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Due to the lack of alternating electric fields and alternating magnetic fields in HVdc transmission system, there has been no sustainable and stable energy harvesting method compatible with them up to now, hindering the application of HVdc sensors. In this letter, we proposed a novel dc energy harvesting method using corona current, and an energy harvesting circuit is constituted with space ion flow generated by dc corona. The feasibility of the proposed method is increased by adding an artificial corona electrode and placing the load before the corona electrode. In addition, it can flexibly operate at any position in an HVdc transmission system according to actual demand. Then the output power is further maximized by adopting a capacitor with high working voltages. The detailed measurement results based on the experimental system validate the effectiveness of the proposed method, with a stable output power as high as 10.15 mW in a dc system of 22 kV. A detailed discussion of the overall performance is finally carried out. [ABSTRACT FROM AUTHOR]

Partial discharge which often occurs at channel stopper of high voltage chip will cause insulation damage of chips which is harmful to the device application. Thus, it is important to improve the whole design to promote chip insulation capacity. In this brief, a novel chip surface shielding structure named U-protector is proposed which can promote the insulation capability of high voltage chips. Through the simulation, it can be found that the maximum electric field strength of chips can decrease 8% with adding U-protector. Moreover, verified by experiments, the partial discharge initial voltage (PDIV) of chips with U-protector can be promoted about 6.1%–12.7% of rated voltage. Furthermore, the universality and practicality of this structure are also investigated which can be used in multiple high voltage chips. [ABSTRACT FROM AUTHOR]

Plasma extraction transit time (PETT) oscillation will cause electromagnetic interference, which is harmful to the device operation. Thus, it is important to estimate the PETT oscillation frequency accurately to suppress this oscillation. While the existing formula for PETT oscillation frequency is approximate due to its divergent problem, in this letter, a modified formula for PETT oscillation frequency is proposed for insulated gate bipolar thyristor devices. The modified formula considers the acceleration process, which is complex but does not change with the electric field. Therefore, the divergence of the formula can be well solved by introducing the modified term. Moreover, the modified formula can be obtained straightforwardly and well match the measured oscillation frequency, which verifies the accuracy of the proposed formula. [ABSTRACT FROM AUTHOR]

In the present study, a test chamber filled with perfluorohexane (FC-72) is set up to investigate partial discharge (PD) in phase-cooling bubbles. Under the non-uniform electric field with needle point-to-hemisphere electrodes, thermal bubbles are generated from the needle point. The difference between PD with and without the bubbles is analyzed to identify features of the discharge in the bubbles. It is observed that the bubbles reduce the PD inception and intensify the discharge. A model of bubble motion is established to investigate bubble behavior in an electric field. Based on the observation of the flow and streamer patterns, a mechanism of PD in bubble flow is established and confirmed by phase-distribution of PDs with bubble transit time. [ABSTRACT FROM AUTHOR]

The focus of this study is on thermal bubbles which limits the application of phase-change cooling technology in high electric fields. In order to investigate the impact of the boil-induced bubble flow on the partial discharge (PD), a PD test chamber is set up which is modified to adjust the intensity of the bubble flow. PD signals and characteristics of the bubble flow are recorded under different heating conditions and electric fields. It is found that thermal bubbles have negligible impact on the PD characteristics under a non-uniform field, but the discharge frequency decreases as the boiling intensity increases. A deviation occurs in the trajectory of bubbles, which makes discharge in bubbles impossible. It is also found that the heat induced fluid affects the density of dielectric liquid and ionization coefficient of the discharge environment, which reduces PD frequency. [ABSTRACT FROM AUTHOR]

The setup for testing radiated disturbance induced by insulated gate bipolar transistor (IGBT) and auxiliary circuits was established. The radiated disturbance characteristics of auxiliary circuits and methods to suppress the radiated electromagnetic interference (EMI) were experimentally studied. The radiated EMI bandwidth of the auxiliary circuit was concentrated in the range 30–300 MHz. The mathematical model for an IGBT was proposed based on the setup, which includes all the structures of the IGBT in detail. The electric fields were calculated from the IGBT model using the method of moments. Moreover, the characteristics of the radiated disturbances due to the IGBT operation and the effects of metal on the radiated electric fields were experimentally and calculatingly studied in the frequency range 1–30 MHz. The metal shielded box of drive can increase the radiated electric fields by approximately 10–30 dB in the range 1–30 MHz. The electric fields for all the frequencies decreased rapidly with the increase of distance. Additionally, methods to shield the IGBT in order to suppress the radiated EMI were proposed. The effective radiated EMI reduction from a shielded net was approximately 20 dB, and that of a shielded box was around 30 dB. [ABSTRACT FROM AUTHOR]

