Search

System strength and inertia inherently provided by synchronous generators (SGs) empower a power system to ride through voltage and frequency disturbances. The requirements of system strength and inertia were not enforced in the National Electricity Market (NEM) of Australia since SGs dominated the generation fleet in the past. However, the increasing wind and solar generation continuously displaces SGs and consequently reduces system strength and inertia in the NEM. This paper proposes a formulation of system strength and inertia constrained generator dispatch to reassure NEM operational security in light of emerging high renewable penetration. A fault current iterative solver is developed to evaluate system strength, in which the current limitation and voltage control logic of inverter-based generators, and the fault current contribution from VAR compensators are properly modelled in the phasor domain. The system strength contribution factor of an SG is defined to linearize system strength constraint for unit commitment (UC). System and sub-network inertia constraints are also formulated for the UC to limit the rate of change of frequency (RoCoF) in the event of generator/interconnector trip. The proposed generator dispatch formulation can fully meet system strength and inertia requirements in the NEM. [ABSTRACT FROM AUTHOR]

Synchronous generators are operating for less time than before or being decommissioned in the National Electricity Market (NEM) of Australia, due to the proliferation of asynchronous wind and solar generation. Sub-networks of the NEM will face inertia shortages in the near future. This paper develops a formulation of zonal inertia constrained generator dispatch for power systems with a diversified generator portfolio including synchronous generators, synchronous condensers, inverter-interfaced generators and energy storages. Zonal inertia constraints are formulated in unit commitment and optimal power flow to limit the rate of change of frequency (RoCoF) in the event of network separation. Load frequency relief is also considered to reduce the ramp rate requirement of primary reserve. The proposed formulation can reduce the average cost of primary reserve and maintain zonal inertia adequacy to constrain RoCoF in case of the trip of the interconnector(s). [ABSTRACT FROM AUTHOR]

Over the last decade, many power systems have significantly changed with the proliferation of renewable generation sources, such as wind and solar photovoltaic. Due to their variability and nonsynchronous nature, new challenges and complexities have emerged regarding operational security of modern power systems. The 2016 South Australia (SA) blackout was the first known blackout due to such a high renewable situation. An official report has recently been published to review the causes and provide the corresponding recommendations for improvement of network operation, control, and security. However, there are still a number of critical issues and debates which remain unsolved, such as network bottleneck identification, overvoltage explanation, pole slip concern, frequency dip mystery, and frequency/voltage instability debate. In this paper, based on the reconstruction of the event, these unsettled issues are prudently analyzed to unveil their root causes. In addition, an innovative scheme is proposed to prevent the blackout by identifying the network separation at an early stage. This research will not only further advance the understanding of the 2016 SA blackout, but also will provide valuable guidelines for the management of future renewable-rich networks. [ABSTRACT FROM AUTHOR]

The installed capacity of wind generation and photovoltaics (PV) in many countries is going to dominate generation fleets in a bid to meet growing renewable energy targets. Synchronous inertia has never been problematic as there was more available than needed, but it is being significantly reduced due to the increasing integration of nonsynchronous renewable generation. When the low bidding priced generation of wind and PV becomes considerably large, conventional economic dispatch algorithms can result in less online synchronous inertia and put power system security at risk. However, the compromise of power system security due to synchronous inertia shortage is not well studied in the literature. This paper develops a synchronous inertia constrained economic dispatch algorithm to satisfy the minimum required synchronous inertia of frequency control. Synchronous condensers and wind reserve are economically allocated to alleviate any shortage of synchronous inertia and frequency control ancillary services (FCAS). A Gaussian particle swarm optimization algorithm is introduced to simultaneously co-optimize the dispatch of synchronous generators and their FCAS, wind reserve, and synchronous condensers. [ABSTRACT FROM AUTHOR]

Food safety is a global health objective, and foodborne diseases represent a major crisis in health. Techniques that are simple and suitable for fast screening to detect and identify pathogenic factors in the food chain are vital to ensure food safety. At present, a variety of analytical methods have been reported for the detection of pathogenic agents. Whereas the sensitivity of detection and quantification are still important challenges, we expect major advances from new assay formats and synthetic bio-recognition elements, such as aptamers. Owing to the specific folding capability of aptamers in the presence of an analyte, aptasensors have substantially and successfully been exploited for the detection of a wide range of small and large molecules (e.g., toxins, antibiotics, heavy metals, bacteria, viruses) at very low concentrations. Here, we review the use of aptasensors for the development of highly sensitive and affordable detection tools for food analysis. [ABSTRACT FROM AUTHOR]

Bombyx mori L. ( B. mori) were exposed to cadmium chloride (CdCl) incorporated in an artificial diet (0, 6.25, 12.5, 25, and 50 mg kg) throughout the larval stage. Changes in malondialdehyde (MDA) and reduced glutathione (GSH) contents and activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), as well as their corresponding messenger RNA (mRNA) levels in the testes of the fifth instar larvae were evaluated. Additionally, spermatozoon deformation in the testes was examined. Upon Cd treatment, the MDA content in the testes was significantly increased in a concentration-dependent manner. Cd-exposed larvae had increased levels of glutathione. Pearson's correlation analysis revealed that SOD and CAT activities were positively correlated ( R = 0.605, P = 0.017). The changing trends in the mRNA levels of these enzymes were not always consistent with those of enzymatic activities. Alterations in GSH-Px activities and mRNA levels were positively correlated ( R = 0.771, P < 0.01). Morphological analysis revealed that Cd deformed and affected the maturation of spermatozoa. Our results collectively support a relationship between Cd and alterations in the levels of antioxidant enzymes in B. mori testes. [ABSTRACT FROM AUTHOR]

Constructing the access roads between wind turbines requires a significant cost when a wind farm is built in hills or mountains. An optimized design of road network can substantially reduce construction costs and increase investment returns. In this paper, we consider a challenging problem of the road network design for a wind farm with complex topography. An automatic contour-based model is developed for road network design, and is incorporated into the optimization of wind farm micrositing to maximize investment returns of the wind farm. The directions of access roads are first deduced from a contour tree, the route projections are then designed by a gradient-bounded algorithm, and the most cost-effective road network is finally obtained by the minimum spanning tree algorithm. The topographic speedup, wind resource grid and Park wake model are incorporated to accurately evaluate the power production of the wind farm. Both the profit of wind energy sales and the cost of access roads are combined into a cost function called net present value, which is optimized using genetic algorithms. Simulation results illustrate that the length of access roads is decreased significantly while the locations of wind turbines are optimized. The proposed method simultaneously optimizes the turbine layout and road network of the wind farm, therefore achieving a more practical and profitable wind farm micrositing. [ABSTRACT FROM PUBLISHER]

Abstract: The micro-siting of wind farms has recently attracted much attention due to the booming development of wind energy. The paper aims to maximize the electrical power extracted from a wind farm while satisfying the required distance between turbines for operation safety. The micro-siting problem is by nature a constrained optimization problem, in which the coupling of wake effects is strong and the number of position constraints between turbines is large. An improved Gaussian particle swarm optimization algorithm is proposed to optimize the positions of turbines in the continuous space. To prevent the premature of the algorithm, a local search strategy based on differential evolution is incorporated to search around the promising region achieved by the particle swarm optimization. A simple feasibility-based method is employed to compare the performance of different schemes. Comprehensive simulation results demonstrate that the micro-siting schemes obtained by the proposed algorithm increase the power generation of the wind farm. Moreover, the execution time of the algorithm is significantly reduced, which is important especially for large-scale wind farms. [Copyright &y& Elsevier]