. Relevant standards uniformly stipulate the size and test conditions of the specimen in analysis of this hygrothermal parameter for porous building materials. However, different porous building materials have different water absorption capabilities due to their pore structures. Therefore, the use of the same test conditions or standards when obtaining the capillary water absorption coefficient of the material will affect the accuracy of the obtained results. In this paper, an experiment with capillary water absorption was performed to study the influence of sample size, ambient temperature and water immersion depth on the capillary water absorption coefficient of foamed cement (FC), aerated concrete (AAC) and coral sand concrete (SHS) with different pore structures. The results show that the sample size and the depth of water immersion have a significant influence on the capillary water absorption coefficient value of FC; the ambient temperature has a significant influence on the capillary water absorption coefficient value of AAC. When temperature increases from 5°C to 35°C, the growth rate of the AAC capillary water absorption coefficient is about 71.3%. The depth of water immersion significantly affects the capillary water absorption coefficient value of the SHS. When the depth of water immersion increases from 3 mm to 10 mm, the growth rate of the SHS capillary water absorption coefficient is about 38.4%.

Due to the effect of the space charges, there is still a lack of effective methods to predict the corona effects of HVDC transmission line based on cage tests. This paper presents a method of using the corona cage to evaluate the radio interference of HVDC transmission lines. First, the condition under which the tests of a corona cage can be equivalent to those of an HVDC transmission line is discussed theoretically. It shows that the key is to make the electric-field distribution around the conductors in the corona cage the same as that around the transmission line. Then, a numerical approach and the Kaptzov's assumption are used to obtain the applied voltage on the conductors in a corona cage in order to set up the same electric-field distribution as that around the transmission line. Reduced-scale tests both in time domain and in frequency domain show that the method is effective. The method can also be extended to investigate the dc corona and its other effects based on cage tests.

Background A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method was developed for the simultaneous determination of highly water-soluble propamocarb and hydrophobic cymoxanil in potato tuber and tomato fruit. Residue behaviors of the fungicides in open field or greenhouse were investigated for the safety evaluation of these two pesticides, and the effects of cultivation conditions, fungicide exposure and fruit size of tomato on residue level are discussed. Results Vegetable samples were extracted with ammonia-acetonitrile, further purified with multiwall carbon nanotubes and analyzed using high-performance liquid chromatography tandem mass spectrometry. The method was validated with fortified samples at different concentration levels (0.05-2.0 mg kg-1 ). Average recoveries ranged from 84 to 111% with relative standard deviations between 0.3 and 5.5%. Limits of quantification (LOQs) were set at the lowest spiking level of 0.05 mg kg-1 . In tomato and cherry tomato, initial residue level of cymoxanil was below LOQ at recommended good agricultural practices. Propamocarb residues were affected by the cultivation conditions, with highest levels of 0.52 and 0.72 mg kg-1 in open field and greenhouse, respectively. In addition, residues of propamocarb in cherry tomatoes were found to be present at 1.25 mg kg-1 . Conclusions The field trial results showed that propamocarb and cymoxanil residues in potato tubers were below LOQ due to the tubers not being exposed to sprayed pesticides. The unexpected high residue levels in cherry tomato seem to indicate that cherry tomato with small size presents certain accumulative effects of propamocarb. © 2020 Society of Chemical Industry.

In this paper, we present the design and simulation of a compound absorber based on metamaterial and magnetic material. The absorber is composed of ferrite layer, metal patch, dielectric layer and metal backboard. Utilizing two different structures of metamaterial absorbers, and arranging them in a special way, an 8.5 dB RCS reduction from 300 MHz to 2 GHz is finally achieved, and the maximum reduction of RCS is 13 dB. The total thickness of the absorber is 4.5 mm that is approximately 1/133 of the working wavelength. Additionally, the absorber can strongly absorb the obliquely incident electromagnetic wave for both transverse electric and transverse magnetic polarizations, even at 40° angle of incidence.

