Hailiang Lu

Room-temperature ferromagnetism in Cu+ implanted ZnO nanowires

We experimentally showed ferromagnetism at above 300?K for ZnO nanowires prepared by reactive vapour deposition and subsequently implanted with 2?at% of Cu. The magnetic moments of the samples annealed in oxygen and in argon at 600??C for 120?min are about 0.42??B and 0.33??B per Cu atom, respectively. No ferromagnetism-related secondary phase existed according to the results of x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy including HRTEM and EELS mapping. It can be concluded that the d9 configuration in the ground state of Cu2+ plays an important role in ferromagnetism. This controllable and shallow doped ion implantation technique may find potential applications in spintronic, especially nano-spintronic, devices.

Hematite nanochain networks: Simple synthesis, magnetic properties, and surface wettability

This paper describes a simple and effective method for the fabrication of hematite (α-Fe2O3) nanochain networks (NCNs) by using carbon nanotubes as templates. The α-Fe2O3 nanochains are made of numerous α-Fe2O3 nanocrystals, which exhibit weak ferromagnetic behavior at room temperature while showing antiferromagnetic behavior at low temperatures below the Morin temperature (180K). Furthermore, the α-Fe2O3 NCNs generate superhydrophilic surface displaying the contact angle of water of 0°. Therefore, the α-Fe2O3 NCNs may be applied in nanomagnetic filters to capture magnetic and paramagnetic micro- and nanocontaminations to obtain high purity liquid.

Impulse Characteristics of Tower Grounding Devices Considering Soil Ionization by the Time-Domain Difference Method

Knowledge of impulse characteristics of tower grounding devices is important for lightning protection of the transmission lines. In this paper, the time-domain difference method is proposed to analyze the impulse characteristics of tower grounding devices. Combined with the soil ionization model and the soil-critical breakdown field strength, the proposed method is capable of modeling nonlinear ionization of the soil. The voltage-response waveform calculated by the proposed method is smooth, which is superior to the waveform calculated by the frequency-domain numerical algorithm. The reduced-scale experiments of grounding devices with different structures were carried out in the laboratory to validate the accuracy of the proposed method. Furthermore, the critical breakdown field strength used in the soil ionization model is measured by the coaxial cylindrical electrodes.

Influence of Deep Earth Resistivity on HVDC Ground-Return Currents Distribution

During monopolar operation or commissioning of high-voltage direct-current (HVdc) links, ground-return current (GRC) leads to power transformer dc bias issues. A GRC model is proposed in this paper, and the penetration depth, penetration ratio, and earth surface potential of various earth models are simulated. The result indicates that the influence of deep earth resistivity increases rapidly by the increasing distance from substations to HVdc electrodes. The simulation results are compared with measured data of GRCs distribution in the Hubei power grid of China. The result demonstrates that the simulation considering deep earth resistivity is credible and the shallow earth model could lead to poor accuracy. Furthermore, earth resistivity measurements are carried out at different geological regions and the deep earth characteristics and the GRCs distribution are quite different. Thus, it can be concluded that to calculate GRCs distribution using uniform earth structure without measurement is not appropriate. Finally, the relationship between accurately measured earth depth and the accuracy ratio of GRCs calculation is analyzed. The result of this paper contributes to determine the depth of earth model in GRCs simulation modeling and earth resistivity measurements.

Study on the effect of corona on hydrophobicity recovery performance of RTV silicone rubber and its failure criterion

Room temperature vulcanized (RTV) silicone rubber is widely used in external insulation of electrical equipment for antipollution flashover because it has many merits such as superior hydrophobicity and migration of hydrophobicity, but it also has weakness such as poor aging performance. The study on the failure criterion of RTV silicone rubber is always a concern since there has been no generally accepted method for its failure criterion. Corona has an important effect on the hydrophobicity and its recovery performance of RTV silicone rubber. In this paper, tests were conducted to reveal the effect of corona on the hydrophobicity recovery performance, and a failure criterion has been proposed. PRTV (permanent RTV) silicone rubber, a commonly used nanocomposite, was selected as the samples to study the hydrophobicity and its recovery after different corona aging time. Before the onset of aging, the factors that affect the accuracy of the contact angle measurement were studied. Fourier transform infrared spectroscopy (FTIR) was employed to find the failure criterion. The results show that, the relatively accuracy of the test data of contact angle can be obtained with 4 μL water drops and proper grounding of the test sample for 2 min. It is also found that the hydrophobicity is permanently lost when the continuous aging time is longer than 70 h under the test conditions, and compared with the virgin samples through FTIR, the peak height of CH3(C-H), Si-CH3 and Si-O-Si in FTIR decreases by 64.9%, 47.0% and 25.9%, respectively for the aged samples. It is suggested that, the variation of peak height of CH3(C-H), Si-CH3 and Si-O-Si in FTIR can be taken as the quantitative index of failure criterion of RTV silicone rubber.

Analysis of Electromagnetic Interference Effects on Gas Pipelines Due to a Nearby Parallel UHV Transmission Line

The inductive coupling between ultra-high voltage (UHV) transmission lines and nearby underground pipelines raises the potential of pipelines which threatens the pipeline security and reliability. In this chapter, a transmission line–pipeline model is established based on the commercial software CDEGS, and the electromagnetic interference is simulated and analyzed. The pipeline potentials at different parallel distances are calculated in consideration of the effect of the overhead grounding wire. The simulation results are in conformity with the theoretical analysis. On this basis, a real 750-kV transmission line, and the nearby gas line model are built and simulated. The results show that the long distance of parallel and oblique approach can lead the maximum pipeline grounding potential raise (GPR) to exceed 100 V, i.e., 10 times of the safety threshold of 10 V. The solution is proposed and simulated in this chapter, and the maximum GPR of a pipeline is reduced to less than 10 V.

Online Monitoring System of the Grounding Status of Transmission Line Towers

The grounding status of transmission line towers is very important to the security and stability of the transmission line. Nevertheless, it is unfeasible and hard to carry out periodical manual checking of the grounding status in field conditions of the transmission line tower so as to find the grounding fault in time. Aiming at the problems, an online monitoring system in terms of the grounding status of transmission line towers is established. The system is composed of the measure device and the server, in which the measure device is based on the clamp meter method to send the tower grounding status to the server automatically and periodically. The measurement principle is simulated and analyzed in this chapter. Moreover, the prototype is tested in the laboratory environment, and the monitoring system is practically tested on the transmission towers. The result shows that the accuracy of the measure device is no less than 93.96 % when grounding resistance is between 0.3 and 100Ω. Furthermore, the practical application shows that the system is effective and can be useful in the application of lightning protection.

Simulation Analyses and Realization of Lightning Current Monitoring System on Transmission Lines

Based on the production and operation situation of the State Grid Corporation of China in recent years, the lightning faults have taken of the majority of the transmission and distribution equipment faults. In order to prevent the lightning damages and control the lightning faults of the transmission lines, it is necessary to study the impacts of the lightning strike on transmission lines. In the course, the primary work is to accurately judge the location and form of the lightning strike. Upon simulation of the current waveform on transmission lines subject to different forms of lightning attacks, the features of lightning current on the insulators and grounding lines have been achieved; then, the judging methods of the polarity and the location of the lightning strike are studied. In order to monitor the waveform, amplitude, polarity and other parameters of lightning current in a real-time manner, a transmission line lightning monitoring system is developed. Based on the judging methods achieved by simulation and monitoring the waveform, the lightning fault location and the form of lightning can be confirmed. The monitoring result shows that this system can provide effective technical guarantee to take pertinent lightning protection measures.