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Flexible DC technology has revolutionary significance in flexibly solving the problem of high proportion of new energy consumption. Due to the vulnerability of high-ratio power electronic equipment and the difficulty in extracting fault information, traditional line protection schemes can no longer be reliably adapted to the flexible DC transmission system. A rapid protection scheme for flexible DC transmission lines based on voltage traveling wave steepness is proposed in this paper. By analyzing the transient characteristics of DC line faults, and utilizing the differences in the steepness and polarity of fault voltage traveling waves on both sides of the current-limiting reactor, the range of effective transient information extraction is increased, and the fault identification inside or outside the region is realized. The faults are classificated by utilizing the significant difference in the degree of voltage traveling wave variation between the faulty and sound poles. Lightning interference is considered and a rapid identification method is proposed by using its initial change characteristics. Finally, the performance of the protection scheme under various influencing factors is verified by simulation, which can identify faults quickly and reliably and has good sensitivity and anti-interference ability.

The build-up and occurrence of earthquakes are due to the accumulation and release of stress in fault zones. When subjected to tectonic extrusion stress, the crystal structure of the minerals within a fault zone will change. In this study, Raman spectroscopy analysis was conducted on the concurrently deposited quartz veins from Shenxigou, along the Yingxiu-Beichuan fault, and from Niyang River mouth, in the southern section of the Milin fault. The test results reveal a 3.29 cm−1 shift in the characteristic 464 cm−1 peak of the quartz in the veins along the fault plane of the Yingxiu-Beichuan fault, which was significantly lower than the shifts in the quartz peaks of the quartz on both sides of the vein. The 464 cm−1 peak shifts of the samples collected 10 m to the NW and 21 m to the SE of the fault plane were approximately 4.40 and 4.62 cm−1. In the veins from the Milin fault, considerable shifts of the 464 cm−1 quartz peaks occurred at the fault plane and to both sides within 5.5 m of the fault plane. No significant change in the 464 cm−1 Raman peak of quartz was observed for the samples 5–28 m to the SE of the fault plane. These results indicate that the tectonic extrusion stress accumulated more easily in proximity to the fault plane, resulting in significant changes in the crystals near the fault plane. We conclude that there is a correlation between the degree of change in the crystal structures of the minerals in thrust fault zones and fault activity, and such a correlation can provide a new method for studying the activity of thrust faults in areas with bedrock.

The amplitude of AC line current at the inverter side is affected by DC commutation failure and fluctuates for a short time after single-phase trip.The fluctuation range increases with the increase of the number of DC commutation failures,resulting in the misjudgment of the traditional single-phase fault nature criterion based on the amplitude of the recovery voltage. To solve this problem,a transmission line fault equivalence model is built firstly to evaluate the impact of DC commutation failure on the sound phase voltage. Then the time domain expressions are derived for the disconnected phase voltage during the recovery voltage stage for different fault nature. After that,a single-phase fault nature identification criterion based on time domain voltage integration is proposed,and its effectiveness is verified by PSCAD/EMTDC simulation. The results show that the proposed method has good resistance to transition resistance and DC interference,and the fault nature identification criterion is suitable for DC commutation failure.

In the present study, nonlinear dynamic process data are mapped into the kernel state space by kernel gauge variable analysis method to obtain decorrelated state data. The time-lapse covariance matrix of the state data is weighted and summed to obtain the time-lapse structure matrix of the state data, and then supervised kernel independent component analysis (SKICA) is established, the independent component feature data is extracted from the status data and the monitoring statistics are constructed to detect the process faults. The data show that kernel independent component analysis (ICA) method (KICA) method can detect slow fault faster than the ICA method, except that the statistical detection ability of F3 and FS is reduced, and the KICA method can significantly improve the detection performance of other faults and statistics. By analyzing the detection results of SKICA method, it is obvious that in the detection process of all five kinds of slow faults, the fault detection capability of SKICA is better than that of ICA and KICA. The results of continuous stirred reactor simulation system show that, compared with the basic linear process, the slow fault detection has a good monitoring performance, it can detect the small deviation in the process sensitively and give alarm information to the slow fault in time, to improve the fault detection rate.

If commutation failure does not occur when single-phase high resistance grounded in single-circuit AC line of inverter,then single-phase circuit breaker tripping may lead to commutation failure. Firstly,the expression of converter bus voltage after single-phase circuit breaker trip is derived by using symmetrical component method. Based on the expression,the main factors affecting the converter bus voltage are analyzed,and it is found that it is related to the equivalent parameters of the system. Then,the influence mechanism of voltage deviation angle of commutator bus on extinction angle is studied. It is found that the zero-crossing forward angle of commutation bus voltage after the single-phase breaker trips is the main factor leading to the decrease of the extinction angle,and commutation failure will be induced in serious cases. Finally,the AC/DC simulation model was built on the PSCAD/EMTDC electromagnetic transient simulation software platform. The simulation verifies the effect of the tripping of single-phase breaker in single-circuit AC line on the commutation process of inverter. The simulation results are consistent with the theoretical analysis.

Abstract Quorum sensing (QS) can function to shape the microbial community interactions, composition, and function. In wastewater treatment systems, acylated homoserine lactone (AHL)-based QS has been correlated with the conversion of floccular biomass into microbial granules, as well as EPS production and the nitrogen removal process. However, the role of QS in such complex communities is still not fully understood, including the QS-proficient taxa and the functional QS genes involved. To address these questions, we performed a metagenomic screen for AHL genes in an activated sludge microbial community from the Ulu Pandan wastewater treatment plant (WWTP) in Singapore followed by functional validation of luxI activity using AHL biosensors and LC–MSMS profiling. We identified 13 luxI and 30 luxR homologs from the activated sludge metagenome. Of those genes, two represented a cognate pair of luxIR genes belonging to a Nitrospira spp. and those genes were demonstrated to be functionally active. The LuxI homolog synthesized AHLs that were consistent with the dominant AHLs in the activated sludge system. Furthermore, the LuxR homolog was shown to bind to and induce expression of the luxI promoter, suggesting this represents an autoinduction feedback system, characteristic of QS circuits. Additionally, a second, active promoter was upstream of a gene encoding a protein with a GGDEF/EAL domain, commonly associated with modulating the intracellular concentration of the secondary messenger, c-di-GMP. Thus, the metagenomic approach used here was demonstrated to effectively identify functional QS genes and suggests that Nitrospira spp. maybe QS is active in the activated sludge community.