Electronic devices are faced with increasing threats from powerful electromagnetic environment with the maturity of high-power technologies. Electronic devices have to guarantee their own normal functions at the same time of resisting powerful EMP. One practical way to do this is to add a pulse guard, which is similar to an FSS radome, to the antenna of an electronic device. This paper introduces the operating principles of EMP protection surface and designs an S-band ultra-wideband self-reconfigurable EMP protection surface. Based on multi-level cascade of metal patch array and metal grid array, a patch-grid-patch self-reconfigurable EMP protection surface is developed, with a diode cascade structure designed within patch layers to achieve self-reconfigurable protection. Performances of such surface were verified through modeling and simulation. Results show that the wave-transparent bandwidth for low-power signals can be as high as more than 1 G, and the shielding effectiveness for high-power EMP can be more than 15 dB. It is obviously a new idea and way of achieving powerful EMP protection for electronic devices.

Water resources utilization, social economy development, and ecological environment protection are key factors in regional sustainable development. Scientific evaluation of regional coordinated development status and diagnosis of regional uncoordinated development constraints will improve the management level of decision-makers. At present, most developing countries have the problem of unbalanced regional development caused by the one-sided pursuit of a certain system. Taking 14 prefecture-level cities in Hunan Province as cases, this paper analyzed the spatial and temporal distribution characteristics of the carrying capacity level of the water resources system, the development level of the social economy system and the protection level of the ecological environment system in each evaluation unit based on entropy weight method and order parameter analysis. Based on the theory of coordinated development, a calculation model of a coordinated development degree was constructed, and the corresponding evaluation criteria were formulated. The spatial and temporal distribution characteristics of a coordinated development degree in each research unit were analyzed and evaluated. The results showed that the average coordinated development degree of Hunan Province from 2004 to 2016 evolved from &ldquo, Light disorder recession&rdquo, to &ldquo, Nearly disorder recession&rdquo, then to &ldquo, Reluctance coordinated development&rdquo, Restricted by different systems, the coordinated development degree in each research unit presented spatial and temporal differences. According to different development stages and the characteristics of different regions, corresponding development strategies can be formulated to provide the guidance for coordinated the development of regions.

In this study, a rapid, sensitive, and selective method was established for the detection of oxathiapiprolin and the metabolite IN-E8S72, as well as its glucose conjugate IN-SXS67 in cucumber using modified QuEChERS procedure combined with HPLC-MS/MS. The LOQs for all compounds were 0.02 mg kg-1, and the average recoveries were 77.4-111.3% with RSDs of 1.0-8.5%. Under the optimized conditions, the established method was successfully used to determine field samples in dissipation and terminal residue studies. The dissipation study results showed that oxathiapiprolin dissipated rapidly in cucumber with half-lives of 2.4-4.0 days. On the basis of the terminal residue results, the risk assessment was conducted, and both the international estimated daily intake (IEDI) or national estimated daily intake (NEDI) of oxathiapiprolin were much less than 100% which indicate a low health risk to consumers. This work provides guidance for establishing MRL of oxathiapiprolin in China and is of great significance for evaluating its dietary risk in cucumber.

With the increasing emphasis on environmental problems and climate change, renewable energy sources have been developed globally to push modern power systems towards sustainability. However, the weather-dependent and non-dispatchable features of renewable energy sources often hinder their integration into power grids and also pose a challenge for peak load regulation. Recently, the complementary operation of multi-energy hybrid systems has been attracting increasing attention as a promising way to overcome the mismatch between renewable energy supply and varying load demand. Multi-energy systems should be operated considering multiple uncertainties since a deterministic method only captures a fixed snapshot of a constantly changing system. In this study, the obtained short-term peak shaving operation of a hydro-wind-photovoltaic hybrid system is developed as a stochastic programming model. The uncertainties of renewable energy production and load demand are thoroughly simulated in the form of synthetic ensemble forecasts and scenario trees. To enhance the computational efficiency, a parallel particle swarm optimization algorithm is developed to solve the stochastic peak shaving model, in which a novel encoding scheme and parallel computing strategy are used. The proposed framework is applied to a hydro-wind-photovoltaic hybrid system of the East China Power Grid. The results of three numerical experiments indicate that the framework can achieve satisfactory peak shaving performance of the power system and enable decision makers to examine the robustness of operational decisions. In addition, it is acceptable for decision makers that joint complementary operation of the hybrid system greatly enhances the peak shaving capacity (with the performance metrics being improved by 95.7%, 96.4% and 30.5%) at the cost of 0.11% loss of total power generation.