With the growing public awareness of environmental protection, the dc ground-level total electric field (TEF) is attracting increasing attention. Especially in high-altitude areas, it has become a key technical factor in deciding conductor types and the height of the transmission line. To determine the altitude effect and correction of the ground-level TEF for HVdc transmission lines, four short bipolar test lines with bundle conductors with the same parameters were built in China at altitudes of 50, 1700, 3400, and 4300 m. Using the test facilities, the dc ground-level TEF was measured over a long period of time, from Jan. 2010 to Nov. 2015. Through a statistical analysis of a large amount of data, the ground-level TEF characteristics of short bipolar test lines at different altitudes were obtained. By comparing the statistical results from different altitudes, it is determined that the dc ground-level TEF and corona inception field strength are linearly dependent on the altitude. Finally, the ground-level TEF and corona inception field strength altitude correction formulas of HVdc transmission lines are proposed. [ABSTRACT FROM AUTHOR]

Polyetheretherketone is used in the packaging of high voltage power electronics as a frame material, and the surface discharge behaviors of polyetheretherketone are the main concerns for the packaging design. Pulse width modulation voltage, which shows a variable duty cycle, is applied to polyetheretherketone at working conditions. The surface discharge behaviors of polyetheretherketone under a positive repetitive pulse voltage of 50 Hz with different duty cycles were investigated in this paper. It is generally considered that the surface discharge inception is mainly related to electric field distribution; however, the pulse width of voltage could significantly affect the surface discharge inception characteristics. In this study, the surface discharge inception voltage, time-integrated streamer images, and cumulative surface discharge patterns under a positive repetitive pulse voltage of 50 Hz were obtained. It was found that the surface discharge inception voltage decreased with the increase in the duty cycle. This relationship was explained by the role of time-lag. Time-lag distribution analysis was performed, and the time-lag distribution was mainly determined by stochastic time-lag. The mean stochastic time-lag was obtained by the Laue plot, and the relationship between the mean stochastic time-lag and applied voltage could be well fitted by the inverse power law. Furthermore, the relationship between the surface discharge inception voltage and duty cycle could be exactly fitted by the inverse power law, which was derived from the relationship between the stochastic mean time-lag and applied voltage. The closely related relationships demonstrate that time-lag plays a critical role in the surface discharge inception at different duty cycles. [ABSTRACT FROM AUTHOR]

Electric fields are regarded as a promising means of graphene oxide reduction, but previous studies have only focused on pristine graphene. Here, based on first principles density functional theory calculations, we report on electric field mediated reduction of neutral and charged O and hydroxyl groups from both pristine and defective graphene sheets. The critical electric field strengths for different species are determined in facilitating a progressive and selective graphene oxide reduction. Our results demonstrate that the presence of vacancy defects significantly inhibits the effectiveness of electric fields as a means of reduction of O and OH functionals, due to the complexities that arise between the functional group and vacancy edge atoms in the presence of an applied electric field. [ABSTRACT FROM AUTHOR]

Ionized field strength on the ground level is one of the fundamental electromagnetic environment parameters of ultrahigh voltage direct current (UHVdc) transmission lines. An algorithm of an upstream boundary element method is presented in this paper to calculate the ionized field on the boundary with a high accuracy. The ionized field is generated and measured in an experimental platform with an HV conductor to a grounded cylindrical corona cage. The relations between ionized field strength and applied voltage, conductor position, and conductor diameter are investigated. Calculations show that the relative error of the ionized field on the HV electrode could be reduced to 0.1% when compared with the analytical solution. Ionized field distribution under the typical ±1100 kV UHVdc transmission lines is also analyzed as the application. [ABSTRACT FROM AUTHOR]

The ionized field is one of significant parameters to evaluate the electromagnetic environment of ultra-high-voltage direct current (UHVDC) transmission lines. The field mill is usually utilized to measure the ionized field on the ground level under the UHVDC power lines. In order to investigate the distortion characteristics of the ionized field with the presence of spaces charges near the probe of the field mill, Poisson's equation and current continuity equation are solved, respectively, based on the finite-element method and Gauss's law in the cylindrical coordinate system. The ionized fields on the surface of the probe are calculated under different ion current densities. An experimental apparatus with corona wire net and ground plate is designed and used to measure the ionized field and ion current density. Experimental results have shown that the measured data are consistent with the calculated ones, which verify the validity of the algorithm presented. The impact of the space charges on the field mill may provide valuable reference for the measurement of the electromagnetic environment of UHVDC projects. [ABSTRACT FROM PUBLISHER]

