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Previous research has indicated that wind power plants can be designed to have less‐variable power generation, thereby mitigating the drop in economic value that typically occurs at high wind power penetration rates. This study investigates the competitiveness of adapted turbine design and the interplay with other flexibility measures, such as batteries and hydrogen storage, for managing variations. The analysis covers seven turbine designs for onshore and offshore wind generation, with different specific power ratings and hub heights. Various flexibility measures (batteries, hydrogen storage and transmission expansion) are included in the optimization of investment and dispatch of the electricity system of northern Europe. Three driving forces for turbine design selection are identified: (1) lowest cost of electricity generation; (2) annual wind production per land area and (3) improved generation profile of wind power. The results show that in regions with good wind resources and limited availability of variation management, it is cost‐efficient to reduce the variability of wind power production by adapting the turbine design. This remains the case when variation management is available in the form of batteries, hydrogen storage and transmission system expansion. Moreover, it is more cost‐effective to improve variability by changing the specific power rating rather than the turbine hub height. [ABSTRACT FROM AUTHOR]

In arid to semi‐arid regions, groundwater is a critical water resource heavily relied upon, with the recharge sources and patterns being predominantly shaped by climate change and regional disparities. To compare the characteristics of groundwater in the endorheic and exorheic river basins with the climate transition zone of Gansu Province, this study uses isotopic hydrochemical analyses. This study summarizes the differences in regional groundwater recharge and evolutionary patterns. The results shows that the distribution patterns of precipitation isotopes in endorheic and exorheic river basins are opposite to those of groundwater isotopes. Specifically, the precipitation in the endorheic areas is more depleted in heavy isotopes, whereas the groundwater is more enriched. Both endorheic areas and exorheic areas exhibit similar characteristics of groundwater hydrochemical evolution, evolving from low‐mineralization Mg2+HCO3− recharge water to Na+Cl− type water with saline characteristics. The former is primarily replenished by surface water, whereas the latter is primarily replenished by precipitation. Variations in recharge patterns along with the differences in climatic conditions lead to distinct groundwater conditions in the two regions. [ABSTRACT FROM AUTHOR]

Land use significantly affects the rate and amount of groundwater recharge. To understand these patterns, stable isotope analyses (δ2H and δ18O) and hydrochemical methods were employed to study the recharge and evolution of groundwater. MixSIAR Bayesian mixture modelling and statistical regression techniques were utilized to investigate the influence of land‐use type on groundwater recharge and to calculate the contribution of various water sources to different groundwater types. These findings are important for effective management and conservation of groundwater resources. The groundwater in all studied areas displayed a magnesium bicarbonate type with notable cation exchange, and also demonstrated the dissolution of carbonate and weathering of silicate. Results from the Bayesian mixture model indicate that 69.3% of the groundwater in the Loess Plateau region was recharged by precipitation, while 86.9% of the groundwater in the loess hilly‐gully region was recharged from the surface water. Groundwater recharge was more rapid in the loess hilly‐gully region than in the Loess Plateau and was less sensitive to the land use type in the former. Dryland‐moderate coverage grassland was found to be most conducive to groundwater infiltration, whereas monotypic dryland and high‐coverage grassland inhibited infiltration to some degree. To maintain balanced soil erosion control, an increase the area of moderate‐coverage grasslands in the Loess Plateau region is recommended. [ABSTRACT FROM AUTHOR]

Converter interfaced distributed generations in a microgrid feed the modulated current of limited magnitude during fault conditions. The protection design and its operation are thus challenging due to limited fault current which is further reduced by Petersen coil grounding in medium‐voltage (MV) level. This paper aims to address this challenge by developing a current‐only directional relay algorithm for the protection of converter dominated MV microgrid with Petersen coil grounding. The relay's operating principle is based on the sign of the change in phase angle of the fault current with respect to the prefault which indicates the direction of fault. The negative and positive changes in current's phase angle determine the fault in forward and reverse direction, respectively. The tripping decision is derived by comparing the binary output of the relay at both ends of the line segment under protection. This requires a simple, flexible and low bandwidth communication channel. Both theoretical analyses and simulation studies have been performed on a typical distribution grid intended to be operated as microgrid. The proposed protection method is suitable for microgrid having the converters with and without reactive power support. Various operating conditions are evaluated, including bidirectional power flow, high resistance fault, different fault types, loading conditions and signals with noise. [ABSTRACT FROM AUTHOR]