Estimating accumulated mechanical load of operating wind turbines (WT) is important to the operation security and lowering operation and maintenance (O&M) costs. This paper aims to estimate the mechanical load of a WT using data from its Supervisory Control And Data Acquisition (SCADA) system. Firstly, input parameters are determined by calculating the correlation coefficients between SCADA data and mechanical loads of the WT. Moreover, the Adaptive Network-based Fuzzy Inference System (ANFIS) is applied to establish the relationship between input parameters and mechanical loads. In order to prove the validity of proposed method, SCADA data and load measurements on seven crucial locations of a 2.5MW WT are collected to compare estimated and measured loads. Results show that the estimated loads are in good agreement with measurements. The coefficients of determination (R2) on different locations of the WT is between 88% and 97%. Using the proposed method, the R2 increases nearly 2%. This method can be used to optimise and lower the cost of operation & maintenance (O&M), for example by prioritising inspections and replacements.

data of the Dynamic Export Coefficient Model

Streamflow simulation gives the major information on water systems to water resources planning and management. The monthly river flows in dry season often exhibit high autocorrelation. The headwater catchment of the Yellow River basin monthly flow series in dry season exhibits this clearly. However, existing models usually fail to capture the high-dimensional, nonlinear dependence. To address this issue, a stochastic model is developed using canonical vine copulas in combination with nonlinear correlation coefficients. Kendall&rsquo, s tau values of different pairs of river flows are calculated to measure the mutual correlations so as to select correlated streamflows for every month. Canonical vine copula is used to capture the temporal dependence of every month with its correlated streamflows. Finally, monthly river flow by the conditional joint distribution functions conditioned upon the corresponding river flow records was generated. The model was applied to the simulation of monthly river flows in dry season at Tangnaihai station, which controls the streamflow of headwater catchment of Yellow River basin in the north of China. The results of the proposed method possess a smaller mean absolute error (MAE) than the widely-used seasonal autoregressive integrated moving average model. The performance test on seasonal distribution further verifies the great capacity of the stochastic-statistical method.

The DC electric field is sometimes accompanied by space charges caused by the partial discharge in the air, which impacts DC electric field measurements. This paper describes the impact factors in the calibration and application of the field mill for measuring the DC electric field with space charges. First, the influence of the space charges on calibration results is evaluated and discussed. Then, both the impact of the height of the meter probe above the ground and the touch resistance between the ground and the meter on the measurement results are investigated. Correct calibration and application methods are presented. The results are expected to be of use to engineers for conducting accurate measurements of the DC electric field with space charges.

With the environmental advantages of solar energy in Lhasa area, the use of solar photovoltaic (PV) in residential power generation is encouraged by China governments incentives, however, what number of battery for energy storage from installing an off-grid PV system under given load profile is not clearly understood yet. This study aims to investigate the economic and technical performance of residential PV system and find the optimal size of battery. The proposed PV system composed of PV arrays, diesel generator and energy storage system (ESS) is established and simulated by means of HOMER (Hybrid Optimization of Multiple Electric Renewables) software. Date of technology parameters, cost parameters and available resource have been used to find the optimal system configuration with the lowest net present cost (NPC). Finally, the optimal sizing of energy storage, state of charge (SOC) for energy storage, the cost of each part and power generation cost under the optimal configuration of this system have been analyzed. The simulation results show this renewable resource can deal with 69% of the annual total electricity production with storage capacity of 416.4 kWh.