Electromagnetic interference (EMI) is mainly caused by the periodic valve switching in HVdc converter stations. This EMI can result in high-frequency conducted and radiative interference toward the adjacent communication, computer equipment, carrier system, and radio stations. Therefore, a wideband model of a converter system is necessary to predict the characteristics of the EMI source. Methods of modeling are proposed, and the equivalent circuits of the main equipment in ultra-HVdc (UHVDC), including valve section, converter transformer, smoothing reactor, filters, and so on, are developed in this paper. The whole wideband model is simulated by PSCAD/EMTDC. Based on this model, the characteristics of the conducted EMI under normal operation conditions are calculated. Ground-level electric field strength and magnetic field strength in and around a UHVDC converter station are calculated. For validity, a comparison between the simulated and the measured data is conducted. [ABSTRACT FROM AUTHOR]

The corridor of the high-voltage direct current transmission lines in China is very complex and there may be buildings near the lines. The conductivity of the building material may influence the electric field in the building. In this paper, based on the upstream FEM, a method is proposed to solve the coupled problem of the ion flow field in the air and the current field in the building model. The numerical results coincide with the analytic results and measurement results. The electric field in and on the building model is analyzed considering different conductivities. [ABSTRACT FROM PUBLISHER]

As ultra-high-voltage direct current (UHVDC) projects are constructed in China, the electromagnetic environment problem is widely concerned. One of the most important problems is the ion-flow field including the human body under the UHVDC lines. But it has not been analyzed sufficiently. In this paper, the 3-D upstream finite-element method, a new method to analyze the 3-D ion-flow field under HVDC lines is proposed and verified by experiments. Then, the method is used to calculate the ionized electric field and the ion current of the human body model under the UHVDC lines. The ionized electric field is significantly distorted by the human body. According to the results, the ionized electric field and the ion current of the human body remarkably increase with the height of the human body model. The results could provide a reference for evaluating the electromagnetic environment and the personal feeling test under the UHVDC lines. [ABSTRACT FROM PUBLISHER]

The HVDC and HVAC transmission lines running on the same tower is a promising technology to improve the transmission capacity of an existing corridor. The ions generated by corona discharge of HVDC transmission lines will strengthen the ground-level electric field, which may endanger human exposure. To investigate how the presence of HVAC transmission lines changes the ion-flow field, experiments are carried out on an indoor test model with bipolar dc and three-phase ac lines. The experiment results are then compared with the simulation results. The experiment and simulation results show that the HVAC transmission lines have a shielding effect on the ion-flow field from the HVDC transmission lines running above. Finally, the ground-level electric field and ion current density of the \pm 800–kV HVDC and 500-kV HVAC transmission lines running on the same tower are calculated. [ABSTRACT FROM PUBLISHER]

A modified method based on the optimized charge simulation method (CSM) is used to predict the corona onset voltage and electric field when the space charges due to the corona are considered. Based on the streamer model of corona discharge, space charges generated near the conductors are predicted. In order to calculate the electric field at the conductor surface, space charges are replaced by some equivalent line charges near the conductor. Because of the existence of space charges, the corona onset electric field is changed a little. After a simplified model of actual power transmission lines is introduced with the help of rough coefficient, the corona onset voltage and corona onset electric field are calculated for different types of conductors finally. [ABSTRACT FROM PUBLISHER]

Abstract: Making use of EMTP, the transient simulation of the currents along the towers and ground wires is performed when the lightning strikes the tower of the power transmission line. The investigation shows that the currents along the towers and ground wires dramatically decrease and can be ignored after 5 spans. And the effect on them for different impulse ground impedances, lightning current injection locations, tower spans, lightning wave impedances and so on are obtained when lightning strike on tower. With the help of Fourier transform, the method of moment is adopted to calculate the transient coating stress voltage of the pipeline and total electric field in the earth when the underground pipeline runs parallel to or crosses the power transmission line. The approximate formulas of the maximum coating stress voltage along the pipeline are proposed for the situation of crossing, which involve the lightning current, soil resistivity, pipeline models, tower grounding structure sizes and separation distance between the pipeline and tower grounding structure. Then, the proposed method can be used to evaluate the safety distance between the pipeline and tower grounding structure with the lightning electrical strength of the anti-corrosion coating of the pipeline. Eventually, if actual distance is less than the calculated value, modeling and analysis of protection measures in the pipeline can be carried out to protect the coating. [Copyright &y& Elsevier]