This study investigates the frequency behaviour in the Nordic power system (NPS) utilising phasor measurement units (PMUs) from different locations in the system. Different metrics are selected or proposed to quantify the system frequency response in case of major disturbances and of daily normal operations. Based on the collected PMU data, there are on average 17.5 major, generator disconnection related, disturbances per year. The maximum absolute rate of change of frequency exceeds 0.1 Hz/s for 20% of these disturbances. The average frequency nadir falls to 49.7 Hz, and the average time to nadir is about 8.7 s. If wind turbines were to be requested to provide inertia support to the system, these four metrics indicate how often, how fast, for how much and for how long the wind turbines should act. Moreover, during daily normal operations, the system has in general longer duration of over‐frequency (f > 50.1 Hz) than under‐frequency (f < 49.9 Hz). These frequency deviations are observed to occur around the hourly clearing of the Nord Pool Spot market and, especially during the hours between 05:00 and 08:00. In order to improve the frequency quality, the Nordic system operators tested and implemented an automatic frequency restoration reserve (aFRR) in addition to the existing manual one. Based on a frequency evaluation, this aFRR is needed most during 4:45–08:15 and 22:00–23:30 o'clock in 2012 in the NPS. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a novel emulsion explosive, which has three primary advantages, namely, the ability to easily adjust various detonation properties to desired values, decrease the overall cost of civil explosive products, and minimize environmental pollution during use. Immediate and time‐related experiments are performed in order to identify changing detonation properties of these new formulas. Our results show that both common clay and hollow glass micro‐spheres (HGMs) function as thermal diluents, which indicates that for a larger quantity of these additives, the weaker are the detonation properties under the condition of our experimental ratios (HGMs: from 5 wt.% to 15 wt.%; common clay: from 0 wt.% to 20 wt.%). Furthermore, a comparison of four alternative emulsion explosive compositions reveals that the longest storage time in this study is 5 weeks with No. 3‐3, which contains 15 wt.% HGMs and 10 wt.% common clay. In addition, nonlinear attenuation is observed and explained for that period. [ABSTRACT FROM AUTHOR]

This study presents the impact on power system frequency control in small power systems based on different generator topologies with a large penetration (50%) of variable speed wind turbines. The impact of a proposed controller is investigated versus various wind speeds. In particular, wind speeds with an average wind speed just below rated wind speed proves to cause the worst frequency fluctuations regardless of the type of backup generation topology investigated during 50% wind-penetration ratio. For this wind-speed session and a hydro-based system, the proposed control system improves the frequency duration outside of the specified range [49.9, 50.1]Hz from 81 to 53% while reducing its delivered energy by only 6%. Furthermore, the proposed control reduces the absolute value of requested reserve by 49% from the hydro unit responsible for primary frequency control. [ABSTRACT FROM AUTHOR]

This study investigates the frequency behaviour in the Nordic power system (NPS) utilising phasor measurement units (PMUs) from different locations in the system. Different metrics are selected or proposed to quantify the system frequency response in case of major disturbances and of daily normal operations. Based on the collected PMU data, there are on average 17.5 major, generator disconnection related, disturbances per year. The maximum absolute rate of change of frequency exceeds 0.1 Hz/s for 20% of these disturbances. The average frequency nadir falls to 49.7 Hz, and the average time to nadir is about 8.7 s. If wind turbines were to be requested to provide inertia support to the system, these four metrics indicate how often, how fast, for how much and for how long the wind turbines should act. Moreover, during daily normal operations, the system has in general longer duration of over-frequency (f > 50.1 Hz) than under-frequency (f < 49.9 Hz). These frequency deviations are observed to occur around the hourly clearing of the Nord Pool Spot market and, especially during the hours between 05:00 and 08:00. In order to improve the frequency quality, the Nordic system operators tested and implemented an automatic frequency restoration reserve (aFRR) in addition to the existing manual one. Based on a frequency evaluation, this aFRR is needed most during 4:45-08:15 and 22:00-23:30 o'clock in 2012 in the NPS. [ABSTRACT FROM AUTHOR]

This study presents a modified vector auto‐regressive moving average (VARMA) modelling procedure to model spatially and temporally correlated wind speed time series over wide geographical areas. The standard VARMA is normally used to model stationary time series with Gaussian distribution. However, wind speed is non‐stationary (mean and variance varies over time) and non‐Gaussian. Hence, a method that can be used to transform wind speed data into a stationary and Gaussian time series is introduced in the modified procedure. To show the applicability of the procedure for different scenarios, six cases are investigated in the North and the Baltic Sea. The results show that the procedure can be used to model spatially and temporally correlated wind speed over a large geographical area. In addition, the resulting model can capture probability distribution and periodic characteristics of the wind speed data. Furthermore, based on the investigated case, it is shown that a vector auto‐regressive model of order three is a reasonable model structure which can be used to model spatially and temporally correlated wind speed in the North and the Baltic Sea area provided that the power transformed wind speed data is normalised by its monthly mean value and its variance. [ABSTRACT FROM AUTHOR]