In line with the requirements of green chemistry, the preparation of eco-friendly pesticide formulations has become an inevitable development trend. In this work, we explored the feasibility of four new ionic liquids (ILs, [Octyl trimethyl ammonium] anions, anions = proline, valine, leucine, tartaric acid) as environmentally-friendly solvents for pesticide emulsifiable concentrates, and also as alternatives to traditional imidazole-based ILs since they do not contain the imidazole ring and the anions are natural substances. The results showed that the solubility of pesticides (clethodim, metolachlor, acetochlor, prochloraz, thiamethoxam, glyphosate, acetamiprid) in water with 25%w/v ILs was significantly improved, especially for acetamiprid, where the solubility was increased 19-fold, while it only increased about 4 to 5-fold after adding imidazole-based ILs in our previous work. In addition, the solubilization mechanism was explored by many methods and found that the solubilization effect does not completely depend on the critical micelle concentration (CMC) value but has a great relationship with the hydrophilicity of the ILs which may affect the size of micelles and release behavior to pesticides. Finally, 1H NMR was used to investigate the solubilization sites of ILs for glyphosate, and the interaction between pesticides and anions was explored by the quantum chemical method.

As one typical land use change, the mechanism of returning farmland to forests (RFF) on nonpoint source pollution (NPS) is not clear, especially at multiple spatial scales. In this study, by using the Soil and Water Assessment Tool (SWAT), the changes in several flow-related and NPS-related indicators across several nested catchments were quantified and compared in the Three Gorges Reservoir Region, China. The results indicated that RFF could reduce the total flow and total phosphorus (TP), which are higher in the dry season (41% and 79%, respectively) than in the wet season (21% and 47%, respectively) at the watershed with a total area of 2423.74 km2. In comparison, RFF has a larger impact on the baseflow index during the wet season (367.02%) than during the dry season (166.54%). The results also indicated that a spatial scaling effect did exist, while the reduction in TP increased from 24.57% to 48.46% as the drainage area increased from 65.92 km2 to 2104.35 km2. Specific thresholds of RFF efficiency were also observed (approximately 2000 km2 for the study area). It is suggested that other source control measures could supplement RFF by stabilizing the efficiency of RFF across different spatial scales. The results of this study could provide valuable suggestions for land use development and water quality protection, especially for large, complex watersheds.

Effective water-quality management requires full understanding of the nonpoint source (NPS) pollutant pathways. However, the spatial scaling effect has become one key barrier for the estimation of baseflow NPS pollutants. In this study, the scaling effect of baseflow NPS pollutants was investigated. The Soil and Water Assessment Tool was used for flow and NPS pollutants simulation at nested river sections, while the baseflow NPS pollutants was then estimated based on 17 levels of nested watersheds in a watershed of China. The results indicated that as the spatial scale increased, the baseflow became an important pathway of NPS pollutants, as its average contribution increased from 0.27 in the small headwater catchment to 0.45 in the nested large watershed. The scaling effects of the baseflow index (BFI) and the contribution of the baseflow NPS pollutants were closely related to the land use distribution among those upstream catchments, whereas for the mainstream, the tributary inflow would become another important reason for the scaling effect. Furthermore, the spatial scaling effect of the BFI was less obvious during the dry period, whereas the spatial scaling of the baseflow NPS pollutants did not show much difference among different hydrological periods.

In this study, the ultrasonic dishwasher was used to remove five pesticides known to be frequently used on rape and grape. As compared with normal water washing, washing with the ultrasonic dishwasher was demonstrated to be more effective for pesticides removal, achieving removal rates between 14.7% and 59.8% on rape, and between 72.1% and 100% on grape. However, there were significant differences in order of the removal rate of five pesticides on rape and grape. From the adsorption experiments and analysis via Freundlich equation, the adsorption index (n, 0.551–1.056 on rape and 0.362–1.478 on grape) and adsorption coefficient (KF, 10−2.47–10−1.65 and 10−3.64–10−1.56 (mg·dm−2)/(mg·L−1)−n on rape and grape) were obtained. Taken together with the observation of the matrix surface by scanning electron microscopy and the evaluation of the physicochemical properties of pesticides, the different pesticides removal may be related to surface structure of the matrix.

Studies on environmental flow have developed into a flow management strategy that includes flow magnitude, duration, frequency, and timing from a flat line minimum flow requirement. Furthermore, it has been suggested that the degree of hydrologic alteration be employed as an evaluation method of river ecological health. However, few studies have used it as an objective function of the deterministic reservoir optimal dispatching model. In this work, a multi-scale coupled ecological dispatching model was built, based on the decomposition-coordination principle, and considers multi-scale features of ecological water demand. It is composed of both small-scale model and large-scale model components. The small-scale model uses a daily scale and is formulated to minimize the degree of hydrologic alteration. The large-scale model uses a monthly scale and is formulated to minimize the uneven distribution of water resources. In order to avoid dimensionality, the decomposition coordination algorithm is utilized for the coordination among subsystems, and the adaptive genetic algorithm (AGA) is utilized for the solution of subsystems. The entire model&mdash, which is in effect a large, complex system&mdash, was divided into several subsystems by time and space. The subsystems, which include large-scale and small-scale subsystems, were correlated by coordinating variables. The lower reaches of the Yellow River were selected as the study area. The calculation results show that the degree of hydrologic alteration of small-scale ecological flow regimes and the daily stream flow can be obtained by the model. Furthermore, the model demonstrates the impact of considering the degree of hydrologic alteration on the reliability of water supply. Thus, we conclude that the operation rules extracted from the calculation results of the model contain more serviceable information than that provided by other models thus far. However, model optimization results were compared with results from the POF approach and current scheduling. The comparison shows that further reduction in hydrologic alteration is possible and there are still inherent limitations within the model that need to be resolved.

A method to restrict the ion-flow field under the high-voltage direct-current (HVDC) transmission line by installing shield wire (SW) is analyzed in this paper. A reduced-scale platform is built up in the laboratory to check the effect of SW on decreasing the electric field and ion current density on the ground. The influence of SW on the ion-flow field is analyzed by an upstream finite volume method (FVM) and the calculated results match the measured ones well. A typical ± 800-kV bipolar HVDC transmission line is analyzed as an application, and it is shown that if the geometric parameters of SW are chosen suitably, the maximum ground-level electric field under the transmission line can be obviously decreased. In engineering design, it is an effective method to restrict the ion-flow field by installing SW under the HVDC transmission line.

A novel algorithm based on the correlation analysis of waveforms to distinguish between the magnetizing inrush and the short-circuit fault current is proposed. The algorithm makes use of the characteristics of differential current waveform in the nonsaturation zone that it is similar to a part of the sinusoidal wave under the short-circuit fault and far different with the sinusoid under the inrush condition. To realize this algorithm, the nonsaturation zone of the transformer is decided by comparing the algebraic sum of sampling data in a short slide window of the differential current under the magnetizing inrush or the short-circuit fault, then two kinds of normal sinusoidal waveforms are structured according to the value and position of the peak point of differential current in the nonsaturation zone. The correlation coefficients between the original waveform and two structured sinusoidal waveforms are calculated, and the magnetizing inrush or fault current is judged according to the average of two correlation coefficients. The experimental results verify that the algorithm can correctly open the differential protection shortly for the internal short-circuit fault in operation, energized with a turn-to-turn short-circuit fault, reliably blocking the protection during the magnetizing inrush, and obtaining good immunity to the saturation of the current transformer. Low computation and requirements contributing to this algorithm are performed in practice.

International audience; This work is devoted to characterization of the deformation and strength properties of cataclastic sandstones. Before conducting mechanical tests, the physical properties were first examined. These sandstones are characterized by a loose damaged microstructure and poorly cemented contacts. Then, a series of mechanical tests including hydrostatic, uniaxial, and triaxial compression tests were performed to study the mechanical strength and deformation of the sandstones. The results obtained show nonlinear stress–strain responses. The initial microcracks are closed at hydrostatic stress of 2.6 MPa, and the uniaxial compressive strength is about 0.98 MPa. Under triaxial compression, there is a clear transition from volumetric compressibility to dilatancy and a strong dependency on confining pressure. Based on the experimental evidence, an elastoplastic model is proposed using a linear yield function and a nonassociated plastic potential. There is good agreement between numerical results and experimental data.

This study has the objective to study the optimized configuration of cooling source of a districted natural gas Combined Cooling Heating and Power (CCHP) system, and as a result, models of cooling source, distribution and system energy efficiency were established. Through a C# program, hourly simulation of operation quantity, power consumption, and equivalent thermal coefficient (ETC) of the cooling system during May to October was conducted under three configuration strategy schemes. The results revealed that when the waste heat of CCHP system was properly utilized, increasing the number of electric chiller could increase primary energy utilization rate. Scheme One with the most electric chiller units (15 units) consumed the most power, but had the highest ETC of 1.031 (mean),which was, respectively, 0.268 and 0.346 higher than that of Scheme Two with 11 electric chiller units and Scheme Three with most steam BrLi absorption chiller units (nine units). Scheme Three needed the most steam which led to the least electricity generated. Although in this scheme, the electric chillers consumed the least power, the average remaining electricity of the CCHP system was the lowest (64,992.4 kWh), which was 21,441.9 and 6,233.8 kWh less than that of Scheme One and Scheme Two. ETC of the three schemes (1.031, 0.763, and 0.685, respectively) were much less than that of electric chiller (2.630), which meant that the main reason for the decrease of primary energy utilization rate of the cooling system was due to low primary energy utilization rate of the distribution system.

The measurement of DC electric field is of great significant. This paper introduces the structure and working principle of the field-mill instrument firstly. Then the calibration method of field-mill instrument in a uniform space-charge-free field is introduced and the error in the calibration is studied by numerical calculation. The calibration coefficient is corrected to be more accurate afterwards. At last, the interaction between the field-mill instruments is discussed. By means of numerical calculation, the shortest distance between two field-mill instruments which can control the measurement error less than 5% is put forward.

The cluster effect of charging load characteristics of the large-number of EVs will put forward a new requirement on the power supply of distribution system. Based on the power load model of single EV charger in consideration of batteries SOC, the normal distribution of initial SOC and Poisson distribution of the time vehicles arrived, a charging station model for the cluster effect of EVs is presented to analyze the load demand in a parking lot in a day. Then an optimization strategy of vehicles charged orderly is proposed. By Monte Carlo simulation, it is verified that the proposed strategy could help on reducing peak and filling valley while meeting EVs users' charging demand.

With more and more EV charging stations accessed to power system, researches on the clustering effect of EV chargers and their influence on the static voltage stability become important and necessary. This paper carries out studies aiming at analysis, modeling and simulation of EV charging station along with its impacts on the static voltage stability of power system. In this paper, the load characteristics of EV charger are deduced separately in the constant-current/constant-voltage charging mode. Then the single EV charger model and the cluster equivalent load model of an EV charging station is established in Matlab/Simulink toolbox, after which its impact on the static voltage stability is studied based on a simple system through simulation.

With the continued growth of wind power installed capacity, as well as the continual emergence of large-capacity wind farm, the impact of wind power on the grid will not be ignored. Studying on the performance characteristics of wind turbine and analyzing the effects on grid and the generators are of great significance to ensure the grid-connected wind turbine safe and reliable operation. In this paper the dynamic model of the induction generator and doubly-fed induction generator of wind turbines are built in PSCAD. Additionally, the static synchronous compensator (STATCOM) model and a vector control method are prompted. The simulation of a single machine infinite bus system containing a wind farm is conducted, which includes two different kinds of wind turbines. By comparing the active power, reactive power, and the output voltage of two different kinds of wind turbines, the effect of STATCOM on fault ride-through capability of wind generators is analyzed when the grid voltage dropped. Simulation result shows that STATCOM has played a big role in maintaining the transient voltage stability of the power system and improves the fault ride-through capacity of wind farms.

To improve the sensitivity of ground fault protection for generators, this paper proposes a novel protection based on the fault components of third harmonic voltage at the terminals and neutral. Two types of protection scheme, i.e. amplitude and phase comparison, are given. The results of simulation and experiment verify that the novel protection is with high sensitivity, is immune to the operating condition of generator, and is of robustness.

In this paper, a system is designed and developed to measure the positive corona current in coaxial wire-cylinder gaps. The characteristic parameters of corona current pulses, such as the amplitude, rise time, half-wave time, and repetition frequency, are statistically analyzed and a new set of empirical formulas are derived by numerical fitting. The influence of space charges on corona currents is tested by using three corona cages with different radii. A numerical method is used to solve a simplified ion-flow model to explain the influence of space charges. Based on the statistical results, a stochastic model is developed to simulate the corona pulse trains. And this model is verified by comparing the simulated frequency-domain responses with the measured ones.